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The southeastern U.S. is considered the “wood-basket” of the world where loblolly pine (Pinus taeda L.) plantations provide tremendous ecological and economic benefits to the region. These plantations are susceptible to various natural and anthropogenic abiotic and biotic stressors and disturbances. The southern pine engravers, Ips avulsus (Eichhoff), I. calligraphus (Germar), and I. grandicollis (Eichhoff), are considered secondary colonizers of stressed, damaged, and dying loblolly pines. However, they may undergo outbreaks and colonize live pine hosts if environmental conditions cause physiological stress to trees. In 2016, >230 concurrent Ips infestations >2 ha in size were documented in Georgia, U.S., reportedly due to severe drought. In these forests, prescribed burning is often conducted every 2–3 years to reduce fuel-loads, improve wildlife habitat, and manage understory vegetation. However, the effects of low-severity prescribed fire on active southern Ips infestations are unknown; fire may exacerbate or alleviate beetle outbreaks. Our objectives were to: (1) compare Ips infestations between burned and unburned sites to determine the short-term effects of prescribed fire on loblolly pine mortality; and (2) determine which site-level and tree-level variables were the best predictors of short-term levels of tree mortality. We monitored 838 pines on ten sites for eight months following prescribed fire in spring 2017. Overall, 69 (8%) trees died with 3.6 times higher tree mortality on unburned sites, and a higher probability of survival on burned sites. At the site-level, binomial logistic regression models including treatment (unburned versus burned) and time since burn were the best predictors of loblolly pine mortality. At the tree-level, model selection showed that treatment, crown mortality level (1–5), Ips activity level (none, low, medium, and high), and tree diameter provided the best predictions of mortality. Prescribed burning may thus help alleviate pest pressure and increase tree resilience in loblolly pine forests in the southeastern U.S.

Natural forest comprises approximately 78% of New Zealand’s total forest area and their dead wood carbon pools contribute to the national carbon balance reported under the United Nations Framework Convention on Climate Change. We investigate the accuracy of coarse woody debris (CWD) carbon stock estimates obtained from periodic inventories of New Zealand’s natural forest. Dimensions and decay classes of standing-dead spars, fallen logs and stumps over 10 cm diameter were assessed in permanent plots during two inventory cycles (2002–07 and 2009–14). Carbon in CWD was estimated by multiplying CWD volume with species-specific mean wood and bark density, a density modifier based on decay class, and the carbon fraction. The measured change in CWD between inventories was obtained by subtracting 2002–07 from 2009–14 mean CWD carbon stocks. This measured change in CWD carbon stocks was compared with the modelled change derived by applying a decay model to 2002–07 stocks to determine the losses from decay and adding inputs from the tree mortality recorded between the two measurement cycles. Estimates of CWD carbon stocks from field measurements were 19.9 and 19.5 tC ha−1 in 2002–07 and 2009–14 respectively, with a statistically non-significant change of −0.4 ± 0.6 tC ha−1 (95% C.I.) over the period between measurements implying that CWD carbon is in a steady state. However, the modelling approach gave a significant increase of 2.5 ± 0.7 tC ha−1, implying that CWD stocks are increasing. It appears likely that the primary reason for the discrepancy between the direct measurement and modelling approaches is that CWD carbon stocks are substantially underestimated using current measurement protocols used in the inventory of New Zealand’s natural forest. If CWD carbon stocks in New Zealand’s natural forests are approximately in balance as implied by the direct measurement of CWD stocks, CWD inputs from mortality would have to be balanced by losses from decay. For this to be true, the CWD pool would have to approximate 35.4 tC ha−1 which is 78% higher than its measured value.

Historical management practices could have a strong effect on the current status of forests and therefore affect the potential for outbreaks of forest pests. We tested whether forest management history and forest tending of Norway spruce affects the potential for bark beetle outbreaks after large disturbances. We also assessed the effect of the proportion of spruce under epidemic situations and different altitudes. For this survey we used long-term data on sanitary felling and forest inventory data. Forest management history was defined by the change in the forest compared to the natural forest composition and was divided into four classes of change in tree species composition. We compared the proportion of spruce and sanitary felling because of bark beetles with the different classes of change in tree species composition. Forest tending was analyzed by looking at how the proportion of realized cut in relation to the planned cut affected sanitary felling. The analysis was done with Bayesian modeling including both spatial autocorrelation and random effects. There was a strong association between the change in the forest tree species composition and the proportion of Norway spruce and sanitary felling because of spruce bark beetles. Interactions were observed between epidemic periods, the proportion of Norway spruce and altitude. Altitude had a negative influence and the proportion of Norway spruce had a positive influence on sanitary felling. During epidemic periods, sanitary felling was amplified at lower altitudes and in areas with a higher proportion of Norway spruce. Furthermore, there was a negative association between the proportion of realized cut in relation to the planned cut and sanitary felling in periods after abiotic stress. It is therefore suggested that monocultures of Norway spruce should be converted to mixed forests and that maintenance of the forest should be improved to increase resistance to bark beetle outbreaks.

There is an intense interest in the effects of timber harvest on forest-dwelling bats due to the potential for timber harvest to reduce available habitat. Knowledge of these effects would be especially significant for the conservation of threatened and endangered bat species, many of which are forest obligates. We conducted a study to determine how endangered Indiana bats (Myotis sodalis) select summer roosts within a managed midwestern forest. In the summers of 2012–2015, we tracked 4 male and 11 female Indiana bats to 49 roosts (nmale = 24, nfemale = 25) in south-central Indiana, USA. We collected roost-, plot-, and stand-scale data on roosts and associated available trees, randomly located throughout the same landscape. We generated 10 matched pairs conditional logistic regression models based on a priori hypotheses on roost selection and ranked them using Akaike’s Information Criteria. Plausible models explaining female roost selection included those describing typical Indiana bat maternity roosts (tall and solar-exposed roosts) and typical tree-cavity bat roosts (tall, solar-exposed roosts close to water and surrounded by snags). Females selected roosts under exfoliating bark on large (averaging 17 ± 2 m in height and 34.8 ± 3.0 cm in diameter) standing dead trees (snags; 72% of roosts) and in bat boxes (20% of roosts) with high solar exposure (28.0 ± 6.0% canopy closure above roosts). For males, the model describing predator avoidance (tall roosts with many available snags and live trees) was the most plausible explanation of roost selection. Males selected for roosts under exfoliating bark on tall trees (23 ± 2 m; 71% snags, 25% live trees) surrounded by snags (4.5 ± 0.7 snags/0.1 ha plot) and live trees (30.4 ± 2.7 live trees/0.1 ha plot). Roost selection models including distance to timber harvest openings were not plausible. However, females roosted in or ≤10 m from harvest openings and first-stage shelterwood cuts more than expected (15 of 25 roosts) based on their availability on the landscape. Males roosted in harvest openings as expected (3 of 24 roosts). Our results demonstrate that a managed midwestern forest provides an array of roosts for Indiana bats and that Indiana bats do not actively avoid roosting near harvest openings in this forest. This suggests that Indiana bats may be able to subsist in managed forests in south-central Indiana, provided adequate maternity roost habitat (i.e., large standing dead trees with high solar exposures) is available.

Warm/dry mixed conifer forests have undergone changes in disturbance regimes, forest structure, species composition, and surface fuel accumulation which have led to increased susceptibility to large, uncharacteristically severe wildfires and pathogenic outbreaks. Ecosystems resilient to fire events return to a similar set of structures (e.g., forest and understory composition and density) or processes (e.g., fire, decomposition rates); however, when exposed to disturbances outside the evolutionary envelope, may transition to a different state (e.g., type conversion). We sampled warm/dry mixed conifer forest stands treated prior to the 2011 Wallow Fire and paired untreated sites five years following the fire. Our objective was to evaluate mid-term ecosystem resiliency in terms of forest structure, bark beetle activity, and tree regeneration. We hypothesized that treated units would have higher mid-term post-fire resiliency compared to untreated units. In 2016, average total tree density remained significantly lower in treated compared to paired untreated units; conifer density and BA decreased in both treated and untreated units. Diameter distributions in 2016 treated units remained similar to those observed in 2012 with the exception of increased density in the smallest diameter class. In untreated units, the majority of tree density reductions occurred in the 10–30 cm dbh classes. Post-fire tree mortality was stable across treated and untreated units, with no significant differences; however, abundant ingrowth of small hardwoods occurred throughout the study area. Large-tree density decreased by about 20% in both treated and untreated units between 2012 and 2016. Evidence of post-fire bark beetles was generally low and patchy throughout the study site; however, beetle activity was more widespread in untreated units. Twice as many trees were attacked by bark beetles in untreated versus treated units suggesting treatments may have reduced post-fire beetle activity. Following wildfire, observed conifer regeneration was lower and hardwood regeneration was higher with increasing burn severity; conifer regeneration was nearly three times higher in treated units. This study suggests that pre-fire fuel reduction treatments contribute less to mid-term resiliency than to short-term resiliency of forested ecosystems. We observed trends of higher resilience to insect outbreaks and potential implications for type change from conifer to deciduous forest. Furthermore, our study underscores the importance of understanding mid-term post-fire recovery, and while it provides insights regarding recovery of these ecosystems, additional monitoring and research is needed to fully understand the implications toward long-term resiliency.

