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The introduction of exotic tree species can have profound effects on the native environment, including habitat use and movement patterns of animals, as well as becoming a management challenge for other land users. Here, we used GPS data from reindeer (Rangifer tarandus) and remote sensing measurements of lichen cover and soil moisture to assess the effects of the exotic lodgepole pine (Pinus contorta) on reindeer husbandry by the Indig-enous S ' ami in northern Sweden. We used locational data from 67 reindeer for three winters to analyze their habitat selection at the second-order selection (placement of home range in the landscape) and third-order se-lection (selection of sites within the home range) in relation to land cover class, terricolous lichen cover as measure of winter forage abundance, topographic features, and distance to roads. We also analyzed remotely sensed abundance of lichens in different forest types, and the association between these forest types and soil moisture as measure of suitability as lichen habitat. Compared to native P. sylvestris, we found that reindeer avoided stands with P. contorta where trees were higher than three meters. If P. contorta was the dominant tree species, reindeer were 60 % less likely to select these stands compared to stands with P. sylvestris, and 40 % less likely if P. contorta was less dominant at both orders of selection. We also found that reindeer selected areas with higher lichen cover. Lichen cover was lower in P. contorta stands compared to stands of the native P. sylvestris, even though P. contorta occurred mainly on dry soils usually favorable for terricolous lichens. We conclude that planting P. contorta on soils suitable for terricolous lichens is likely to reduce forage availability for reindeer and turn habitats earlier preferred by reindeer into avoided habitat, resulting in an overall reduction of winter grazing grounds. The effects of stands with P. contorta, albeit covering a comparatively small percentage of the reindeer husbandry area, need to be seen in context with generally declining terricolous lichen abundance due to land uses like forestry and other cumulative effects by external pressures on reindeer husbandry.

Over 18 million hectares of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) forests have been affected by a massive mountain pine beetle outbreak in western Canada. The ensuing need for reforestation compels forest managers to deploy more drought-resistant stock in anticipation of a hotter and drier future climate. Recent studies suggest that naturally occurring lodgepole pine × jack pine (Pinus banksiana Lamb.) hybrids may be more drought-resistant than pure lodgepole pine. We used single-nucleotide polymorphism markers to determine the level of jack pine introgression present in the region J lodgepole pine seed orchard, in northwest Alberta, and we identified six hybrid genotypes with 10%–18% jack pine introgression for further study. We compared the performance of open-pollinated seedlings of lodgepole, jack, and hybrid pines under well-watered and drought conditions in a greenhouse experiment. Seedlings were subjected to repeg ated drought cycles, withholding water for either 2 or 3 weeks. We found that hybrid pines grew significantly faster than lodgepole pine under well-watered conditions while retaining the high tolerance to prolonged drought exhibited by lodgepole pine seedlings, a particularly beneficial combination of traits during the critical stage of establishment. We therefore suggest the deployment of hybrid lodgepole pine as a strategy to promote adaptation to hotter and drier future climates.

Peer reviewed: True, Funder: University of Cambridge; Id: http://dx.doi.org/10.13039/501100000735, While droughts, intensified by climate change, have been affecting forests worldwide, pest epidemics are a major source of uncertainty for assessing drought impacts on forest trees. Thus far, little information has documented the adaptability and evolvability of traits related to drought and pests simultaneously. We conducted common-garden experiments to investigate how several phenotypic traits (i.e. height growth, drought avoidance based on water-use efficiency inferred from δ13C and pest resistance based on defence traits) interact in five mature lodgepole pine populations established in four progeny trials in western Canada. The relevance of interpopulation variation in climate sensitivity highlighted that seed-source warm populations had greater adaptive capability than cold populations. In test sites, warming generated taller trees with higher δ13C and increased the evolutionary potential of height growth and δ13C across populations. We found, however, no pronounced gradient in defences and their evolutionary potential along populations or test sites. Response to selection was weak in defences across test sites, but high for height growth particularly at warm test sites. Response to the selection of δ13C varied depending on its selective strength relative to height growth. We conclude that warming could promote the adaptability and evolvability of growth response and drought avoidance with a limited evolutionary influence from pest (biotic) pressures.

1. Tree-species mixture effects (e.g. complementarity and facilitation) have been found to increase individual-tree productivity, lessen mortality and improve recruitment in forests worldwide. By promoting more efficient and complete resource use, mixture effects may also lessen individual-tree-level water stress, thus improving drought resistance. We investigated the influence of mixture effects on tree productivity, mortality and recruitment across broad compositional and moisture gradients in high-elevation Interior West US mixed-conifer communities, where Populus tremuloides (trembling aspen) is the major contributor to functional diversity. Our goal was to provide a more complete scientific foundation for managing these drought-prone, fire-excluded systems under an uncertain climate. 2. We used landscape-scale national forest inventory data to examine mixture effects on P. tremuloides and the major associated conifer species, Pseudotsuga menziesii, Pinus contorta, Abies lasiocarpa and Picea engelmannii. Using generalized linear mixed modelling, we isolated the influences of P. tremuloides relative density and climate on tree-level (stems ≥ 12.7 cm DBH) growth, mortality and stand-level recruitment (presence/absence of new trees). Cold-season precipitation (PPT) and warm-season vapour pressure deficit (VPD) served to represent soil moisture supply and demand, respectively. Populus tremuloides growth declined as interspecific density increased. In contrast, Pinus contorta and A. lasiocarpa growth increased with P. tremuloides density. For all species except A. lasiocarpa and P. menziesii, growth increased under higher PPT and VPD. 3. Populus tremuloides mortality increased under high VPD but not with interspecific relative density. We found limited evidence that A. lasiocarpa mortality decreased as P. tremuloides density increased. Populus tremuloides recruitment declined steeply above 25% interspecific relative density. We found a decline in conifer recruitment odds as P. tremuloides density increased, ranging from strong in P. contorta to insubstantial in P. engelmannii. 4. Synthesis. Our findings have implications for sustaining mixed-conifer communities impacted by climate change and historical fire exclusion. Mixtures of P. tremuloides and conifers may improve conifer growth while adversely impacting P. tremuloides growth relative to pure stands. Higher conifer productivity combined with lower P. tremuloides recruitment at high conifer relative density may accelerate succession.

The success of invasive plants is influenced by many interacting factors, but evaluating multiple possible mechanisms of invasion success and elucidating the relative importance of abiotic and biotic drivers is challenging, and therefore rarely achieved. We used live, sterile or inoculated soil from different soil origins (native range and introduced range plantation; and invaded plots spanning three different countries) in a fully factorial design to simultaneously examine the influence of soil origin and soil abiotic and biotic factors on the growth of invasive Pinus contorta. Our results displayed significant context dependency in that certain soil abiotic conditions in the introduced ranges (soil nitrogen, phosphorus or carbon content) influenced responses to inoculation treatments. Our findings do not support the enemy release hypothesis or the enhanced mutualism hypothesis, as biota from native and plantation ranges promoted growth similarly. Instead, our results support the missed mutualism hypothesis, as biota from invasive ranges were the least beneficial for seedling growth. Our study provides a novel perspective on how variation in soil abiotic factors can influence plant-soil feedbacks for an invasive tree across broad biogeographical contexts.

