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The Scots pine (Pinus sylvestris L.) is the second-most widely used tree species in forestry in Latvia and is the only species used for afforestation on nutrient poor soils that cover considerable forest land in Latvia. Several studies have shown that, in such conditions, the lodgepole pine (Pinus contorta var. latifolia) may be more productive in terms of biomass and yield. It is important to consider climate change studies to assess the potential for a larger-scale use of the lodgepole pine in forestry. The aim was to assess the intra-annual height growth patterns of both species, the differences between them, and the influence of meteorological parameters on their height growth. Their height growth was monitored on a weekly basis in two sampling sites in central Latvia, and the height increment curves were described by Gompertz's model. The height growth dynamics of individual trees and species differed notably, indicating the potential for the selection of the best-adapted genotypes. Our results indicate that the early onset of the active growth phase might be the most important factor determining the total height increment for both species. Temperature-related meteorological parameters were the only ones with a statistically significant influence on pines height growth and only when at least one of the variables were standardised prior to the analysis. A temperature increase had a slightly stronger positive effect on the growth of the lodgepole pine, indicating that it might be suitable for more intensive use in forestry under the climate change scenarios for Latvia. [ABSTRACT FROM AUTHOR]

Mixing tree species could be a silviculture model that allows early harvest of short-rotation trees, while longer-rotation crop trees remain in the stand. We examined the effects on growth and tree characteristics in a planted experiment with lodgepole pine (LP) and elite-bred Scots pine (SP) in mixed (50/50) and monospecific plots in three different spacings (at 28 years of age after planting). The future development under different thinning regimes, including net present value for one rotation, was analyzed using the Heureka simulation software. As expected, LP had higher survival and initially more rapid growth than SP, with highest stand productivity and biomass production in LP monoculture during a rotation period as a result. However, intimate mixtures of SP and LP at the two widest spacings could give greater production and economic benefits, compared to SP in monoculture. It seems that elite-bred SP will differ in competitiveness against LP, depending on spacing for growth and some quality traits (branch and bark thickness, height of green crown). The findings support developing management systems for combining sparsely planted, and expensive, elite-bred SP in mixture with other trees that maintains high stem volume production and secures certain properties of trees and stands. [ABSTRACT FROM AUTHOR]

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Ectomycorrhizal fungi (plant symbionts) are diverse and exist within spatially variable communities that play fundamental roles in the functioning of terrestrial ecosystems. However, the underlying ecological mechanisms that maintain and regulate the spatial structuring of ectomycorrhizal fungal communities are both complex and remain poorly understood. Here, we use a gradient of mountain pine beetle (Dendroctonus ponderosae) induced tree mortality across eleven stands in lodgepole pine (Pinus contorta) forests of western Canada to investigate: (i) the degree to which spatial structure varies within this fungal group, and (ii) how these patterns may be driven by the relative importance of tree mortality from changes in understory plant diversity, productivity and fine root biomass following tree death. We found that the homogeneity of the ectomycorrhizal fungal community increased with increasing tree death, aboveground understory productivity and diversity. Whereas, the independent effect of fine root biomass, which declined along the same gradient of tree mortality, increased the heterogeneity of the ectomycorrhizal fungal community. Together, our results demonstrate that large-scale biotic disturbance homogenizes the spatial patterns of ectomycorrhizal fungal communities.

Aims: Our goal was to better understand tree growth and photosynthetic responses to variations in plant available water and elucidate the role of the inverse texture effect in snow dominated montane forests. Methods: We measured tree ring carbon isotope composition and annual growth over a 31-year record for lodgepole pine (Pinus contorta Douglas ex Loudon) growing on three different-aged glacial till surfaces in Wyoming, USA. Results: Soils of different ages developed on till surfaces from three separate glaciation events were significantly different in clay content and distribution with depth; maximum clay content at depth ranged from 19 to 20% on the two youngest till surfaces, but was as high as 36% on the oldest till surface. Ring growth was lowest at the youngest till sites, and only on these coarse-textured soils was growth positively correlated with annual maximum snow water equivalent (SWEmax). Δ13C was highest for trees at these young till sites, suggesting that hydraulic conductivity and stomatal conductance is comparatively high during growth periods on these coarse-textured soils. Conclusion: Taken together, we found that age of glacial till and related soil texture differences strongly influenced tree-ring growth and Δ13C response of lodgepole pine to interannual variation in precipitation and drought severity, but responses did not support an inverse texture effect in these semi-arid forest systems. [ABSTRACT FROM AUTHOR]

