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Aim: Increased tree mortality linked to droughts and fires is occurring across temperate regions globally. Vegetation recovery has been widely reported; however, less is known about how disturbance may alter forests structurally and functionally across environmental gradients. We examined whether dry forests growing on low‐fertility soils were more resilient to coupled extreme drought and severe fire owing to lower tree mortality rates, higher resprouting success and persistence of juveniles relative to wetter forests on more fertile soils. Location: Fire‐tolerant eucalypt forests of temperate southeastern Australia. Time period: 2020–2023. Major taxa studied: Eucalyptus, Corymbia, Angophora. Methods: Demographic surveys of tree mortality and regeneration in all combinations of dry/wet forest, fertile/less fertile substrates exposed to extreme drought and fire were conducted. We used Bayesian regression modelling to compare tree mortality, diameter, response traits, population structure and occurrence of fire scars between substrates/forest types. Results: Overall mortality (20%–33%) and topkill (34%–41%) were within historically reported ranges for various forests and soil types. However, we observed an atypical trend of increased mortality and topkill in the largest trees, particularly when they had structural damage from past fires. Trees in wet forests on more fertile soils had the highest levels of mortality. Numbers of persistent resprouting juveniles were highest in dry forests on low‐fertility soils. Dry forests growing on low‐fertility soils appear more resilient to compound disturbances due to lower rates of mortality and higher rates of juvenile persistence. Wet forests on more fertile soils may experience greater demographic change due to higher mortality of small and large trees. Main conclusions: Mesic forests on relatively fertile soils were found to be at relatively high risk of demographic change from compound disturbances. Combined, fire and drought are likely to reduce the number of large trees in affected areas, with consequences for forest carbon cycling and storage. [ABSTRACT FROM AUTHOR]

Humid mountain forests (HMF) in Mexico have been heavily degraded by anthropogenic activities. A key conservation strategy consists of propagating HMF species in forest nurseries for subsequent repopulation in degraded areas. We evaluated genetic diversity in three natural populations (Huitepec, Bazom, and Mitzitón) and one nursery population of Styrax magnus Lundell (Styracaceae) in Chiapas, Mexico. We expected a lower genetic diversity in the nursery than in wild populations. Styrax magnus is restricted to the Mexican state of Chiapas, close to the border with Guatemala and is likely to be at risk of extinction due to habitat loss and its low establishment rate. We used ten enzyme loci to determine genetic diversity. Genetic structure was examined by calculating genetic differentiation (Fst) and Nei's genetic distances (Nei, Am Nat 106:283–292, 1972), in addition a Bayesian analysis was performed. The populations examined showed a moderate (He = 0.31) average genetic diversity. Bazom was the most distant and genetically differentiated population and showed the lowest genetic diversity (He = 0.21). Mitzitón was the most diverse population (He = 0.40), whereas the nursery population showed an intermediate diversity (He = 0.30). We found a high level of total genetic differentiation (Fst = 0.48, P < 0.001), suggesting a limited gene flow between the populations studied. Our results suggest that propagation in the nursery promotes an intermediate level of genetic diversity (He) relative to wild populations, likely because the nursery population was made up by random seed collection from several sites. The genetic monitoring of introduced populations is highly recommended for an in-depth assessment of the success of actions aiming to conserve and restore HMF in Chiapas. [ABSTRACT FROM AUTHOR]