The sister species, lodgepole pine (Pinus contorta var. latifolia Engelm.) and jack pine (Pinus banksiana Lamb), face pressures from a multitude of biotic agents, including mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902) and their pathogenic fungal associates (e.g., Grosmannia clavigera (Rob.-Jeffr. & R.W. Davidson) Zipfel, Z.W. de Beer & M.J. Wingf.), mistletoe (Arceuthobium americanum Nutt. ex A.Gray), and the pathogen causing western gall rust (Cronartium harknessii E. Meinecke). Here, we report new stem tissue transcriptome resources developed for lodgepole and jack pines subjected to these biotic stresses. The annotated transcriptomes were compared to determine species-specific responses to the necrotrophic G. clavigera and the biotrophic Cronartium harknessii. We focused on chitinases, a family that includes members with well-documented roles in defense. Putative chitinase family members were identified via annotation, sequence similarity to reference chitinase genes, phylogenetic analyses, and in silico motif characterization. RNA-Seq revealed marked differences in the responses of lodgepole and jack pine chitinases to G. clavigera and Cronartium harknessii. The potential for adaptive variation in chitinases was investigated by assessing the level of genetic differentiation between and within lodgepole and jack pines using single nucleotide polymorphisms within chitinases. These analyses illustrate the potential of combining transcriptomic and genotyping resources to investigate genotype–phenotype correlations for non-model species.

Gravel mining is prevalent in forest landscapes across Canada, typically resulting in complete loss of vegetation and topsoil. Despite such extreme disturbance, lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) trees are thriving at unreclaimed gravel pits located in central-interior British Columbia, possibly owing to, at least in part, the association of pine trees with their endophytic bacteria. To test this possibility, several bacterial strains were previously isolated from pine trees growing at these pits; of the strains isolated, 14 were identified as effective nitrogen fixers. In this study, we evaluated the inoculation effect of these 14 strains on lodgepole pine growth under nitrogen-poor conditions. Eighteen months after sowing and inoculation, each strain had colonized the rhizosphere and internal tissues of pine seedlings and had significantly enhanced their length (24%–65%) and biomass (100%–300%). Notably, three Pseudomonas strains increased pine seedling length by 1.6-fold and biomass by 4-fold. Most strains also demonstrated substantial potential to promote plant growth via phosphorus solubilization, siderophore production, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, indole-3-acetic acid production, lytic enzyme activity, and catalase activity. Our results suggest that such nitrogen-fixing bacteria could be sustaining pine growth on bare gravel, indicating a possible ecological association that may explain natural tree regeneration in such a disturbed ecosystem.

Increased climatic variability can impact tree physiological processes beyond what is predicted from changes in mean conditions. We assessed the sensitivity of conifer saplings to spatial and temporal variability in meteorological conditions, taking advantage of the end of California’s historic drought and the exceedingly wet winter of 2017. We sought to understand how very dry and very wet conditions constrain photosynthesis and growth in four regionally dominant conifers and whether sensitivity in these processes changes across a 500 m gradient in elevation. All species demonstrated phenotypic plasticity in response to temporal differences in precipitation on both inter-annual and seasonal timescales. Net photosynthesis in Pinus contorta decreased from an early season 2016 average of 12.4 to 6.89 μmol CO2 m−2 s−1 later in the summer, but increased 14.1% between seasons in the wet year. By contrast, elevation had almost no effect on instantaneous photosynthetic gas exchange, CO2 response curve parameters, or stem water potential in any of the years for any of the species. Effects of the heavy snow year (2017) on needle growth differed between elevations. Pinus contorta showed a 38.9% increase in average needle length at the lower two elevations but a 31.6% decrease at the highest site compared to the height of the drought. Despite these differences, biological variation was dampened compared to the physical variation between years, suggesting these trees can effectively withstand substantial meteorological variability. Our results show that these species demonstrated considerable ability to tolerate and recover from an extreme drought event.

We studied the recovery of tree- and stand-level carbon (C) storage in a lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forest in northern British Columbia that experienced substantial (∼83%) mortality in 2006–2007 (total loss by 2013 = 86%) during a severe mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins, 1902) infestation. Earlier work suggested that this forest recovered positive annual C storage 3 years after attack based on eddy covariance measurements. We sought to confirm these results by examining C storage in surviving pine trees using tree core analysis. Average growth release of surviving lodgepole pine trees was 392% (range of –53% to 2326%) compared with mean decadal growth prior to MPB attack. Nearly 97% of trees underwent a growth release, considerably higher than the 15%–75% reported for lodgepole pine in previous studies. Mean annual stem C storage of the surviving trees in this study was highly correlated (r = 0.88) with 10 years of annual net ecosystem productivity estimates made using the eddy covariance technique, indicating that surviving lodgepole pine remain an important part of C recovery after MPB attack. Mean annual stem C storage was also highly correlated (r = 0.92) with the cumulative percentage of downed stems per hectare at the site, suggesting that increased availability of resources is likely assisting the growth release.

Legacy effects from one disturbance may influence successional pathways by amplifying or buffering forest regeneration after the next disturbance. We assessed vegetation and tree regeneration in non-serotinous Sierra lodgepole pine (Pinus contorta var. murrayana) stands after a 1984 wildfire which burned with variable severity and again after a high-severity subsequent fire in 2012. The legacy effects of the 1984 fire were amplified; seedlings and saplings were abundant in areas initially burned at low severity (1267 stems ha−1) despite high reburn severity, but regeneration was low in areas twice burned at high severity (31 stems ha−1). Our results suggest that the severity of the 1984 fire may have influenced post-2012 tree regeneration by creating variable fuel loading, which may have affected soils, litter cover and shade after the 2012 fire and therefore affected seedling establishment and survival. A canopy seed bank of unburnt cones from trees killed by the 2012 fire potentially contributed to a strong effect of prior burn severity on regeneration after the 2012 fire despite a lack of serotinous or resprouting tree species, although the influence of this canopy seedbank was likely limited to the year following the fire. Our results suggest that a low- to moderate-severity fire increases forest resilience relative to a high-severity fire even when the next fire burns at high severity.

