Lodgepole Pine Forests Research Articles

Soil Nitrogen Leaching in Logged Beetle-Killed Forests and Implications for Riparian Fuel Reduction.

Recent extensive forest mortality and subsequent salvage logging may threaten the water supply from headwater catchments in western North America. Land managers confronting current insect outbreaks and projected increases in forest disturbance require information about the potential water quality consequences of these changes. This study is a hillslope-scale evaluation of soil N and C leaching in lodgepole pine forests that have experienced 80% overstory tree mortality. I measured extractable inorganic and ion resin exchangeable-N forms, in situ net mineralization and nitrification, and leaching in upland and riparian forests with the following treatment combinations: (i) uncut upland with uncut riparian, (ii) harvested upland with uncut riparian buffer, and (iii) harvested upland with harvested riparian. This design permitted comparison of N cycling and leaching in 30-m-wide riparian buffers and a riparian fuel break designed to remove canopy fuels and reduce wildfire concerns in areas with extensive bark beetle infestation. Harvesting increased NO-N, total dissolved N, and dissolved organic C leachate concentrations in upland landscapes but had little effect on net N transformations. Leachate N and C concentrations were 1.5 times higher in riparian buffers downslope of harvested uplands than those in riparian zones downslope of uncut uplands. Riparian forest harvest increased N leaching relative to uncut buffers, although postharvest concentrations remained well below regional water quality standards. Thus, while this study provides evidence that N leaching from dead buffers is low, it also suggests that riparian fuel reduction may complement wildfire mitigation objectives without compromising watershed protection.

Multiyear weather anomalies associated with range shifts by the mountain pine beetle preceding large epidemics

The recent range expansion of the mountain pine beetle, Dendroctonus ponderosae Hopk. (Coleoptera: Curculionidae), into evolutionarily naïve lodgepole and jack pine forests of northwestern Canada has triggered concern that continued eastward expansion through the boreal forest will threaten other pine species native to eastern North America. This unprecedented breach of a historic geoclimatic barrier was precipitated by a “hyperepidemic” west of the Rocky Mountains comprising the largest mountain pine beetle eruption in recorded history. We assessed climate-related latitudinal shifts of pre-outbreak populations of mountain pine beetle in western Canada over a 26-year period preceding the hyperepidemic, as movements of pre-outbreak populations determine, in part, the extent of subsequent outbreaks. We used digitized records of annual aerial overview surveys (1965–1979, 1986–1996) of tree-killing activity, comprising > 122,000 individual infestation polygons, and temperature and aridity data to associate trends in deviations of weather variables from historical averages with latitudinal shifts by the insect. Overall, we found that seasonal and multiyear weather phenomena such as anomalous temperature increases in a stable aridity regime, or vice-versa, and warmer-than-normal winter temperatures explained small but significant variation in northward annual range shifts after factoring out spatial and temporal variation. The numbers of discrete, tree-killing infestations increased rapidly during 1965–1979, and northward range shifts of 300 km in the early 1970s coincided with abnormally dry conditions. Mountain pine beetle populations advanced northward by 391 km from 1965 to 1996. Consistently high infestation levels of the mountain pine beetle occurred simultaneously with above-average temperatures that extended for nearly a decade immediately preceding the hyperepidemic. Climate-associated range shifts can provide gateways to rapid range expansions, and evoke concern with regard to future impacts of other bark beetle species inhabiting regions likely to experience multiyear droughts and/or temperature increases under climate change.

Green-tree retention and relative habitat use by mule deer (Odocoileus hemionus) 20 years after harvest of Douglas-fir (Pseudotsuga menziesii) – Lodgepole pine (Pinus contorta) forest