Tree survival is a performance metric for urban forestry initiatives, and an understanding of the factors that influence mortality can help managers target resources and enhance survival. Furthermore, urban tree planting investments depend on tree survival to maximize ecosystem services. In this literature review, we categorized factors commonly associated with urban tree mortality and summarized mortality rates published in 56 studies, focusing on studies of trees along streets, in yards, and in landscaped parks. Study designs included quantitative field monitoring of uneven-aged tree populations and tracking planting cohorts of even-aged trees, as well as qualitative analyses. Annual mortality rates ranged from 0.6 to 68.5% for cohort studies and 0 to 30% for repeated inventories of uneven-aged trees. The 1st, 2nd, and 3rd quartiles of annual mortality were 2.8 to 3.8%, 4.4 to 6.5%, and 7.1 to 9.3% for planting cohorts, and 1.6%, 2.3 to 2.6%, and 3.0 to 3.3% for repeated inventories of uneven-aged trees (ranges reflect studies that reported a range for the time period or mortality rate). For cohort studies, annual mortality tended to be highest during the first five years after planting. The most commonly cited biophysical factors associated with mortality were taxa (15 articles), tree size/age (13 articles), and site characteristics (12 articles). The most commonly cited human-related factors were stewardship, maintenance, and vandalism (15 articles). More long-term studies are needed to investigate how site characteristics influence mortality, including rarely examined soil and microclimate characteristics. Future research should also examine institutional structures related to mortality outcomes, as well as parcel-level sociodemographic factors and resident behaviors. [ABSTRACT FROM AUTHOR]

Global warming is driving plant range shifts towards higher latitudes, where plants encounter different light environment (photoperiod and light spectral quality) than that to which they are adapted. Light environment may indirectly influence the belowground part of the plant, where trees associate with ectomycorrhizal (ECM) and other biotrophic fungi. We studied joint impacts of warming and light climate on Scots pine (Pinus sylvestris) and its root-associated fungi in a reciprocal transplantation study, where pine seedlings from southern and northern tree populations were grown under similar experimental temperature in southern (60°N) and northern (69°N) Finland. Based on fungal ITS rDNA, the abundance of Basidiomycota, and ECM fungi in particular, was highest in the roots of southern pines in the south and in northern pines in the north, and seedling biomass was determined by population origin. Our results imply that root-associated fungi may respond differentially in native vs. non-native light environment of the host plant. [ABSTRACT FROM AUTHOR]

Long-term ecological and genetic studies in natural populations of tree species require marking techniques so that individuals can be re-visited over time, even in difficult terrain. Both GPS coordinates and physical labels have disadvantages that can make re-finding trees difficult. We tested passive and semi-active radio frequency identification (RFID) tags and readers as a means to relocate individual trees. Passive RFID tags do not provide a good solution because of low transmission power of hand-held readers and strong directionality. Semi-active RFID tags provide detection over longer distances, but also suffer from strong directionality. Active RFID tags promise an improvement over semi-passive tags, and could be evaluated in a future study. We conclude that RFID technology has the potential to improve the ability of researchers to locate individual trees repeatedly under natural conditions, and can be used in conjunction with other marking techniques such as physical tags and GPS coordinates.

Long-term ecological and genetic studies in natural populations of tree species require marking techniques so that individuals can be re-visited over time, even in difficult terrain. Both GPS coordinates and physical labels have disadvantages that can make re-finding trees difficult. We tested passive and semi-active radio frequency identification (RFID) tags and readers as a means to relocate individual trees. Passive RFID tags do not provide a good solution because of low transmission power of hand-held readers and strong directionality. Semi-active RFID tags provide detection over longer distances, but also suffer from strong directionality. Active RFID tags promise an improvement over semi-passive tags, and could be evaluated in a future study. We conclude that RFID technology has the potential to improve the ability of researchers to locate individual trees repeatedly under natural conditions, and can be used in conjunction with other marking techniques such as physical tags and GPS coordinates. [ABSTRACT FROM AUTHOR]

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Forest ground heterogeneity can affect interactions among tree species and control the assembly of local forest communities. Less is known of the effects of spatial heterogeneity on the maintenance of tree genetic variation through small-scale genotype × environment (G × E) interactions. We measured growth variation within and among 17 Betula pendula genotypes, planted in a clear-cut forest site through the summers 2009-2011. We assessed the spatial heterogeneity at two scales: among forest stands having history of the same or different tree species combinations (treated as replicate blocks), and along a gradient of within-block forest density, revealed by the stump density. To add a temporal perspective, we distinguished between old (cut 50 years earlier) and new stumps (cut one year earlier). The broad-sense heritabilities for growth were 0.093-0.055 and the coefficients of genotypic variation 0.37-0.21 in 2009-2011. The growth difference among the genotypes was 3.5-5.5 fold, significant in all years, and the rank of genotype means correlated positively between the years. The most favourable block had 106 % higher growth than the least favourable block and the amount of total variation explained by block increased from 0.4 % in 2009 to 6.9 % in 2011. Genotype × block interaction was marginally significant in 2009, but not later. Similarly, the response of growth to old stump density in sapling vicinity varied among the genotypes in 2009, but not later. In 2010 and 2011, the mean growth increased by 50-91 % along the old stump density gradient. Our results suggest that despite creating significant variation in sapling growth the small-scale forest ground heterogeneity, which reflects the recent forest history, may not significantly contribute to the maintenance of genetic variation in B. pendula populations. [ABSTRACT FROM AUTHOR]

