Can fire exclusion zones enhance postfire tree regeneration? A simulation study in subalpine conifer forests

Looking beyond the mean: Drivers of variability in postfire stand development of conifers in Greater Yellowstone

Potential productivity of three interior subalpine forest tree species in British Columbia

Tree ring analyses and an interpolated climate model (ClimateBC) were used to compare radial growth responses to climate variables among three coexisting, ecologically distinct conifer species, including interior spruce (Picea glauca x Picea Engelmannii), lodgepole pine (Pinus contorta var. latifolia) and subalpine fir (Abies lasiocarpa) across a range of climate conditions in western Canada, and altitudinal treelines in the Engelmann Spruce-Subalpine Fir forests in central British Columbia (BC). Ring-width chronologies were developed and correlated with site-specific climate data in the past 50 years from 1953-2002. June-July temperature appeared to be the dominant climate factor influencing radial growth of spruce across the sample sites, and the relationships changed from positive to negative as summer site temperature increased. Growth-climate relationships of lodgepole pine and subalpine fir varied within species. October-March temperatures appeared to be important for growth of lodgepole pine and subalpine fir at colder sites in BC. The Pacific Decadal Oscillation during October and March was also important for pine and fir at altitudinal treelines. Given the species- and site-specific growth responses to climate, future climate change will likely alter interactions among coexisting species, potentially leading to changes in species dominance, compositions and distribution of forest communities.--P.ii.

Widespread tree mortality caused by outbreaks of native bark beetles (Circulionidae: Scolytinae) in recent decades has raised concern among scientists and forest managers about whether beetle outbreaks fuel more ecologically severe forest fires and impair postfire resilience. To investigate this question, we collected extensive field data following multiple fires that burned subalpine forests in 2011 throughout the Northern Rocky Mountains across a spectrum of prefire beetle outbreak severity, primarily from mountain pine beetle (Dendroctonus ponderosae). We found that recent (2001-2010) beetle outbreak severity was unrelated to most field measures of subsequent fire severity, which was instead driven primarily by extreme burning conditions (weather) and topography. In the red stage (0-2 y following beetle outbreak), fire severity was largely unaffected by prefire outbreak severity with few effects detected only under extreme burning conditions. In the gray stage (3-10 y following beetle outbreak), fire severity was largely unaffected by prefire outbreak severity under moderate conditions, but several measures related to surface fire severity increased with outbreak severity under extreme conditions. Initial postfire tree regeneration of the primary beetle host tree [lodgepole pine (Pinus contorta var. latifolia)] was not directly affected by prefire outbreak severity but was instead driven by the presence of a canopy seedbank and by fire severity. Recent beetle outbreaks in subalpine forests affected few measures of wildfire severity and did not hinder the ability of lodgepole pine forests to regenerate after fire, suggesting that resilience in subalpine forests is not necessarily impaired by recent mountain pine beetle outbreaks.

BackgroundWildfires, like many disturbances, can be catalysts for ecosystem change. Given projected climate change, tree regeneration declines and ecosystem shifts following severe wildfires are predicted. We reviewed scientific literature on post-fire tree regeneration to understand where and why no or few trees established. We wished to distinguish sites that won’t regenerate to trees because of changing climate from sites where trees could grow post fire if they had a seed source or were planted, thus supporting forest ecosystem services for society and nature, such as timber supply, habitat, watershed protection, and carbon storage.ResultsOur literature review showed that little to no post-fire tree regeneration was more common in low-elevation, dry forest types than in high-elevation forest types. However, depending on the region and species, low tree regeneration was also observed in high elevation, moist forests. Regeneration densities varied by species and seedling densities were attributed to distances to a seed source, water stress or precipitation, elevation, slope, aspect, and plant competition. Our findings provide land managers with two primary considerations to offset low tree regeneration densities. First, we supply a decision support tool of where to plant tree seedling in large high severity burned patches. Second, we recommend possibilities for mitigating and limiting large high severity burned patches to increase survival of trees to be sources of seed for natural regeneration.ConclusionsFew or no tree seedlings are establishing on some areas of the 150+ forest fires sampled across western US, suggesting that forests may be replaced by shrublands and grasslands, especially where few seed source trees survived the wildfires. Key information gaps on how species will respond to continued climate change, repeated disturbances, and other site factors following wildfires currently limit our ability to determine future trends in forest regeneration. We provide a decision tree to assist managers in prioritizing post-fire reforestation. We emphasize prioritizing the interior of large burned patches and considering current and future climate in deciding what, when, and where to plant trees. Finally, managing fires and forests for more seed-source tree survival will reduce large, non-forested areas following wildfires where post-fire management may be necessary.