For the past two decades in the Czech Republic, Norway spruce (Picea abies) trees have been weakened by drought and subsequent attack by Armillaria root disease and bark beetles (Ips typographus, I. duplicatus, and Pityogenes chalcographus). We determined whether thinning of trees decreased mortality at 40 forest locations in the Czech Republic. The majority of the locations experienced long-term drought stress and very low groundwater levels. We also identified the species of Armillaria associated with the spruce decline and determined the reliability of visual detection of Armillaria infection. The mortality of trees at the 40 locations increased nearly linearly during the 5 years of the study. Sites were established in 2012, thinned or not thinned in October 2012, and were assessed in September and October in each year from 2012 to 2016. Thinning, with an intervention intensity of 30–40%, did not alter tree mortality at the locations. The proportion of dead trees was significantly greater in older than in younger stands in the last 3 years of the study. Among the trees that were suspected of being attacked by Armillaria based on visual inspection by foresters, 53% were confirmed (supported by statistical significance) to be infected by Armillaria spp. after morphological and genetic assessment. Among the trees with confirmed infections, 56% were infected by Armillaria ostoyae, 32% were infected by A. cepistipes, and 1% were infected by A. gallica (the rest could not be identified). Resinosis was positively associated with the occurrence of A. ostoyae. This species was more common on loamy flat locations, whereas A. cepistipes was more common on stony, sloped locations. The occurrence of Armillaria was negatively associated with increasing pH. Although our results indicate that spruce decline is strongly associated with the presence of Armillaria and that visual detection of Armillaria is reliable, management options for reducing Armillaria infection and damage appear to be highly limited. Forest managers should begin preparing to convert stands of Norway spruce to stands of other tree species that are better adapted to the local conditions and that are less susceptible to attack by Armillaria species.

Wood decay fungus Pyrofomes demidoffii is a cosmopolitan spp. and considered as an important source of damage to Juniperus spp. The aim of the study was to assess the wounding factors of Juniperus procera and their relation to a disease occurrence of P. demidoffii in some afromontane forests of Ethiopia. Disease survey and sample collection was conducted during 2010 in Adaba-Dodola and in Menagesha forests. In Adaba-Dodola forest, sampling was conducted in highly disturbed forest blocks named as non-“WAJIB” and in a relatively undisturbed forest (“WAJIB”) named after the local Afan Oromic language. WAJIB blocks are constitute of Forest Dwellers Association established to protect forest, whereas a non-WAJIB blocks are people living in villages found adjacent to forests with little role in protection of forest. In both study areas, a study quadrat of 20 × 20 m2 within the plot was established at 100 m intervals along a regular grid. In each sampling unit, comprehensive survey was conducted to determine the occurrence of infection by P. demidoffii. About 657 trees (310 in Adaba-Dodola forest and 347 in Menagesha forest) were assessed for the typical signs and symptoms of P. demidoffii. Natural and anthropogenic wounding factors were assessed, and their relationships with disease occurrence of P. demidoffii were determined. Pyrofomes demidoffii was noticed as fruiting bodies and/or white rot on the juniper stands. The disease occurrence of P. demidoffii was significantly higher in juniper stands with a mixed wounding factors followed by wounding by bark-peeling (P

Standing dead trees, or snags, represent post-disturbance biological legacies in forest ecosystems, and intentional creation of new snags is increasingly common during forest treatments. The abundance, volume, size, and distribution of snags can affect wildlife communities and stand-level biological diversity. Characteristics such as the wood properties of different tree species, environmental conditions, and cause of tree death (e.g., insects, disease, senescence, wind, fire) can influence decomposition and subsequent use of snags by wildlife. The objectives of this study were to characterize decay patterns in jack pine (Pinus banksiana) snags that had been killed by prescribed fire, topping, and girdling and determine the effects of these treatments on subsequent snag use by subcortical insects and primary cavity-nesting birds. The prescribed fire, topping, and girdling treatments were implemented in 2003, 2004, and 2007, respectively; bird excavations were quantified in 2014 and insect activity was measured in 2016. One-way analysis of variance tests were used to examine any differences among treatments in snag characteristics, decay characteristics, past insect activity, and past use by birds. An information theoretic approach to model selection was then used to rank potential predictors of bird foraging activity and cavities. The topping treatment had unique decay characteristics relative to the other two treatments; topped snags had the highest levels of past insect colonization, were softer, and had higher proportions of loose bark remaining on the boles. Trees killed by prescribed fire had the greatest number of foraging excavations and cavities. Girdled snags had the lowest evidence of past insect colonization and showed different levels of decay and insect use at different vertical positions on the snag bole. Comparison of candidate models showed that a model containing treatment type alone was the highest ranked when predicting foraging by birds, while snag diameter was the highest ranked when predicting the presence of cavities. A model containing treatment and snag density was also a highly ranked for predicting cavity presence. Our findings suggest that different jack pine snag treatments result in unique decay trajectories that may influence snag use by an array of wildlife taxa. Our characterization of three snag creation treatments can also inform options for generating snags, depending on the desired outcome, when management for biological legacies and wildlife habitat is of interest within mixed-pine forests of the Great Lakes region.

Sustainable management of European forests aims to ensure economic targets (timber production) as well as ecological aims of the forest (maintenance of biodiversity). Smaller-sized clear-cutting followed by artificial planting creates a mosaic of small forest patches suitable for many small mammals including three possible pest species – the bank vole (Clethrionomys glareolus), the field vole (Microtus agrestis) and the common vole (Microtus arvalis). The vole gnawing pattern was studied on a number of small-sized clearings (up to 2 hectares) situated in managed forests in the Czech Republic (Central Europe). Damage by voles gnawing occurred almost in all study areas; mostly damaged were saplings on clearings at the age up to 5 years after planting, with herb layer dominated by grasses and situated above 700 m a.s.l. The field vole was identified as the main pest species and its density was identified as the most important predictor of gnawing occurrence even though its density on clearings was usually lower than that of the bank vole. Gnawing by voles caused direct mortality of saplings to a greater degree than other biotic factors including deer fraying and browsing; however, saplings were able to repress the effect of gnawing by natural re-grow of bark and the majority of damaged saplings survived, even though with significant stem deformations. While strong inter-annual variation in damage rate is reported in northern Europe, damage rates in Central European managed forests are lower (at about 3.5% per annum) but more consistent with only moderate inter-annual variation. As a result, despite the relatively low rate of damage which may occur in any given year, damage levels can accumulate over several years after planting with significant economic implications for forestry management.

Forest mega-fires have become a global phenomenon in recent decades including in south-eastern Australia where large areas of forest have been fire-killed with loss of human lives and property and impacting carbon sequestration and greenhouse gas emissions. The vast extent and impact of mega-fires has induced a re-evaluation of fuel reduction methods as a key management strategy in wildfire risk mitigation in many countries. This study investigated the impact of a commercial thinning in Eucalyptus delegatensis forest on fuel hazard, fuel loads and wildfire behaviour, eight years after completion of a bay and outrow thinning operation. At the stand level, thinning reduced overstorey tree stocking by more than 50%, increased canopy openness and stimulated the growth of retained trees. Thinning also encouraged the profuse regeneration of over 1000 saplings ha −1 of E. delegatensis, mostly in the outrows, compared with no sapling regeneration in unthinned forest. A system of additive biomass equations was developed to estimate total biomass and component biomass (stem wood, bark, branches and foliage) of individual trees. The aboveground tree carbon was 433 ± 49 Mg C ha −1 in unthinned forest and 322 ± 47 Mg C ha −1 in thinned forest. Thinning decreased surface fuel hazard ratings and fuel loads but had no significant effect on the mass of coarse woody fuels. Fire simulation under severe to extreme weather conditions, as occurred in the 2006/7 Great Divide Fires, indicated an almost 30% reduction in fireline intensity and about 20% reduction in the rate of spread and spotting distance in thinned forest compared with unthinned forest. This study indicates the potential of thinning to reduce wildfire severity and to increase the fire-survival of E. delegatensis .

Tree-killing bark beetles are globally the most destructive forest pests and their impacts have increased in recent decades. Such an increase has been consistently reported from Europe and North America, and it is, with high confidence, driven by climate change. We investigated how the scientific community in both continents responded to this situation by conducting a comprehensive search of the Scopus database from 1970 to 2020. Studies that investigated interactions between climate change and two prominent bark beetles in Europe and North America, the European spruce bark beetle Ips typographus (ESBB) and the mountain pine beetle Dendroctonus ponderosae (MPB), were identified. We used several hierarchical search criteria, starting from general aspects of pest – climate change interactions, to studies with clear implications for management and policies. We found that authors investigating the two bark beetle species mentioned climate change in publications beginning in 1998, and have constituted 8.9 and 13.8 % of all studies on ESBB (N = 987) and MPB (N = 1479) recorded in Scopus. However, only part of these studies addressed climate change as a fundamental or integral part of their research design (59.1 % in ESBB and 38.7 % in MPB). We identified 30 studies on ESBB and 50 studies on MPB which informed efforts towards improving bark beetle management strategies to address climate change-affected ecosystem dynamics. Publications on both insects consistently highlighted the importance of vegetation management aiming to reduce the risk and severity of outbreaks and prevent large-scale population expansion. Only a minor portion of studies placed their findings into the context of relevant policies and legislation, and this connection was particularly lacking in studies on MPB. We conclude that research on bark beetle management under climate change has received inadequate attention and it lags behind observed and foreseen global-scale impacts. We suggest that focused and applied research with clear management implications is needed to develop new climate-adapted and evidence-based management strategies.

Dealing with tree mortality caused by forest pests is one of the most demanding challenges in forest protection and management. The current spruce bark beetle infestation in the Polish part of the Bialowieza Forest (BF), which started in 2012, is considered the largest in history and has nearly eliminated Norway spruce (Picea abies (L.) Karst) as a major forest tree species there. This research analyzed the dynamics and spatial extent of the BF outbreak from 2015 to 2019. The extensive beetle epidemic caused a more than six times higher number of infested trees in 2019 as compared to 2015. Under the conditions of the unprecedented ongoing I. typographus outbreak, the dynamics of spruce stand mortality varied across the study area. A lower spruce mortality was observed in Bialowieza National Park as compared to other forest districts. Host and environmental factors influenced the timing of spruce mortality. Spruce height, stand age, the proportion of spruce, the share of area covered by tree crowns, excluding spruce and dominant species in the stands, were the key factors of bark beetle infestation. The most intensive outbreak progressed in stands older than 100 years dominated by spruce, and areas with the lowest dynamics of spruce dieback were localized in mixed young forests or pine stands. The methods and results presented in this study serve as baseline information, supporting the efforts to model the spread of bark beetles and future decision-making.

