Grazinglands occupy 26% of Earth’s land surface and provide important provisioning services. Past research has shown that higher plant diversity may promote ecosystem productivity and stability. First, we investigated if plant species diversity mediates the response of ecosystem productivity to variation in precipitation and management intensity in grazinglands across the US. Second, we investigate how plant diversity influences stability in productivity.
We used remote sensing data and field measured vegetation data from two ecological networks: 14 NEON (NSF’s National Ecological Observatory Network) sites and 5 LTAR (USDA’s Long-Term Agroecosystem Research Network) sites, which encompass 11 NEON domains. Sites followed the same method to measure species richness at different spatial scales (1, 10, 100, 400-m2). We built species-area relationship curves (SAR) and estimated the slope of the SAR for each plot at each site. For each plot, we obtained remotely-sensed Gross Primary Productivity (30 m resolution, 16-day cadence), temperature, precipitation, and drought index from the Google Earth Engine for the period from1986 to 2018. We used GLMMs to relate annual GPP and variation in GPP across years (using coefficient of variation) to species richness (diversity at 1m2 and slope of the SAR) and climate variables.
Results/Conclusions
GPP varied 6-fold across NEON and LTAR sites, with the lowest GPP observed at drier sites (e.g., Jornada Experimental Station, NM)and the highest GPP observed at wetter sub-tropical grazinglands (e.g., Archbold Biological Station, FL). Sites with low GPP also displayed more variation in GPP between years (1986-2018). Species diversity metrics (Species richness, slope of the SAR), drought index, and vegetation class explained 65% of the variation in mean annual GPP. Plots that were more diverse tended to have higher productivity. Variation in GPP between years was best explained by vegetation class and species diversity, but this model only explained 20% of the variation in productivity stability.
Although much work has been conducted on the relationship of plant diversity to productivity and stability, coordinated research, across a range of agroecosystems, is needed to identify general patterns. Our work shows higher diversity is associated with greater productivity and higher stability in grazinglands, but more work is needed to fully understand which species functional groups/traits drive this relationship and identify how diversity impacts other important agroecosystem functions (e.g., pollination) and conservation goals. We anticipate applying this framework to croplands edges and prairie strips.