Print PageWithin the California oak-grassland ecosystem, there has been large scale, mechanical-chemical woody species removal for commercial fuel wood harvest and livestock production goals. These practices have increased carrying capacities for grazing livestock; however, concurrent changes in other ecosystem services have received limited attention. State and transition models (STMs) have been utilized to catalog ecological information and assess management risks and benefits on rangeland sites. Historically, STMs have been based on expert knowledge of dominant vegetation dynamics with limited integration of quantitative data on ecosystem services such as water supply and carbon sequestration. We utilized the Sierra Nevada gravelly loam foothill ecological site at the UC Sierra Foothill Research and Extension Center (SFREC) as a model system to compare levels of multiple ecosystem services (e.g., water supply, carbon sequestration, agricultural production) across currently recognized vegetation-based states in this ecological site. Soil and vegetation properties indicative of key ecological functions and services were sampled within hierarchically nested sample units across an existing gradient of oak woodland management at SFREC, including undisturbed oak woodland canopy, thinned oak savanna, and type-converted annual grassland states.
Results/Conclusions
Integration of ecosystem services into existing STMs for the Sierra Nevada gravelly loam foothill ecological site revealed mixed results for functional differences for current vegetation-defined states. Infiltration capacity, a key soil process determining water supply, was approximately 10X greater in woodland states than in type-converted grassland states; however, even the lowest infiltration rates exceeded the 100 year rainfall event for the region by more than a factor of 4, likely meaning no real functional differences in water supply between these states. In oak woodlands, herbaceous plant diversity and total carbon were 1.3X and 1.6X greater, respectively, than in type-converted grasslands. However, agricultural productivity was 2.5X greater in these type-converted grasslands relative to woodland states. These results suggest that STMs solely based on vegetation communities do not fully reflect functional differences/similarities in ecosystem services between states. These results also support utilizing a data-driven approach integrating soil and plant based processes in developing ecosystem service-based STMs to guide range management and restoration for desired multiple outcomes.