The effects of herbivory on plant invasions are broadly discussed, and many studies have led to widely debated theories. In particular, the effects of herbivores on pine invasion found in different studies vary; in some cases, they controlled their expansion, and in others, they promoted it. On the other hand, vulnerability to invasion by pines differs between community types. Sites with dunes and bare ground are the most heavily invaded, followed by grasslands, while shrublands and forests are least invaded. Because current evidence is mostly observational, some of the varying responses of pine invasions to herbivory should be examined further through replicated experiments. Here, we address experimentally the extent to which preference for the non‐native invasive Pinus contorta by domestic sheep (Ovis aries) depends on the vegetation type. We installed experimental enclosures within two adjacent communities, grassland and shrubland, and in each one, we planted seedlings of P. contorta Douglas and established a sheep density typically recommended for the study area. The number of browsed seedlings, the number and type of branches browsed per seedling, the reduction in height and probability of survival immediately after browsing period were recorded. The number of browsed seedlings and damage to the terminal bud were higher in grassland than in shrubland, while the number of browsed branches per seedling was higher in shrubland than grassland. The reductions in height and probability of survival immediately after browsing were similar in both communities. These results show that moderate levels of sheep herbivory could reduce 20% seedling survival in both communities; nevertheless, the damage patterns differ between them. The sheep browsed more substantial number of seedlings in grasslands than in shrublands. However, if sheep find the seedlings, they damage it more in shrublands. These results suggest that experimental studies comparing communities are important for pine invasion management. [ABSTRACT FROM AUTHOR]

We present an account of Rhizopogon introduced from plantings of exotic pine plantations in Argentine Patagonia. Nuc rDNA internal transcribed spacer ITS1-5.8S-ITS2 (ITS) and nuc 28S rDNA (28S) sequences were used to identify specimens from Argentina and examine their relationships with geographically different Rhizopogon species. Based on phylogenetic analyses, we confirm that four species of Rhizopogon occur in pine plantations across Patagonia. Several Rhizopogon collections from Pinus ponderosa plantations across different provinces cluster with R. arctostaphyli, a species within R. subg. Amylopogon. The majority of Patagonian Rhizopogon, however, form three different lineages in R. subg. Roseoli. The first of these, R. roseolus sensu Trappe, includes numerous collections from Pinus ponderosa, P. contorta, and P. radiata stands of North American affiliation. The second, R. roseolus sensu Martin and Garcia from P. ponderosa plantations, clusters in clade IIIa of the R. roseolus complex, which also includes the holotype collection of R. mohelnensis from the Czech Republic. The third species in R. subg. Roseoli, and fourth species overall from Patagonia, is R. granuloflavus from Pinus ponderosa plantations. Multiplex polymerase chain reaction (PCR) of numerous Roseoli samples failed to produce an amplicon indicative of either Japanese or New Zealand shoro. [ABSTRACT FROM AUTHOR]

Phytopathogenic ophiostomatoid fungi are common associates of bark beetles and contribute to beetle-associated mortality of trees. Mountain pine beetle outbreaks in Canada are facilitating novel associations between its vectored fungi (Grosmannia clavigera , Leptographium longiclavatum and Ophiostoma montium) and jack pine. How the induced defense-related metabolite responses of jack and lodgepole pines vary in response to the fungi is unknown. Understanding this variation is important to clarifying pine susceptibility to and the physiological impacts of infection. We used a comparative metabolite profiling approach to investigate the defense-related signaling, carbon utilization/mobilization, and synthesis responses of both pines to the fungi. Both pine species largely exhibited similar metabolite responses to the fungi. The magnitude of pine metabolite responses positively reflected pathogen virulence. Our findings indicate that pines can recognize and metabolomically respond to novel pathogens, likely due to signals common between the novel fungi and fungi coevolved with the pine. Thus, jack pine is likely as susceptible as lodgepole pine to infections by each of the MPB-vectored fungi. Furthermore, the magnitude of the metabolite responses of both pines varied by the eliciting fungal species, with the most virulent pathogen causing the greatest reduction in carbohydrates and the highest accumulation of defensive terpenes. [ABSTRACT FROM AUTHOR]

Subalpine forests in the northern Rocky Mountains have been resilient to stand-replacing fires that historically burned at 100-to 300-year intervals. Fire intervals are projected to decline drastically as climate warms, and forests that reburn before recovering from previous fire may lose their ability to rebound. We studied recent fires in Greater Yellowstone (Wyoming, United States) and asked whether short-interval (<30 years) stand-replacing fires can erode lodgepole pine (Pinus contorta var. latifolia) forest resilience via increased burn severity, reduced early postfire tree regeneration, reduced carbon stocks, and slower carbon recovery. During 2016, fires reburned young lodgepole pine forests that regenerated after wildfires in 1988 and 2000. During 2017, we sampled 0.25-ha plots in stand-replacing reburns (n = 18) and nearby young forests that did not reburn (n = 9). We also simulated stand development with and without reburns to assess carbon recovery trajectories. Nearly all prefire biomass was combusted ("crown fire plus") in some reburns in which prefire trees were dense and small (=4-cm basal diameter). Postfire tree seedling density was reduced sixfold relative to the previous (long-interval) fire, and high-density stands (>40,000 stems ha-1) were converted to sparse stands (<1,000 stems ha-1). In reburns, coarse wood biomass and aboveground carbon stocks were reduced by 65 and 62%, respectively, relative to areas that did not reburn. Increased carbon loss plus sparse tree regeneration delayed simulated carbon recovery by >150 years. Forests did not transition to nonforest, but extreme burn severity and reduced tree recovery foreshadow an erosion of forest resilience. [ABSTRACT FROM AUTHOR]

