As one of the most productive regions of the US Great Plains, tallgrass prairie provides critical ecosystem functions and services. Though it is well-known that disturbances including fire, drought, and grazing influence grasslands, quantifying the capacity to withstand disturbance (resistance) and the capability to recover from disturbance (resilience) provides important insight for predicting grassland stability with forecasted climate change.
In this study, we address two questions: (1) how resistant and resilient was the tallgrass prairie to the extreme 2012 drought event? And (2) does resistance and resilience vary according to fire and grazing management regimes?
Our study site was the Konza Prairie Biological Station in Northeast Kansas. This site has a long-term fire (burned every 1, 4, and 20 years) and grazing (grazed by bison, and ungrazed) watershed-scale experimental design, which allowed us to assess how the 2012 drought interacted with these key drivers. We utilized an NDVI dataset generated from Landsat 7, with a 30m*30m spatial resolution during 1999-2019 and conducted repeated measures ANOVA to compare the NDVI anomaly of each grid two years before, during, and two years after the extreme one-year drought events.
Results/Conclusions
During 2012, NDVI declined sharply in all watersheds, regardless of fire or grazing regime, and all fully recovered the next year. This suggest that tallgrass prairie has low resistance, but high resilience to extreme drought. However, watersheds with three burning treatments showed different degrees of resistance and resilience. Generally, annually-burned watersheds had lower resistance but higher resilience, while the watersheds burned every 20 years had the highest resistance but relatively lower resilience. Furthermore, when comparing the NDVI anomaly between grazed and ungrazed watersheds, we found that among the watersheds burned every 20 years, those grazed by bison have significantly lower resistance than the ungrazed ones. This is likely due to the negative impact of bison grazing on soil moisture. Ultimately, the results suggest that grazing plays an important role in grassland ecosystems’ vulnerability to extreme drought.