Mature Lodgepole Pine Forests Research Articles

Landscape variation in tree regeneration and snag fall drive fuel loads in 24-year old post-fire lodgepole pine forests.

Escalating wildfire in subalpine forests with stand-replacing fire regimes is increasing the extent of early-seral forests throughout the western USA. Post-fire succession generates the fuel for future fires, but little is known about fuel loads and their variability in young post-fire stands. We sampled fuel profiles in 24-year-old post-fire lodgepole pine (Pinus contorta var. latifolia) stands (n=82) that regenerated from the 1988 Yellowstone Fires to answer three questions. (1) How do canopy and surface fuel loads vary within and among young lodgepole pine stands? (2) How do canopy and surface fuels vary with pre- and post-fire lodgepole pine stand structure and environmental conditions? (3) How have surface fuels changed between eight and 24years post-fire? Fuel complexes varied tremendously across the landscape despite having regenerated from the same fires. Available canopy fuel loads and canopy bulk density averaged 8.5Mg/ha (range 0.0-46.6) and 0.24kg/m3 (range: 0.0-2.3), respectively, meeting or exceeding levels in mature lodgepole pine forests. Total surface-fuel loads averaged 123Mg/ha (range: 43-207), and 88% was in the 1,000-h fuel class. Litter, 1-h, and 10-h surface fuel loads were lower than reported for mature lodgepole pine forests, and 1,000-h fuel loads were similar or greater. Among-plot variation was greater in canopy fuels than surface fuels, and within-plot variation was greater than among-plot variation for nearly all fuels. Post-fire lodgepole pine density was the strongest positive predictor of canopy and fine surface fuel loads. Pre-fire successional stage was the best predictor of 100-h and 1,000-h fuel loads in the post-fire stands and strongly influenced the size and proportion of sound logs (greater when late successional stands had burned) and rotten logs (greater when early successional stands had burned). Our data suggest that 76% of the young post-fire lodgepole pine forests have 1,000-h fuel loads that exceed levels associated with high-severity surface fire potential, and 63% exceed levels associated with active crown fire potential. Fire rotations in Yellowstone National Park are predicted to shorten to a few decades and this prediction cannot be ruled out by a lack of fuels to carry repeated fires.

Understory Plant Community Composition Is Associated with Fine-Scale Above- and Below-Ground Resource Heterogeneity in Mature Lodgepole Pine (Pinus contorta) Forests.

Understory plant communities play critical ecological roles in forest ecosystems. Both above- and below-ground ecosystem properties and processes influence these communities but relatively little is known about such effects at fine (i.e., one to several meters within-stand) scales, particularly for forests in which the canopy is dominated by a single species. An improved understanding of these effects is critical for understanding how understory biodiversity is regulated in such forests and for anticipating impacts of changing disturbance regimes. Our primary objective was to examine the patterns of fine-scale variation in understory plant communities and their relationships to above- and below-ground resource and environmental heterogeneity within mature lodgepole pine forests. We assessed composition and diversity of understory vegetation in relation to heterogeneity of both the above-ground (canopy tree density, canopy and tall shrub basal area and cover, downed wood biomass, litter cover) and below-ground (soil nutrient availability, decomposition, forest floor thickness, pH, and phospholipid fatty acids (PLFAs) and multiple carbon-source substrate-induced respiration (MSIR) of the forest floor microbial community) environment. There was notable variation in fine-scale plant community composition; cluster and indicator species analyses of the 24 most commonly occurring understory species distinguished four assemblages, one for which a pioneer forb species had the highest cover levels, and three others that were characterized by different bryophyte species having the highest cover. Constrained ordination (distance-based redundancy analysis) showed that two above-ground (mean tree diameter, litter cover) and eight below-ground (forest floor pH, plant available boron, microbial community composition and function as indicated by MSIR and PLFAs) properties were associated with variation in understory plant community composition. These results provide novel insights into the important ecological associations between understory plant community composition and heterogeneity in ecosystem properties and processes within forests dominated by a single canopy species.

Rapid Increases in forest understory diversity and productivity following a mountain pine beetle (Dendroctonus ponderosae) outbreak in pine forests.

The current unprecedented outbreak of mountain pine beetle (Dendroctonus ponderosae) in lodgepole pine (Pinus contorta) forests of western Canada has resulted in a landscape consisting of a mosaic of forest stands at different stages of mortality. Within forest stands, understory communities are the reservoir of the majority of plant species diversity and influence the composition of future forests in response to disturbance. Although changes to stand composition following beetle outbreaks are well documented, information on immediate responses of forest understory plant communities is limited. The objective of this study was to examine the effects of D. ponderosae-induced tree mortality on initial changes in diversity and productivity of understory plant communities. We established a total of 110 1-m2 plots across eleven mature lodgepole pine forests to measure changes in understory diversity and productivity as a function of tree mortality and below ground resource availability across multiple years. Overall, understory community diversity and productivity increased across the gradient of increased tree mortality. Richness of herbaceous perennials increased with tree mortality as well as soil moisture and nutrient levels. In contrast, the diversity of woody perennials did not change across the gradient of tree mortality. Understory vegetation, namely herbaceous perennials, showed an immediate response to improved growing conditions caused by increases in tree mortality. How this increased pulse in understory richness and productivity affects future forest trajectories in a novel system is unknown.