• Residual lodgepole pine trees favored defense over growth after beetle outbreak. • Higher tree mortality increased resin duct density of healthy asymptomatic trees. • Stand density affected the pre-outbreak growth-defense relationship of pine trees. • Bark beetle outbreaks may select phenotypically-resistant pines to future attacks. Millions of hectares of lodgepole pine trees have been affected by the recent mountain pine beetle outbreaks, which also left significant numbers of live host trees in some areas. Studies have primarily focused on the changes of forest conditions in post-outbreak stands, but whether such changes impact the growth, defense, and their interactions of residual pine trees is generally unknown. In this study, we compared the growth-defense relationship of lodgepole pine trees between pre- and post-outbreak periods by examining annual radial growth rates and xylem resin duct characteristics. We also tested the effects of varying percent host tree mortality and forest stand density on the growth-defense relationship of residual pine trees. We found that resin duct densities of residual pine trees were higher and resin ducts occupied larger areas in the xylem in post-outbreak period than in pre-outbreak period. Following outbreak, the percent host mortality showed a positive relationship with the resin duct density of all healthy residual trees, while stand density did not impact any of the resin duct characteristics. We conclude that bark beetle outbreaks can alter the growth, defense, and their interactions of residual pine trees, especially in stands with greater levels of pine mortality. This study also provides an empirical evidence, suggesting that residual trees might be more resistant to future bark beetle attacks. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal fungi (plant symbionts) are diverse and exist within spatially variable communities that play fundamental roles in the functioning of terrestrial ecosystems. However, the underlying ecological mechanisms that maintain and regulate the spatial structuring of ectomycorrhizal fungal communities are both complex and remain poorly understood. Here, we use a gradient of mountain pine beetle (Dendroctonus ponderosae) induced tree mortality across eleven stands in lodgepole pine (Pinus contorta) forests of western Canada to investigate: (i) the degree to which spatial structure varies within this fungal group, and (ii) how these patterns may be driven by the relative importance of tree mortality from changes in understory plant diversity, productivity and fine root biomass following tree death. We found that the homogeneity of the ectomycorrhizal fungal community increased with increasing tree death, aboveground understory productivity and diversity. Whereas, the independent effect of fine root biomass, which declined along the same gradient of tree mortality, increased the heterogeneity of the ectomycorrhizal fungal community. Together, our results demonstrate that large-scale biotic disturbance homogenizes the spatial patterns of ectomycorrhizal fungal communities. [ABSTRACT FROM AUTHOR]

The mountain pine beetle (MPB) (Dendroctonus ponderosae) is one of the most prevalent disturbance agents in western conifer forests. It utilizes various species of pines (Pinus spp.) as host trees. Eruptive populations can cause extensive tree mortality. Since the late 1990s, extensive outbreaks have occurred from the southern Rockies to British Columbia. In Colorado, lodgepole pine (P. contorta) forests have been the most affected. Since 1996, about 3.4 million acres of lodgepole and ponderosa pine (P. ponderosa) forests have exhibited MPB-caused tree mortality. A large portion of the larger diameter trees have been killed with significant reductions in basal areas and tree densities. Tree mortality has impacted many forest ecosystem services including fiber production, hydrology, nutrient cycling, wildlife habitat, property values, and recreation. In this article, we examine and summarize some of what we have learned about MPB impacts from observations and research over the past two decades in Colorado. [ABSTRACT FROM AUTHOR]

Genetic parameters, performance of provenances, and genotype by environment interaction (G × E) for diameter at breast height (DBH), survival, and modulus of elasticity of time-of-flight (MOEtof) (an indirect measure of stiffness), were investigated in six lodgepole pine progeny trials, aged 33-36 years, within three breeding zones in northern Sweden. Provenances of Yukon origin had the highest growth but lowest stiffness at higher latitude, while those of British Columbia (BC) origin grew faster at lower latitudes and had highest stiffness within zone 5. Combined-site heritability estimates ranged from 0.09 to 0.19 for DBH, from 0.19 to 0.27 for MOEtof, and from 0.13 to 0.26 for survival. Type-B genetic correlations () were generally high for all studied traits, except for DBH and survival in zone 4 ( = 0.74 and 0.40, respectively) and for MOEtof in zone 2 ( = 0.46). On the basis of the results obtained in this study, G × E for stiffness in northern Sweden and unfavourable growth-stiffness genetic correlation should be considered in selective breeding programmes of lodgepole pine. To achieve the highest stiffness for lodgepole pine, provenances of Yukon origin should be planted at lower latitudes and those of BC origin should be planted at lower elevations within the tested breeding zones. [ABSTRACT FROM AUTHOR]