The mountain pine beetle (Dendroctonus ponderosae Hopkins) is a bark beetle that is native to pine forests of western North America and the Black Hills of South Dakota. Recent eastward range expansion into stands of jack pine (Pinus banksiana) and associated hybrids with lodgepole pine (Pinus contorta) in western Canada has created concern that the insect will continue moving eastward. In the Great Lakes region, mountain pine beetle would encounter novel species of pines and associated insect fauna; interactions with which are largely unexplored. We baited logs of jack pine with lures for mountain pine beetle and Ips grandicollis (Eichhoff) alone and in combination in a 2 × 2 factorial design in the Black Hills of South Dakota. Both insects occur in this region, but not jack pine, a common species in the Great Lakes region of North America at risk of invasion by mountain pine beetle. We measured attraction and reproduction of insects that colonized the logs. Ips grandicollis were significantly more attracted to logs of jack pine baited with their aggregation pheromone, ipsenol, than unbaited logs or those baited with pheromones of mountain pine beetle and myrcene, a host volatile. Colonization by I. grandicollis was inhibited by the presence of lures for mountain pine beetle. We also found larvae of longhorn borers, likely ­ Monochamus spp., infesting logs. These borers, which act as competitors and facultative predators of bark beetles, were significantly attracted to logs baited with ipsenol over those baited with lures for mountain pine beetle. Our results suggest that if mountain pine beetle were to invade the Great Lakes Region, common bark and wood-boring species such as I. grandicollis and longhorn borers would not compete with mountain pine beetles at tree-colonizing stages, and thus could pose little resistance to invasion.

Outbreaks of tree-killing insects are intensifying globally, affecting economies, human well-being, and driving ecosystem transitions. The Czech Republic has recently become Europe’s epicenter of the outbreak of spruce bark beetle Ips typographus, the most aggressive species in Eurasia. We investigated a countrywide outbreak dynamic during the period 2003–2019, with a special focus on the period 2017–2019 when the outbreak reached an unprecedented intensity. In order to identify main outbreak drivers, we investigated annual time series of the volume of trees killed by bark beetles in the Czech districts (n = 77), and a suite of climatic and forest structure-related predictors using Generalized Additive Models. Finally, we reviewed a large body of public materials to understand broader social, ecological, and economic implications of the outbreak. We found that bark beetles were damaging 0.2–1.4% of Norway spruce growing stock annually across the Czech Republic in the period 2003–2016. This level increased to 3.1–5.4% in 2017–2019, causing the total depletion of spruce in some regions. The long-term bark beetle dynamics (2003–2019) was driven by the combination of wind disturbance and climatic drivers, represented in our study by annual temperature anomaly and Standardized Precipitation-Evapotranspiration Index. However, the effect of wind was diminished during the period 2017–2019, whereas the effect of drought dominated. Our findings thus suggest a transition from wind- to drought-driven bark beetle dynamics. The outbreak and subsequent large-scale salvaging and wood transportation affected quality of life of people in a broad vicinity of outbreak areas. Extensive management actions aggravated some of the notorious conflicts between forest management and nature conservation, and highlighted the poor harmonization of respective policies. A decrease in timber price, an excessive workload, and other cascading effects caused severe revenue loss, requiring state interventions amounting to ca 260 million EUR in 2018–2019. We suggest that increasing frequency of climate extremes in combination with the unfavorable forest structure pushed Central European spruce forests to the margin of their ecological space and unfolded large-scale forest transformations. Effective responses will require fundamental structural changes in the regional forest-based sector, particularly aiming at increased social and ecological resilience.

The Indiana bat (Myotis sodalis) is a federally listed endangered species negatively impacted by human disturbance, habitat change, and disease. Habitat protection and management of summer roosting habitat and cave hibernacula are recommended for the recovery of this species. We studied roost tree and landscape characteristics of 19 known summer maternity colony habitats in Illinois and Iowa upland oak-hickory (Quercus-Carya) forests. Landscape variables can be highly correlated in fragmented forest habitats and not all the roost tree and landscape variables are relevant to roost tree selection. We employed an algorithm to approximate the data set by using singular value decomposition (SVD) to identify the primary factors governing the selection of maternity roosts. The proposed method (formally referred to as a feature selection algorithm) approximates the data by discarding highly correlated features and features that can be removed without incurring much loss of information. Results indicated that summer maternity roosts were trees closer to forest edge, larger in diameter and typically trees with crowns in the upper canopy of the forest. In addition, partial bark cover and locations within 1 km of water bodies positively influenced the tree selection. Although live or dead shagbark hickory (Carya ovata) were preferred as maternity roosts, snags of other trees species common to Midwest upland oak-hickory forests were also used. We incorporated a joint probability density estimation and the Wilcoxon rank sum test to investigate the relationship between tree species and dead/live tree status for roost tree selection. There was sufficient evidence to infer that the chosen live trees were taller and in more favorable locations compared to the chosen snags. We further observe that the joint distribution for quantitative attributes among dead or declining shagbark hickory was not significantly different compared to the other chosen tree species, indicating that a lack of shagbark hickory may not limit the Indiana bat population. Knowledge of these complex relationships regarding maternity roost habitat preferences is useful for future management of the Indiana bat throughout Midwest oak-hickory forests.

Snags provide essential habitat for numerous organisms and are therefore critical to the long-term maintenance of forest biodiversity. Resource managers often use snag creation to mitigate the purposeful removal of snags at the time of harvest, but information regarding how created snags change over long timescales (>20 y) is absent from the literature. In this study, we evaluated the extent to which characteristics of large (>30 cm diameter at breast height [DBH]) Douglas-fir ( Pseudotsuga menziesii ) snags created by topping had changed after 25–27 y. We also tested whether different harvest treatments and snag configurations influenced present-day snag characteristics. Of 690 snags created in 1989–1991, 91% remained standing during contemporary surveys and 65% remained unbroken along the bole. Although most snags were standing, we detected increased bark loss and breaking along the bole relative to prior surveys conducted on the same pool of snags. Although snag characteristics were not strongly influenced by snag configuration, we found that snags in one harvest treatment (group selection) experienced less bark loss and had lower evidence of use by cavity-nesting birds (as measured by total cavity cover) relative to snags created with clearcut and two-story harvest treatments. Our results indicate that Douglas-fir snags created by topping can remain standing for long time-periods (≥25 y) in managed forests, and that the influence of harvest treatment on decay patterns and subsequent use by wildlife is an important consideration when intentionally creating snags for wildlife habitat.

Felled trap trees have been traditionally used to control bark beetles in central Europe. There is, however, little research on the method and on factors affecting trap tree performance. We therefore evaluated the effect of felling date, tree diameter, site shading, and weather conditions on the pattern of trap tree infestation by bark beetles. An experiment was conducted at two localities with contrasting forest damage rates and bark beetle outbreak phases in the Czech Republic during three periods: December to April of 2004–2005, 2005–2006, and 2006–2007. For each of the three periods, eight dates of trap tree felling were equally spaced. On each date and at each locality, 5–7 trees located at the open forest edge were felled (295 trap trees in total). The number of Ips typographus (Linnaeus, 1758) entry holes dm−2 counted in May each year was used as the response variable. Neural network-based regression models were used to identify the variables that most affected trapping performance. The performance of the regression models in terms of Pearson’s correlation between observed and predicted entry hole densities ranged from 0.15 to 0.93. The effect of predictor variables on the recorded entry hole density was much lower in the forest with a culminating bark beetle outbreak than in the forest with outbreak in retrogradation phase. For trap trees felled before winter, trapping performance was positively associated with the length of the period that the trap trees were covered by snow. The trap trees exposed to higher heat sums tended to show lower entry hole density than trap trees exposed to lower heat sums. The results indicate that, in forests with high beetle densities, there are few options for increasing trap tree performance based on selection of specific sites, tree characteristics, or felling dates. The identified sensitivity of trap trees to weather indicates that trees should be felled just before beetles emerge if conditions have been relatively warm and snowless but can be felled far in advance under cooler conditions with regular snow. Finally, the results indicate that foresters should continue to use large-diameter trees located on non-shaded sites as felled trap trees.

Across the western United States, the three primary drivers of tree mortality and carbon balance are bark beetles, timber harvest, and wildfire. While these agents of forest change frequently overlap, uncertainty remains regarding their interactions and influence on specific subsequent fire effects such as change in canopy cover. Acquisition of pre- and post-fire Light Detection and Ranging (LiDAR) data on the 2012 Pole Creek Fire in central Oregon provided an opportunity to isolate and quantify fire effects coincident with specific agents of change. This study characterizes the influence of pre-fire mountain pine beetle (MPB; Dendroctonus ponderosae) and timber harvest disturbances on LiDAR-estimated change in canopy cover. Observed canopy loss from fire was greater (higher severity) in areas experiencing pre-fire MPB (Δ 18.8%CC) than fire-only (Δ 11.1%CC). Additionally, increasing MPB intensity was directly related to greater canopy loss. Canopy loss was lower for all areas of pre-fire timber harvest (Δ 3.9%CC) than for fire-only, but among harvested areas, the greatest change was observed in the oldest treatments and the most intensive treatments [i.e., stand clearcut (Δ 5.0%CC) and combination of shelterwood establishment cuts and shelterwood removal cuts (Δ 7.7%CC)]. These results highlight the importance of accounting for and understanding the impact of pre-fire agents of change such as MPB and timber harvest on subsequent fire effects in land management planning. This work also demonstrates the utility of multi-temporal LiDAR as a tool for quantifying these landscape-scale interactions.

