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Disturbance and succession have long been of interest in ecology, but how landscape patterns of ecosystem structure and function evolve following large disturbances is poorly understood. After nearly 25 years, lodgepole pine ( Pinus contorta var. latifolia) forests that regenerated after the 1988 Yellowstone Fires (Wyoming, USA) offer a prime opportunity to track the fate of disturbance-created heterogeneity in stand structure and function in a wilderness setting. In 2012, we resampled 72 permanent plots to ask (1) How have postfire stand structure and function changed between 11 and 24 yr postfire, and what variables explain these patterns and changes? (2) How has landscape-level (among-stand) variability in postfire stand structure and function changed between 11 and 24 yr postfire? We expected to see evidence of convergence beginning to emerge, but also that initial postfire stem density would still determine trajectories of biomass accumulation. After 24 yr, postfire lodgepole pine density remained very high (mean = 21,738 stems/ha, range = 0-344,067 stems/ha). Stem density increased in most plots between 11 and 24 yr postfire, but declined sharply where 11-yr-postfire stem density was >72,000 stems/ha. Stems were small in high-density stands, but stand-level lodgepole pine leaf area, foliage biomass, and live aboveground biomass increased over time and with increasing stem density. After 24 yr, mean annual lodgepole pine aboveground net primary production ( ANPP) was high (mean = 5 Mg·ha−1·yr−1, range = 0-16.5 Mg·ha−1·yr−1). Among stands, lodgepole pine ANPP increased with stem density, which explained 69% of the variation; another 8% of the variation was explained by environmental covariates. Early patterns of postfire lodgepole pine regeneration, which were contingent on prefire serotiny and fire severity, remained the dominant driver of stand structure and function. We observed mechanisms that would lead to convergence in stem density (structure) over time, but it was landscape variation in functional variables that declined substantially. Stand structure and function have not converged across the burned landscape, but our evidence suggests function will converge sooner than structure. [ABSTRACT FROM AUTHOR]

Large disturbances such as the 1988 Yellowstone fires produce considerable spatial heterogeneity in ecosystem processes across landscapes, in part by affecting vegetation structure. However, the persistence of this heterogeneity with time since disturbance, and thus the role of large disturbances in shaping the heterogeneity of ecosystem processes over large spatial and temporal scales, remains unclear. Such an inquiry requires that variability as well as mean conditions of forest structure and growth be examined if changes are to be projected for heterogeneous postdisturbance landscapes. We studied a chronosequence of unburned, mature lodgepole pine stands (stand ages ranging from 50 to 300 or more years) to examine the variability in stand density, leaf-area index (LAI), and stem growth [basal area increment (BAI), a surrogate for aboveground net primary productivity (ANPP)] with stand age, the relationships between these factors, and how these factors were related to stand and site characteristics. Variation in LAI and BAI was explained primarily by differences in stand density and age (r2?=?0.51 for both LAI and BAI), and both LAI and BAI were most variable in the youngest age class [coefficient of variation (CV), 38% and 41% for LAI and BAI]. The relationship between LAI or BAI and stand density was significantly weaker (r2<0.20) at stand ages characterized by canopy closure (50-175 years), suggesting that stand structure and production are closely linked. Thus, the spatial variability of stand production, which is initially very high following large fires in this landscape, is detectable for over a century before successional changes in forest structure greatly affect the initial postdisturbance landscape pattern of stand production. Given the recent focus on spatial heterogeneity of ecosystem processes across large landscapes, projecting changes in postdisturbance patterns of stand production has very strong significance for ecosystem science. [ABSTRACT FROM AUTHOR]

