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Pinyon-juniper woodland expansion: can a historical perspective guide management of future landscape change?
Peter J. Weisberg, University of Nevada-Reno, Reno NV
Landscape ecologists commonly use historical information to understand current landscape patterns or to develop forecasts for future landscape change. In particular, historical range of variability (HRV) concepts have guided management decisions about responding to disturbance events or using management actions to emulate or alter natural disturbance regimes. Pinyon-juniper woodland expansion has a strong historical component, and historical information has been used to infer underlying causes and to recommend management responses. Yet how relevant is historical information in a world with rapidly changing climate and ecologically significant plant species invasions?
This paper explores the relevance of a historical context for understanding and managing pinyon-juniper woodland dynamics, including expansion into adjacent vegetation types. Underlying causes of expansion, including grazing history, fire exclusion, historical deforestation, and climate change, are explored in light of spatiotemporal patterns of recent change as derived from tree-ring studies, remote sensing analyses and simulation modeling exercises. For one study area in the central Great Basin, historical fire regimes in woodland areas were characterized by infrequent, small, high-severity fires, although most reconstructed fires originated in narrow valley bottoms once dominated by sagebrush grassland. While it is difficult to reconstruct historical fire regimes for shrub-dominated plant community types where pinyon-juniper woodland has recently established, dynamic landscape modeling can be used to bracket the uncertainty of fire regime parameters with respect to species’ life history traits and current age distribution patterns of trees. Historical patterns and reconstructed mechanisms underlying woodland expansion help to define the landscape context for contemporary management; however, management models derived from historical information must be expanded to include expected scenarios for climate change and plant species invasion. Recent loss of pinyon-juniper woodland due to drought mortality and fire, and expansion of cheatgrass into much of the burned area, suggest new foci for understanding and managing patterns of tree dominance across the Great Basin.
Email: pweisberg@cabnr.unr.edu