Disturbances have altered community dynamics in boreal forests with unknown consequences for belowground ecological processes. Soil fungi are particularly sensitive to such disturbances; however, the individual response of fungal guilds to different disturbance types is poorly understood. Here, we profiled soil fungal communities in lodgepole pine forests following a bark beetle outbreak, wildfire, clear-cut logging, and salvage-logging. Using Illumina MiSeq to sequence ITS1 and SSU rDNA, we characterized communities of ectomycorrhizal, arbuscular mycorrhizal, saprotrophic, and pathogenic fungi in sites representing each disturbance type paired with intact forests. We also quantified soil fungal biomass by measuring ergosterol. Abiotic disturbances changed the community composition of ectomycorrhizal fungi and shifted the dominance from ectomycorrhizal to saprotrophic fungi compared to intact forests. The disruption of the soil organic layer with disturbances correlated with the decline of ectomycorrhizal and the increase of arbuscular mycorrhizal fungi. Wildfire changed the community composition of pathogenic fungi but did not affect their proportion and diversity. Fungal biomass declined with disturbances that disrupted the forest floor. Our results suggest that the disruption of the forest floor with disturbances, and the changes in C and nutrient dynamics it may promote, structure the fungal community with implications for fungal biomass-C.

Wildfire is a ubiquitous disturbance agent in subalpine forests in western North America. Lodgepole pine ( Pinus contorta var. latifolia), a dominant tree species in these forests, is largely resilient to high-severity fires, but this resilience may be compromised under future scenarios of altered climate and fire activity. We investigated fire occurrence and post-fire vegetation change in a lodgepole pine forest over the past 2500 years to understand ecosystem responses to variability in wildfire and climate. We reconstructed vegetation composition from pollen preserved in a sediment core from Chickaree Lake, Colorado, USA (1.5-ha lake), in Rocky Mountain National Park, and compared vegetation change to an existing fire history record. Pollen samples ( n = 52) were analyzed to characterize millennial-scale and short-term (decadal-scale) changes in vegetation associated with multiple high-severity fire events. Pollen assemblages were dominated by Pinus throughout the record, reflecting the persistence of lodgepole pine. Wildfires resulted in significant declines in Pinus pollen percentages, but pollen assemblages returned to pre-fire conditions after 18 fire events, within c.75 years. The primary broad-scale change was an increase in Picea, Artemisia, Rosaceae, and Arceuthobium pollen types, around 1155 calibrated years before present. The timing of this change is coincident with changes in regional pollen records, and a shift toward wetter winter conditions identified from regional paleoclimate records. Our results indicate the overall stability of vegetation in Rocky Mountain lodgepole pine forests during climate changes and repeated high-severity fires. Contemporary deviations from this pattern of resilience could indicate future recovery challenges in these ecosystems.

Herbivores modulate the structure and composition of plant communities, including plant invasions. This is conditioned by plant palatability which can be reduced by its chemical or physical traits. The effects that ungulates browsing has on pine invasions are variable and the empirical evidence on the causes of this variability is scarce. We experimentally explored how sheep browsing preference varies between seedlings of pine species with different invasiveness; Pinus contorta (high invasiveness), P. ponderosa (medium invasiveness), P. radiata (medium invasiveness) and P. jeffreyi (low invasiveness). Secondly, we quantified anti-herbivory chemical compounds and physical traits of these species and related them with sheep preference observed. The browsing incidence of P. contorta was 68%, P. ponderosa 58%, P. radiata 29%, and P. jeffreyi 84%. Among anti-herbivory traits analyzed, α-pinene concentration had a negative effect on the probability of a terminal bud being browsed and on browsing intensity. Meanwhile, foliar toughness was negatively related to browsing intensity and water concentration was positively related to browsing intensity. Also, the most invasive species, P. contorta, was highly damaged. Thus, sheep herbivory could be slowing pine invasion rate; suggesting that could be considered a tool to control early invasions, especially for this particular species.

Disturbances are frequent events across the Canadian boreal forest and can affect both below‐ and above‐ground ecosystem processes. How disturbances change below‐ground soil fungal communities and in‐turn affect pine establishment and performance is poorly understood. Such understanding has become increasingly important in light of observed changes in disturbance regimes in recent years due to climate change. We used a greenhouse experiment to determine how soil inoculum collected from lodgepole pine stands undisturbed (control) or disturbed by fire, mountain pine beetle outbreak, logging and salvage logging affect pine seedling performance in western Canada. We first characterized whether fungal communities of seedling roots change as a function of inoculum source, and then determined whether changes in fungal community composition impact pine seedling performance (biomass and height). Root fungal communities of pine seedlings from logged and salvage logged disturbances differed from their respective paired controls, while soils from natural disturbances (fire and beetle outbreak) did not. Among disturbances, the pine root fungal communities of fire and salvage logged disturbances differed. In parallel to the root fungal communities, seedling performance also decreased when comparing logging and salvage logging disturbances to paired controls. Among disturbance treatments, seedlings from the salvage logged disturbance did not grow as big as seedlings inoculated with soils from burned forests. Synthesis and application. Our findings indicate that anthropogenic disturbances (logging and salvage logging) can have cross‐generational impacts on pine seedling performance, through functional shifts in seedling root fungal community structure. Furthermore, the impacts of soil fungi on pine seedlings appear to be pronounced following salvage logging, stressing the importance of compound disturbance events. These findings may be important to land managers considering clear‐cut logging or salvage logging in pine forests, particularly where soil biotic communities are likely to be one of the predominate factors in pine establishment.

The large-scale introduction of lodgepole pine (Pinus contorta ssp. latifolia, LP) into Swedish forests was initiated around 1970, and currently 520,000 hectares of the forest land are dominated by the species. Even though the tree has mostly serotine cones, adapted to open after forest fires, it has proved able to self-regenerate in Sweden. This study is the first to present, scientifically, the extent of self-regeneration covering the whole current range of LP-forests in Sweden. LP-saplings were recorded for three years, 2015–2017, in 8194 subplots distributed over 214 randomly selected LP-stands from latitude 59.6–66.9°N and altitude 88–710 m asl. Of all subplots, 3% contained LP-saplings, and regeneration was found in 53% of all stands. The probability of finding LP-saplings was significantly dependent on the plots’ distance from the edge of the LP-stand, and 78% of all saplings were found within and up to 15 m beyond the stand edge. Most, 63%, of the plots with LP were found on disturbed ground such as wheel tracks, roadsides and where there had been site preparation. The results show that LP can naturally spread under a range of conditions in the studied region. The regeneration is, however, concentrated in particular stands and should be possible to control with monitoring programmes and measures to eradicate self-dispersed trees in unwanted areas.