Severe, stand-replacing wildfire substantially depletes nitrogen (N) stocks in subalpine conifer forests, potentially exacerbating N limitation of net primary productivity in many forested regions where fire frequency is increasing. In lodgepole pine (Pinus contorta var. latifolia) forests in the Greater Yellowstone Ecosystem (GYE), long-term data show surface soil and biomass N stocks are replenished during the first few decades following wildfire, but the source(s) of that N are unclear. We measured acetylene reduction rates in multiple cryptic niches (i.e., lichen, moss, pine litter, dead wood, and mineral soil) in 34-year-old lodgepole pine stands in the GYE to explore the rates, temporal patterns, and climate controls on cryptic N fixation. Acetylene reduction rates were highest in late May (0.376 nmol C2H4 g-1 h-1) when moisture availability was high compared with early August and mid-October when moisture was relatively low (0.112 and 0.002 nmol C2H4 g-1 h-1, respectively). We observed modest rates of nitrogenase activity in a few niches following a mid-summer rain event, suggesting that moisture is an important factor regulating field-based N fixation rates. In a laboratory experiment, moss responded more strongly to temperature and moisture variation than all other niches. Acetylene reduction rates in dead wood increased with temperature but not moisture content. No other niches showed clear responses to either moisture or temperature manipulation. Together, the field and laboratory results suggest that frequent asynchrony between favorable temperature and moisture conditions may limit N fixation rates in the field. Overall, total annual cryptic N fixation inputs (mean: 0.26; range: 0.07-2.9 kg N ha-1 year-1) represented <10% of the postfire biomass and surface soil N accumulation in the same stands (39.4 kg N ha-1 year-1), pointing to a still unknown source of ecosystem N following fire.

Forest structure and regeneration following a mountain pine beetle epidemic in southeastern Wyoming

A comparison of ectomycorrhiza communities from three conifer species planted on forest gap edges

Recruitment limitation in forests: Lessons from an unprecedented mountain pine beetle epidemic

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. &amp; R.W. Davidson) Zipfel, Z.W. de Beer &amp; 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.

Since Grand Teton National Park adopted a natural fire policy in the early 1970's, four major fires have burned within the park which created a chronosequence of post-burn successional ecosystems. The burns encompassed forests varying in composition from Englemann spruce (Picea englemanil) /subalpine fir (Abies lasiocarpa) /lodgepole pine (Pinus contorta) (Beaver Creek, Mystic Isle) to Englemn spruce / subalpine fir (Waterfalls Canyon) to primarily lodgepole pine (Huckleberry Mountain).

Treeline elevation is expected to shift upward in response to climate warming. However, over half of alpine treelines worldwide appear to be lagging, possibly due to moisture limitations. Seedling niches tend to have narrower climate envelopes than those of mature, established trees, and regeneration requirements can vary substantially among species. We examined the density and species composition of recruitment at alpine treeline sites west and east of the Continental Divide, Central Rocky Mountains. &amp;#160;In the arid Colorado Front Range, the Divide results in a rain shadow on the east side due to orographic uplift. We stratified our sampling effort by proximity to subalpine limber pine (Pinus flexilis), a generalist, drought-tolerant conifer with a patchy metapopulation distribution in the Front Range. We expected to find higher abundance of limber pine regeneration than that of drought-averse Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) in two regeneration height categories (&amp;#8804; 100 cm and &amp;#8804; 20 cm). Regeneration occurred at low densities on both sides of the Continental Divide and did not differ significantly between sites east and west of the Divide. Regeneration density also did not differ significantly between communities dominated by limber pine and communities dominated by Engelmann spruce and subalpine fir. However, the quadrats with highest regeneration densities were east of the Divide where limber pine was the dominant conifer. These sites were also in the rain shadow and associated with higher climate water deficit and lower growing season precipitation. Limber pine also comprised the majority of this regeneration. The site with the highest observed regeneration rates also had high rates of viable limber pine seed production at treeline. We observed a significantly higher proportional abundance of limber pine in the 100 cm regeneration class (relative to established trees) in quadrats east of the Divide, corresponding to establishment roughly in the last 30-70 years. The greater proportional abundance in limber pine regeneration at these treeline study sites occurred despite increasing temperatures, reduced growing season precipitation, and increased climate water deficit over the past 30 years. Drought-tolerant limber pine may therefore be the best-suited conifer in this region to persist and to migrate to higher elevations as temperatures continue to increase. Our findings underscore the importance of considering differences in seedling tolerances (niches) among different species in alpine treeline systems when aiming to predict landscape-scale treeline responses to climate warming.

Black bear (Ursus amerlcanus) damage to 108 lodgepole pine (Pinus contorta) trees was found i n a mixed conifer habitat i n central Oregon.No trees o f three other conifer species were injured.Eighty-nine percent o f the damage occurred i n the same year.Nearly 20% o f the freshly damaged trees had bark removed from more than 75% o f the circumference and, judging from the fate o f trees damaged i n prior years, probably succumbed.

The study tests whether the lethal effect of overwintering Engelmann spruce seed in its O-horizon affects Douglas-fir, lodgepole pine and subalpine fir seeds and whether the O-horizons of the three associated species have the same lethal effect on seeds. All seed treatments of each species were stratified in petri dishes in the pure O-horizon (unsterilized and autoclaved) of each species. Seed treatments were untreated, 10% slurry of 50% Captan and powdered 75% Captan.All untreated seeds demonstrated the lethal quality of unsterilized Engelmann spruce O-horizon. Its effects on untreated seeds and powder treated seeds were as follows: Engelmann spruce seed 3.5 and 77.3% (germination of untreated and powdered respectively), subalpine fir seed 1.3 and 20.8, Douglas-fir seed 9.5 and 84.8 and lodgepole pine seed 11.9 and 85.7. Subalpine fir O-horizon was lethal to its own seeds but only moderately harmful to seeds of other species. Douglas-fir O-horizon had a significant adverse effect on its own seeds and was only moderately harmful to seeds of other species. Lodgepole pine O-horizon was almost neutral to all seeds. Autoclaving of the O-horizons and powder treatment of seeds produced similar results.

Influence of repeated fertilization on forage production for native mammalian herbivores in young lodgepole pine forests