Short‐term resistance of ecosystem properties and processes to simulated mountain pine beetle attack in a novel region

Natural forest disturbance regimes are changing, as evidenced by expansion of the mountain pine beetle (MPB) north and east from British Columbia into pine forests east of the Canadian Rockies. Thus, research that examines potential impacts of shifting disturbance regimes on ecosystem properties and processes in these forests is needed. We examined short‐term effects (up to one year after treatment) of three treatments that emulated MPB attack and associated forest management disturbance (i.e., moderate and high intensity simulated MPB attack, salvage harvest) on above‐ and below‐ground properties and processes of mature lodgepole pine forests in MPB's recently expanded range east of the Rockies. While the salvage logging treatment showed dramatic effects on the understory plant community and downed woody material with several less dramatic below‐ground responses, there were no effects of the moderate MPB attack, and only limited below‐ground responses to the high intensity attack. The salvage logged stands showed decreases in species richness and understory plant cover, increases in small downed wood, litter cover, forest floor pH, and plant available Ca, Mg, and P, and differences in multiple microbial properties compared with the other treatments. The high intensity simulated MPB attack showed increased respiration rates of several carbon substrates compared with the salvage treatment. There was considerable variation among years for many below‐ground variables (e.g., multiple soil nutrients, microbial respiration rates and phospholipid fatty acids), and these were unrelated to treatments. For the majority of below‐ground response variables, differences among study years rather than differences due to the MPB treatments suggest that inter‐annual variability exerts a stronger influence than does disturbance effects of MPB red attack. The lack of potential response to MPB attack in the short‐term suggests these forests are resistant to change early after attack, and/or have high ecological inertia. In contrast, salvage logging had immediate and dramatic effects. We don't yet know how these pine forests will develop under this modified disturbance regime of partial canopy disturbance, but it appears likely that salvage logging will push these stands in a potentially very different direction than the modified natural disturbance regime due to MPB will.

Linkages between the forest floor microbial community and resource heterogeneity within mature lodgepole pine forests

Below-ground microbial communities are influenced by a wide variety of above and below-ground abiotic and biotic factors. Thus, variation in properties, such as vegetation composition and cover, litter cover, soil pH, and nutrient availability likely influence their structure and composition. Examining microbial community variation within forests dominated by just a single tree species provides insights into the factors, other than dominant tree species, that influence the structure and function of below-ground microbial communities at the within-stand scale. In this study we examined fine scale (within-stand) patterns in microbial communities within mature lodgepole pine forests, and their relationships with abiotic and biotic factors. Specifically, the existence of fine-scale microbial structure (using phospholipid fatty acids – PLFAs) and function (using respiration of multiple carbon substrates – MSIR) community types; which PLFAs and carbon substrates were indicators of these, and which above- and below-ground properties and processes were related to these community types. At 108 sampling points in 12 0.48-ha plots abundance of understory plants, canopy tree size and cover, downed wood biomass, forest floor thickness, litter cover, pH, decomposition rate, available soil nutrients, microbial PLFAs and MSIR were assessed. Cluster and indicator species analysis revealed four fine-scale structural (PLFA) and four functional (MSIR) microbial community types. The biotic and abiotic variables measured had low explanatory power for describing the MSIR communities but high explanatory power for describing the PLFA communities. The main factors contributing to the separation of the structural (PLFA) microbial community types were understory plant species. Our findings suggest that the spatial partitioning of understory plant species and their rhizosphere resources (e.g., root exudates, nutrients) creates heterogeneity that influences the patterns of variation in below-ground microbial communities, in particular the microbial structure.

Allometric Model Development in Lodgepole Pine Forests of the Greater Yellowstone Ecosystem

Allometric equations for estimating above­ and belowground biomass of lodgepole pine have been developed in Alberta, Canada, southeastern British Columbia, southeastern WY, and in Washington and Oregon (Johnstone 1971; Comeau and Kimmins 1989; Pearson et al. 1984; Gholz et al. 1979, respectively). More recently, allometric equations for young lodgepole pine saplings have also been developed in Yellowstone National Park (YNP) for aboveground biomass by Turner et al. (2004), and for belowground biomass by Litton et al. (2003). However, because of variability in latitude, growing conditions, substrate and climate, existing equations that predict biomass for mature lodgepole pine trees are not appropriate for use in the Greater Yellowstone Ecosystem (GYE), and new allometric equations specific for the GYE are needed. In this study, we will develop new allometric equations for predicting above- and belowground biomass in mature lodgepole pine forests of the GYE.

