Grazing lands in CA provide myriad ecosystem services beyond animal production, including the regenerative potential for soil C sequestration and climate change mitigation. Since rangelands contain 30% of all soil C, livestock management could make these soils either a source or sink of atmospheric CO2. One promising management strategy for soil C sequestration is AMP grazing. AMP grazing is characterized by short grazing intervals with moderate-high stocking densities. Animals are moved frequently to reduce overgrazing and chronic defoliation and to allow ample plant recovery between grazing events. Further, AMP grazing is non-prescriptive, meaning that land-managers observe ecosystem function and adapt grazing intensity and recovery periods accordingly. These features differentiate AMP from other more simplistic grazing practices, such as continuous or mob grazing (high stocking densities without adaptive management). Continuous grazing (CONT), with no or low rotation, is the most common grazing management regimen globally. Under these circumstances, livestock exhibit repetitive overgrazing on some areas and have been recognized as detrimental to plant communities and soil C stocks.
Ranchers report benefits of AMP grazing likely related to soil C sequestration, such as increased forage productivity and quality, water infiltration, increased biodiversity and perennialization. However, high temporal and spatial variability of soil C dynamics in rangelands necessitate research to elucidate the impacts of AMP and other grazing management regimes on a regional basis. In California, highly variable net primary productivity (NPP), dominance of exotic annual grasses, and drought limit both plant-litter and root-exudate inputs to the soil, which are known mechanisms of soil C sequestration (24). AMP grazing may increase soil C sequestration in CA rangelands by (a) increasing competitiveness of perennial grasses (or grasses with greater rooting volume) by preventing chronic defoliation (b) increasing root-carbon allocation, (c) increasing nutrient turnover, and (d) managing adaptively according to weather and forage availability. Thus, the underlying mechanisms and utility of AMP grazing for both improving both soil heath and increasing above ground biodiversity needs to be explored in this unique CA context.
The overall objective of this project is to understand the ecological implications of different grazing management on CA rangelands, at the ranch scale by asking two key questions:
Q1: How do soil C sequestration, C persistence, and other ecosystem services differ in CA rangelands under AMP grazing compared with CONT grazing?
***Q2: How does above ground biodiversity change between AMP and CONT grazing in CA rangelands?
*** This will be the primary objective of the SPUR student
The undergraduate will be primarily focused on Q2 of the project, and will be responsible for:
- Preliminary literature review of common grass, forb, and shrub species on CA rangelands
- Working with the researcher to design sampling techniques consistent with current study framework
- Identifying appropriate measures of biodiversity, including plant community composition and wildlife
- Data collection on 15 ranches
- Excellent communication skills
- Flexible Spring 2020 class schedule
- Ability to travel with the researcher to ranches across CA
- Strong plant ID skills, especially CA grass and rangeland species