COS 32-4 - Making up for it: Compensation drives community recovery two decades after dominant species removal in a mesic grassland

Abstract: Dominant species play a major role in maintaining ecosystem function (e.g., productivity), yet the long-term impact of their loss is understudied. Communities likely exhibit decreased production in the short-term following the loss of a dominant species, however new dominant species may emerge over time to compensate. We sought to understand how plant communities respond to the loss of two dominant species and assess how long that it would take for a key ecosystem function – aboveground net primary productivity (ANPP) – to recover (i.e., for compensation to occur). To address these objectives, we conducted a targeted removal of two perennial C₄ grass species, Andropogon gerardii and Sorghastrum nutans, that contribute >80% to ANPP. These removals occurred in native tallgrass prairie at the Konza Prairie Biological Station located in northeastern Kansas. Species-level responses to removal of the dominants were recorded from 1996-2019 as absolute cover and presence/absence, along with ANPP.



We found that A. gerardii abundance (measured as cover and biomass) did not fully recover until 23 years after removal (2019). However, S. nutans abundance recovered more rapidly and exceeded that in control plots by 3 years after removal (2000, p< 0.0001). A major shift in functional group abundance occurred from 1997-2000. Forbs, notably Ambrosia psilostachya and Salvia azurea, initially increased in abundance in removal plots (1997) but were quickly replaced by graminoids (2000), including the subordinate C₄ grasses, Schizachyrium scoparium and Sporobolus compositus. These grass species largely compensated for ANPP loss, though ANPP was not equivalent in removal and control plots until 15 years after removal (2011). These results suggest that the ability of dominant species to recover from their loss can vary dramatically. We found that S. nutans returned to pre-removal abundance within 3 years, but it took A. gerardii over two decades. Compensation occurred not because A. gerardii recovered, but rather due to compensation by less common grasses.