Mule deer (Odocoileus hemionus) are a major mammal species in many interior Douglas-fir (Pseudotsuga menziesii) forest ecosystems in western North America. During winter in areas of relatively high snowpacks, mule deer seem to require older trees with large crowns for snow interception, but these forests are often targeted for harvest. Green-tree retention (GTR) may offer a solution to this conundrum. We tested three hypotheses (H) that, at 20–22 years after harvest, (H1) abundance (e.g., basal area and density of residual trees and understory stand structure) of conifers, (H2) abundance, species richness, and diversity of understory vegetation, and (H3) relative habitat use by mule deer, will decline with lower levels of tree retention. Fecal pellet-groups of deer were counted in summer and winter periods for three years in replicated stands of dispersed retention, aggregated retention, patch-cut, group selection, and uncut forest in mixed Douglas-fir - lodgepole pine (Pinus contorta) forest in southern British Columbia, Canada.Mean basal area, density, and canopy closure of overstory Douglas-fir trees were generally greater in the patch-cut, group selection, and uncut forest sites than dispersed and aggregated retention sites, and hence supported the overstory part of H1. Mean density of understory conifers did not support H1 as the majority of these trees were in the dispersed and aggregated retention stands. There was no difference in mean abundance nor species richness of understory vegetation among treatment sites. Mean species diversity tended to be 1.4–1.8 times higher in the patch-cut and group selection than the other sites, and hence provided weak support for H2. Patch-cut and group selection sites were dominated by Douglas-fir trees in both the overstory and understory, along with potential forage shrub species, and were used by deer more than the dispersed and aggregated retention stands in both summer and winter. Relative habitat use by deer in uncut forest was greater than the retention stands and generally similar to the patch-cut and group selection sites in both seasons. These results suggest that partial harvesting of these mixed Douglas-fir – lodgepole pine stands across a range of opening sizes (e.g., 0.1 to 2–5 ha) should provide suitable habitat for mule deer over time.

Biological Aspects of Mountain Pine Beetle in Lodgepole Pine Stands of Different Densities in Colorado, USA

Research Highlights: The biology of mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins, in Colorado’s lodgepole pine forests exhibits similarities and differences to other parts of its range. Brood emergence was not influenced by stand density nor related to tree diameter. The probability of individual tree attack is influenced by stocking and tree size. Findings have implications for understanding MPB as a disturbance agent and for developing management strategies. Background and Objectives: MPB causes extensive tree mortality of lodgepole pine, Pinus contorta Douglas ex Loudon, across the western US and Canada and is probably the most studied bark beetle in North America. However, most of the current knowledge on the biology and ecology of MPB in lodgepole pine comes from the Intermountain Region of the US and western Canada. Little information is available from Colorado. This is the first study addressing effects of stand stocking levels on the biology of MPB and quantifying phloem consumption. In addition, although data are available on the conditions that foster stand infestation, this is the first study estimating the probability of individual tree attack among stands of known different stocking. Materials and Methods: Studies were conducted in managed lodgepole pine stands in Colorado. Unbaited traps were used to monitor MPB flight across stands of different densities. Cages were used to monitor emergence and bark samples to determine attack densities, and phloem consumption in trees growing under different stocking. Beetle collections were used to determine emergence across the growing season. Tree mortality data from plots of different densities were used to examine the probability of individual tree infestation. Results: More beetles were caught flying through higher density stands. More attacks were observed in lower stocking stands but there were no differences in the number of insects emerging nor phloem consumption. There was no relationship between tree size and beetle emergence. Peak flight occurred in early to mid-August and only one peak of beetle emergence occurred. The probability of tree attack was influenced by stand stocking and tree diameter. Conclusions: In general, aspects of the biology of MPB in Colorado exhibit similarities and differences with other regions. The data suggest the need to more closely examine how MPB functions in stands of different stocking and how the distribution of tree sizes influence the probability of infestation and extent of mortality in stands. Biological characteristics of MPB in Colorado need further examination, particularly as climate change continues to manifest. Baseline information will be critical to refine management approaches, and extend the understanding of how MPB contributes to shape forest composition and structure in Colorado.

Landscape Topoedaphic Features Create Refugia from Drought and Insect Disturbance in a Lodgepole and Whitebark Pine Forest

Droughts and insect outbreaks are primary disturbance processes linking climate change to tree mortality in western North America. Refugia from these disturbances—locations where impacts are less severe relative to the surrounding landscape—may be priorities for conservation, restoration, and monitoring. In this study, hypotheses concerning physical and biological processes supporting refugia were investigated by modelling the landscape controls on disturbance refugia that were identified using remotely sensed vegetation indicators. Refugia were identified at 30-m resolution using anomalies of Landsat-derived Normalized Difference Moisture Index in lodgepole and whitebark pine forests in southern Oregon, USA, in 2001 (a single-year drought with no insect outbreak) and 2009 (during a multi-year drought and severe outbreak of mountain pine beetle). Landscape controls on refugia (topographic, soil, and forest characteristics) were modeled using boosted regression trees. Landscape characteristics better explained and predicted refugia locations in 2009, when forest impacts were greater, than in 2001. Refugia in lodgepole and whitebark pine forests were generally associated with topographically shaded slopes, convergent environments such as valleys, areas of relatively low soil bulk density, and in thinner forest stands. In whitebark pine forest, refugia were associated with riparian areas along headwater streams. Spatial patterns in evapotranspiration, snowmelt dynamics, soil water storage, and drought-tolerance and insect-resistance abilities may help create refugia from drought and mountain pine beetle. Identification of the landscape characteristics supporting refugia can help forest managers target conservation resources in an era of climate-change exacerbation of droughts and insect outbreaks.

