Applying ecological site concepts to adaptive conservation management on an iconic Californian landscape

Authors: Spiegal, Sheri; BARTOLOME, JAMES - University Of California; WHITE, MICHAEL - Non ARS Employee

Submitted to: Rangelands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2016
Publication Date: 12/15/2016
Publication URL: http://handle.nal.usda.gov/10113/5570586
Citation: Spiegal, S.A., Bartolome, J.W., White, M.D. 2016. Applying ecological site concepts to adaptive conservation management on an iconic Californian landscape. Rangelands. 38:365-370.

Interpretive Summary: On large ranches, predicting the effects of grazing on ecology and economics can be complicated by the spatial and temporal variability characteristic of rangeland landscapes. A promising approach for organizing the variability and improving predictions about management consists of classifying the landscape into divisions defined by geology, topography, and soils (ecological sites), cataloguing the ecological dynamics of those divisions through time (state-and-transition models), and using that information to develop alternative grazing strategies to be tested over time (adaptive management). We adopted this approach for 40,000 ha of grasslands on Tejon Ranch, the largest privately owned parcel in California. The ranch operates under a land use agreement that emphasizes both economic and conservation goals. Our ecological site classification approach differed from that typically used by the USDA, in that each Tejon ecological site is based on a “geologic landform” class instead of a class derived from soils maps. Using plot data to develop and fine-tune our models, we found that the Holocene Flats Ecological Site had the highest potential for enhancement of conservation values through altered grazing practices predicted to favor several taxa, including the San Joaquin kit fox, blunt-nosed leopard lizard, and native annual forbs. The predicted responses are currently being tested and monitored.

Technical Abstract: Tejon Ranch is a spectacular landscape valued for its biological diversity, livestock production, and cultural heritage. Situated at the convergence of three of California’s major biogeographic zones, it is the largest, contiguous private property in the state. Since 2008, the ranch has operated under a conservation agreement that established adaptive livestock management for conservation and economic outcomes. We developed and applied ecological site concepts to adaptive conservation-focused grazing on 40,000 ha of grasslands on the ranch. Environmental heterogeneity, non-equilibrium system controls, and unpredictable rainfall required novel ecological site descriptions (ESDs) and state-and-transition models (STMs) to understand system history and dynamics, and to predict responses to management. Each ecological site is based on a “geologic landform” class: a unique combination of biogeographic region, geologic material and age, dominant formative geomorphology, elevation, and slope that supports a distinct set of soils and vegetation dynamics. We randomly established 57 permanent plots within geologic landform classes. Sampling these plots over several years allowed us to evaluate the spatial and temporal variation within and among geologic landform classes and to build data-driven, quantitative ESDs and STMs. Using these models, we developed hypotheses about suitable management practices for conservation goals. We discuss in detail the Holocene Flats ESD, which we identified as having the highest potential for enhancement of conservation values through altered grazing practices predicted to favor several taxa, including the San Joaquin kit fox, blunt-nosed leopard lizard, and native annual forbs. The predicted responses are currently being tested and monitored.