Context: Disturbances create spatial variation in environments that may influence animal foraging. Granivory by rodents can influence seed supply and thus plant establishment. However, effects of disturbance patterns on rodent seed removal in western North American conifer forests are generally unknown.Objectives: We conducted a study in lodgepole pine (Pinus contorta var. latifolia) forests of Greater Yellowstone (Wyoming, USA) to answer: (1) How do seed removal and rodent activity vary between recently burned and adjacent unburned forests and with distance from fire perimeter? (2) Which microhabitat conditions explain variability in seed removal and rodent activity?Methods: One or two years after wildfires, we established transects (n = 23) with four stations each: at 10 and 40 m from the fire perimeter in both burned and unburned forest. At stations, we deployed trays with lodgepole pine seeds and cameras pointed at trays for 28 days and quantified habitat structure and seed abundance.Results: Seed removal, which averaged 85%, and diurnal rodent activity did not differ between burned and unburned forests or with distance from the fire perimeter; however, nocturnal rodent activity was lower in burned forests. Seed removal and diurnal rodent activity were not associated with any microhabitat conditions we measured. However, nocturnal rodent activity was associated with microhabitat in both burned and unburned forests.Conclusions: High seed removal rates suggested that rodent foraging was not reduced by high-severity wildfire. If observed seed removal represents natural conditions, post-dispersal seed predation could influence post-fire recruitment of a widespread foundation tree species. [ABSTRACT FROM AUTHOR]

Non-indigenous conifers are considered invasive to the coastal dune heathland in Denmark, and massive clearing is carried out in an attempt to recreate and keep the original heathland. Burning is a common method for managing, but its feasibility to control the seed bank of conifers has not been investigated. This project shows that the burning of logged conifer trees will often eliminate seeds of lodgepole pine, mugo pine and Sitka spruce, even when the seeds were placed into a depth of five centimeters in the soil. The effect on seeds depends on the fuel load and the fire conditions (e.g., dryness, wind, and temperature). If the seeds were exposed to a high temperature, the seeds were not able to germinate afterward. The temperature was about 80 °C for all species. If the sum of temperatures based on temperature records every 30 s exceeded between 12,000 and 14,000 °C no seeds were able to germinate. The relationship between the mean temperature of the burns and the germination rate at seeds placed in various soil depths was modelled. Findings should be interpreted cautiously as each depth-species combinations were not replicated in space or time due to practical constraints.

• High severity fires reduce microbial abundance and richness. • Bacterial communities recover faster than fungal communities after wildfires. • Impact of fire on microbial communities decrease with soil depth. • Fire increases the abundance of pyrophilous "fire-loving" fungi and bacteria. • Multiple disturbances have synergetic effects on reducing mycorrhizal richness. Lodgepole pine forests are under threat due to wildfires of increasing severity and frequency coupled with tree mortality from insect outbreaks. Soil microbial communities, which drive biogeochemical cycles and partner in mycorrhizal symbiosis with lodgepole pines, play critical roles in the ability of these forests to survive and regenerate in the face of simultaneous global change threats. How soil microbial communities are influenced by fire severity and soil depth and how they recover over time in lodgepole pine forests with existing insect-driven mortality remains an open question. Here, we sampled two soil depths (0–5 and 5–15 cm) and various burn severities across a ten-year wildfire chronosequence in the Southern Rocky Mountains. We used qPCR of 18S and 16S rRNA genes to assess changes in fungal and bacterial abundance and ITS2 and 16S amplicon sequencing to assess fungal and bacterial richness and composition. Our results show that: 1) higher severity fires led to larger reductions of both fungal and bacterial abundance and richness, 2) the impact of fire on fungal and bacterial communities was modulated by soil depth, with more severe impacts in shallower soils 3) both fungal and bacterial communities exhibit a partial recovery of abundance and species richness in older fires, 4) fire severity is the main driver of fungal and bacterial community structure but its effect varied across time, 5) pyrophilous "fire-loving" fungi and bacteria exhibit an increased abundance in burned plots, particularly in recent fires, and 6) symbiotic ectomycorrhizal fungi are particularly hard hit by the compound effect of the beetle-driven tree mortality and wildfires. They exhibit a consistently low abundance and richness in the high severity plots which did not recover over time, and unburned plots have a depauperated ectomycorrhizal community. [ABSTRACT FROM AUTHOR]

Abstract Spatial variation in cone serotiny in Rocky Mountain lodgepole pine (Pinus contorta ssp. latifolia) across Yellowstone National Park influences initial pine recruitment after stand‐replacing fire with tremendous population, community, and ecosystem consequences. A previous study showed that much of the spatial variation in serotiny results from the balance of selection arising from high frequencies of fire favoring serotiny countered by opposing selection exerted by American red squirrels (Tamiasciurus hudsonicus) as seed predators. This earlier study, however, assumed stable local red squirrel densities over multiple generations of pines. Here, we examine environmental properties that might contribute to long‐term stability in the densities of red squirrels among sites. We found that the amount of clay in the soil, an indicator of plant and fungal growth—the latter an important food resource for red squirrels—and the coefficient of variation (CV) in diameter at breast height (DBH) of forest trees together account for a substantial amount of variation in red squirrel density. Soil development occurs over very long time scales, and thus, intersite variation in the amount of clay is unlikely to shift across pine generations. However, CV of DBH and squirrel density increase with stand age, which acts to amplify selection against serotiny with increasing interfire interval. Regardless, much of the variation in the CV of DBH is accounted for by soil bulk density, mean annual temperature, and surface curvature, which are unlikely to vary in their relative differences among sites over time. Consequently, these soil and abiotic attributes could contribute to consistent spatial patterns of red squirrel densities from one pine generation to the next, resulting in consistent local and spatial variation in selection exerted by red squirrels against serotiny.