Question What are the drivers of structural changes and mortality in oak-beech forests over 50 yrs of natural succession? Location Twelve unmanaged forest sites, comprising a large environmental gradient in the Swiss lowlands. Method By using repeated inventory data from more than 17 600 individually tagged trees, the dynamics of oak-beech stands over the past 50 yrs were analysed. Generalized linear mixed-effects models were fitted to quantify annual mortality rates of oak and beech based on DBH, stand basal area, precipitation and slope. Results Stand basal area increased, whereas tree density decreased over time. At most sites, the relative importance of oak decreased gradually compared to beech. Mortality increased over time for both oak and beech, but the increase was stronger for oak. Oak and beech mortality decreased with increasing DBH and tended to increase with precipitation. Additionally, oak mortality increased with stand basal area, whereas no such trend was found for beech. Conclusion Our study indicates that mortality in Central European oak-beech forests is driven by a combination of stand structures (i.e. tree size and stand basal area) and climate. However, the influence of climate on oak mortality is comparably low. Increasing oak mortality with stand basal area is a plausible consequence of its lower relative competitiveness and higher demand for light. Thus, in forests developing towards higher stand basal area, the ecologically important oak is increasingly outcompeted by beech, unless competition is reduced through management or disturbances. [ABSTRACT FROM AUTHOR]

Many indicators/indices provide information on whether the 2010 biodiversity target of reducing declines in biodiversity have been achieved. The strengths and limitations of the various measures used to assess the success of such measures are now being discussed. Biodiversity dynamics are often evaluated by a single biological population metric, such as the abundance of each species. Here we examined tree population dynamics of 52 families (192 species) at 11 research sites (three vegetation zones) of Japanese old-growth forests using two population metrics: number of stems and basal area. We calculated indices that track the rate of change in all species of tree by taking the geometric mean of changes in population metrics between the 1990s and the 2000s at the national level and at the levels of the vegetation zone and family. We specifically focused on whether indices based on these two metrics behaved similarly. The indices showed that (1) the number of stems declined, whereas basal area did not change at the national level and (2) the degree of change in the indices varied by vegetation zone and family. These results suggest that Japanese old-growth forests have not degraded and may even be developing in some vegetation zones, and indicate that the use of a single population metric (or indicator/index) may be insufficient to precisely understand the state of biodiversity. It is therefore important to incorporate more metrics into monitoring schemes to overcome the risk of misunderstanding or misrepresenting biodiversity dynamics. [ABSTRACT FROM AUTHOR]

The present study was conducted in three planted and primary forest stands in Nongkhyllem Wildlife sanctuary and its adjoining reserve forests to investigate the impact of plantation on soil properties, plant diversity, vegetation structure and regeneration status. Soil status measured in terms of soil organic carbon, total Kjeldahl nitrogen, available phosphorus and potassium were significantly low in the plantation as compared to primary forests. A total of 5184 individuals belonging to 127 woody species (> 5 cm dbh) and 53 families were identified in the study area. The species richness was high (51-94) in the primary forests as compared to plantation (31 - 67). The basal area was high in Sal plantation (94 m2 ha-1) than the other forest stands (38 - 84 m2 ha-1). In terms of density, Dipterocarpaceae, Verbenaceae, Lauraceae and Theaceae were the dominant families. Species richness and density decreased with increasing diameter classes in all the stands. The overall age structure based on the density of seedling, sapling and adult individuals showed a growing and healthy population in all the stands. However, the density of seedling and sapling was low in plantation as compared to primary forest. Results revealed that the plantation of monoculture tree species decreases species richness, alters vegetation composition and regeneration status and leads to low soil fertility. [ABSTRACT FROM AUTHOR]

