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Submitted to: Meeting Proceedings
Publication Type: Proceedings Publication Acceptance Date: 3/10/2016 Publication Date: 7/20/2016 Citation: Porensky, L.M., Blumenthal, D.M., Derner, J.D. 2016. Wildfires cause long-term plant community conversion in a western Great Plains steppe. In: A. Wiaasa, H.A. Lardner, et al (Eds.). The future management of grazing and wild lands in a high-tech world: Proceedings 10th International Rangeland Congress, Saskatoon, SK, July 16-22, 2016. pp 691-692. Interpretive Summary: Technical Abstract: Long-term impacts of wildfire vary dramatically across rangeland ecosystems. Frequent fire can promote productivity and biodiversity in some locations (Fuhlendorf et al. 2006), but in other regions this same disturbance can cause catastrophic ecosystem shifts, including the loss of dominant plant species and invasion by exotic plants (Davies et al. 2011). Understanding the short- and long-term effects of fire is critical for the successful management of rangeland ecosystems. However, in many regions the role of fire is still poorly understood. Here we describe associations between wildfire and plant community composition in the Thunder Basin ecoregion, which covers more than 800,000 ha in northeast Wyoming. Nestled within the larger Powder River Basin, Thunder Basin is located in the ecotone between northern mixed grass prairie to the northeast, shortgrass steppe to the southeast, and shrub steppe to the west. In this region, livestock producers, energy developers, and conservation interests are struggling to co-manage a spatially extensive, biophysically complex, and water-limited landscape. Wide variation in soil types, topography, and the abundance of both shrubs and grasses makes it difficult to understand and predict the long-term effects of wildfire in this landscape. To advance our understanding of wildfire in complex landscapes and to help inform management, we asked three questions: 1) How does wildfire influence plant community composition? 2) Are the effects of wildfire on plant communities short-term or persistent? and 3) Does wildfire interact with other environmental factors to influence community composition? From a database of perimeters for wildfires that burned between 1988 and 2012, we identified regions in the Thunder Basin that had burned only once since 1988. We also used local knowledge to identify burns that occurred in 1937 and 1974. For each ecological site within each fire, we randomly placed a 30 m-long transect which was paired with an unburned transect located outside the burn but within 1000 m of the fire perimeter. Paired transects were matched based on grazing allotment, ecological site, slope, aspect, elevation and topographic wetness index. We sampled 79 transect pairs across 32 fires. For each transect aerial cover of each species was determined within a 50 x 20 cm quadrat at ten systematically spaced locations, end of growing season biomass was clipped by functional group, and shallow soils cores (0-30 cm deep) were collected for determining surface soil texture. We used nonmetric dimensional scaling ordination to investigate variability in plant community composition and determined whether community-level variability was associated with historical wildfire, soil type or other factors. We also used linear mixed models and model selection to investigate the responses of key plant species and functional groups to wildfire and landscape context. Historical wildfires in Thunder Basin induced both short-term and long-term shifts in plant community composition. Compared to paired, unburned sites, burned sites had lower shrub cover, higher perennial grass cover, lower cactus cover, and higher forb cover (Fig. 1). Effects of wildfire on cactus and forb cover diminished over time, but effects on shrubs and perennial grasses were persistent. Inside the oldest fires, shrubs had not recovered and perennial grass cover remained significantly elevated. Historical wildfires were not associated with invasion of Bromus tectorum (cheatgrass) or Bromus arvensis (Japanese brome). Aside from fire, we found that soil texture, cover of other plant species, and microclimate (slope and aspect) were key drivers of annual brome abundance. Soil texture, slope and aspect also had important impacts on plant community composition and functional group biomass. Wildfires induced plant community shifts that persisted for over |
