Trajectories of change in sagebrush steppe vegetation communities in relation to multiple wildfires
Repeated perturbations, both biotic and abiotic, can lead to fundamental changes in the nature of ecosystems including changes in state. Sagebrush-steppe communities provide important habitat for wildlife and grazing for livestock. Fire is an integral part of these systems, but there is concern that increased ignition frequencies and invasive species are fundamentally altering these systems. Despite these issues, the majority of studies of fire effects in Artemisia tridentata wyomingensis-dominated systems have focused on the effects of single burns. The Arid Lands Ecology Reserve (ALE), in south-central Washington (U.S.A.), was one of the largest areas of continuous shrub-steppe habitat in the state until large wildfires burnt the majority of it in 2000 and 2007. We analysed data from permanent vegetation transects established in 1996 and resampled in 2002 and 2009. Our objective was to describe how the fires, and subsequent post-fire restoration efforts, affected communities successional pathways. Plant communities differed in response to repeated fire and restoration; these differences could largely be ascribed to the functional traits of the dominant species. Low elevation communities, previously dominated by obligate seeders, moved farthest from their initial composition and were dominated by weedy, early successional species in 2009. Higher elevation sites with resprouting shrubs, native bunchgrasses and few invasive species were generally more resilient to the effects of repeated disturbances. Shrub cover has been almost entirely removed from ALE, though there is evidence of recovery where communities were dominated by re-sprouters. Cheatgrass (Bromus tectorum) dominance was reduced by herbicide application in areas where it was previously abundant but increased significantly in untreated areas. Several re-sprouting species, notably Phlox longifolia and Poa secunda, expanded remarkably following competitive release from shrub canopies and/or abundant cheatgrass. Our results suggest that community dynamics can be understood through a state-and-transition model with two axes (shrub/grass and native/invasive abundance), though such models also need to account for differences in plant functional traits and disturbance regimes. We use our results to develop an illustrative model that will be expanded with further research.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1049649
- Report Number(s):
- PNNL-SA-86059; ECAPE7; TRN: US201218%%127
- Journal Information:
- Ecological Applications, Vol. 22, Issue 5; ISSN 1051-0761
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ABUNDANCE
ARID LANDS
CANOPIES
COMMUNITIES
DISTURBANCES
DOMESTIC ANIMALS
ECOLOGY
ECOSYSTEMS
FUNCTIONALS
HABITAT
HERBICIDES
IGNITION
PLANTS
SHRUBS
TRAJECTORIES
Artemisia tridentata
Arid Lands Ecology Reserve
Bromus tectorum
fire effects
Hanford Reach National Monument
herbicide
native seeding
Non-metric multi-dimensional scaling
PERMANOVA
repeated disturbance
restoration
State and transition model