This study was conducted to quantify growth responses of three major commercial conifer species (lodgepole pine (Pinus contorta Douglas ex Loudon var. latifolia Engelm. ex S. Watson), interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco), and spruce (white spruce (Picea glauca (Moench) Voss) and hybrid spruce (Picea engelmannii Parry ex. Engelm. × Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carrière))) to various fertilizer blends in interior British Columbia, Canada. Over 25 years, growth-response data were repeatedly collected across 46 installations. The fertilizer blends were classified into three groups: nitrogen only; nitrogen and sulfur combined; and nitrogen, sulfur, and boron combined. The growth responses for stand volume, basal area, and top height were calculated through absolute and relative growth rate ratios relative to a controlled group. Fertilizer blend, inverse years since fertilization, site index, stand density at fertilization, and their interactions with the fertilizer blend were used as explanatory variables. The magnitude and significance of volume and basal area growth responses to fertilization differed by species, fertilizer-blend groups, and stand-condition variables (i.e., site index and stand density). In contrast, the response in top height growth did not differ among fertilization blends, with the exception of the nitrogen and sulfur fertilizer subgroup for lodgepole pine. The models developed in this study will be incorporated into the current growth and yield fertilization module (i.e., Table Interpolation Program for Stand Yields (TIPSY)), thereby supporting guidance of fertilization applications in interior forests in British Columbia.

Western gall rust (Cronartium harknessii (J.P. Moore) E. Meinecke) is a pathogen that affects lodgepole pine (Pinus contorta Douglas ex Loudon var. latifolia Engelm. ex S. Watson) and has the potential to reduce lumber product yields derived from stands managed for the commercial production of timber. A dataset containing repeated measurements from 7775 trees located within the province of British Columbia, Canada, was used to develop equations that predict annual rates of stem infection, post-infection mortality, and the location of large stem galls. Results showed that annual rates of infection peaked between 3 and 5 years following stand establishment. Few new infections were predicted to occur beyond the stand age of 15 years. For an individual tree, the probability of first infection increased as its height increased relative to stand top height. The rate of mortality increased with the number of stem infections and was highest among trees infected within the first 3 years following planting. Mortality rates decreased thereafter, with many trees likely to survive to rotation. The equations predicting rust incidence and mortality were added to the Tree and Stand Simulator (TASS), an individual-tree growth model used within the province. A final equation predicting the location of large galls was added and allows TASS to account for losses due to the removal of stem defects during lumber manufacturing.

Promoting ecological resilience to increasing disturbance activity is a key management priority under warming climate. Across the Northern Hemisphere, tree mortality from widespread bark beetle outbreaks raises concerns for how forest management can foster resilience to future outbreaks. Density reduction (i.e., thinning) treatments can increase vigor of remaining trees, but the longevity of treatment efficacy for reducing susceptibility to future disturbance remains a key knowledge gap. Using one of the longest-running replicated experiments in old-growth subalpine forests, we measured stand structure following a recent (early 2000s) severe mountain pine beetle (MPB; Dendroctonus ponderosae) outbreak to examine the legacy of historical (1940s) thinning treatments on two components of resilience. We asked: 'How did historical thinning intensity affect (1) tree-scale survival probability and stand-scale survival proportion (collectively "resistance" to outbreak) for susceptible trees (lodgepole pine [Pinus contorta] ≥ 12 cm diameter) and (2) post-outbreak stand successional trajectories?' Overall outbreak severity was high (MPB killed 59% of susceptible individuals and 78% of susceptible basal area), and historical thinning had little effect on tree-scale and stand-scale resistance. Tree-scale survival probability decreased sharply with increasing tree diameter and did not differ from the control (uncut stands) in the historical thinning treatments. Stand-scale proportion of surviving susceptible trees and basal area did not differ from the control in historically thinned stands, except for treatments that removed nearly all susceptible trees, in which survival proportion approximately doubled. Despite limited effects on resistance to MPB outbreak, the legacy of historical treatments shifted dominance from large-diameter to small-diameter lodgepole pine by the time of outbreak, resulting in historically thinned stands with ~2× greater post-outbreak live basal area than control stands. MPB-driven mortality of large-diameter lodgepole pine in control stands and density-dependent mortality of small-diameter trees in historically thinned stands led to convergence in post-outbreak live tree stand structure. One exception was the heaviest historical thinning treatments (59-77% basal area removed), for which sapling dominance of shade-tolerant, unsusceptible conifers was lower than control stands. After six decades, thinning treatments have had minimal effect on resistance to bark beetle outbreaks, but leave persistent legacies in shaping post-outbreak successional trajectories.

Mountain meadows provide a number of ecosystem services, including sequestering carbon, storing and regulating the release of water, and maintaining biodiversity. However, as with other grassland systems, many meadows are currently experiencing woody plant encroachment. In my first chapter, I used a landscape scale survey of mountain meadows in the central Sierra Nevada to quantify the extent of conifer encroachment, the density of encroaching conifers, and determine if synchronous temporal patterns of encroachment existed. By examining overall encroachment density among 310 meadows in the central Sierra Nevada, I found that essentially all high elevation meadows, up to the krummholz vegetation zone near treeline, have some degree of encroachment. Using natural variation in physical parameters among meadows, as well as variation in climatic conditions since the early 1900s, I was able to identify conditions conducive to conifer recruitment and/or survival. When I correlated annual recruitment with climatic conditions since 1930, conditions during the year of germination were unimportant with success instead depending on conditions during a 3-year seed production period and a 6-year seedling establishment period. Applying a temporal model based on climate during both seed production and seedling establishment periods to downscaled output from four global climate models indicates that the average meadow will convert to forest by the end of the 21st century. Given the ubiquitous nature of conifer encroachment in the central Sierra Nevada, in my second chapter I explored important life stages driving encroachment and the environmental factors influencing each. Using a 4-year study of 30 meadows in Yosemite National Park, I examined seed availability, germination, establishment, and adult survival. I found that seed was abundant throughout most of the interior of the meadows. Germination and seedling emergence showed high interannual variability, and locations with new germinants tended to be those that melted later and experienced more gradual summer dry-down than locations without new germinants. The mortality curve showed that mortality levels off around age 10, leading me to define establishment as survival to 10 years of age. During this establishment phase, most trees occurred in locations where soils reached relatively dry levels by the end of the summer, as opposed to locations that did not dry down as strongly, which had no establishing trees. Adult trees (>10 years) were also found in locations that experienced strong dry down. However, matrix population models built for Pinus contorta in these meadows showed that the asymptotic growth rate of tree numbers in meadows was more sensitive to adult survival than to germination or establishment. Thus, it appears that adult survival drives overall population growth, while microsite constraints on germinants and young seedlings drives the spatial distribution of encroaching trees. Having determined that adult survival has a strong influence on population growth rate of conifers in meadows, and assuming that years of poor adult tree growth indicate years of increased mortality, my third chapter focused on adult growth rates and the influence of climate. Using tree cores from 80 trees in 12 different meadows and from 144 trees in the forest immediately surrounding those 12 meadows, I was able to show that growth patterns of trees in meadows are more similar to each other than they are to growth patterns of trees in the adjacent forest. Thus, there appears to be a distinct topoclimate shared by geographically separate meadows. Meadow tree growth was sensitive to interannual climate variability both during the winter and during the growing season, with growing season effects dependent on the phase of the Pacific Decadal Oscillation. My work shows that conifer encroachment into subalpine meadows is common throughout the central Sierra Nevada. Both recruitment and adult growth are likely to increase with anthropogenic climate change, assuming that responses to climate are stationary. Even if these assumptions are violated, meadows are likely to change toward forest habitat in the short term. This reduction in meadows has management implications, and may result in the loss of important ecosystem services that meadows provide.

