Climatic change, such as drought, is taking place in tandem with disturbances. While natural disturbances are generally discrete in time, human-induced chronic resource alterations are continuous and often cumulative pulses that directly impact biota and drive ecosystem responses. Although disturbances will continue to be important drivers of ecosystem dynamics, they will concurrently occur with chronic resource alterations. Thus, a more comprehensive understanding of how this scenario will impact ecosystem dynamics is needed. Our study is part of a global drought network of experiments (DroughtNet) which assesses the sensitivity of grasslands and forests worldwide to imminent drought. In Central Oklahoma, at Kessler Atmospheric and Ecological Field Station, we used rain interception shelters or rain water addition to impose a gradient of precipitation treatments (chronic disturbance) at +50%, 0%, -20 %, -40 %, -60 %, -80%, -100% (n=3 and N=21) and an aboveground biomass clipping treatment (acute disturbance) in a fully factorial design. We asked the following questions: (1) Do acute and chronic disturbances interact to alter species-specific traits and relative abundance? (2) Do concurrent acute and chronic disturbances influence community-level above- and belowground traits and compositional similarity? To answer these questions, we quantified above- and belowground traits, as well as plant species composition across our experimental plots.
Results/Conclusions
After one year of experiment, we found no differences between plant species composition under acute and chronic disturbance compared with ambient plots. To explore responses of plant community traits, we used species-specific foliar cover and species-specific leaf area (SLA) for six commonly occurring plant species to calculate community-weighted means (CWM). Similarly to species composition, community SLA did not changed in precipitation or clipping manipulations. Alternately, we found that the clipping but not the drought treatments, promote specific root length (SRL) at shallow (0-15cm) but not deeper soils (15cm-45cm). Taken together, climate-induced shifts in plant community composition will likely modify or counteract the direct impact of climate change on prairie ecosystem functioning. These indirect effects should be considered when predicting the manner in which global change will alter ecosystem functioning. Our data also emphasize the need to investigate further above- and belowground functional traits that are likely to shift under natural and chronic disturbances, as well as taking into account more number of species in order to better understand the response of the system to environmental changes.