Natural disturbances such as windthrow and bark beetle Ips typographus L. outbreak often affect protected areas with non-intervention type of management located in close proximity to managed forest stands. This raises concerns about the migration of the beetle outbreak from non-intervention zones to adjacent managed forests. In this study we analyzed the spatiotemporal dynamics of large-scale disturbances by intervention and non-intervention type of management in the Tatra mountains (Central Europe). We collected a time series of Landsat images from 2003 to 2014, and applied maximum likelihood classification to map the extent of forest, windthrow, clear-cuts, beetle outbreak and fire. Our classified maps achieved high overall accuracies: 0.93 ± 0.03 ⩽ OA ⩽ 0.96 ± 0.03. The extent of forest declined over the study period. We found higher rate of beetle induced tree mortality in non-intervention versus intervention zone. Within two growing seasons after the windthrow, beetle infestation occurred in close proximity to uncleared windthrow (

International audience; Tree microhabitats (cavities, conks of fungi, bark features) play an important role for both rare and specialized species biodiversity; their preservation should therefore be targeted by biodiversity-friendly forest practices. However, when compared to other old-growth characteristics like deadwood or large trees, tree microhabitats have only recently been studied so related scientific knowledge is still relatively limited. Defining target values for microhabitat densities in managed forests is mostly based on expert knowledge rather than quantitative empirical data. We compared the densities of microhabitat-bearing trees between managed forests, where wood is still harvested, and strictly protected forest reserves, where harvesting has been abandoned, in 17 French forests (222 plots) located in both lowlands and mountain regions. We found that microhabitat densities are generally higher in strict forest reserves than in managed forests and that this difference is mainly driven by standing dead and large living trees. Though scarce, standing dead trees over-contribute to the difference observed while large trees played a lesser but significant role. In addition, contrary to results obtained for other old-growth characteristics (such as deadwood volumes), the difference between managed and strict forest reserves was higher in mountain than in lowland forests. For individual microhabitats, five out of eleven microhabitats in mountains and only one in lowland (woodpecker cavities) were significantly more numerous in strict forest reserves than in managed forests. Finally, total microhabitat density and density of specific microhabitats such as cavities and bark features increased with time since the last harvest. This increase was also mainly supported by standing dead microhabitat-bearing trees. Compared to previous studies in comparable contexts, the densities we estimated were generally higher; however, such comparisons could only be made for the most documented microhabitat types. Our results support the idea that management abandonment favours the abundance and diversity of microhabitats. However, microhabitat dynamics remain poorly known and only long-term monitoring will help understand underlying mechanisms of recruitment. In the meantime, our results may inspire forest managers in their application of daily biodiversity-friendly practices.

Mammalian browsers can cause ecologically and economically significant damage to important tree species, particularly at the vulnerable seedling stage. Some tree species or particular parts of trees are less preferred as a result of chemical defences – harnessing such defences could reduce the appeal of more preferred trees and thus their loss to browsing. We tested the potential of birch bark extract, a forestry by-product, to protect seedlings of Scots pine Pinus sylvestris from two globally significant browsers: moose Alces alces and red deer Cervus elaphus . We quantified the responses by captive animals to extract application as a function of both the distance between seedlings and whether the extract was applied to all or alternate seedlings. Both moose and red deer consumed pine seedlings less frequently when seedlings were treated with birch bark extract, but their responses differed when only alternate seedlings were treated. At inter-seedling distances equivalent to those used in forestry, red deer browsed untreated seedlings more frequently when alternate seedlings were treated than when none were treated (associational susceptibility), whereas moose browsed untreated seedlings less frequently with treated than untreated neighbours (associational refuge). These neighbourhood effects were not evident at inter-seedling distances three times larger or smaller than those used in forestry. There was also no significant difference in the frequency of browsing on treated seedlings in alternate compared to completely treated arrangements at any inter-seedling distance. Red deer removed significantly less foliage from treated than untreated seedlings once browsed. Browsing by moose followed a similar but non-significant trend. The relative number of untreated to treated seedlings browsed was 2:1 for red deer and 4:1 for moose. Red deer used a finer scale of selection than moose for choosing between seedlings, consistent with their smaller body mass. However, the coarser-scale of selection used by moose resulted in consumption of more untreated relative to treated seedlings. Our study highlights the potential of existing plant defensive chemistry, harvested from forestry by-products, to reduce herbivore damage to tree seedlings. We also demonstrate the need to consider both plant associational effects and the foraging strategies of the dominant herbivores in applying repellents.

Browsing of poplar clones by wild ungulates is a widespread problem in short rotation coppice (SRC) plantations in Central Europe. We investigated the influence of poplar genotype on ungulate browsing intensity, identified the most browsing-resistant poplar clone and explored its repellent potential. Inspection of 11 poplar clones at 7 unfenced SRC plantations in the Czech Republic revealed the most avoided poplar clone by wildlife was Populus nigra × P. maximowiczii ʻMax-4’. Namely P. maximowiczii contributed to the repellent effect of ʻMax-4’ according to the analysis of impacts of individual parental poplar species on the browsing intensity of their hybrid progeny. In contrast, P. deltoides increased attractiveness of its hybrid progeny for browsing ungulates. Poplar browsing and bark stripping/fraying were not correlated. A subsequent feeding experiment with twigs of two poplar clones that had shown contrasting attractiveness for browsing in the field (intensively browsed P. × euroamericana AF24’ vs. avoided P. nigra × P. maximowiczii ʻMax-4’) demonstrated that red deer hinds (Cervus elaphus L.) bred on an experimental farm preferred ʻAF24’ over ʻMax-4’. There was no difference between consumption of fresh and wilted twigs of ʻMax-4’ suggesting the repellent compounds are stable over time. To uncover the chemical nature of repellent compounds, red deer hinds at the farm were offered grain fodder supplemented with polar and non-polar extracts of ʻMax-4’ shoots, commercial repellent (Stop Z) or empty carrier (controls). Non-polar extract of ʻMax-4’ produced transient feeding avoidance suggesting its potential as a game repellent, though optimisation of the extraction procedure and dosage is necessary.

Many tree-dwelling species inhabit microhabitats that develop slowly in diseased or injured trees. Conservation planning would benefit from explicit knowledge of these processes, notably for resolving conflicts with timber production, arboricultural or public safety goals. We reviewed published rates of development of five selected common tree microhabitats and the factors affecting those rates in living trees. Most of the 71 relevant studies found globally focused on tree-cavities and exposed wood, while the development of witches’ broom, bark pocket and dendrotelm microhabitats remains poorly described. Three time parameters emerge as central: minimum tree age; rate of formation; and persistence time of the microhabitat. Among the studied microhabitats, large side cavities are formed in the oldest trees, seldom hosting large vertebrates in trees

Snags (standing dead trees) are important components of forest ecosystems that, among other benefits, provide critical habitat for many species of wildlife, but also represent important safety concerns to firefighters, forest workers, and the public. We identified factors that influence the fall rates of lodgepole pines, Pinus contorta Dougl. ex Loud., killed by bark beetles during a severe regional-scale outbreak of mountain pine beetle, Dendroctonus ponderosae Hopkins, that occurred in 2004–2012. Data were obtained during annual assessments (2010–2019) of a network of 107 0.081-ha circular plots installed in P. contorta forests in Colorado, Idaho, Montana, Utah and Wyoming, U.S. A total of 3789 P. contorta snags were monitored, and in each case we recorded, among other variables, the year the snag was created and the year the snag fell to the forest floor. Among snag age classes (i.e., number of years since tree death), the highest number of snags (1046) were 12 years since death (YSD), and those 13 and 14 YSD exhibited the lowest fall rates to date (

Jarrah (Eucalyptus marginata) forest is one of the most widespread native forest types of south west Western Australia (SWWA) and provides timber, firewood, wildlife habitat, water production, catchment protection and recreation. To inform management aimed at optimizing these values, a thinning trial in even aged regrowth forest was commenced in 1965. A second thinning and N and P fertilizer treatment was applied in 1986. The effect of thinning and fertilizer on tree and stand level growth and allometry was evaluated. Thinning resulted in higher values of under bark diameter at breast height (DBHUB) and tree height, and lower values of height diameter ratio (HDR), stand basal area under bark (BAUB) and stem number per unit area. Growth of DBHUB increased with a decrease in stand density. Growth of stand BAUB peaked at intermediate stand densities. Fertilizer increased growth in DBHUB and stand BAUB. Height growth was significantly greater in thinned plots. Thinning had a significant effect on the allometric relation between diameter at breast height over bark (DBHOB) and each of height, HDR and crown width (CW) while fertilizer had a significant effect on the allometric relation between DBHOB and each of height and HDR. Height and CW increased with an increase in DBHOB but HDR decreased. Larger sized trees resulting from thinning and addition of fertilizer are likely to provide a higher volume of timber, firewood, fruits (important food for threatened cockatoos), and improved visual amenity. As thinning had a positive effect on diameter and height growth and self-thinning in jarrah is relatively low (0.20% yr−1), thinning may be a valuable management tool to accelerate development of larger trees which can be beneficial for both timber production and conservation.