Microhabitat conditions and landscape pattern explain nocturnal rodent activity, but not seed removal, in burned and unburned lodgepole pine forests

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. 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? 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. 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. 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.

Productivity and Costs of Two Beetle-Kill Salvage Harvesting Methods in Northern Colorado

Two ground-based timber harvesting methods have been commonly used for beetle-kill salvage treatments after a bark beetle epidemic in northern Colorado. A “lop and scatter” method uses a mobilized stroke delimber to delimb and buck trees at the stump, leaving tree tops and limbs on the forest floor, while a whole-tree harvesting method brings the entire tree to the landing where it is delimbed and bucked, and thus produces logging residue piles at the landing as a byproduct. We conducted a detailed comparative time study of the two harvesting methods to develop productivity and cost models and compared the performance of the two methods under various site conditions. We applied the productivity and cost models to lodgepole pine forest stands totaling 3400 hectares of the Colorado State Forest State Park to estimate salvage harvesting costs for each forest stand and identify the least costly harvesting options. The results show that the estimated stump-to-truck timber production costs were $30.00 per oven dry ton (odt) for lop and scatter and $23.88 odt−1 for the whole-tree method in our study harvest unit. At the forest level, the estimated average stump-to-truck costs were $54.67 odt−1 and $56.95 odt−1 for lop and scatter and whole-tree harvesting, respectively. Skidding distance and downed trees affect the harvesting costs of both methods, but their influence appears to be more significant on the whole-tree method.

The Cariboo Alpine Mesonet: sub-hourly hydrometeorological observations of British Columbia's Cariboo Mountains and surrounding area since 2006

Abstract. This article presents the development of a sub-hourly database of hydrometeorological conditions collected in British Columbia's (BC's) Cariboo Mountains and surrounding area extending from 2006 to present. The Cariboo Alpine Mesonet (CAMnet) forms a network of 11 active hydrometeorological stations positioned at strategic locations across mid- to high elevations of the Cariboo Mountains. This mountain region spans 44 150 km2, forming the northern extension of the Columbia Mountains. Deep fjord lakes along with old-growth western redcedar and hemlock forests reside in the lower valleys, montane forests of Engelmann spruce, lodgepole pine and subalpine fir permeate the mid-elevations, while alpine tundra, glaciers and several large ice fields cover the higher elevations. The automatic weather stations typically measure air and soil temperature, relative humidity, atmospheric pressure, wind speed and direction, rainfall and snow depth at 15 min intervals. Additional measurements at some stations include shortwave and longwave radiation, near-surface air, skin, snow, or water temperature, and soil moisture, among others. Details on deployment sites, the instrumentation used and its precision, the collection and quality control process are provided. Instructions on how to access the database at Zenodo, an online public data repository, are also furnished (https://doi.org/10.5281/zenodo.1195043). Information on some of the challenges and opportunities encountered in maintaining continuous and homogeneous time series of hydrometeorological variables and remote field sites is provided. The paper also summarizes ongoing plans to expand CAMnet to better monitor atmospheric conditions in BC's mountainous terrain, efforts to push data online in (near-)real time, availability of ancillary data and lessons learned thus far in developing this mesoscale network of hydrometeorological stations in the data-sparse Cariboo Mountains.

Subwatershed-Level Lodgepole Pine Attributes Associated with a Mountain Pine Beetle Outbreak

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.