The response of woody species to anthropogenic disturbances was studied in three forest stands viz., Swer, Nonglang and Nongkrem representing subtropical humid forests of the area. These forest stands were preserved till recently as sacred groves on the basis of religious beliefs. However, during the past decade, some portions of these sacred groves have been disturbed due to product extraction following erosion in religious beliefs. The diversity and regeneration of woody species present in these forests has been studied to assess the response of the species to human disturbance. A total of 114 woody species (≥5cm dbh) were identified in the three forests. The species richness in disturbed stands was significantly lower in the disturbed stand (24-26) than the undisturbed stands (60- 32). The density also followed a similar trend in Swer and Nonglang forest stands whereas, it increased from 898 stems ha-1 in the undisturbed stand to 954 stems ha-1 in the disturbed stand at Swer. The basal area of woody species was significantly higher in the undisturbed stands (27- 62 m2 ha-1) than the disturbed stands (3.14- 58.25 m2 ha-1). The distribution of density in different dbh classes resulted in a reverse J-shaped curve in all the undisturbed stands, while in the disturbed stands, there was a reduction in density in the higher dbh classes. The densities of seedlings and saplings were significantly higher in the undisturbed stands than the disturbed stands, although seedling density far exceeded the sapling density in all the stands. The proportion of species showing no regeneration was high in the undisturbed stand as compared to the disturbed stand. Results revealed that species richness significantly got reduced, tree population structure showed a decrease in higher girth class individuals and the regeneration status of the species was also altered due to disturbance. [ABSTRACT FROM AUTHOR]

This study deals with the effects of flooding on alluvial soils and riparian forests in the basins and sub-basins of southern Québec (Canada). These riparian environments are sensitive to hydroclimatic variations, which may increase with current climate change, which is why it is important to analyse them. The study areas were divided by flood frequency based on government maps that show flood recurrence intervals of 0 to 20 years and 20 to 100 years. Woodlands located outside of the floodplains were also analysed for comparison to measure and better determine the effect of floods on soils and forest stands. Soil depletion is found in the frequent-flood zones (FFZ), which results in lower total organic carbon (mean values of 1.9%-3.7% in FFZ vs 3.2%-5.9% in no-flood zones [NFZ]) and total nitrogen (mean values of 0.1%-0.2% in FFZ vs 0.2%-0.3% NFZ). Field observations and measurements show that the aboveground biomass (plant litter) is reduced or absent from the active flood zones. The structure and composition of tree stands are relatively comparable from one zone to another, but a slightly lower rate of small (5-10 cm dbh [diameter at breast height]) and intermediate (10-15 cm dbh) trees can be noted in FFZ, and tree diversity (Shannon index) and species richness are also slightly lower. The mechanical action of water in trees during floods and the burial of seedlings through the accumulation of fine alluvial deposits could negatively impact forest regeneration in active floodplains. [ABSTRACT FROM AUTHOR]

Seed predation has major effects on the reproductive success of individuals, spatial patterns of populations, genetic variability, interspecific interactions and ultimately in the diversity of tree communities. At a Brazilian savanna, I evaluated the proportional crop loss of Eriotheca gracilipes due the Blue-Fronted Amazon (Amazona aestiva) during a fruiting period. Also, I analyzed the relationship between proportional crop loss to Amazons and both fruit crop size and the distance from the nearest damaged conspecific. Trees produced from 1 to 109 fruits, so that Amazons foraged more often on trees bearing larger fruit crop size, while seldom visited less productive trees. Moreover, the relationship between fruit crop sizes and the number of depredated fruits was significant. However, when only damaged trees were assessed, I found a negative and significant relation between fruit crop size and proportional crop loss to Blue-Fronted Amazons. Taking into account this as a measure more directly related to the probability of seed survival, a negative density dependent effect emerged. Also, Amazons similarly damaged the fruit crops of either close or distant neighboring damaged trees. Hence, in spite of Blue-Fronted Amazons searched for E. gracilipes bearing large fruit crops, they were swamped due to the presence of more fruits than they could eat. Moderate seed predation by Blue-Fronted Amazons either at trees with large fruit crops or in areas where fruiting trees were aggregated implies in an enhanced probability of E. gracilipes seed survival and consequent regeneration success.