Bark stripping by Asiatic black bears ( Ursus thibetanus ) has a serious impact on conifer plantations in Japan, resulting in physical damage to the tree trunks and reduction of the value of the timber. The aim of this study was to clarify whether these plantations are more prone to damage by bears at particular times and sites, to more effectively prevent this damaging behavior. The study was conducted at Kusaki University Forest of Tokyo University of Agriculture and Technology in Gunma Prefecture, central Japan. To determine where, when, and how frequently bears strip the bark, we established circular plots in each of 65 stands and felled all trees that had been damaged by bears. In total, we felled 1639 damaged trees, analyzed 1490 samples ( Cryptomeria japonica : 1236, Chamaecyparis obtusa : 254) across the 65 study stands, and calculated the timing of bark stripping for each by counting the number of annual growth rings in each tree. Generalized linear mixed models were then used to examine the effects of various spatiotemporal factors on bark stripping. In terms of temporal variation, we found no relationships between the occurrence of bark stripping by bears and the meteorological conditions from the previous November to the previous March. In terms of spatial variation, there was no relationship between the occurrence of bark stripping by bears and the environmental characteristics of the stands. We did, however, find that stands that experienced bear damage in the previous year were more prone to experiencing bear damage in the current year, and furthermore, the rate at which damage of trees spread during the 10 years after the first occurrence of a damaged tree was significantly faster in young stands. These findings will allow forest managers to predict the conditions that make conifer stands more prone to bear damage, allowing them to make effective forest management plans. Additionally, to reduce bear damage, foresters should focus on direct protection efforts that they would like to protect from bears.

Future anthropogenic-induced changes to the earth’s climate will likely include increases in temperature and changes in precipitation that will increase the frequency and severity of droughts. Insects and fungal diseases are important disturbances in forests, yet understanding of the role of drought in outbreaks of these agents is limited. Current knowledge concerning the effects of drought on herbivorous insect and pathogen outbreaks in U.S. forests is reviewed, and compared between the relatively mesic and structurally diverse forests of the eastern U.S. and the more xeric forests of the western U.S. Theory and limited evidence suggests a non-linear relationship between drought intensity and outbreaks of aggressive bark beetle species (i.e., those capable of causing extensive levels of tree mortality), where moderate droughts reduce bark beetle population performance and subsequent tree mortality, whereas intense droughts, which frequently occur in the western U.S., increase bark beetle performance and tree mortality. There is little evidence for a role of drought in outbreaks of the southern pine beetle (Dendroctonus frontalis), the only bark beetle species that causes large amounts of tree mortality in the eastern U.S. Defoliators do not show consistent responses to drought. The response of sapfeeders to drought appears non-linear, with the greatest performance and impacts at intermediate drought intensity or when drought is alleviated by wetter periods. Interactions between tree pathogens and drought are poorly understood, but available evidence suggests reduced pathogen performance and host impacts in response to drought for primary pathogens and pathogens whose lifecycle depends directly on moisture (humidity). In these cases, rates of reproduction, spread, and infection tend to be greater when conditions are moist. In contrast, secondary fungal pathogens (i.e., those that depend on stressed hosts for colonization) are anticipated to respond to drought with greater performance and host impacts. In the western U.S., drought increases stress on trees severely infected by mistletoes thereby predisposing mistletoe-infected trees to attack by insects, particularly bark beetles and wood borers. Research needed to advance understanding of drought impacts on forest insects and diseases, and the role of forest management in mitigation of infestations during drought are discussed.

The current outbreak of eastern larch beetle ( Dendroctonus simplex LeConte) in Minnesota, USA, ongoing since 2000, has been characterized with a severity and duration unprecedented in previous outbreaks within the state. This study investigates the relationship between tamarack mortality due to eastern larch beetle and extant stand and site characteristics. Observations of tree attribute information and site condition collected over the course of the outbreak from nearly 15,000 tamarack trees in three different ecological regions of Minnesota were modeled using linear regression. Increasing tree diameter was the best indicator of tamarack mortality within the northern limits of the state’s tamarack range and during the later portion of the outbreak. Tamarack density was negatively related to tree mortality in the north-central region during the later outbreak, while the density of co-located non-host gymnosperms was positively related to tree mortality in areas of marginal host distribution. A temporal change in the importance of predictor variables suggests that the influence of tree and site characteristics evolved as the outbreak progressed and subsequent mortality increased. A greater understanding of the factors associated with tamarack mortality and how the those factors change over time and space will help to inform management practices and mitigate the impacts of this bark beetle on the tamarack resource in Minnesota.

The simultaneous control of insect pests and compliance of conservation targets in conifer-dominated forests has intensified public debate about adequate post-disturbance management, particularly in protected areas. Hence, mechanical bark treatments, such as debarking, of disturbance-affected trees have been widely promoted as an on-site method of pest control that accounts for conservation targets because woody biomass is retained. However, the effects of debarking to non-target biodiversity remain unclear. We analyzed data from a two-and-a-half-year field survey of wood-inhabiting fungi, saproxylic beetles and parasitoid wasps in twelve artificial windthrows, created by pulling down mature Norway spruce trees (Picea abies) with winches. Each experimental windthrow comprising one control tree, one completely debarked tree and one bark-scratched tree. Insects were sampled using stem emergence traps. Fruiting bodies of wood-inhabiting fungi, number of wood wasp emergence holes, and number of holes made by foraging woodpeckers were assessed by visual counts. We recorded the amount of time needed to complete debarking by machine, bark-scratching by machine and bark-scratching by chainsaw each on 15 separate trees to estimate the economic costs of mechanical bark treatments. Our results revealed that both debarking and bark-scratching significantly decreased numbers of the emerging target pest Ips typographus to in median 4% (debarked) and 11% (scratched bark) of the number of individuals emerging from untreated control trees. Compared to control trees, debarking significantly reduced the species density of wood-inhabiting fungi, saproxylic beetles, and parasitoid wasps. By contrast, bark-scratching did not reduce the overall species density of wood-inhabiting fungi, saproxylic beetles or parasitoid wasps. The time needed for bark-scratching by machine was significantly lower than debarking, whereas bark-scratching by chainsaw needed a similar amount of time as conventional debarking. However, bark-scratching did have some negative effects in common with debarking, such as the significant reduction of wood wasps emergence holes and the reduction of holes made by foraging woodpeckers. Hence, bark-scratching of downed trees, like debarking, might affect higher trophic levels of biodiversity and should be applied only if pest management is urgently needed. We urge policy makers and natural resource managers to rapidly shift current pest management toward new techniques of bark-scratching, particularly in protected areas. Such a shift in post-disturbance pest-control will foster ecosystem integrity at lower economic cost compared to debarking.

Bark beetle (Curculionidae, Scolytinae) outbreaks have been extensive and severe across the western United States in recent decades, and assessments of tree mortality are critical for documenting patterns and increasing understanding of drivers and impacts. Aerial surveys have produced a rich data set that includes damage severity, year and location of damage, and beetle and tree species. Here we update a data set of bark beetle-caused tree mortality for the western United States to include five additional years (now 1997–2018) and use these data to characterize recent outbreaks and compare with earlier tree mortality. We estimated “mortality area” (MA), the canopy area of beetle-killed trees and a more accurate representation of outbreak impacts than “affected area”, as well as the number of killed trees. Recently, the US Forest Service changed survey approaches, creating challenges for linking observations from the old and new approaches. We compared four methods to harmonize these approaches to produce consistent time series of tree mortality. General similarity of MA occurred in several methods; however, the range of results indicated some uncertainty. Based on limited analyses and a desire to be conservative in damage estimates, we suggest that the FHPR1-R4 method, which produced intermediate mortality among the methods, is most realistic for representing tree mortality from bark beetles. Using this recommended method, we found that bark beetles caused 4.3 Mha of MA and 3.8x109 killed trees when summed across space, time, and bark beetle/host combination (range among methods: 1.5–7.4 Mha and 1.2–6.3 x 109 killed trees). This total mortality area was 4.7% of forest area in the western United States; 28% of this mortality occurred in 2013–2018. Annual tree mortality remained high recently, with values comparable to earlier years, and was a result of combinations of outbreaks of different beetle species in different regions with different timing. Bark beetles continue to be agents of significant forest disturbance in the western United States. Given a range of mortality area results from the different methods, we encourage further evaluation of estimates using independent observations.

Acute Oak Decline (AOD) is devastating thousands of native oaks, Quercus robur and Q. petraea, in the UK and continental Europe. The syndrome is principally caused by multiple, interacting bacterial species that degrade inner bark tissues. The level of host predisposition required prior to AOD infection is unknown. The two spotted oak buprestid Agrilus biguttatus is strongly associated with AOD, although its role remains unclear. To investigate the nature of predisposition in AOD, to explore the role of the beetle in the syndrome, and to examine growth trends after AOD onset, the stem growth of 243 trees with a range of severity of AOD symptoms was analysed at five sites in England. Novel mixed effects dendrochronological modelling methods were developed. The presence/absence of A. biguttatus exit holes in the trees was not specifically linked with reduced stem growth, nor was there evidence of further reductions in growth after the onset of AOD symptoms. Instead, trees with long-term AOD symptoms show significantly reduced growth compared to asymptomatic trees from as far back as the 1930s, following a period of widespread decline in English Oaks. These results suggest that a cohort of oak trees across Britain was permanently damaged in the 1930s and predisposed to develop AOD symptoms decades later. Additionally, correlations with climatic variables suggest that diseased trees are less able to take advantage of good growing conditions in the spring and autumn. This study sheds light on how historical episodes of stress may impact the future resilience of oaks to disturbance, and supports the use of dendrochronological modelling as a technique to study the underlying health status of oak tree populations, and to better understand tree decline episodes.