In many regions, alien conifers have spread widely at lower elevations and are increasingly found colonizing alpine areas. Although studies have addressed conifer invasions at low elevations, little is known about the rates and constraints on spread into higher elevations. Here, we assess the relative importance of climate and the availability of regeneration microsites on the establishment of the alien species Pinus contorta into a high elevation site in New Zealand. Spread has occurred from two stands planted at the elevation of the native treeline (1347–1388 masl) in the 1960s. Most stems established between 1350 and 1450 masl and P. contorta individuals were found up to 270 m above the original plantings. Although the population has increased by 180% in the last 20 years, population growth rate has been declining. Furthermore, comparisons with studies from other mountain ranges around the world and at low elevations in New Zealand suggest this is a relatively limited spread. Our results suggest that climate variation did not have a significant effect on establishment patterns, as opposed to availability of regeneration microsites. Soil and alpine mat microsites favoured establishment of P. contorta and, although these microsites did not appear to be saturated, microsite availability may be an important limiting factor for the spread of P. contorta. Thus management strategies should focus on preventing spread in addition to removing already established stems.

Increased mortality of forest trees, driven directly or indirectly by climate change, is occurring around the world. In western North America, whitebark pine, a high elevation keystone species, and lodgepole pine, a widespread ecologically and economically important tree, have experienced extensive mortality in recent climate-driven outbreaks of the mountain pine beetle. However, even in stands experiencing high levels of mortality, some mature trees have survived. We hypothesized that the outbreak acted as a natural selection event, removing trees most susceptible to the beetle and least adapted to warmer drier conditions. If this was the case, genetic change would be expected at loci underlying beetle resistance. Given we did not know the basis for resistance, we used inter-simple sequence repeats to compare the genetic profiles of two sets of trees, survivors (mature, living trees) and general population (trees just under the diameter preferred by the beetles and expected to approximate the genetic structure of each tree species at the site without beetle selection). This method detects high levels of polymorphism and has often been able to detect patterns associated with phenotypic traits. For both whitebark and lodgepole pine, survivors and general population trees mostly segregated independently indicating a genetic basis for survivorship. Exceptions were a few general population trees that segregated with survivors in proportions roughly reflecting the proportion of survivors versus beetle-killed trees. Our results indicate that during outbreaks, beetle choice may result in strong selection for trees with greater resistance to attack. Our findings suggest that survivorship is genetically based and, thus, heritable. Therefore, retaining survivors after outbreaks to act as primary seed sources could act to promote adaptation. Further research will be needed to characterize the actual mechanism(s) of resistance.

Plants interact simultaneously with multiple organisms, including ectomycorrhizal (EM) fungal symbionts which benefit plants by facilitating resource acquisition. Yet, their role in induced plant defenses that rely on the allocation of plant resources has received little attention. We investigated whether EM fungi can affect the induction of defense-related monoterpenes in greenhouse-grown lodgepole pine (Pinus contorta var. latifolia) seedlings, and whether such effects differed between EM fungal species occurring alone or in combination. Fungal interactions on growth media were also assessed to complement the greenhouse study. Our study revealed that the production of certain monoterpenes is influenced by the fungal species colonizing pine roots. Furthermore, pine seedlings did not necessarily benefit from having associations with multiple EM fungi, as we found contrasting effects of single vs. multiple species of fungi on induced monoterpene responses. Finally, monoterpene responses were altered when early-colonizing species inhibited the colonization or development of later-arriving species. We conclude that the presence of EM fungi can impact host susceptibility to insect and pathogen attack, suggesting that seedlings establishing in areas lacking fungi that promote the induction of tree defense chemicals may suffer from increased susceptibility to future pest damage. [ABSTRACT FROM AUTHOR]

Abstract: Forests sequester large amounts of carbon annually and are integral in buffering against effects of global change. Increasing atmospheric CO2 may enhance photosynthesis and/or decrease stomatal conductance (gs) thereby enhancing intrinsic water‐use efficiency (iWUE), having potential indirect and direct benefits to tree growth. While increasing iWUE has been observed in most trees globally, enhanced growth is not ubiquitous, possibly due to concurrent climatic constraints on growth. To investigate our incomplete understanding of interactions between climate and CO2 and their impacts on tree physiology and growth, we used an environmental gradient approach. We combined dendrochronology with carbon isotope analysis (δ13C) to assess the covariation of basal area increment (BAI) and iWUE over time in lodgepole pine. Trees were sampled at 18 sites spanning two climatically distinct elevation transects on the lee and windward sides of the Continental Divide, encompassing the majority of lodgepole pine's northern Rocky Mountain elevational range. We analyzed BAI and iWUE from 1950 to 2015, and explored correlations with monthly climate variables. As expected, iWUE increased at all sites. However, concurrent growth trends depended on site climatic water deficit (CWD). Significant growth increases occurred only at the driest sites, where increases in iWUE were strongest, while growth decreases were greatest at sites where CWD has been historically lowest. Late summer drought of the previous year negatively affected growth across sites. These results suggest that increasing iWUE, if strong enough, may indirectly benefit growth at drier sites by effectively extending the growing season via reductions in gs. Strong growth decreases at high elevation windward sites may reflect increasing water stress as a result of decreasing snowpack, which was not offset by greater iWUE. Our results imply that increasing iWUE driven by decreasing gs may benefit tree growth in limited scenarios, having implications for future carbon uptake potential of semiarid ecosystems. [ABSTRACT FROM AUTHOR]

