Press-pulse interactions: effects of warming, N deposition, altered winter precipitation, and fire on desert grassland community structure and dynamics.
Global environmental change is altering temperature, precipitation patterns, resource availability, and disturbance regimes. Theory predicts that ecological presses will interact with pulse events to alter ecosystem structure and function. In 2006, we established a long-term, multifactor global change experiment to determine the interactive effects of nighttime warming, increased atmospheric nitrogen (N) deposition, and increased winter precipitation on plant community structure and aboveground net primary production (ANPP) in a northern Chihuahuan Desert grassland. In 2009, a lightning-caused wildfire burned through the experiment. Here, we report on the interactive effects of these global change drivers on pre- and postfire grassland community structure and ANPP. Our nighttime warming treatment increased winter nighttime air temperatures by an average of 1.1 °C and summer nighttime air temperature by 1.5 °C. Soil N availability was 2.5 times higher in fertilized compared with control plots. Average soil volumetric water content (VWC) in winter was slightly but significantly higher (13.0% vs. 11.0%) in plots receiving added winter rain relative to controls, and VWC was slightly higher in warmed (14.5%) compared with control (13.5%) plots during the growing season even though surface soil temperatures were significantly higher in warmed plots. Despite these significant treatment effects, ANPP and plant community structure were highly resistant to these global change drivers prior to the fire. Burning reduced the cover of the dominant grasses by more than 75%. Following the fire, forb species richness and biomass increased significantly, particularly in warmed, fertilized plots that received additional winter precipitation. Thus, although unburned grassland showed little initial response to multiple ecological presses, our results demonstrate how a single pulse disturbance can interact with chronic alterations in resource availability to increase ecosystem sensitivity to multiple drivers of global environmental change.
Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM, 87131, USA.
Scott L
SL
Collins
Department of Zoology, University of Wisconsin, 430 Lincoln Drive, 545 Birge Hall, Madison, WI, 53706, USA.
Laura M
LM
Ladwig
Department of Botany, University of Wyoming, Laramie, WY, 82071, USA.
Matthew D
MD
Petrie
Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM, 87131, USA.
Sydney K
SK
Jones
Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM, 87131, USA.
John M
JM
Mulhouse
Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM, 87131, USA.
James R
JR
Thibault
Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM, 87131, USA.
William T
WT
Pockman
D003889:Desert Climate; D017753:Ecosystem; D005390:Fires; D065948:Grassland; D006109:Poaceae; D011891:Rain; D012621:Seasons; D012987:Soil
D012987:Soil

Bouteloua eriopoda
; 
Bouteloua gracilis
; aboveground net primary production; desert grassland; fire; nighttime warming; nitrogen addition; soil moisture; species richness