Despite different levels of complexity among biomass models, it is unclear how much patterns of biomass production and allocation differ between mountain and lowland forests, and how much neglecting this difference biases carbon pool estimations. To address this question, we studied chronosequences of 24 Fagus sylvatica and 24 Picea abies stands in Poland, located both in lowlands and highlands (12 stands of each species per category). We cut and weighted 192 sample trees, and we measured carbon content in wood, bark, branches and leaves. We also developed allometric tree- and stand-level models of biomass and carbon mass. Using log-transformed linear models we checked the effect sizes of elevation category (lowland and highland) on estimate output. We found small, statistically insignificant differences in biomass allocation patterns, carbon content and allometric trajectories in trees between lowland and highland stands. Tree-level allometric models without elevation category had higher accuracy than models including elevation category and explained 96.8–99.8% of biomass variability. Biomass and carbon stock of species studied was positively correlated with stand volume, age, basal area and height, and negatively with stand density. However, the differences between lowlands and highlands were low and did not exceed 38 Mg ha−1 (for P. abies foliage biomass, with model root mean squared error of 37.638 Mg ha−1). Our results revealed transferability of models developed using lowland and highland populations of the studied species. This will increase confidence in methods used to estimate carbon pools.

Outbreaks of the European spruce bark beetle Ips typographus kill extensive areas of Norway spruce forests in Central Europe, affecting both protected areas and neighboring commercial forests. In protected areas, uncontrolled (non-intervention) management allows natural beetle-induced tree mortality, while in commercial forests infested trees are salvage-logged in order to lower I. typographus numbers and stabilize wood production. However, the effects of active pest controls on I. typographus population are often ambiguous, and little is known about how antagonists, beetle density, or intraspecific competition help terminate I. typographus outbreaks. To answer this question, we studied I. typographus population development, breeding performance, and natural antagonists under intervention and non-intervention management in the High Tatra Mts. from 2014 to 2017. We used sentinel logs and windthrown trees, following the current legislation in Tatranský narodný park (TANAP, Slovakia) and Tatrzanski Park Narodowy (TPN, Poland). Both parks are mountainous, are covered by Norway spruce forests that have been extensively affected by windthrows and extensive I. typographus outbreaks over the last 20 years, and are zoned under intervention and non-intervention types of management. We found that I. typographus was a dominant species and that its numbers gradually increased during the study, but that the numbers of maternal galleries in sentinel logs (from 50 to 300 per m2) and sex ratio (1 male:2.5 females) remained the same among years. The length of maternal galleries and egg production (per m2 of bark), however, gradually declined, and breeding performance decreased from 10 daughter beetles per female in 2014 to almost zero in 2017. These parameters did not significantly differ between intervention and non-intervention sites. Antagonists were not abundant and had limited effects on I. typographus numbers. Active intervention did not affect I. typographus population dynamics or rates of parasitism but increased numbers of Thanasimus beetles, which are predators of bark beetles. In other words, intervention increased the numbers of some natural enemies of I. typographus but did not affect I. typographus population dynamics. Because control measures did not reduce I. typographus numbers in the intervention zone, the natural ecological processes crucial for maintaining ecosystem functioning and biodiversity were evidently preserved.

Whitebark pine (Pinus albicaulis) is a critical forest species of Northern Rocky Mountain upper subalpine ecosystems, yet little is known about the physiological response of whitebark pine to disturbance (e.g. fire, bark beetles, and pathogens) across a range of diverse environmental gradients. Resin-based defenses have long been recognized as the primary mechanism by which conifers respond to attack by bark beetles and pathogens and several studies have linked resin duct properties to survivorship during periods of increased beetle activity. However, to our knowledge, no studies have compared axial resin ducts in the secondary xylem of whitebark pine across pairs of living and dead whitebark pine trees to better understand survivorship following multiple disturbances including mountain pine beetle and white pine blister rust. We found a clear distinction in growth and defense characteristics between live and dead whitebark pine. Across our study sites on the Flathead Indian Reservation in northwestern Montana, live whitebark pine produced larger resin ducts with a greater annual investment in resin-based defenses than whitebark pine that died. Resin duct size, duct area, and relative duct area were all greater in live whitebark pine (by 56%, 48%, and 57%, respectively) and these were the most important variables influencing whitebark pine survivorship. In contrast, whitebark pine that had died grew faster over time (22% larger ring widths) than their live counterparts and also produced more resin duct structures (20% more ducts on average). Whitebark pine at our study sites exhibit differing strategies in the allocation of resources toward growth and defense, with the majority of survivors of recent disturbance investing more in defensive structures than growth. Our results support the idea that maintaining genetic variability and the associated suite of differing physiological traits promotes diverse response strategies to a complex array of biophysical and biological stressors that might leave a species vulnerable to extinction across its range.

This study investigates temporal shifts in Norway spruce (Picea abies) mortality, stand structure characteristics, and stand complexity facilitated by a bark beetle (Ips typographus) outbreak that affected an unmanaged subalpine forest region in Tatra National Park, Poland in the late 2000s. Changes in survivorship and stand structure characteristics (diameter (DBH), basal area, height, age, and crown length ratio) of nearly 2500 spatially-referenced trees located in 64 long-term survey plots were compared over four time periods that spanned the duration of the outbreak disturbance event. Stand structure characteristics, topographic factors (slope, elevation, and aspect), and solar equinox radiation were tested as predictors of mortality for multiple stages in the outbreak using boosted regression tree modeling. Our findings showed that: (1) spatial synchrony was not reflective of mortality severity; (2) mortality rates increased significantly as the outbreak progressed; (3) the stand’s structure was altered significantly by the outbreak (larger trees were killed most frequently); (4) stand structure characteristics were the best predictors of mortality in all stages of the outbreak, though topographic factors and solar equinox radiation also exhibited moderate to strong predictive power in some stages; and (5) stand complexity decreased significantly as the outbreak progressed. This illustrates the inherently complex nature of bark beetle outbreaks on fine spatial scales and suggests that the extent and severity of spruce mortality during an outbreak event is largely dependent on the relative stage of the outbreak and the structure of the stand.

Aspen mortality and overstory dieback have occurred at unusually high levels throughout Colorado and western North America over the past fifteen years. Findings from southwestern Colorado indicated dieback and mortality was clearly related to climate stress, coupled with disease and insect attack. To determine whether similar amounts and causes of mortality were occurring in other mountainous regions of Colorado and southern Wyoming, we determined the health status of aspen on five national forests during 2009–2010. We established 500 random characterization plots in aspen-dominated stands on four of the five national forests and 97 detailed measurement plots, with half in ‘damaged’ and half in ‘healthy’ aspen stands (as defined by USDA Forest Service aerial detection surveys). Overstory aspen was healthy overall, in spite of nearly ubiquitous presence of disease among plots (99%) and high incidence of insect damage (50–75%); in detailed plots standing adult dead aspen percentages ranged from 20% to 33% among the five national forests. Adult aspen in damaged stands occurred at lower densities, and had thinner crowns (41% dead crown, compared to 16% in healthy stands). Damaged stands also had more standing dead adult trees (37%) than in healthy stands (16%). The proportion of live sapling stems and density of saplings did not differ between healthy and damaged stands. Incidence of select mortality agents, including wood-boring insects ( Agrilus liragus and Saperda calcarata ) (40% in damaged, 18% in healthy), aspen bark beetles ( Procryphalus mucronatus and Trypophloeus populi ) (31% in damaged, 12% in healthy) and Cytospora canker (caused by fungi in the genus Cytospora ) (40% in damaged, 18% in healthy) was considerably greater among damaged stands. Aspen bark beetles were more common on south-facing sites than east or west-facing sites (27%, 17%, and 15%, respectively); Cytospora canker was less common on sites above 2800 m (23%) than on lower-elevation sites (28–34%). Prevalence of wood borers, aspen bark beetles and Cytospora canker were all significantly and negatively correlated with latitude among at least two of three aspen size classes. Attempts to model various measures of health of adult aspen (i.e. crown dieback and stem mortality) using site and climatic variables were largely unsuccessful. Since no differences were detected in density of regeneration between damaged or healthy stands, we conclude that most stands will persist upon the landscape for the foreseeable future. Further, we note that although observed densities of regeneration in damaged stands are not as great as levels observed following complete stand removal, suckering does occur, and stems are measurably healthier than regeneration in healthy stands.

Management of Norway spruce monocultures in Europe is becoming increasingly difficult due to frequent natural disturbances. Their transformation could be especially challenging if several disturbances interact. In 2003 a spruce bark beetle outbreak damaged large tracts of spruce bottomland successional forest in southeast Slovenia where overabundant ungulate populations are present. In openings (5.4–7.5 ha in size) in four salvaged forest compartments, we studied the effects of meso-relief, forest edge, seed trees and fencing on vegetation succession and tree regeneration. In 2005 and 2013 we sampled seedling density on 240 plots according to height class and species. In the second inventory we also assessed distance to seed trees and on a subsample of the plots the coverage of vascular plants. The results indicated sufficient natural regeneration and niche partitioning among species groups, with Norway spruce seedlings being more successful at stand edges, pioneers and anemochorous broadleaves in gap centres, and zoochorous broadleaves on plateaus as opposed to sinkholes. Seedling density of all anemochorous broadleaves was higher closer to seed trees. Spruce seedling abundance was negatively associated with the cover of herbaceous vegetation and that of pioneer trees with shrubs. Fencing resulted in significantly greater density, height and coverage of seedlings as well as a higher share of broadleaves. While bark beetle outbreak triggered regeneration of broadleaves, overbrowsing acted in the opposite direction by facilitating spruce. Thus, to accelerate successional development and to prevent a spruce dominated alternative ecosystem state, a significant reduction in deer abundance is needed. To safeguard seed sources, promote seed dispersal by encouraging perches and shelters, and preserve potential habitats, some damaged trees should be retained during salvaging operations.