Warming temperatures are allowing native insect herbivores to expand into regions that previously exceeded their thermal tolerance, encounter new host species, and pose significant threats to native communities. However, the dynamics of these expansions remain poorly understood, particularly in the extent to which outbreaks remain reliant on emigration from historical hosts or are driven by local reproduction within novel hosts in the expanded range. We tested these non-mutually exclusive hypotheses using spatially explicit data on mountain pine beetle (Dendroctonus ponderosae), which historically undergoes intermittent outbreaks in low-elevation lodgepole pine (Pinus contorta), but is now causing severe mortality in a high-elevation endangered species, whitebark pine (Pinus albicaulis). We compiled data from 2000 to 2019 across British Columbia, Canada, at 1-km2 resolution, and analyzed spatiotemporal patterns of beetle infestations, lodgepole pine distributions, expansion into habitats dominated by whitebark pine, and the likelihood of future outbreaks in all pine communities under simulated conditions. Overall, we found strong support for the hypothesis of emigration from the historical host species continuing to be a major driver of outbreaks in the more recently accessed host. First, beetle population pressure was consistently the best predictor of infestation severity in both lodgepole and whitebark pine, and appeared to be mostly unidirectional from lodgepole to whitebark pine. Second, infestations in lodgepole pine were of a longer duration than those in whitebark pine, which appeared too brief to sustain transitions from endemic to eruptive dynamics. Furthermore, resource depletion appears to drive emigration from lodgepole pine, whereas in whitebark pine drought appears to favor establishment of immigrants although bioclimatic factors and stand structure preclude self-sustaining outbreaks. Finally, we project that most pine in British Columbia will be at risk in the event of a new major outbreak. We describe implications for conserving and protecting whitebark pine and to other climate-driven range expansions.

Successful host plant colonization by tree-killing bark beetle-symbiotic fungal complexes depends on host suitability, which is largely determined by host defense metabolites such as monoterpenes. Studies have shown the ability of specific blends of host monoterpenes to influence bark beetles or their fungal symbionts, but how biologically relevant blends of host monoterpenes influence bark beetle-symbiotic fungal interaction is unknown. We tested how interactions between two host species (lodgepole pine or jack pine) and two fungal symbionts of mountain pine beetle (Grosmannia clavigera or Ophiostoma montium) affect the performance of adult female beetles in vitro. Beetles treated with the propagules of G. clavigera or O. montium or not treated (natural fungal load) were introduced into media amended with a blend of the entire monoterpene profile of either host species and beetle performance was compared. Overall, host blends altered beetle performance depending on the fungal species used in the beetle amendment. When beetles were amended with G. clavigera, their performance was superior over beetles amended with O. montium in either host blend. Furthermore, G. clavigera-amended beetles performed better in media amended with host blends than without a host blend; in contrast, O. montium-amended beetles performed better in media without a host blend than with a host blend. Overall, this study showed that host defense metabolites affect host suitability to bark beetles through influencing their fungal symbionts and that different species of fungal symbionts respond differentlly to host defense metabolites.

Survival and growth of Siberian larch (SL, Larix sibirica Ledeb.) were compared with those of three conifer species native to Alberta, Canada: lodgepole pine (LP; Pinus contorta var. latifolia Engelm. ex S. Watson), white spruce (WS, Picea glauca (Moench) Voss), and jack pine (JP, Pinus banksiana Lamb.) at 12, 10, and 3 trial locations, respectively. The average data age was 18 years (range: 3 to 27 years). Survival of SL averaged 4.2% and 6.5% worse than LP and WS, respectively, while it was 5% better than JP. SL grew 25%, 94%, and 23% taller than LP, WS, and JP, respectively. Stem forking rates were similar between SL and LP, WS, and JP. The best seed sources for Alberta were mature trees established in Alberta and Saskatchewan of unknown initial provenances. The Russian Altai Mountain source grew well at high elevations, while the Finnish Raivola performed well in the northern, low-elevation area. Open-pollinated progeny tests of 58 families planted in five diverse locations yielded individual-tree narrow-sense heritabilities and family mean heritabilities for height at age 15 of 0.15 and 0.59, respectively. The type B between-site genetic correlation was 0.44, indicating a strong genotype × environment interaction. SL has performed well in Alberta, and its growth can be further improved by selection and breeding from appropriate seed sources.

This study investigated the origins and spread patterns of Heterobasidion root disease in three Pinus contorta Dougl. ex Loudon plantations established on forest and agricultural land and subjected to three different management scenarios. Trees with decline symptoms and stumps remaining from the previous rotation were sampled for fungal isolations. Ten isolates of Heterobasidion parviporum Niemelä & Korhonen and 425 of Heterobasidion annosum (Fr.) Bref. were tested for clonality through somatic compatibility tests. The following conclusions were reached: (i) P. contorta is highly susceptible to H. annosum and H. parviporum and both pathogens cause dieback of P. contorta; (ii) H. annosum from previous-rotation P. sylvestris stumps can effectively transfer to P. contorta; (iii) the pathogens may form constantly expanding territorial clones; (iv) basidiospores of both pathogens colonise stumps of P. contorta (primary infections); (v) H. parviporum clones expanded more slowly than clones of H. annosum; (vi) clonal spread proceeded more quickly from stumps with established secondary infections than from stumps with primary infections; (vii) H. annosum can persist in pine stumps for at least 26 years; and (viii) stump treatment should be considered to control Heterobasidion primary infections.