Allometric Model Development in Lodgepole Pine Forests of the Greater Yellowstone Ecosystem

Changes in climatic patterns in western North America may modify natural fire regimes, resulting in alterations in forest structure and productivity (Amiro et al. 2000). More frequent fues would create substantial landscape-scale heterogeneity and, consequently, variability in how individual trees and stands allocate biomass in response to the differences in forest structure (Chapin et al. 2002; Turner et al. 2004). For example, in the lodgepole pine (Pinus contorta var. latifolia [Engelm. ex Wats.] Critchfield) forests of the Greater Yellowstone Ecosystem (GYE), recent and historic fires have created a complex mosaic of forest stand structures and aboveground net primary production (NPP) (Turner et al. 1997, 2004). The quantification of forest structure and function at large spatial scales requires accurate measurements of aboveground and belowground tree biomass. Allometric equations for estimating above­ and belowground biomass of lodgepole pine have been developed in Alberta, Canada, southeastern British Columbia, southeastern WY, and in Washington and Oregon (Johnstone 1971; Comeau and Kimmins 1989; Pearson et al. 1984; Gholz et al. (1979, respectively). More recently, allometric equations for young lodgepole pine saplings have also been developed in Yellowstone National Park (YNP) for aboveground biomass by Turner et al. (2004), and for belowground biomass by Litton et al. (2003). However, because of variability in latitude, growing conditions, substrate and climate, existing equations that predict biomass for mature lodgepole pine trees are not appropriate for use in the GYE, and new allometric equations specific for the GYE are needed. In this study, we will develop new allometric equations for predicting above- and belowground biomass in mature lodgepole pine forests of the GYE. The specific objectives of this study were to: (1) develop allometric models for predicting above and belowground biomass of mature lodgepole pine trees in the GYE, and determine how these equations differ with stand density and age; (2) compare and contrast allometric equations developed in this study to allometric equations developed in other locations to determine applicability across geographic loc-ations independent of forest structure.

Above-and Belowground Carbon Allocation in Developing and Mature Lodgepole Pine Forests in Yellowstone National Park: A Progess Report

It has been proposed that forests will act as a sink for -50% of the anthropogenic C02 projected to be released into the atmosphere by the year 2050 as global net primary productivity in forests increases (DeLucia et al. 1999). Coniferous forest ecosystems dominate a large portion of the Earth's land area, and fire plays an important role in the natural disturbance regime of these ecosystems (Archibald 1995). Quantifying the components of the carbon cycle during ecosystem recovery from fire is fundamental for determining how fire and changes in fire frequency alter regional and global carbon budgets (Auclair and Carter 1993, Houghton 1996, Burke et al. 1997). Clearly, if we are to model the effects of terrestrial ecosystems on global carbon budgets, we must develop a better understanding of the role that natural disturbance plays in the carbon dynamics of these systems. Processes that occur after fire may be more important for carbon cycling than the immediate return of carbon to the atmosphere through biomass oxidation (Auclair and Carter 1993). For example, primary productivity following fire is reduced or eliminated until new chlorophyll is synthesized in new leaf area. In addition, aboveground detrital inputs are greatly altered and formerly live roots become available for decomposition. Moreover, litter quality changes with the oxidation of fine fuels; soils and litter become warmer with the removal of overstory shading and a change in albedo; and soils become wetter because of essentially no post-fire transpiration and very little interception of rain and snow. These changes can increase decomposition and soil respiration (Burke et al. 1997), releasing as much as three times more carbon to the atmosphere as the amount released by the initial fire (Auclair and Carter 1993). Notably, carbon is assimilated by new plant growth in fire-adapted ecosystems, with perhaps little net effect on atmospheric C02 (Crutzen and Goldhammer 1993). In addition to large effects on carbon budgets at the stand scale, fire and landscape variables interact to produce a mosaic of different vegetation types (Anderson and Romme 1991, Turner et al: 1997a and b, Foster et al. 1998). The resulting spatial heterogeneity in tree density, herbaceous cover, and species composition in Yellowstone National Park (YNP) will influence primary production and carbon storage for many years. Therefore, to determine the long-term effects of fire on carbon release and storage following fire, information is needed on how processes differ among sites as a function of community structure and stand age. YNP is an ideal study area for this kind of research. Our objective is to answer two questions: 1) How does the relative abundance of trees, shrubs, and herbs influence above- and belowground carbon storage and flux values in young post-fire stands? 2) How do above- and belowground carbon storage and fluxes in young post-fire stands differ from those in nearby mature forests?

Modifying Lodgepole Pine Stands to Change Susceptibility to Mountain Pine Beetle Attack

The premise that mature lodgepole pine forests are susceptible to mountain pine beetle attack when physiologically stressed was supported experimentally by manipulating the canopy density and availability of nitrogen in a 120—yr—old forest exposed to a high population of beetles. Where canopy density was reduced, ether by us or by the insects, surviving trees significantly increased their resistance to attack over a 3—yr period. Increased resistance was reflected by changes in wood production per unit of leaf area (tree growth efficiency). Improved nitrogen nutrition hastened tree recovery but did not prevent attacks by beetles until growth efficiencies exceeded 100 g of wood production per square metre of foliage. Growth efficiency, as here defined, is an index of vigor that may reflect the relative ability of susceptible trees to produce defensive compounds following attack.