Abstract Estimating marten (Martes spp.) survival rates in managed forests is important for comparisons with vital rates in unmanaged forests, and data across populations in different forest types are needed in meta-analyses. We estimated survival rates of a Pacific Marten (Martes caurina) population from 1993 to 1998. This population experienced no fur trapping and occurred in an atypical habitat of sparse tree-canopy cover, small tree diameters, and many natural openings and logging clearcuts. In the beetle-damaged, salvage-logged Lodgepole Pine (Pinus contorta) forest, downed wood and snags were removed and slash piles were accumulated to mitigate logging effects. The average annual probability of adult (≥1 y) survival was 0.684, sx̄ = 0.104 (n = 53). The overall adult survival did not differ between years or between the sexes across years. Average annual survival of young (<1 y) was 0.753, sx̄ = 0.118 (n = 26). Seasonal survival of adults (0.945, sx̄ = 0.027) and young (0.974, sx̄ = 0.026) was highest in winter (December through February), and lowest in summer (June through August; adults = 0.853, sx̄ = 0.035; young = 0.902, sx̄ = 0.046). Adult winter survival was significantly greater than summer survival; and for adult females, winter survival was greater than in the other seasons (other seasons range = 0.862 to 0.903) and greater than male winter survival (0.918, sx̄ = 0.039), because there were no known female losses during the period (survival = 1.0). Based on evidence at field recovery sites and laboratory necropsies, predators were associated with 74% of all recovered marten carcasses, including Coyote (Canis latrans), Bobcat (Lynx rufus), American Badger (Taxidea taxus), and raptors of unknown species. Slash piles were used by marten, but the mitigation experiment was discontinued after logging. We suggest that slash piles may have helped sustain the local population of marten in the short term. [ABSTRACT FROM AUTHOR]

Mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB) is an aggressive bark beetle that attacks numerous Pinus spp. and causes extensive mortality in lodgepole pine (Pinus contorta Douglas ex Loudon; LPP) forests in the western United States and Canada. We used pre-outbreak LPP attributes, cumulative MPB attack severity, and areal extent of mortality data to identify subwatershed-scale forest attributes associated with severe MPB-caused tree mortality that occurred across the Northern Rockies, USA from 1999-2014. We upscaled stand-level data to the subwatershed scale to allow identification of large LPP areas vulnerable to MPB. The highest mortality occurred in subwatersheds where LPP mean basal area was greater than 11.5 m² ha-1 and LPP quadratic mean diameter was greater than or equal to 18 cm. A coarse assessment of federally-owned LPP-dominated forestland in the analysis area indicated about 42% could potentially be silviculturally treated. Silvicultural management may be a suitable option for many LPP forests, and our hazard model can be used to identify subwatersheds with LPP attributes associated with high susceptibility to MPB across landscape spatial scales. Identifying highly susceptible subwatersheds can help prioritize general areas for potential treatments, especially where spatially extensive areas of contiguous, highly susceptible LPP occur. [ABSTRACT FROM AUTHOR]

The recently discovered Cassia Crossbill (Loxia sinesciuris) occurs only in 2 small, isolated mountain ranges in southern Idaho, USA: the South Hills and the Albion Mountains. The species faces 2 major threats from climate change related to its reliance on seeds of Rocky Mountain lodgepole pine (Pinus contorta latifolia). First, increased numbers of hot summer days (>32°C) since 2003 apparently caused premature cone opening and seed shedding, leading to reduced seed availability and an 80% decline in Cassia Crossbill densities between 2003 and 2011. Second, climate change is predicted to prevent recruitment and could potentially cause the extirpation of lodgepole pine from the South Hills and Albion Mountains by 2080. This extirpation would cause the extinction of Cassia Crossbills, because they are unable to compete for lodgepole pine seeds elsewhere. Although recent summers with fewer hot days have allowed Cassia Crossbills to recover, determining their status will require using density across habitat types to estimate population size. We estimated the density of Cassia Crossbills at 137 locations and used conditional modeling to evaluate the influence of 12 habitat metrics on the species' habitat use. Cassia Crossbills more commonly used larger, mature lodgepole pine stands, and north-facing slopes where cones experience less insolation and more likely retain seeds despite hot summer days. Their estimated range was 67 km² of lodgepole pine forest, with a population of ~5,800 individuals (95% confidence interval: 3,100-11,000). Given their restricted distribution, small population, and reliance on mature lodgepole pine, the threats posed to Cassia Crossbills by climate change represent a considerable conservation challenge. [ABSTRACT FROM AUTHOR]