Many saproxylic insects (insects dependent on deadwood) are threatened because the amounts of suitable substrate, coarse woody debris (CWD), are low in managed forests. Harvesting clear-cut stumps for bioenergy will decrease these amounts further and may therefore contribute to loss of biodiversity. Earlier studies have demonstrated that many saproxylic beetle species utilise clear-cut stumps. However, the importance of stumps compared with other kinds of deadwood remains unknown. In particular, some species adapted to sun-exposed deadwood created by disturbances might, in managed forest landscapes, be dependent on stumps in clear-cuts. In the present study we quantify the proportions of landscape-wide populations of saproxylic beetles that are recruited from clear-cut stumps in a managed boreal forest landscape. The amount of bark on clear-cut stumps and population densities (beetles per m 2 bark) were estimated for a 24,499 ha landscape in Sweden. Our data were pooled with estimates from a similar study in the same landscape, including all other types of CWD and beetle densities. The clear-cut stumps were estimated to contribute 15.5% of total bark to CWD in the landscape. For spruce, clear-cut stumps contributed 37.9% of the total bark. Of 39 analysed beetle species, 13 were estimated to have more than 10% of their populations in clear-cut stumps, 9 more than 50%, and 5 more than 80%. Clear-Cut stumps are thus an important breeding substrate for many beetle species and consequently, intensive stump harvest risks decreasing biodiversity.

Because of their significant impact on forests, tree-killing bark beetles have been widely studied at epidemic population densities. However, bark-beetle outbreaks emerge from populations at low, endemic levels, where population maintenance and growth depend on scarce, ephemeral resources such as lightning-struck trees, weakened and suppressed standing trees or wind-felled trees, depending on the species. The longevity of these resources strongly influences population dynamics, but very little is known in this respect. We tested the hypothesis that the driving factor reducing the availability of fallen trees is the decrease of their nutritional quality. We analysed the qualitative changes of the phloem of spruces artificially uprooted at different times (2–17 month before the experiment started) and simultaneously exposed during the same flight season to attacks of the major forest pest in Eurasia, Ips typographus . We also measured the impact of resources’ decay on the insects’ fecundity and the quality of their offspring. Our results show a surprisingly slow decrease of phloem quality over time . The beetles could develop on the oldest (17 month-old) resources with no significant differences in terms of fecundity, progeny body mass and global energy acquisition. Although they retain their nutritional quality over long periods, transient resources are exposed to other factors that make them rapidly unsuitable for I. typographus . We suggest that interspecific competition is probably the most influential of them, and acts as a major driver in the beetles’ race for new resources.

Impacts of drought on tree mortality in high-elevation mixed-conifer forests of southwestern U.S. are poorly understood. A recent extended and severe drought in the region provided an opportunity to investigate the patterns and factors associated with tree mortality in this forest type. Specifically, we quantified mortality that occurred between 1995 and 2008 of four tree species, white fir (Abies concolor), limber pine (Pinus flexilis), trembling aspen (Populus tremuloides), and Douglas-fir (Pseudotsuga menziesii), in mixed-conifer forests over three sites in northern Arizona within 84, 0.02 ha plots. We found: (1) varied but substantial tree mortality (4–56% by basal area) in most species between 1996 and 2006 in association with recent severe and prolonged drought; (2) tree mortality differed among sites and species with aspen and white fir having the most mortality (>30% by basal area); (3) relationships between tree mortality and most climatic factors (e.g. temperature, precipitation, Palmer Drought Severity Index) were lagged 1–4 yr; (4) bark beetle attack and intraspecific tree basal area were consistently and positively related to tree mortality for most species and sites, whereas topographic and other stand characteristics were less consistently related to mortality. Results show that aspen, Douglas-fir, and white fir were more vulnerable to recent drought-associated mortality than limber pine. Associations between tree mortality and intraspecific basal area support further evaluation of treatments that reduce intraspecific competition within stands to lower risks of tree mortality in southwestern mixed conifer forests.

Bark beetles are among the main biotic hazards affecting forests worldwide. Aerial surveys are an appropriate and commonly used tool for detecting and monitoring bark beetle infestations at the landscape scale. However, a considerable time-lag in the aerial-surveyed data limits its use, e.g. for analyses which include temporary factors. This temporal lag is caused by the gradual decay of the host tree following a bark beetle attack. A change in the spectral signature in aerial imagery indicates an attack with a delay of several weeks or even months. Thus, aerial-surveyed infestation data suffer a temporal shift, i.e. infestations detected for a specific time period cannot be directly assumed to have been initiated within that same period. The present study introduces an algorithm which assigns the most probable time of Ips typographus L. attack to infestations detected by aerial surveys. To calculate the infestations initiated within a certain year x the algorithm considers the potential attack period, the assumed time-lag, as well as the date of aerial surveys and the amount of detected infestation from the years x, x − 1 and x + 1. The deviation between infestations detected by aerial survey and those actually initiated (as calculated by the algorithm) quantifies the correction effect, i.e. the time-lag bias. The algorithm was then applied to a data set which covers a time series of 26 consecutive years, including both managed and non-managed infestations. To account for uncertainty in the input variables or to mimic varying environments the application considers three different scenarios. Over all three scenarios results indicate substantial deviations, which may be either positive or negative. Further, deviation is shown to be affected by the length of the time-lag and the attack period, as well as by variations in survey dates and infestation frequency of consecutive years. Finally, the time-corrected infestation data provides a threefold benefit: (i) The temporal pattern of oscillating population dynamics is truly reflected. (ii) Comprehensive correlation analyses which include dynamic environmental covariates, e.g. temperature, precipitation, or antagonists, are facilitated. (iii) Aerial-surveyed and ground-surveyed monitoring data can be easily related whether within a region or between regions. In conclusion, this study increases the value of aerial-surveyed infestation data for bark beetle monitoring and research.

Bark beetle outbreaks have increased in Europe and North America. To mitigate damage efficiently during outbreaks, robust models predicting where the risk for tree mortality is highest across forest landscapes and better understanding of the underlying mechanisms are required. Using Boosted Regression Trees, we modelled relative risks of infestation by the spruce bark beetle Ips typographus (L.) across a 130,000 ha managed lowland forest landscape in southern Sweden during three years of an outbreak and at a resolution of 100 × 100 m. A second nearby landscape of similar size was used for validation. Both predictors reflecting forest susceptibility and beetle pressure were used. Forest susceptibility predictors included volume per ha of host and non-host trees, tree height and distance to the nearest clear-cut harvested during the last four years, all based on interpretations of satellite images. Bark beetle predictors were based on locations and sizes of previous year infestation spots recorded by helicopter. Model outcomes were similar across years, and there was no major reduction in performance when extrapolating predictions in space or time, indicating the modelled relationships have high reliability. Area under curve (AUC) values varied from 0.729 to 0.818. Including bark beetle predictors increased the AUC value somewhat in one of two years. The most important predictor was volume per ha of the host tree, Norway spruce Picea abies (L.) Karst., which reflects the probability of bark beetles encountering suitable trees. This variable was strongly positively correlated with risk up to 200 m3 ha−1. Unexpectedly, the volume of the non-host birch was also positively correlated with infestation risk up to 25 m3 ha−1. Tree height was associated with increased infestation risk above heights of 10 m in 2008 and 15 m in 2009. In 2007 and 2008 there was a weak negative relationship between infestation risk and distance to the nearest clear-cut. Additionally, our study shows that in managed forest landscapes the I. typographus-killed trees are distributed in many small infestation spots spread out over the landscape. We demonstrate that high-resolution risk-rating maps can be successfully created for large landscapes using easily accessible satellite data of forest characteristics and aerial surveys of infestation spots. The distribution of killed trees in many small infestation spots, poses a challenge for the forest owners to find and remove colonized trees before the new generation emerge. Our results suggest that mitigation efforts in managed lowland forest should focus on high volume spruce stands.

An outbreak of spruce bark beetle (Ips typographus [L.]) in the Tatra Mountains in the Slovak Republic and Poland, Central Europe, was analysed. The study area was nearly 3000 ha. The 11 year outbreak lasted from 1990 to 2000. Three outbreak phases were identified: 1990–1994 (incipient epidemic), 1995–1996 (epidemic) and 1997–2000 (post-epidemic). More than 118,000 m3 of trees were damaged by wind and bark beetles. The analysis considered the relationship and succession of these two types of disturbances. Discrimination analysis, a multiple linear regression and boosted regression trees were used to determine the influence of 11 variables on tree mortality initiation and severity. The wind–bark beetles disturbance system was primarily influenced by stand related factors. Tree mortality initiation primarily depends on stand age and related changes in Norway spruce size and vitality. Wind caused tree mortality severity was primarily related to the tree or stand characteristics as well. The roles of host and environmental factors in the initiation and severity of tree mortality were influenced by the I. typographus outbreak phase. Stand, site and solar radiation variables were the most important factors impacting tree mortality severity caused by this disturbance system, especially in the epidemic phase. However, the severity of tree mortality caused by wind was primarily correlated with the stand characteristics. With the exception of elevation, the roles of the studied factors were similar in all gradation phases.

