More extreme rainfall patterns and plant community structure in native tallgrass prairie

Background/Question/Methods

Global climate change models predict that rainfall patterns will become more extreme and less frequent in the US Great Plains, resulting in more variable growing season precipitation. Changes in precipitation regimes are likely to have significant ecological consequences on grassland plant community composition and structure. Previous research has shown that interannual variation in total precipitation is correlated with above-ground net primary productivity and plant species composition. However, we know less about how increased precipitation variability (fewer, larger events) will affect plant community structure in native tallgrass prairie. We used 15 years of data from the Rainfall Manipulation Plots (RaMPs) at Konza Prairie in northeastern Kansas USA to determine how increased precipitation variability impacted plant species composition and structure in native tallgrass prairie. The RaMPs infrastructure maintains total ambient growing season precipitation, but half the plots (n=6) receive a rainfall regime that includes fewer but larger rain events with longer intervals between events during each growing season.

Results/Conclusions

Total richness was consistently higher in the altered timing treatment on average over the duration of the experiment due to an increase in both grass and forb richness. Total cover was also higher on average under altered precipitation timing, primarily due to an increase in forb cover rather than grass cover. However, this effect was not seen until after seven years of altered precipitation, showing a lag effect as predicted by the Hierarchical Response Model. Several other measures of community structure were generally unaffected by the altered precipitation treatment. The delayed effect on plant cover indicates differential sensitivity of ecosystem and community responses to altered rainfall timing, and reinforces the importance of long-term studies of precipitation variability. Our results show that many aspects of community structure are likely to be relatively stable under a more variable precipitation regime. However, the consistently higher levels of forb cover and richness in our altered precipitation treatment suggests that future increases in precipitation variability will significantly influence this functional component in native tallgrass prairie.