Press–pulse interactions: effects of warming, N deposition, altered winter precipitation, and fire on desert grassland community structure and dynamics

Abstract

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.

Sensitivity of plant species to warming and altered precipitation dominates the community productivity in a semiarid grassland on the Loess Plateau

“…However, though warming negatively affected soil moisture ( Figure 6), warming did not significantly decreased community ANPP in our study. This contrasts with the results of many other studies in which warming either increased (Collins et al, ;Cowles, Wragg, Wright, Powers, & Tilman, 2016;Wu, Dijkstra, Koch, Peñuelas, & Hungate, 2011) or decreased (Rustad et al, 2001) aboveground plant biomass. Similar to the warming effect, precipitation reduction also decreased soil moisture but did not change community ANPP, which was again different from results from most previous studies (Hoover, Knapp, & Smith, 2014;Reichmann & Peters, 2013).…”

“…In a previous study, Zavaleta, Shaw, Chiariello, Mooney, and Field () reported that global changes affected plant species richness primarily driven by changes in forbs richness. Collins et al () found that warming significantly increased biomass of forbs after a wildfire. These results, together with our findings, suggested that forbs were likely to be highly sensitive to environmental changes and were decreased primarily by drought.…”

The combined effects of an extreme heatwave and wildfire on tallgrass prairie vegetation

“…Our results support the idea that multiple perturbations are more likely to result in state changes (Paine et al., ). For instance, wildfire in the Chihuahuan desert altered the response to ongoing experimental warming and precipitation manipulations (Collins et al., ) and following experimental warming in shrublands across Europe, recently disturbed areas experienced greater vegetation loss than undisturbed areas (Kröel‐Dulay et al., ). Similar synergistic relationships between climate extremes and disturbance have been proposed for ecosystems ranging from semi‐arid woodlands (Allen & Breshears, ) to tropical forests (Brando et al., ; Staal et al., ) and coral reefs (Mumby, Wolff, Bozec, Chollett, & Halloran, ).…”

Minimal mortality and rapid recovery of the dominant shrub Larrea tridentata following an extreme cold event in the northern Chihuahuan Desert

“…Winter climate is influential in many ecosystems (Ladwig et al., ) and experimental manipulations help examine the response of ecological systems to changing winter conditions (Kreyling, ). Snow manipulations test for the ecological consequences of altered winter precipitation (Kreyling, Haei, & Laudon, ; Loik, Griffith, & Alpert, ), and warming manipulations track ecosystem changes following gradual increases in temperature (Collins et al., ; Wu, Dijkstra, Koch, Penuelas, & Hungate, ), yet our understanding of the response of plant communities to winter climate extremes is often limited to opportunistic studies following extreme climate events, as large‐scale cooling experiments are generally not practical. For example, ice storms in hardwood forests can temporarily increase canopy openness and shift community composition based on species shade tolerance (Arii & Lechowicz, ; Rhoads et al., ; Shao, Huang, Liu, Kuang, & Li, ; Weeks, Hamburg, & Vadeboncoeur, ).…”