Abstract: The North American lodgepole pine Pinus contorta has been planted on 660 000 ha in Sweden. We compared the performance of Ips typographus and Pityogenes chalcographus in storm‐felled and standing pheromone‐baited trees of the historical host species Norway spruce (Picea abies) and lodgepole pine. In the first summer after a storm, I. typographus colonized 0.2% and P. chalcographus colonized 2.4% of the storm‐felled lodgepole pines compared with 31% and 25%, respectively, of the storm‐felled Norway spruces. In the second summer 1.6% and 41.5% of the lodgepole pines were colonized by I. typographus and P. chalcographus, respectively. The reproductive success of I. typographus was five‐fold higher in Norway spruce than in lodgepole pine. Other species colonizing lodgepole pine were Ips duplicatus, Orthotomicus proximus, Orthotomicus laricis, Monochamus sutor and Pissodes pini. The male attack densities of both bark beetle species required to overcome defences of standing pheromone‐baited trees were much higher in lodgepole pine than in Norway spruce. The reproductive success of I. typographus and P. chalcographus was approximately five‐ and 14‐fold higher, respectively, in Norway spruce than in lodgepole pine. Larvae of the most important groups of bark beetle enemies were present in both storm‐felled and standing pheromone‐baited lodgepole pines colonized by I. typographus and P. chalcographus. In the standing trees, the densities of enemy larvae were lower in lodgepole pine than in Norway spruce, whereas the opposite was true for storm‐felled trees. [ABSTRACT FROM AUTHOR]

Increased mortality of forest trees, driven directly or indirectly by climate change, is occurring around the world. In western North America, whitebark pine, a high elevation keystone species, and lodgepole pine, a widespread ecologically and economically important tree, have experienced extensive mortality in recent climate-driven outbreaks of the mountain pine beetle. However, even in stands experiencing high levels of mortality, some mature trees have survived. We hypothesized that the outbreak acted as a natural selection event, removing trees most susceptible to the beetle and least adapted to warmer drier conditions. If this was the case, genetic change would be expected at loci underlying beetle resistance. Given we did not know the basis for resistance, we used inter-simple sequence repeats to compare the genetic profiles of two sets of trees, survivors (mature, living trees) and general population (trees just under the diameter preferred by the beetles and expected to approximate the genetic structure of each tree species at the site without beetle selection). This method detects high levels of polymorphism and has often been able to detect patterns associated with phenotypic traits. For both whitebark and lodgepole pine, survivors and general population trees mostly segregated independently indicating a genetic basis for survivorship. Exceptions were a few general population trees that segregated with survivors in proportions roughly reflecting the proportion of survivors versus beetle-killed trees. Our results indicate that during outbreaks, beetle choice may result in strong selection for trees with greater resistance to attack. Our findings suggest that survivorship is genetically based and, thus, heritable. Therefore, retaining survivors after outbreaks to act as primary seed sources could act to promote adaptation. Further research will be needed to characterize the actual mechanism(s) of resistance. [ABSTRACT FROM AUTHOR]

Temperate and boreal conifer forests are dormant for many months during the cold season. Climate change is altering the winter environment, with increased temperature, altered precipitation, and earlier snowmelt in many locations. If significant enough, these changes may alter patterns of dormancy and activity of evergreens. Here we studied the factors limiting photosynthetic activity of a high-elevation subalpine forest that has undergone substantial warming in recent decades. We tested the hypothesis that this warming has been significant enough to allow photosynthesis during sunny warm days in winter. Using thermal imagery, we found that foliage in winter was sometimes near the temperature optimum for photosynthesis, but no net carbon gain occurred for most of the cold season. Water transport was limited by blockage of sap transport by frozen boles, but not by frozen soils. Foliar carotenoid content was much higher during winter, driven largely by increases in the pool size of the photoprotective xanthophyll cycle. There was no seasonal change in chlorophyll or lutein content. Net carbon uptake began only as boles thawed, with no difference in timing among tree species, and the spring increase in canopy-level photosynthetic capacity occurred before sap transport was detected. The seasonality of gross primary productivity (GPP) was strongly linked to seasonality of xanthophyll cycle deepoxidation state in all species. Seasonality of GPP was detectable with two metrics of canopy color – the Green Chromatic Coordinate and Green-Red Vegetation Index (a proxy for the newly proposed MODIS-based chlorophyll/carotenoid index or CCI). Both indices were significantly correlated with GPP. Together these results indicate the potential for airborne or near-surface remote sensing of leaf color to serve as a metric of photosynthetic activity in evergreen forests, and to monitor physiological changes associated with the progression in and out of winter dormancy. [ABSTRACT FROM AUTHOR]

Quantifying prey taken by Pacific Marten ( Martes americana caurina) helps to understand local habitat requirements of the species. We collected 250 scat samples associated with at least 53 marten in a salvage-logged Lodgepole Pine ( Pinus contorta)-Bitterbrush shrub ( Purshia tridentata) forest in south-central Oregon. The frequency of occurrence of food items included 98.0% mammals, 36.0% arthropods, 23.2% birds, 9.2% plants, 2.0% hares and rabbits, and 0.8% reptiles. Among mammals, 72.4% were vole-sized and 47.2% squirrel-sized. Chipmunks ( Neotamias spp., 27.6%) and ground squirrels ( Spermophilus spp., 28.0%) had the highest occurrence by size group, respectively. Frequency varied little between summer and winter. Male marten preyed on a greater proportion of mice ( Peromyscus spp.) than females, especially in summer, and in winter females preyed on a greater proportion of voles ( Microtus spp.) than did males. Female marten also preyed on a greater proportion of birds in winter than did males, whereas males had a greater proportion in summer. We compare our findings with a concurrent study in northeastern Oregon and discuss the importance of slash piles from the indirect evidence in the frequently logged forest type to help inform habitat management of the species and prey. [ABSTRACT FROM AUTHOR]