In north-central Alberta, lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia) and jack pine (Pinus banksiana Lamb.) form a mosaic hybrid zone, the spatial extent of which remains poorly defined. We sought to refine the genetic and geographic distribution of this hybrid zone in western North America to provide information important in predicting future risk of mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreaks. We used 29 single nucleotide polymorphism (SNP) markers to discriminate lodgepole pine, jack pine, and their hybrids. We compared and contrasted spatial patterns of hybridization in northern and southern forest zones based on the colonization history of the two species. We found that patterns of introgression were more similar between the zones than expected by chance, but there were significant differences between these regions at specific loci. Using logistic regression, we created a robust predictive model to distinguish among lodgepole pine, jack pine, and their hybrids using a combination of geographic and environmental predictors. Using model selection based on Akaike information criterion, we found that location, elevation, and moisture are important predictors for species class. Quantification of the genetic differences between these two regions, combined with an accurate model for predicting the spatial distribution of lodgepole pine, jack pine, and their hybrids, provides essential information for continued effective management of forest resources.

Quantitative genetic variation of fiber-dimension traits and their relationship with diameter at breast height (DBH) and solid-wood traits (i.e., density and modulus of elasticity (MOE)) was investigated in lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.). A total of 823 increment cores were sampled from 207 half-sib families at two independent progeny trials, aged 34–35 years, located in northern Sweden. High-resolution pith-to-bark profiles were obtained for radial fiber width (RFW), tangential fiber width (TFW), fiber wall thickness (FWT), and fiber coarseness (FC) using SilviScan. Heritabilities ranged from 0.29 to 0.74, and inheritance increased with cambial maturity. Estimated age–age genetic correlations indicate that early selection between ages 5 and 8 years is highly efficient. Our results indicate that selection for a 1% increase in DBH or MOE incurs a negligible effect on fiber-dimension traits and maximum genetic gains are reached when DBH and MOE are considered jointly. Moreover, simultaneous improvement of growth and stiffness is achievable when a selection index with 7 to 10 economical weights for MOE relative to 1 for DBH is incorporated. However, the unfavorable relationship between solid-wood traits and pulp and paper related traits suggests that breeding strategies must be implemented to improve wood quality of lodgepole pine for multiple uses.

Mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae, Scolytinae), is a significant forest disturbance agent with a widespread distribution in western North America. Population success is influenced by temperatures that drive phenology and ultimately the adult emergence synchrony required to mass attack and kill host trees during outbreaks. In addition to lifestage-specific developmental rates and thresholds, oviposition timing can be a source of variance in adult emergence synchrony, and is a critical aspect of mountain pine beetle phenology. Adaptation to local climates has resulted in longer generation times in southern compared to northern populations in common gardens, and the role of oviposition rate in these differences is unclear. Oviposition rates and fecundity in a northern population have been described, although data are lacking for southern populations. We assessed southern mountain pine beetle oviposition rates and fecundity in a range of temperatures using a non-destructive technique that included frequent X-ray imaging. We found that oviposition rate and fecundity vary independently such that a female with high oviposition rate did not necessarily have high fecundity and vice versa. Observed fecundity within the 30-day experimental period was lowest at the lowest temperature, although estimated potential fecundity did not differ among temperatures. Females at varying temperatures have the potential to lay similar numbers of eggs, although it will take longer at lower temperatures. Southern mountain pine beetle reared in Pinus strobiformis Engelm. (Pinaceae) had a higher upper threshold for oviposition, a similar lower threshold, and slightly greater potential fecundity compared to a northern population reared in Pinus contorta Douglas. A comparison of modeled oviposition rates between the two populations, which could be influenced by host tree, suggests that differences in oviposition rate do not explain observed differences in total generation time. Our oviposition model will facilitate development of a phenology model for southern mountain pine beetle populations.

Water availability acts as a major constraint on productivity in many sub-humid forest regions. Precipitation can be an important limiting factor for tree growth in such areas, but the strength of the relationship can vary by habitat and species, as well as with tree size and local hydrology. We quantified the influence of past weather conditions on the growth of two conifer species (Pinus contorta and Picea glauca) across a water-limited forest landscape in western Canada. The two species differ in moisture requirements and are segregated across a local elevational gradient, and so we expected them to exhibit different sensitivities to precipitation. We also expected that larger trees and those more distant from creeks would have a stronger response to precipitation. A hierarchical Bayesian model fit to the annual ring widths of 387 trees showed that historical precipitation from 1951 to 2016 had a positive overall effect on radial growth. The magnitude of precipitation effects on radial tree growth varied with creek proximity (a proxy for the soil moisture provided by an elevated water table in the valley bottom) and tree size. Precipitation had a greater positive influence on the growth of larger P. glauca trees, as well as individuals of both species at far and intermediate distances from creeks. Precipitation had a weaker but still positive effect on P. glauca trees growing close to creeks. Tree growth rates may change with the predicted greater inter-annual variability of precipitation under climate change, but the magnitude of these responses appear to vary by species, size, and creek proximity. Overall changes in tree growth are expected to be relatively small as trees are well-adapted to cope with the variation in water availability across a moisture-limited landscape.

Questions: The change in the frequencies of invasive higher plant species in different habitat types was investigated using Danish monitoring data from 2004 to 2014. Location: Denmark. Methods: The occurrence data were collected in circles with a radius of 5 m at a number of plots within 923 sites. The sampling intensity was irregular with sampling intervals ranging from one to three years. The hierarchical occurrence data were fitted in a hierarchical model, where the site-specific occurrence probabilities were modelled by latent variables. Results: The overall frequency of invasive higher plant species increased significantly in this 11-year period in two of the seventeen habitat types, i.e. on coastal dunes and on dry heathland. The frequency of the dominating invasive species, Rosa rugosa, Pinus contorta, and Prunus serotina, was observed to increase significantly in three, two, and one out of the seventeen habitat types, respectively, whereas the frequency of Pinus mugo was found to decrease significantly in one habitat type. Conclusions: The frequency of invasive higher plant species has not stabilized and is still increasing in some or several Danish habitat types. Furthermore, trend analyses of a selected subset of invasive plant species may serve as an important early warning signal that may be used in the management of ecosystems.

The aim of our study was to compare the growth rates of lodgepole pine (Pinus contorta Dougl.) with those of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L.) in plantations. The experimental plots were established in 1988, 1989 and 1994 in the southern part of the Leningrad region. In 2014, the condition of the plants on those plots was examined and their linear parameters were measured. The comparison of Scots pine with lodgepole pine of the same age growing in similar soil conditions has shown that Scots pine has only an insignificant advantage over lodgepole pine in the growth rate. In the mixes of Norway spruce and lodgepole pine, Norway spruce considerably suppresses the growth of lodgepole pine. Lodgepole pine has successfully adapted to the climatic conditions of the Leningrad region of Russia, which is easy to see from the well-preserved plantations and their annual bearing. No significant damage because of either diseases or insect pests has been revealed. It is for the first time that the volume yield of lodgepole pine was determined in 20-to 26-year-old experimental plantations in the Leningrad region of Russia.