Effects of Stand Structure, Browsing, and Biophysical Conditions on Regeneration Following Mountain Pine Beetle in Mixed Lodgepole Pine and Aspen Forests of the Southern Rockies

Aspen (Populus tremuloides) and lodgepole pine (Pinus contorta var. latifolia) co-occur in the southern Rocky Mountains (USA), where mountain pine beetle (MPB, Dendroctonus ponderosae) has caused extensive lodgepole pine mortality since the late 1990s. Both species excel in post-disturbance high-light environments, but lodgepole pine has generally been thought to establish poorly on undisturbed seedbeds, and aspen suckering may be inhibited by intact aspen overstory. We ask whether lodgepole pine and aspen will regenerate in sufficient quantities to revegetate these forests. We visited a random sample of aspen and lodgepole pine stands across the affected landscape in northern Colorado and southern Wyoming to measure regeneration and overstory mortality. Lodgepole pine regeneration is occurring in 85% of stands, and most stands have >550 stems ha−1. The median aspen sucker density was 6175 stems ha−1. Surprisingly, neither lodgepole pine nor aspen regeneration density was related to overstory mortality level. Animal damage is currently affecting aspen in these forests. Over 50% of stands had damage to 60% or more of their suckers, but 30% of stands had <20% of their stems damaged. Browsed stems were significantly shorter for their ages and were shorter than the 2.5-m height threshold for possible elk browsing. However, the results suggest that sufficient quantities of down lodgepole pine may protect aspen from damage and allow aspen to successfully recruit to the overstory. Multiple regression analysis showed that down lodgepole pine basal area, followed by browsing pressure, were the most important predictors of sucker height and the proportion of suckers browsed. Although 15% of stands had no lodgepole pine regeneration, aspen and lodgepole pine forests are generally regenerating despite animal browsing on aspen. This study is the first to present a regional perspective on regeneration in MPB-affected lodgepole pine and aspen forests, and overall, intervention does not seem necessary to ensure a mix of both species in the future.

Survival and Predators of Pacific Marten in a Salvage-Logged Pine Forest, South-Central Oregon

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, sx = 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, sx = 0.118 (n = 26). Seasonal survival of adults (0.945, sx = 0.027) and young (0.974, sx = 0.026) was highest in winter (December through February), and lowest in summer (June through August; adults = 0.853, sx = 0.035; young = 0.902, sx = 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, sx = 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.

Stand dynamics 11 years after retention harvest in a lodgepole pine forest

Structurally diverse forests provide resilience to an array of disturbances and are a mainstay of multiple-resource management. Silviculture based on natural disturbance can increase structural heterogeneity while providing other ecological and economic benefits. One useful silvicultural tool for promoting structural heterogeneity is retention harvesting, whereby a portion of forest stands are left unlogged, transitioning even-aged stands to multi-aged. We report stand and tree dynamics 11 years after retention harvest in a central Montana Rocky Mountain lodgepole pine forest with evidence for a mixed-severity fire regime. Treatments were implemented on 16 experimental units with prescriptions for two 50% overstory basal area retention patterns (Aggregated and Dispersed) crossed with two levels of prescribed fire use (Burned and Unburned). The aim of this study was to identify (1) how retention harvest spatial pattern affects stand dynamics, (2) if stand dynamics after retention treatments are more simply attributable to tree size and competition, or if retention pattern affects dynamics beyond those measures, and (3) how stem and basal area heterogeneity varied over the 11-year measurement period. Retention pattern affected overstory density, growth, mortality, and regeneration density and stocking. After controlling for the fine-scale factors of tree size and competition, overstory mortality, regeneration stocking, and regeneration height growth did not vary by treatment-scale factors. Fine-scaled factors explained significant variation in overstory basal area growth, but at the scale of experimental units, growth was also greater in Dispersed treatments. Prescribed burning interacted with retention pattern to influence overstory tree growth, increased overstory mortality, and increased regeneration height growth. Overstory heterogeneity (e.g., in basal area) degraded more rapidly in treatments with the Dispersed spatial pattern than Aggregated. This study evaluates novel silvicultural treatments in a lodgepole pine forest and highlights the tradeoffs between retention patterns combined with broadcast burning on forest change. Our results are useful for planning silvicultural treatments in multiple-use forests designed to promote structural complexity and resilience to disturbances.