Lodgepole pine ( Pinus contorta var. latifolia Engelm.) ecosystems of central British Columbia face cumulative stresses, and management practices are increasingly scrutinized. We addressed trade-offs between 'light-on-the-land' versus more aggressive silvicultural approaches by examining plant communities and indicator species (non-natives, berry producers, epiphytes, mycotrophs, pine rust alternate hosts) across a gradient of five or six site preparation treatments at the Bednesti trial (established 1987). We tested whether more severe site preparation ( i) caused plant community composition to diverge from a 35- to 46-year-old reference forest, ( ii) accelerated succession by hastening crown closure, or ( iii) delayed succession by promoting seral species. Nonmetric multidimensional scaling (NMDS) ordination showed all treatments converging toward the reference forest composition. At 10 years, succession was incrementally delayed by more severe treatments; at 25 years, only burned windrows were still delayed. Mixed-effects models based on site preparation severity were better than crown closure models for 11 of 13 variables tested, suggesting that mostly belowground processes drive succession in these infertile ecosystems. Invasive hawkweeds persisted on all treatments at 25 years. Limited, contradictory data did not support using mechanical or fire treatments to reduce alternate hosts of pine stem rusts. Long-term trials such as Bednesti highlight the need for ecosystem-specific strategies and diverse approaches to accommodate conflicting benefits and risks of disturbance in forests. [ABSTRACT FROM AUTHOR]

The effectiveness of nitrogen (N) fertilization in improving tree growth in saline forest soils is poorly understood. Hence, in this study, the interactive effect of N fertilization and salt stress on seedling physiology and growth was examined to improve our understanding of possible mechanisms for fertilization to mitigate salt stress. We compared physiological characteristics, growth, and foliar and root nutrient concentrations in lodgepole pine ( Pinus contorta ) and white spruce ( Picea glauca ) seedlings planted in a peat-mineral soil mix during a three months study with N fertilization (0 and 300 mg N seedling −1 ) and salinity (0, 50, 100, 150 mmol L −1 NaCl) in a greenhouse experiment. Nitrogen fertilization significantly increased net photosynthetic rates ( P n ) and N concentrations in needles and roots, resulting in improved seedling height and root collar diameter growth and total seedling biomass for both species when seedlings were subjected to low salinity (50 mmol L −1 NaCl), while it did not help tree growth under high salinity (150 mmol L −1 NaCl). The physiological responses to combined salt stress and N fertilization did not differ between the two species; however, fertilization improved the growth of pine seedlings more than that of spruce seedlings under different salinity levels. The results suggest that the effectiveness of N fertilization in mitigating the salinity effect on seedling growth was species specific. Our study demonstrates that N fertilization improves tree growth through enhanced photosynthesis and N nutrition under low salinity and provides valuable insights into strategies to manage N nutrition in saline boreal forest soils. [ABSTRACT FROM AUTHOR]

This paper analyzes sapwood variability and allometry within individuals of Populus tremuloides, Pinus contorta, Pinus banksiana, Picea mariana, and Picea glauca. Outside bark diameter at breast height (DBH) and sapwood depth (sd) in four cardinal directions were measured in individuals in stands in Alberta and Saskatchewan, Canada. The microscopical analysis of wood anatomy was used to measure sd, and the error associated with the measures was observed. Sapwood allometry analyses examined the influence of DBH on sd and on sapwood area (SA). All species were observed to have varying sapwood depths around the trunk with statistical analyses showing that Pinus banksiana has a well defined preference to grow thicker in the North-East side. The largest sd values were observed for the Populus tremuloides set. Unlike Populus tremuloides and Picea glauca, for the species Pinus contorta, Pinus banksiana, and Picea mariana, incremental growth in DBH does not directly drive sapwood growth in any direction. For these three species, SA increases only because of increases in DBH as sd remains nearly constant. These results show that sapwood depth and sapwood area seem to behave differently in each studied species and are not always proportional to the tree size as is normally assumed. [ABSTRACT FROM AUTHOR]

There are two general approaches for reducing the negative impacts of mountain pine beetle, Dendroctonus ponderosae Hopkins, on forests. Direct control involves short-term tactics designed to address current infestations by manipulating mountain pine beetle populations, and includes the use of fire, insecticides, semiochemicals, sanitation harvests, or a combination of these treatments. Indirect control is preventive, and designed to reduce the probability and severity of future infestations within treated areas by manipulating stand, forest and/or landscape conditions by reducing the number of susceptible host trees through thinning, prescribed burning, and/or alterations of age classes and species composition. We emphasize that “outbreak suppression” is not the intent or objective of management strategies implemented for mountain pine beetle in the western United States, and that the use of clear, descriptive language is important when assessing the merits of various treatment strategies.