RUSSIAN JOURNAL OF FOREST SCIENCE, 2019, No. 6, P. 524-532 COMPARISON OF PHYSIOLOGICAL AND BIOCHEMICAL INDICATORS OF SCOTS PINE AND LODGEPOLE PINE SHOOTS IN MIDDLE TAIGA ZONE, THE KOMI REPUBLIC G. N. Tabalenkova 1 , R. V. Malyshev 1 , M. S. Atoyan 2 1 Institute of Biology, Komi Scientific Centre, Ural Branch of the Russian Academy of Sciences Kommunisticheskaya st. 28, Syktyvkar, 167982, Russia E-mail: tabalenkova @ ib . komisc . ru 2 Pitirim Sorokin Syktyvkar State University Petrozavodskaya st. 12, 167005 Syktyvkar, Russia Received 4 June 2018 Physiological and biochemical monitoring of shoots of Scots pine and lodgepole pine were held on plantations in taiga, the Repulic of Komi. Here we show that the length of needles and the size of terminal bud of lodgepole pines are larger than of Scots pines. Intensity of photosynthesis of Scots pine of 95.4 μmol CO 2 h -1 g -1 of dry mass was twice as high than of the lodgepole pine. Larger assimilating area and longer growth period compensated low photosynthetic activity of the lodgepole pine. Water content in needles of the studied species decreased from 66 % in June to 56 % in February. Share of frozen water share in winter was 58 % of the total water content. Needles of lodgepole pine had higher water content and lower share of frozen water in April, indicating the earlier wake-up after winter. The temperature of phase transition between water and ice in needles and buds were almost the same in winter and significantly differed during the vegetation period. Lodgepole pine shoots actively grew under low above-zero temperatures in early spring. Thus, the specie had longer vegetation period, and the specie override the Scots pine by the increment rate. The physiological and biochemical indicators of the lodgepole pine fit to the regional climate. Hence, it could be used for plantation. Keywords: growth, water content, heat emission, energy conservation, carbohydrates, pigments, CO 2 exchange, Scots pines, lodgepole pines. Acknowledgements: This study was supported in the framework of the project GR0414-2016-0001 and the Program of the Urals Division of the Russian Academy of Sciences 18-4-4-20. DOI: 10.1134/S002411481906010X REFERENCES Aitken S.N., Hannerz M., Genecology and gene resource management strategies for conifer cold hardiness, In: Conifer Cold Hardiness Dordrecht: Springer, 2001, pp. 23-53 (596 p.). Alekseev V.M., Zhigunov A.V., Bondarenko A.S., Burtsev D.S., Introduktsiya sosny skruchennoi v usloviyakh Leningradskoi oblasti (Introduction of Pinus contorta in the Leningrad Region), Izvestiya vysshikh uchebnykh zavedenii. Lesnoi zhurnal , 2014, No. 3 (339), pp. 24–33. 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Wilding conifers, the naturally regenerated scions of exotic conifer species, are a major ecological and economic issue in New Zealand. Hyperspectral imagery could provide a useful means of monitoring the efficacy of wilding control measures but little research has examined this possibility. Data were collected from an experiment, that included thirty-nine young Pinus contorta (Douglas) trees allocated to a control and two herbicide treatments (triclopyr butoxyethyl ester and diquat dibromide monohydrate). The objectives of this research were to examine the temporal impacts of herbicide on needle discolouration, spectral properties and tree physiology and to develop models to predict photosynthetic parameters from hyperspectral data. In accordance with obvious discolouration on the first day after treatment, values of net photosynthesis rate (A), electron transport rate (ETR), stomatal conductance (G) and optimal quantum yield of photosystem II (Fv/Fm) declined rapidly for plants treated with diquat. Discolouration following application of triclopyr was not evident before the second week, and values of A, ETR, G and Fv/Fm declined slower than those of diquat. Of the tested narrow-band spectral indices calculated from needle spectra photochemical reflectance index (PRI) exhibited the strongest correlation with the four photosynthetic parameters and R2 values between PRI and A, Fv/Fm, ETR and G were, respectively, 0.53, 0.46, 0.68 and 0.29. Models that used raw spectra as inputs showed that sparse partial least squares (SPLS) outperformed the three other approaches tested (PLS, Support Vector Machines, Elastic Net) and R2 values using this approach for A, Fv/Fm, ETR and G were, respectively, 0.64, 0.62, 0.65 and 0.42.

High-severity, infrequent fires in forests shape landscape mosaics of stand age and structure for decades to centuries, and forest structure can vary substantially even among same-aged stands. This variability among stand structures can affect landscape-scale carbon and nitrogen cycling, wildlife habitat availability, and vulnerability to subsequent disturbances. We used an individual-based forest process model (iLand) to ask: Over 300 years of postfire stand development, how does variation in early regeneration densities versus abiotic conditions influence among-stand structural variability for four conifer species widespread in western North America? We parameterized iLand for lodgepole pine (Pinus contorta var. latifolia), Douglas-fir (Pseudotsuga menziesii var. glauca), Engelmann spruce (Picea engelmannii), and subalpine fir (Abies lasiocarpa) in Greater Yellowstone (USA). Simulations were initialized with field data on regeneration following stand-replacing fires, and stand development was simulated under historical climatic conditions without further disturbance. Stand structure was characterized by stand density and basal area. Stands became more similar in structure as time since fire increased. Basal area converged more rapidly among stands than tree density for Douglas-fir and lodgepole pine, but not for subalpine fir and Engelmann spruce. For all species, regeneration-driven variation in stand density persisted for at least 99 years postfire, and for lodgepole pine, early regeneration densities dictated among-stand variation for 217 years. Over time, stands shifted from competition-driven convergence to environment-driven divergence, in which variability among stands was maintained or increased. The relative importance of drivers of stand structural variability differed between density and basal area and among species due to differential species traits, growth rates, and sensitivity to intraspecific competition versus abiotic conditions. Understanding dynamics of postfire stand development is increasingly important for anticipating future landscape patterns as fire activity increases.

Genetic control of microfibril angle (MFA) transition from juvenile wood to mature wood was evaluated in Norway spruce (Picea abies (L.) Karst) and lodgepole pine (Pinus contorta Douglas ex Loudon). Increment cores were collected at breast height (1.3 m) from 5664 trees in two 21-year-old Norway spruce progeny trials in southern Sweden and from 823 trees in two lodgepole pine progeny trials, aged 34–35 years, in northern Sweden. Radial variations in MFA from pith to bark were measured for each core using SilviScan. To estimate MFA transition from juvenile wood to mature wood, a threshold level of MFA 20° was considered, and six different regression functions were fitted to the MFA profile of each tree after exclusion of outliers, following three steps. The narrow-sense heritability estimates (h2) obtained for MFA transition were highest based on the slope function, ranging from 0.21 to 0.23 for Norway spruce and from 0.34 to 0.53 for lodgepole pine, while h2 were mostly non-significant based on the logistic function, under all exclusion methods. Results of this study indicate that it is possible to select for an earlier MFA transition from juvenile wood to mature wood in Norway spruce and lodgepole pine selective breeding programs, as the genetic gains (ΔG) obtained in direct selection of this trait were very high in both species.

