The Ecological Basis for Grassland Conservation Management at Tejon Ranch, California

Grasslands in California's inland Mediterranean climate zone vary greatly over time and space, largely due to fluctuating rainfall and heterogeneous geology, topography, and soils. In light of a dramatic invasion of exotic species into these grasslands, conservation management goals typically include the preservation and enhancement of native vegetation. Developing specific management targets to achieve these goals, however, is complicated by uncertainty about pre-invasion conditions and the spatial and temporal complexity of the system. The Tejon Ranch, the largest, contiguous, privately-owned property in the state, supports 44,000 ha of California's inland Mediterranean grassland. The mission of the Tejon Ranch Conservancy (Conservancy) is to preserve, enhance, and restore the native biodiversity of Tejon Ranch. In 2009, the Conservancy partnered with the University of California Range Ecology Lab led by James Bartolome to describe the grasslands on the ranch, in order to build the understanding required for management planning. As a doctoral researcher and co-leader of the study from 2010 to 2014, my objective was to develop a scientific framework to inform reliable predictions about the distribution of plant species over space and time in the ranch's grasslands. I investigated three basic questions: 1. Does species composition correlate with geologic, topographic, and edaphic landscape composition, at differing spatial scales?2. What are the drivers of inter-annual community change at the ecological site scale?3. What are the alternative states of the ecological sites?Chapter 1 is a description of how I investigated the first question in the western Mojave Desert landscape of the ranch. I collected topographic, edaphic, and ground cover data at 35 small (0.25 m2) plots across a 64 km2 (6.4 x 107 m2) extent in the spring of 2010. Fortuitously, the timing and amount of rainfall in 2009-2010 resulted in high diversity and abundance of native annual forbs and grasse