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

Abstract Stand thinning and fertilization are silvicultural practices designed to enhance wood and biomass production. Applications of nitrogen-based fertilizers make nutrients potentially available to all trees, plants, and wildlife in a given forest ecosystem, and therefore may affect productivity of forage plants for native mammalian herbivores. Species associated with areas of forest fertilization in temperate and boreal zones of North America include mule deer (Odocoileus hemionus), elk (Cervus elaphus), moose (Alces alces), and woodland caribou (Rangifer tarandus), snowshoe hare (Lepus americanus), and several species of voles. Impacts of fertilization on forest plant species may have important consequences for the nutrition, cover, and consequent survival of these herbivores, particularly in winter. This study tested the hypothesis (H1) that large-scale repeated fertilization, up to 20 years after the onset of treatments, would enhance the biomass production of forage plants, particularly grass, forb, shrub and tree species for native mammalian herbivores. A secondary hypothesis (H2) predicted that mosses and terrestrial lichens would decline as part of the ground vegetation in fertilized stands. Study areas were located in lodgepole pine (Pinus contorta var. latifolia) stands near Summerland, Kelowna, and Williams Lake in south-central British Columbia, Canada. Each study area had eight replicate stands: four unfertilized, and four fertilized five times at 2-year intervals. Mean biomass of total grasses responded dramatically starting in the first year after fertilization. Total forbs and herbs also followed this pattern, although not to a significant degree until after the second and third applications of fertilizer. All of the dominant grasses and forbs serve as summer forage for mule deer, moose, elk, and woodland caribou. Fireweed (Epilobium angustifolium), a preferred forage for mule deer, increased in fertilized stands. Grasses and dominant herbs in fertilized stands provide excellent forage and cover habitat for snowshoe hares and Microtus voles. Mean biomass of total shrubs was not affected by fertilization. However, saskatoon berry (Amelanchier alnifolia), prickly rose (Rosa acicularis), and red raspberry (Rubus idaeus) increased significantly in biomass in fertilized stands. Willow (Salix spp.) also increased in biomass, but was variable across treatment stands. Snowshoe hares respond favourably to enhanced shrub growth for food and cover in fertilized stands. All of these shrubs are readily eaten by deer, moose, and elk, and their structural attributes provide security and thermal cover. Mean biomass of understory Douglas-fir (Pseudotsuga menziesii) responded positively to fertilization, but subalpine fir (Abies lasiocarpa) and the three deciduous tree species did not. Dwarf shrubs such as kinnikinnick (Arctostaphylos uva-ursi), twinflower (Linnaea borealis), and dwarf blueberry (Vaccinium caespitosum) declined in fertilized stands. Thus, H1 was partially supported for some species. Increasing cover of grasses and nitrophilous herbs, and canopy cover from rapidly growing crop trees, in fertilized stands may have contributed to the decline of some dwarf shrubs. Mean crown volume index of total mosses and terrestrial lichens declined significantly in fertilized stands, thereby supporting H2. Mean biomass of total grasses (increase), R. acicularis (increase), and V. caespitosum (decline) were significantly affected after one application of fertilizer. Repeated applications of fertilizer may enhance biomass of some additional forage forbs and shrubs, but reduce biomass of some dwarf shrubs, mosses, and lichens.

Pinus albicaulis Engelm. (Whitebark Pine) in Mixed-Species Stands throughout Its US Range: Broad-Scale Indicators of Extent and Recent Decline

We used data collected from &gt;1400 plots by a national forest inventory to quantify population-level indicators for a tree species of concern. Whitebark pine (Pinus albicaulis) has recently experienced high mortality throughout its US range, where we assessed the area of land with whitebark pine present, size-class distribution of individual whitebark pine, growth rates, and mortality rates, all with respect to dominant forest type. As of 2016, 51% of all standing whitebark pine trees in the US were dead. Dead whitebark pines outnumbered live ones—and whitebark pine mortality outpaced growth—in all size classes ≥22.8 cm diameter at breast height (DBH), across all forest types. Although whitebark pine occurred across 4.1 million ha in the US, the vast majority of this area (85%) and of the total number of whitebark pine seedlings (72%) fell within forest types other than the whitebark pine type. Standardized growth of whitebark pines was most strongly correlated with the relative basal area of whitebark pine trees (rho = 0.67; p &lt; 0.01), while both standardized growth and mortality were moderately correlated with relative whitebark pine stem density (rho = 0.39 and 0.40; p = 0.031 and p &lt; 0.01, respectively). Neither growth nor mortality were well correlated with total stand basal area, total stem density, or stand mean diameter. The abundance, extent, and relative growth vs. mortality rates of whitebark pine in multiple forest types presents opportunities for management to encourage whitebark pine recruitment in mixed-species stands. The lodgepole pine forest type contained more whitebark pine seedlings (35%) than any other forest type, suggesting that this forest type represents a potential management target for silvicultural treatments that seek to facilitate the recruitment of whitebark pine seedlings into larger size classes. National forest inventories in other countries may use a similar approach to assess species of concern.