Overhunting in tropical forests reduces populations of vertebrate seed dispersers. If reduced seed dispersal has a negative impact on tree population viability, overhunting could lead to altered forest structure and dynamics, including decreased biodiversity. However, empirical data showing decreased animal-dispersed tree abundance in overhunted forests contradict demographic models which predict minimal sensitivity of tree population growth rate to early life stages. One resolution to this discrepancy is that seed dispersal determines spatial aggregation, which could have demographic consequences for all life stages. We tested the impact of dispersal loss on population viability of a tropical tree species, Miliusa horsfieldii, currently dispersed by an intact community of large mammals in a Thai forest. We evaluated the effect of spatial aggregation for all tree life stages, from seeds to adult trees, and constructed simulation models to compare population viability with and without animal-mediated seed dispersal. In simulated populations, disperser loss increased spatial aggregation by fourfold, leading to increased negative density dependence across the life cycle and a 10-fold increase in the probability of extinction. Given that the majority of tree species in tropical forests are animal-dispersed, overhunting will potentially result in forests that are fundamentally different from those existing now. [ABSTRACT FROM AUTHOR]

This paper reports a simulation-based exploration into the computation of point and interval estimates for data arising from sequential sampling of populations with a variety of underlying distributions. Weconclude that the coverage probability of the standard frequentist confidence interval estimates is overstated. The effect of non-normal behavior in the underlying population upon the properties of the interval estimate varies, depending upon the severity and type of anomaly(skewness, kurtosis, etc). Sequential sampling of certain nonsymmetric distributions performed very poorly compared with simple random sampling. We assess other interval estimates that do not overstate the coverage probability if the underlying population is normal (Gaussian). [ABSTRACT FROM AUTHOR]

Effects of multicollinearity, autocorrelation and two sampling strategies were studied on two new variable-exponent taper equations usingMonte Carlo simulations. These two equations were derived from Kozak's 1988 model. Results of the study indicated that predictions are unbiased even if the taper model has severe multicollinearity and autocorrelation. On the other hand, the estimations are considerably more variable when severe multicollinearity. exists. The use of single observations per tree (uncorrelated errors) does not improve the predictive ability of the functions. Taper functions based on a uniform selection of sample trees predict the response variables well, but provide poorer estimates of the parameters than random selection. [ABSTRACT FROM AUTHOR]

Between June 1993 and June 1994, 112 farmers in the oil palm (Elaeisguineensis)-cassava (Manihot esclentus) belt of southeastern Nigeriawere interviewed to determine the status and agroforestry potential of Dacryodes edulis. Between 50% and 100% of respondents in differentstates within the belt owned D. edulis trees. On average, a farmer owned 9.3 trees, the largest number being 16, by farmers in Imo State.Twenty percent of farmers in the system rated D. edulis their best farm tree. It was present in all the farm niches: homegardens (51.4%),tree crop plots (20.7%) food crop plots (11.4%), secondary forest/fallow (14.2%) and virgin forest (2.5%). The tree is planted primarily for home consumption and sale to generate cash. At the current densities, on-farm D. edulis trees generally did not decrease yield of companion crops or trees. Except for ring weeding around the stem, D. edulis trees received little or no management attention. More than 50% of the trees produced 33 to 50 kg of fruit tree-1 annually.This is valued at US $0.4 to 0.8 kg-1. Farmers were willing to plant more D. edulis trees provided trees with traits such as less height for easy harvesting of fruits, larger fruit, more fruits, sweeter fruits and year round production of fruits were available. Possible agroforestry technologies into which D. edulis may fit includelive fences, scattered trees in food crop fields, shade trees in tree crop plots and contour bund or hedgerow planting. Research is required to determine best tree accessions, canopy management strategies, optimum tree population and improved methods on post- harvest handling of fruits. [ABSTRACT FROM AUTHOR]