AUTHORS: Virginia H. Dale*, University of Tennessee; Charlie C. Crisafulli, US Department of Agriculture Forest Service; Henriette I. Jager, Amy K. Wolfe, Rebecca A. Efroymson – Oak Ridge National Laboratory
ABSTRACT: Ecological disturbances are occurring with greater frequency and intensity than in the past. Furthermore, multiple events or different types of disturbances can undermine the ability of environmental systems to recover, and interacting disturbances can cause ecological systems to transition to new, undesirable states. Under projected shifts in disturbance regimes and patterns of recovery, societal and environmental impacts are expected to be more extreme and occur over a larger area. Furthermore, reestablishment may be to a new state or what some call an “emerging ecosystem,” whose properties then influence future risks and resilience to subsequent disturbances. The need to proactively address risk and resilience is pressing. Managing complex ecosystems to maintain essential characteristics in the face of an uncertain future is challenging. Therefore, I offer a perspective on risk and resilience that encompasses interactions among ecosystems, human organizational dynamics and infrastructure, and evolving technological capabilities. Management decisions need to address (1) hazard assessment, monitoring, and mitigation; (2) natural resource use and management of ecosystem services; and (3) interfaces among humans, technologies, and emerging ecosystems. The spectacular eruption of Mount St. Helens on 18 May 1980 was the largest and most deadly volcanic eruption in historical times in the conterminous United States. I will review lessons distilled from the 37-year body of research, which has strongly influenced and even reshaped our understanding of biological community assembly and successional processes. Because the future is uncertain and unknowable, ecologists must be cognizant of how disturbance patterns become integrated into planning of future infrastructure and protection. Ecological research can test and demonstrate the benefits of protecting or proactively managing important features and places, circumstances, and processes that enhance provisioning of ecosystem services. It is time to demonstrate how ecological science applied to human-environmental systems can reduce risks and enhance resilience in a complex, changing world.
AUTHORS: Caroline Gagné*, University of Quebec in Montreal, Institute of temperate forest science and Center for forest research; Frédérik Doyon, University of Quebec in Outaouais, Institute of temperate forest science and Center for forest research; Christian Messier, University of Quebec in Montreal, University of Quebec in Outaouais, Institute of temperate forest science and Center for forest research; Élise Filotas, University of Quebec Téluq and Center for Forest Research
ABSTRACT: Since the 1800s, forested areas in southern Québec have shrunk and became highly fragmented as they have thereafter undergone several successive anthropogenic disturbances. This study aims at answering the following questions: 1) can historical land-uses and forest disturbances be related to a species and functional diversity erosion in the southern Québec temperate forest and 2) is the local ecosystem memory more important than the external memory for explaining species and functional diversity variations? During the summer 2015, tree sampling was conducted within 64 sites in the Montérégie region. A total of 17 functional response traits were then selected and a search in the literature and trait databases was done in order to obtain trait values for each species present in sampling sites. Traits were divided in sub-groups representing different ecological processes related to tree life cycle and functional diversity index was computed for each of them. Then explanatory variables related to historical land-uses and disturbances were computed for the years 1930-40, 1958, 1983 and 2015 and for 4 spatial scales (30m, 60m, 600m and 2km radii). This was done using photo-interpretation and data integration from multiple data sources. Data exploration was done using correlation analyses and final analyses were done with hierarchical multiple linear regression models. We found strong relationships between some historical land-uses and disturbances and tree species abundance, tree diversity and functional diversity. For species and functional diversity, landscape contextual variables were better predictors than the in-site ones. In fact, some old historical land-uses and disturbances (1930-40 and 1958) still have a strong influence on the current tree species and functional diversity. These results plaid for suggesting that external ecosystem memory has a larger influence on species and functional diversity than local memory.
AUTHORS: Brooke A. Cassell, Portland State University; Robert M. Scheller, North Carolina State University; E. Louise Loudermilk, USDA Forest Service; Matthew D. Hurteau, University of New Mexico
ABSTRACT: Temperatures in the western USA are rising, leading to earlier snowmelt, smaller snowpack, drier fuels, and longer fire seasons. In dry mixed-conifer forests, these conditions are already resulting in more frequent and more severe wildfires, and this trend is projected to continue. Fuel treatments, including mechanical removal of trees and prescribed burning, are known to be effective in reducing wildfire behavior, particularly in forests that were historically dominated by frequent fire-maintained forest types, but the effectiveness of these treatments is uncertain under climate change. Better understanding of the factors that influence the effects of fuel treatment on wildfire activity at large spatial scales and over time is needed while accounting for complex interactions among forest dynamics, fire sizes and severities. We investigated these interactions by simulating forest succession, forest management, and wildfire activity under historical weather and extreme fire weather in a mixed-conifer landscape in the Blue Mountains region of central Oregon. Forest succession and disturbance (e.g., tree harvest, prescribed burning, and wildfire) were dynamically modeled over a 100-year period. We used scenario-building to compare the effectiveness of different management strategies at reducing the spread and severity of wildfire. Spatial optimization of treatments on the landscape was achieved by running 1000 simulation-years of wildfire under extreme conditions on an unmanaged landscape to identify locations that are most likely to burn at high severity (i.e., with a high proportion of tree mortality). Concentrating fuel treatments in these locations was at least as successful, and in some scenarios more successful, at reducing wildfire spread and severity at the landscape scale as placing treatments across the entire landscape. The results of this study offer insight to forest management under extreme weather conditions and help inform decision-making by identifying strategies for spatially optimizing fuel treatments.