Importance of the canopy in determining on‐going regeneration and stand successional development in lodgepole pine forests

AbstractQuestionWhat are the processes driving regeneration and successional pathways in Pinus contorta subsp. latifolia Douglas ex Loudon forests?LocationCanadian Rockies, Alberta, Canada.MethodsWe used five 1‐ha long‐term permanent plots, dendrochronological stand reconstruction and detailed spatial analysis of stem‐mapped data.ResultsEstablishment of shade‐intolerant species mainly occurred within 20 years post‐fire but important later recruitment of these species was observed in the drier plots, primarily in gaps in stands that had more open canopies. Shade‐tolerant species established quickly following fires on moister sites but, despite apparent seed source availability after the stand‐initiating fire, their establishment was delayed in the drier sites, most likely due to moisture limitations. Shade‐tolerant regeneration was clustered around shade‐tolerant trees that had established immediately post‐disturbance; this suggests the latter served as seed sources and perhaps created favourable microsites for establishment.ConclusionCompetition for light, dispersal limitation and moisture limitations were all processes influencing regeneration and successional pathways in these P. contorta stands. Although initial studies in these stands had suggested some of the stands could potentially be self‐perpetuating P. contorta forests, our results suggest that all plots studied will likely transition towards dominance of shade‐tolerant species. However the rate of this transition will likely be slower in the drier sites compared to the moister sites since the density of shade‐tolerant regeneration was much lower in these sites and took longer to establish (ca. 70–90 years) post‐disturbance.

Simulation of net ecosystem productivity of a lodgepole pine forest after mountain pine beetle attack using a modified version of 3-PG

Abstract The most recent mountain pine beetle (MPB) (Dendroctonus ponderosae) outbreak in British Columbia (BC), which began in the late 1990s, killed ∼54% of the mature merchantable lodgepole pine and was expected to impact gross primary productivity (GPP), ecosystem respiration (R) and thus net ecosystem productivity (NEP) of infested stands. Eddy-covariance (EC) measurements of carbon dioxide and water vapor fluxes have been made in an almost single-species not-salvage-harvested lodgepole pine stand in northern interior BC during the decade following beetle attack in 2006 to determine the effects on the carbon (C) and water balances. We modified the 3-PG (Physiological Principles in Predicting Growth) model to simulate the effects of MPB attack on the stand. Modifications included a sub-model for heterotrophic respiration, which originates from the decomposition of two substrates, soil organic matter and coarse woody debris from the falling dead trees, thus permitting the determination of R and NEP. The modified model was used to simulate C balance components using model parameter values mostly taken from the literature with some estimated from in-situ measurements. Modelled monthly and annual stand-level GPP, R and NEP agreed well with respective EC-estimated values during the decade following attack. Modelled annual GPP, R and NEP decreased by about 52%, 35% and 126%, respectively, in the first year following attack compared to pre-attack values. Modelled GPP and R, as well as EC-estimated GPP, showed a relatively steady increase over the following decade, while R derived from the EC measurements changed little in the first eight years after attack and then increased in the last two years. EC-estimated GPP in 2016 exceeded the estimated pre-attack value by 9%, while modelled and EC-estimated R in 2016 exceeded 2005 values by 6% and 15%, respectively. Modelled NEP indicated that the recovering stand became a C sink a year later than indicated by the EC measurements, but both modelled and measured annual NEP increased significantly between 2007 and 2016. Our observations and modelling results show that the remaining trees and the growing understory enabled the not-salvage-harvested stand to recover from insect attack within a decade, with the stand functioning as a weak, yet distinct, C sink in the last two years of the study period. This suggests that the management strategy of not harvesting attacked stands can be beneficial for the C balance of attacked stands with similar characteristics and in similar climates.

