Northern Arizona University Flagstaff, AZ, United States
Background/Question/Methods
Altered fire regimes and a warming climate in the southwestern U.S. have the potential to impact recovery of forest understory community composition and ecosystem function following wildfire Trait-based plant ecology provides a means of assessing the impacts of varying levels of disturbance on community composition and ecosystem function and can be used to understand trajectories of recovery following uncharacteristically severe wildfire. We quantified the effects of increasing burn severity and experimental climate warming on a key ecosystem function and three plant functional traits (PFTs) over the first two post-fire years in a northern Arizona Pinus ponderosa forest understory. We asked the following research questions: 1) How do burn severity and warming influence decomposition rates over time? 2) How do burn severity and warming affect community composition and plant functional trait (specific leaf area (SLA), leaf dry matter content (LDMC), and plant height) diversity over time? 120 plots were established along a burn severity gradient including unburned, low, and high severity burn areas. Open-top warming chambers were employed to produce ~1.2°C of warming in 2020, 10 months after the initial fire. Trait and function data were collected in Fall 2020 and 2021.
Results/Conclusions
Composition of the plant community differed between burn severities in both year one and year two. We found that the combination of experimental warming and high burn severity significantly affected decomposition rate (F(2,73) = [3.475], p = 0.036) and community-weighted mean (CWM) LDMC (H (5) = 15.4, P = 0.0086) in the first year post-fire. Trait expression and decomposition rates had converged by the second year across the burn severity gradient and with experimental warming. CWM SLA was significantly lower in high severity plots in year one post-fire (H (2) = 9.75, P = 0.007), but this effect was no longer apparent after the second year of recovery. High burn severity alone did result in lower CWM LDMC (H (2) = 66.9, P < 0.0001) in year two. Our results suggest that trait expression and decomposition are impacted by both fire severity and warming shortly following the initial burn, but that trait expression and function rapidly converge across this gradient and in the presence of experimental warming despite significantly different community composition.
