Research has demonstrated that aboveground net primary production (ANPP) is driven by annual precipitation. ANPP could also respond to seasonal precipitation, which has received less attention. As climate change is expected to alter precipitation seasonality in regions with distinct dry and wet seasons, such as subtropical biomes, ANPP may become more affected by seasonal precipitation. To address this knowledge gap, this study focused on subtropical grasslands in central Florida (Buck Island Ranch) to investigate how seasonal precipitation affects two provisioning ecosystem services, forage as ANPP and cattle production. Long-term datasets (1989 to 2019) on weather, ANPP, and cattle productivity were analyzed with linear models; precipitation was grouped by wet and dry seasons, with the consideration of legacy effects. ANPP data included field measurements from two dominant grassland types on the ranch (improved and semi-native grasslands), and remotely-sensed MODIS data. Cattle productivity at the ranch was measured as annual cow pregnancy rate and number of calves. The hypotheses were that seasonality of precipitation would affect ANPP, with higher ANPP in years with wetter dry seasons; cattle were expected to respond positively to increases in forage quantity. Wet season precipitation was expected reduce ANPP in years with wetter wet seasons.
Results/Conclusions
Results from field measurements showed that ANPP was influenced by a two-year legacy of precipitation, increasing as annual precipitation increased (R2=15%; p<0.05). Greater wet season precipitation reduced ANPP in models with effects of one legacy year of precipitation and season start date, with little effect of current year precipitation (R2=14%; p<0.05). Dry season precipitation, however, showed a positive effect on ANPP with one legacy year of precipitation (R2=16%; p<0.05). Results from remote data for ANPP across the ranch showed similar trends to the field data and followed trends expected in the hypothesis; greater dry season precipitation increased ANPP (R2=22%; p<0.05). Seasonal precipitation also affected cattle production, though no legacy effects were present; increased dry season precipitation reduced cow pregnancy rate (R2=24%; p<0.05) and total number of calves (R2=28%; p<0.05), contrary to the hypothesis. There was no effect of wet season precipitation on either cow pregnancy rate (R2=12%; p>0.05) or total number of calves (R2=6%; p>0.05). Further analyses will investigate the relative importance of climatic and management factors in driving ANPP and cattle production. The different effects of dry and wet season precipitation on cattle demonstrate that seasonality of precipitation, rather than total annual precipitation, affects cattle performance in subtropical grasslands.