The role of succession in the evolution of flammability

Fire-prone ecosystems contain plants that are both fire-adapted and flammable. It has been hypothesized that these plants were under selection to become more flammable, but it is unclear whether this could be adaptive for an individual plant. We propose arrested succession as a robust mechanism that supports the evolution of flammability in surface fire ecosystems without the need to invoke group selection or additional fitness benefits. We used the natural history of lodgepole pine (Pinus ponderosa) forests, longleaf pine (Pinus palustris) forests, and tall grass prairies to create a general mathematical model of surface fire ecosystems and solved for the evolutionarily stable strategy (ESS) level of flammability. In our model, fires always kill understory plants and only sometimes kill overstory plants. Thus, more flammable plants suffer increased mortality due to fires, but also more frequently arrest succession by clearing their understory of late successional competitors. Increased flammability was selected for when the probability of an overstory plant dying from an individual fire was below a maximum threshold and the rate of succession relative to fires was above a minimum threshold. Future studies can test our model predictions and help resolve whether or not plants have been selected to be more flammable.

Successful Colonization of Lodgepole Pine Trees by Mountain Pine Beetle Increased Monoterpene Production and Exhausted Carbohydrate Reserves.

Lodgepole pine (Pinus contorta) forests have experienced severe mortality from mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins) in western North America for the last several years. Although the mechanisms by which beetles kill host trees are unclear, they are likely linked to pine defense monoterpenes that are synthesized from carbohydrate reserves. However, how carbohydrates and monoterpenes interact in response to MPB colonization is unknown. Understanding this relationship could help to elucidate how pines succumb to bark beetle attack. We compared concentrations of individual and total monoterpenes and carbohydrates in the phloem of healthy pine trees with those naturally colonized by MPB. Trees attacked by MPB had nearly 300% more monoterpenes and 40% less carbohydrates. Total monoterpene concentrations were most strongly associated with the concentration of sugars in the phloem. These results suggest that bark beetle colonization likely depletes carbohydrate reserves by increasing the production of carbon-rich monoterpenes, and other carbon-based secondary compounds. Bark beetle attacks also reduce water transport causing the disruption of carbon transport between tree foliage and roots, which restricts carbon assimilation. Reduction in carbohydrate reserves likely contributes to tree mortality.

Microclimate differences above ground-layer vegetation in lichen-dominated pine forests of north-central British Columbia

Lodgepole pine forests of north-central British Columbia have patchy ground-layer vegetation, typically dominated by either fruticose lichens, feathermosses, or ericaceous vascular plants; this patchy structure has been shown to correspond with environmental variables that likely moderate the ground-layer microclimate. To investigate the potential role of microclimate on patterns of dominance of ground-layer functional groups, we recorded temperature and relative humidity above the ground-layer vegetation during 25 summer days over patches dominated by mat-forming lichens, feathermosses, or vascular plants. Data were summarized for raw microclimate attributes and daily water potential of the air, and in terms of modelled equilibrium water content of moss or lichen thalli. Analysis of variance revealed significant differences in the water potential of air above the three patch types under sunny conditions, but not under overcast conditions. Differences in vegetation cover were only associated with differences in atmospheric moisture when using data from sunny periods during the daytime. These data confirm that lichens occupy microclimatic niches that are distinctly drier than those of feathermosses or vascular plants, and corroborate the suggested mechanism by which canopy or soil properties influence these types of ground-layer vegetation.

Short-term understory plant community responses to salvage logging in beetle-affected lodgepole pine forests

Abstract Recent bark beetle outbreaks in western North American subalpine forests have prompted managers to salvage log some beetle-affected stands. We examined the short-term (i.e., two to three years post-treatment) consequences of such salvage logging on vascular understory plant (i.e., graminoid, forb, and shrub) communities. At 24 lodgepole pine (Pinus contorta) sites in Colorado, USA, that had been attacked by mountain pine beetles (Dendroctonus ponderosae), we evaluated how logging operations impacted understory plant species richness, cover, and composition by comparing paired unlogged and logged stands. At half of the sites, we also evaluated how logging-related slash management and site preparation activities impacted understory plant cover by comparing experimentally-implemented treatments. Average total species richness increased 18% following logging due to an increase in graminoids and forbs, while average total cover decreased 33% due to a decrease in shrubs. Experimental treatments showed that, within logged stands, average total and shrub cover were greatest where slash was retained on-site and lowest where slash was taken off-site and the soil was scarified. Average exotic species richness more than doubled after logging but values were low even in logged stands, while average exotic cover was unaffected by logging. Taken together, our results suggest that salvage logging following beetle outbreaks altered understory plant communities in the short-term by making them richer, sparser, more graminoid- and forb-dominated, less shrub-dominated, and somewhat more invaded by exotics. Our results also suggest that slash management and site preparation activities can impact the magnitude of some of the understory plant community changes brought about by logging.