AUTHORS: Lucas Harris, Alan H. Taylor – Pennsylvania State University
ABSTRACT: Future change in dry forest systems is likely to be abrupt and nonlinear, with severe disturbancepotentially causing persistent changes in vegetation types. A gridded network of field plots spaced 90 m apart (n = 439) was surveyed at five sites at the lower-elevation forest ecotone on the east side of the Sierra Nevada, California, in areas burned between 2002 and 2008 to evaluate post-fire tree regeneration and to characterize the influence of local topography, water balance and vegetation on post-fire forest recovery. Each site encompassed the elevational range of Jeffrey pine (Pinus jeffreyi) forest from shrub steppe and pinyon pine-dominated (Pinus monophylla) woodland at the downslope end to mixed-conifer forest at the upslope end, with areas of Cercocarpus ledifolius interspersed. Plots where all trees were killed by the fire and no seedlings or saplings were present were characterized by lower actual evapotranspiration, more southwesterly aspects, more gradual slopes, less leaf litter and lower shrub cover than in corresponding areas where tree regeneration was present. Statistical modeling of tree regeneration presence by individual tree species and for all species combined revealed that the relative influence of topography, water balance and vegetation on tree regeneration varied by species, but that high actual evapotranspiration and nearby (< 15 m away) live trees were common factors that were critical for regeneration of each species. These results suggest that variability in water balance and local climate generated by complex terrain and vegetation structure affect post-fire tree regeneration, and that forest loss is likely to occur in drier and sparsely vegetated portions of the sites.
ABSTRACT: Every year in the contiguous United States (U.S.), on average 2.3-2.7 million hectares of wildlands were burned; and fire burned area also showed a strong increasing trend since about 1990. Wildland fires have profound ecosystem and social consequences. For instance, fire burning releases greenhouse gases and aerosols into the atmosphere; and frequently returning fires can also modify landscape and ecosystem functions. In particular, many of the fire impacts on wildland ecosystem functions are made through fire-altered vegetation spatial structure and species composition, such as potentially increased ecosystem vulnerability to the invasion of non-native species. Forests are significant biological components of the land system, which play a critical role in carbon cycles and provide numerous ecosystem services and products. An improved understanding of fire disturbance impacts on forest community structures is therefore important for forest management under consistent disturbances from fires and other agents.Investigations on post-fire forest succession and community structure changes are often of local scales with limited spatial coverage. Understanding of fire impacts on forest community structure and species composition over a broad geographical scale is still scarce. Here, we incorporated large data sets, including the U.S. Forest Inventory and Analysis (FIA) data, MODIS derived the Global Fire Emission Database Version 4 (GFEDv4), and the Monitoring Trends in Burn Severity (MTBS) database, to investigate how fire disturbances, including their severity, may have impacted forest community structure and species composition in the contiguous U.S. over recent years. Preliminary results suggested that fire disturbances had highly variable impacts on post-fire forest community species composition, seedling regeneration, and understory layer coverage of different forest types and geographical regions, which also depended on fire severities. Our results highlight the importance of long-term monitoring data of fire occurrence and forest dynamics for meeting forest management and research needs.
AUTHORS: Monica G. Turner*, Department of Integrative Biology, University of Wisconsin-Madison; Brian J. Harvey, School of Environmental and Forest Sciences, University of Washington; Winslow D. Hansen, Department of Integrative Biology, University of Wisconsin-Madison; Kristin H. Braziunas, Department of Integrative Biology, University of Wisconsin-Madison
ABSTRACT: Novel fire regimes have the potential to erode forest resilience (ability to tolerate disturbance without shifting to a new state) in fire-prone forest landscapes. In Greater Yellowstone (Wyoming, USA), lodgepole pine (Pinus contorta var. latifolia) forests have been highly resilient to large, stand-replacing fires that historically burned at 100 to 300-yr intervals. However, fire-return intervals (FRI) are projected to decline substantially by mid-century as climate warms, increasing the likelihood that forests will re-burn prior to recovery from previous fire. Opportunities to study ecological effects of short-interval fires remain rare in any landscape, but the Yellowstone fires of 2016 included >18,000 ha of short-interval (70,000 stems/ha) to sparse (
AUTHORS: Brian Buma*, University of Alaska; Sarah Bisbing, University of Nevada Reno; John Krapek, University of Alaska Southeast; Greg Wiles, Wooster College; Allison Bidlack, Alaska Coastal Rainforest Center; Glenn Wright, University of Alaska Southeast
ABSTRACT: Understanding the drivers and patterns of primary and secondary succession are among the oldest questions in ecology, and integral to the study of landscape change, modeling, and ecosystem response to climate change. These processes are often examined via chronosequences, which carry the assumption that space can, in fact, be substituted for time. This assumption is rarely checked due to a lack of long-term data. In this study, we expanded the longest running primary succession study in the world (the William S. Cooper plots in Glacier Bay, Alaska, now running for 101 years) to examine successional trajectories and the role of spatial factors and stochasticity in community composition from both a regional and local perspective. After approximately 140 years since initiation, the ecological communities and dominant cover types better reflect variation in early (1916-1935) community composition rather than plot age. General cover type and richness appears to be primarily driven by location rather than time, and significant spatial structuring at the plot scale reflect exclusion of potential “later” successional species. The current communities appear stable, reflecting multiple generations and little to no establishment of other canopy species, despite available seed and ample time. At the plot scale, variation in species is related to stochastic establishment in the early landscape. Soil development, carbon, and nitrogen stocks are spatially consistent, with little spatial structure. These results indicate that space and stochastic effects early in a plot's history shape community composition for at least 140 years, and that alternate, apparently stable regimes can persist for long-periods of time in the early successional environment driven by stochastic establishment and spatial constraints.