Organisms dependent on dead wood (i.e., saproxylic) are some of the most threatened by changes in the forest environment. Aside from anthropogenic disturbances resulting in forest fragmentation and a decrease in dead wood, the expansion of homogenous closed-canopy forests due to successional changes is identified as the main threat for many saproxylic organisms. It is especially important in major conservation areas in Europe. Thus, studies combining knowledge about the habitat requirements of saproxylic species with the impacts of different types of forest management on populations of these organisms are essential to identify effective conservation strategies. In this study, we focused on three threatened saproxylic beetles with similar ecology, i.e., Cucujus cinnaberinus, C. haematodes and Boros schneideri, in a close-to-natural forest. The study was conducted in the stronghold of these species in temperate Europe, the Bialowieza Forest in Poland, based on a field survey of more than 11,000 dead wood pieces. We investigated the habitat requirements of these species and their relationships with the environment at the tree and landscape levels. We further analysed the distribution of these beetles in forests under various levels of management intensity. Based on the results of the present study and published data on compositional changes in the forests in the study area, we attempt to formulate implications related to the conservation of the studied beetles. Cucujus cinnaberinus was the most widespread and frequent species, with a preference for high-diameter dead aspens in managed forests with high dead wood amounts. The second most abundant species, C. haematodes, preferred downed ashes and alders with rather fragmented bark. Its distribution was spatially aggregated in unmanaged forests. The rarest beetle in this study, B. schneideri, was associated with forests with large dead pines. Our results confirm the importance of the Bialowieza Forest for the three threatened saproxylic beetles. The study also revealed the highly diversified demands of these beetles, which may not be met in the future if the abundance of the preferred habitat tree species is declining. We recommend a conservation strategy that combines non-intervention towards naturally developed deadwood with monitoring of tree recruitment and if necessary, measures to assure recruitment of particular tree species, e.g., pine and aspen. Future studies should investigate the role of natural disturbances for recruitment of these tree species and thus, the long-term persistence of associated saproxylic beetle species.

Primates bark-strip trees in forest plantations worldwide, producing large economic losses. The primate and tree species involved, the spatial and temporal patterns of this problem, the effectiveness of the methods used to mitigate damage and the causes of this behavior are not yet understood. I conducted a literature review of this topic, focusing on documents reporting primates bark-stripping trees in forest plantations and forests. The data set consisted of 51 documents of which 46 corresponded to bark-stripping of trees in forest plantations and five in managed forests. Thirteen non-human primate species have been recorded bark stripping trees of commercial value worldwide. Three of these, the chacma baboon (Papio ursinus), the black capuchin monkey (Sapajus nigritus) and Sykes´s monkey (Cercopithecus albogularis), are responsible for most of the damage reported in large scale plantations, affecting mostly pine (Pinus sp.) plantations in five African and two South American countries. With fewer reports, orangutans (Pongo pygmaeus) affect large scale Acacia mangium plantations in Indonesia, and yellow baboons (Papio cynocephalus) and vervets (Chlorocebus aethiops) pine plantations in Malawi and Zimbabwe respectively. The Barbary macaque (Macaca sylvanus) bark-strips Atlas cedars (Cedrus atlantica) in Moroccan forests. Eucalyptus sp. plantations, both small and large-scale, are less frequently affected by gorillas, two colobine monkeys, howler monkeys, capuchins, baboons and chimpanzees. Actions to mitigate this problem, including the massive killing of primates, had proven ineffective in the long term. Bark-stripping of pines tends to be more seasonal than that of Eucalyptus, and their damage of higher incidence and intensity. The most frequently cited hypothesis for why primates bark-strip trees in plantations is that they consume soft bark when or where their natural food is scarce. However, this hypothesis is not generally supported by empirical evidence. Eucalyptus bark may be sought after for its high sodium content. Pines are apparently bark-stripped to consume the sugary phloem during their growing season, when bark is presumably more easily peeled off. If this hypothesis were correct, a management method based on diversionary feeding could alleviate the damage produced by primates to coniferous trees of commercial value. Fil: Di Bitetti, Mario Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú | Universidad Nacional de Misiones. Instituto de Biología Subtropical. Instituto de Biología Subtropical - Nodo Puerto Iguazú; Argentina. Centro de Investigaciones del Bosque Atlántico; Argentina

In July 2013, an EF1 tornado and straight line winds caused extensive forest damage in the Scientific Forest Management Area of Baxter State Park in northern Maine, USA. Subsequent salvage operations removed damaged trees from some areas, while leaving blowdown in other areas. Undisturbed control, blowdown, and blowdown + salvage (hereafter, salvage) treatments were established within and adjacent to damaged forests. Bark beetles (Coleoptera: Curculionidae: Scolytinae) and woodborers (Coleoptera: Buprestidae, Cerambycidae; Hymenoptera: Siricidae) were trapped using semiochemical-baited traps from within each of these areas over a three-year period (2014–2016). Disturbance-initiated outbreaks of Dendroctonus rufipennis were a major concern after the windstorm. However, D. rufipennis populations were low throughout the three-year experiment, and were captured more often in controls than in the two disturbed treatments. Overall, bark beetles and woodborers were captured at higher numbers in the two disturbed treatments, relative to controls. Individual species responses varied, with many species found more often in one of the disturbed treatments compared to controls. Species richness and abundance were generally higher in disturbed treatments than in controls. Blowdown and salvage treatments were also more similar to one another than to controls. Large amounts of dead wood provided easily exploitable habitat for wood-inhabiting insects in treatments; however, no evidence of alarming population increases of primary bark beetles were observed, suggesting that salvage operations are not always necessary to protect residual trees from attack by damaging bark beetles.

Atlantic oakwoods are of high conservation value in western Europe. Developing effective conservation management policies requires data on the dynamics of woodland over long time scales. Such data are not available through monitoring or documentary records so palaeoecological data have been investigated. Pollen and charcoal data from four western Irish woods covering up to 7000 years have been analysed to provide information on changes in alpha and beta diversity, rates of change and fire history over time. These analyses reveal that the most significant changes in biodiversity relate to the loss of Pinus sylvestris from these woods followed by their exploitation and subsequent management for timber, charcoal and tan bark. The structure and composition of the present day woods still display a strong legacy from their exploitation and this raises important questions relating to the long-term conservation management of these woods.

Prescribed fire is a common management practice in fire-tolerant forests, and one that has potential carbon costs. Previous assessments of the carbon costs of prescribed fire regimes in temperate Australia have been based on little empirical data, and have focused on direct fire effects (area burnt, fuel consumed) but have largely ignored potentially substantive indirect effects on tree mortality and growth. This study measures effects of four prescribed fire treatments on standing tree-based carbon stocks, and on individual tree growth and mortality, in a fire-tolerant eucalypt forest of south-eastern Australia. Prescribed fire treatments were as a factorial combination of two seasons (autumn or spring) and two frequencies (3-yearly ‘High’, or 10-yearly ‘Low’), were replicated over five study areas, and involved 2–7 low-intensity fires over 27 years. Total standing tree-based carbon stocks (live and dead) were significantly less in prescribed fire than control treatments. However, the mean carbon difference (25 Mg ha −1 ) had a wide 95% confidence interval (2–48 Mg ha −1 ), indicating a high degree of uncertainty about the magnitude of prescribed fire effects in these native forests. Overall decreases were consistent with detection of both direct and indirect effects of prescribed fire treatments. Direct combustion effects on bark were minimal (c. 0.2–0.4 Mg ha −1 ), but were also indicated by significantly less carbon in dead large stems in fire than control treatments despite evidence of marginally increased mortality of individual large stems in the former. Indirect effects of repeated prescribed fires were also detected as significantly decreased mean annual diameter increment of individual large Eucalyptus obliqua over 27 years (particularly of stems 20–50 cm diameter). With respect to prescribed fire type, small live stem densities and associated carbon stocks were greater in autumn than spring, and in Low than High frequency treatments, and carbon stocks in large dead stems were greater in High than Low frequency treatments. This suggested that c. 10-yearly fires in autumn provided the most scope for maintaining future capacity to fix carbon. Nonetheless, decreases in total standing tree-based carbon stocks were not significantly different among prescribed fire treatments, suggesting tree-based carbon stocks were more influenced by prescribed fire per se than by fire season or frequency.

Several days of hourly fuel moisture sampling were carried out in Southern Tasmania in dry and damp eucalyptus forest to test fuel moisture prediction models used in Australia, and to provide information on equilibrium moisture content and response time for use in more complex models. Moisture contents of near surface, surface, profile litter and bark fuels were measured, along with standard weather variables. On one set of four consecutive days fuel temperatures were also measured with thermocouples. One of the simple empirical fuel moisture prediction models worked well on the litter fuels for which it was intended, but another of the simple models in common use, predicted poorly, particularly on the damp site. One of the simple models was modified, and gave acceptable predictions for profile litter. Another simple model was calibrated to give good predictions for near surface, bark and litter fuels in the middle of the day. A more physically-based ‘bookkeeping’ model for estimating response time and EMC worked very well on all strata but the litter profile. Response times of all fuel strata were of the order of 1 h. A process based model worked slightly better than the EMC estimation model for near surface, litter and bark fuel and considerably better for profile litter, especially on the damp site. On the whole these models performed better than the simple empirical models, but they were tuned to various degrees by site information.

Aboveground biomass was studied in Castanea sativa Mill. coppice stands in north-west Spain, and biomass equations were fitted at three levels (individual tree, stool and stand). Four systems of biomass estimation were developed. In two of the systems, the following individual tree variables were taken into account: standing tree variables and stump dimension variables. In the other two systems, biomass was estimated at stool and stand level, respectively. In order to represent the existing range of ages, stand densities and sites in the study area, samples of 120 trees (for the individual tree level), 45 stools (for the stool level) and 70 plots (for the stand level) were chosen for study. The trees were felled and destructively sampled to separate biomass into the following components: wood, bark, thick branches, medium branches, thin branches and leaves. Several equations for quantifying the biomass of the different biomass components were evaluated. Heterocedasticity was corrected for by weighted fitting. To guarantee the additivity of the different biomass components, the equations were fitted simultaneously by nonlinear seemingly unrelated regressions (NSURs). The different biomass levels considered accounted for between 60% and 90% of the total variability, depending on the level and component evaluated. Most of the equations developed in this study were evaluated with an independent dataset, which confirmed the good performance of the biomass equations for prediction purposes.