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ARS Home » Plains Area » Temple, Texas » Grassland Soil and Water Research Laboratory » Research » Publications at this Location » Publication #324960
Title: Species composition but not diversity explains recovery from the 2011 drought in Texas grasslands

Author
item XU, XIA - Iowa State University
item Polley, Herbert
item HOFMOCKEL, KIRSTEN - Iowa State University
item WILSEY, BRIAN - Iowa State University

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2017
Publication Date: 3/3/2017
Citation: Xu, X., Polley, H.W., Hofmockel, K., Wilsey, B.J. 2017. Species composition but not diversity explains recovery from the 2011 drought in Texas grasslands. Ecosphere. 8(3):e01704. doi:10.1002/ecs2.1704.

Interpretive Summary: Drought usually is assumed to affect grassland productivity only during the period of water limitation. Vegetation productivity is expected to rebound to pre-drought levels when rains return, although there is accumulating evidence of a ‘legacy’ or lagged effect of drought on grasslands. We assessed possible legacy effects of the historic 2011 drought in central Texas on grassland production by comparing pre-drought to post-drought aboveground production of vegetation communities planted to different combinations of all native or all exotic (non-native) grassland species. The drought reduced aboveground production by 90%, but also triggered a shift in species relative abundances in both native and exotic communities that reduced biomass production per unit of rainfall in the years following the drought. The magnitude of the pre-drought to post-drought decline in biomass per rainfall was similar in native and exotic communities, but resulted from different patterns of vegetation change in the two community types. The pre-drought to post-drought decline in biomass per rainfall was greater in native communities in which drought reduced forb abundance and in exotic communities in which drought reduced abundance of tall grass species. Our results are contrary to the common assumption that grassland production rebounds quickly following drought. Drought altered grassland productivity for several years after rains returned by altering plant community composition. This ‘legacy’ effect of drought must be included in mathematic simulations of vegetation in order to accurately predict climate impacts on grasslands and the services they provide.

Technical Abstract: Coupled climate-carbon cycle models implicitly assume that vegetation recovery from extreme droughts is immediate and complete. Here, we found that an extreme drought in 2011 initiated a state transition and resulted in shifted ecosystem functions in an 8 year study comparing native and exotic experimental communities in central Texas. The drought decreased aboveground biomass (AGB) by 90% and triggered species reorganization that led to a new post-drought state. The new state following drought was associated with a significant reduction in biomass production per unit of rainfall (BpR) and a lessening of the effects of grassland origin (native vs. exotic) on BpR. The magnitude of pre-drought to post-drought differences in BpR was similar between native and exotic communities. However, differences in BpR increased with increases in the proportion of C3 forb biomass in native communities and tall grass biomass in exotic communities. Our results indicate that the 2011 drought produced a strong legacy effect by altering plant community composition to the extent that BpR, an ecosystem function, shifted with possible long-term repercussions. Our results contrast with the assumption of current climate-vegetation models, highlighting delayed recovery of grassland ecosystems from extreme droughts.