Summary • The spatial mapping of genets from sporocarps allows determination of the primary modes of reproduction of ectomycorrhizal fungi. The goals of this research were to determine the relative size, density, and persistence of genets of Russula brevipes , a late successional basidiomycete, in mature stands of lodgepole pine ( Pinus contorta ) and Sitka spruce ( Picea sitchensis ). • Sporocarps were mapped and genets were identified using species-specific hypervariable microsatellite markers. • Most of the sporocarps sampled in clumped aggregations were the same genet and occupied areas less than 3 m. The largest distance measured between two sporocarps of the same genet was 18 m. In local populations of R. brevipes associated with Sitka spruce, genets were comprised of largely related individuals, whereas in lodgepole pine, most genets appeared unrelated. • High genotypic diversity in Sitka spruce stands suggests frequent mating and recombination between local inhabitants from primary establishment of basidiospores. In lodgepole pine, fewer, unrelated genotypes of R. brevipes indicates that multiple sources of colonization arose from infrequent, long distance spore dispersal events.

Climate change is projected to significantly affect the vulnerability of forests across the western United States to wildfires, insects, disease, and droughts. Here, we provide recent mortality estimates for large trees for 53 species across 48 ecological sections using an analysis of 23,215 Forest Inventory plots and a Random Forest classification model. Models were also used to predict mortality in future FIA inventories under the RCP 4.5 emissions scenario. Model performance indicated species identity as the most important predictor of mortality under both current and future scenarios, with contributions from climate and soil variables. Our results show relatively high levels of recent mortality in the Middle and Southern Rocky Mountains driven by high mortality in Populus tremuloides, Pinus contorta, Pinus albicaulis, and Abies lasiocarpa. Low levels of mortality were observed in several species, with

Changing climate and disturbance regimes are increasingly challenging the resilience of forest ecosystems around the globe. A powerful indicator for the loss of resilience is regeneration failure, that is, the inability of the prevailing tree species to regenerate after disturbance. Regeneration failure can result from the interplay among disturbance changes (e.g., larger and more frequent fires), altered climate conditions (e.g., increased drought), and functional traits (e.g., method of seed dispersal). This complexity makes projections of regeneration failure challenging. Here we applied a novel simulation approach assimilating data-driven fire projections with vegetation responses from process modeling by means of deep neural networks. We (i) quantified the future probability of regeneration failure; (ii) identified spatial hotspots of regeneration failure; and (iii) assessed how current forest types differ in their ability to regenerate under future climate and fire. We focused on the Greater Yellowstone Ecosystem (2.9 × 106 ha of forest) in the Rocky Mountains of the USA, which has experienced large wildfires in the past and is expected to undergo drastic changes in climate and fire in the future. We simulated four climate scenarios until 2100 at a fine spatial grain (100 m). Both wildfire activity and unstocked forest area increased substantially throughout the 21st century in all simulated scenarios. By 2100, between 28% and 59% of the forested area failed to regenerate, indicating considerable loss of resilience. Areas disproportionally at risk occurred where fires are not constrained by topography and in valleys aligned with predominant winds. High-elevation forest types not adapted to fire (i.e., Picea engelmannii-Abies lasiocarpa as well as non-serotinous Pinus contorta var. latifolia forests) were especially vulnerable to regeneration failure. We conclude that changing climate and fire could exceed the resilience of forests in a substantial portion of Greater Yellowstone, with profound implications for carbon, biodiversity, and recreation.

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.

Many current tree improvement programs are incorporating assisted gene flow strategies to match reforestation efforts with future climates. This is the case for the lodgepole pine (Pinus contorta var. latifolia), the most extensively planted tree in western Canada. Knowledge of the structure and origin of pathogen populations associated with this tree would help improve the breeding effort. Recent outbreaks of the Dothistroma needle blight (DNB) pathogen Dothistroma septosporum on lodgepole pine in British Columbia and its discovery in Alberta plantations raised questions about the diversity and population structure of this pathogen in western Canada. Using genotyping-by-sequencing on 119 D. septosporum isolates from 16 natural pine populations and plantations from this area, we identified four genetic lineages, all distinct from the other DNB lineages from outside of North America. Modeling of the population history indicated that these lineages diverged between 31.4 and 7.2 thousand years ago, coinciding with the last glacial maximum and the postglacial recolonization of lodgepole pine in western North America. The lineage found in the Kispiox Valley from British Columbia, where an unprecedented DNB epidemic occurred in the 1990s, was close to demographic equilibrium and displayed a high level of haplotypic diversity. Two lineages found in Alberta and Prince George (British Columbia) showed departure from random mating and contemporary gene flow, likely resulting from pine breeding activities and material exchanges in these areas. The increased movement of planting material could have some major consequences by facilitating secondary contact between genetically isolated DNB lineages, possibly resulting in new epidemics.

International audience; Key messageThe 19-year monitoring study revealed continuously positive and dynamic responses of tree growth to logging residue loadings. However, the lack of changes in soil nutrients suggested that increased growth might result from enhanced nutrient cycling with no net accumulation in the soil.ContextUnderstanding how logging residue loadings affect soil nutrients and forest growth is critical for designing management strategies for sustaining long-term productivity in forest ecosystems.AimsWe aimed to examine the relationships among logging residue loadings, soil nutrients, and tree growth over a long-term field experiment in lodgepole pine (Pinus contorta Doug. ex Loud.) forests.MethodsWe established a field experiment in 1996 to examine the responses of lodgepole pine growth and soil nutrients to four residue loading treatments in the central interior of British Columbia, Canada. The four treatments were removal of all residues on the forest floor (N, 0 mg ha−1), residues loading similar to whole-tree harvesting (W, 35–45 mg ha−1), residues loading similar to stem-only harvesting (S, 60–70 mg ha−1), and residues loading similar to that found in disease- or insect-killed forests (D, 100–120 mg ha−1).ResultsLogging residue loadings had significantly positive and dynamic effects on diameter and height growths. The logging residue loadings did not significantly change soil nutrients in mineral soil pools in the long run, and there was no difference in tree growth between the treatments S and W over the study period.ConclusionLogging residue loadings significantly improved tree growth. The lack of response of soil nutrients leads to the hypothesis that nutrient fluxes from logging residues might play a more important role in tree growth in lodgepole pine forests. Our results can have important implications for bio-energy production and designing of nature-based practices for sustainable forest productivity.