Cottonwoods (Populus spp.) represent an important tree component of riparian plant communities within the winter range of the northern Yellowstone elk (Cervus elaphus) herd, yet young cottonwoods are highly palatable to ungulates. To assess potential herbivory impacts associated with wild ungulates following the removal of gray wolves (Canis lupus), long-term cottonwood recruitment and stand dynamics were studied. While results indicated that the establishment of young cottonwoods is an ongoing process in Yellowstone's northern range, their relatively small stature and hedged appearance were indicative of high browsing pressure by wild ungulates, principally elk. At five study sites, the diameter at breast height (dbh) of all cottonwood trees ≥5 cm was determined; increment cores were also obtained for developing tree age vs. dbh relationships. At the La Duke Spring and Devils Slide Sites, which represent refugia sites since elk have limited access (due to local terrain conditions and cultural developments), cottonwood recruitment has been occurring during the last half century, indicating that climatic factors have not prevented cottonwood recruitment during that time. However, over this same period cottonwood recruitment no longer occurred at sites within the Soda Butte and Lamar Valleys. The overall decline in cottonwood recruitment at these locations occurred following the extirpation of wolves from Yellowstone National Park in the 1920s. At the Buffalo Ranch Site, where ranching of buffalo [bison] (Bison bison) and activities associated with culling of elk were centered, cottonwood recruitment continued after the loss of wolves but stopped following the curtailment of ungulate management activities at these facilities in the late 1960s. Taken together, data from the five sites reported herein along with the results of other studies provide compelling evidence that the absence of wolves in the northern Yellowstone has had a major impact on the recruitment of cottonwood and other woody browse species. [ABSTRACT FROM AUTHOR]

The effect of the community composition of soil microbes on ecosystem processes has received relatively little attention. Here we examined the variation in soil microbial composition in a Yellowstone National Park grassland and the effect of that variation on the growth, in a greenhouse, of the dominant grass in the community. Plants and their rhizospheric soil were collected from paired, Poa pratensis-dominated grassland plots located inside and outside a 40-year-old exclosure. P. pratensis aboveground, belowground, and whole plant growth were greater in pots with soil communities from grazed grassland compared to fenced grassland, indicating (1) soil microbial communities differed, and (2) this difference influenced the growth of the plant that dominated both grasslands. Treating pots with fungicide (benomyl) suppressed the soil community influence, indicating that different fungal communities caused the soil microbe effect. In addition, two lines of evidence are consistent with the hypothesis that arbuscular mycorrhizal fungal (AMF) species composition affected P. pratensis: (1) a divergence in AMF spore communities in the two field soils, and (2) little evidence of pathogenic fungi. These findings emphasize the need to examine the role that the composition of the soil microbial community plays in controlling terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

The greater Yellowstone Area ecosystem experienced major wildfires in 1988, resulting in a substantial number of catchments being burned. We studied diatom assemblage structure at 14 sites over 5 years in catchments ranging from 0 to over 90% burned. Coefficient of variation for selected physical measures provided a good assessment of the degree of disturbance experienced by the various sites and correlated highly with percentage of catchment burned. Principal components analysis quantitatively estimated the degree of temporal change in diatom assemblages at a site. The more extensively burned catchments showed the greatest amount of structural change in diatom taxa among years. Navicula permitis Hust. and Nitzschia inconspicua Grun. were predominant in the heavily disturbed systems, whereas Achnanthes minutissima Kuetz., A. lanceolata (Breb.) Grun., Rhoicosphenia curvata (Kuetz.) Grun. ex Rabh., and Diatoma hiemale var. mesodon (Ehr.) Grun. were common in less disturbed streams. The results demonstrate that recovery trajectories of lotic diatom assemblages following major landscape-scale disturbances are a function of disturbance intensity resulting from differences in catchment characteristics. [ABSTRACT FROM AUTHOR]

We present a technique for modelling conditional burn probability patterns in two dimensions for large wildland fires. The intended use for the model is strategic program planning when information about future fire weather and event durations is unavailable and estimates of the average probabilistic shape and extent of large fires on a landscape are needed. To model average conditional burn probability patterns, we organised historical fire data from Yellowstone National Park, USA, into a set of grids; one grid per fire. We captured various spatial relationships inherent in the gridded data through use of geometric variables in the main model and by incorporating an autoregressive covariance structure. The final model had 'good' predictive ability with an AUC of 0.81 (1.0 is perfect prediction) and the estimated coefficients are consistent with theory and reflect how fires usually behave on the study site landscape. This technique produces a predictive model with finer detail than most landscape-wide models of burn probability and it has advantages over simulation methods for strategic planning because it does not require multiple runs of spread simulation models or information on fire duration. We present a technique for estimating conditional probability of burn patterns for large fires. Patterns quantify the conditional probability that points near an ignition will burn and illustrate the probabilistic shape and extent of a fire. Predictive ability is good and estimated coefficients are consistent with expectations. [ABSTRACT FROM AUTHOR]