Strong N and P co-limitation constrains post-fire community composition and productivity in arctic tundra.

Abstract:

Successional post-fire trajectories in arctic tundra vary greatly with some ecosystems rapidly recovering and productivity and others experiencing shifts towards increased shrub cover. The main causes of these different trajectories remain poorly understood, but are hypothesized to be controlled by post-fire nutrient availability. Here we monitored the decadal (1-12 years post-fire) recovery of productivity, via eddy covariance C fluxes, and community composition at a Severely- and Moderately- burned tundra site within the largest tundra fire on the North Slope, the 2007 Anaktuvuk River fire. We found significant shifts in vegetation composition and productivity that were dependent on burn severity with larger increases in productivity and shrub cover at the Severely burned site. In post-fire years 9-12, we implemented a multi-factorial nitrogen (N), phosphorus (P), and nitrogen+phosphorus (N+P) addition experiment at the Severely and nearby Unburned site to understand these shifts further. Both Severely- and Unburned- tundra demonstrated strong co-limitation with increased shrub cover and ecosystem productivity in the N+P addition plots after 3 years of fertilization. N- and P- addition alone provided no significant changes in community composition or productivity at either site. Unburned N+P addition plots resembled control plots at the Severely burned site, indicating that community and productivity changes at the Severely burned site were driven by increased post-fire N and P availability. These results highlight the importance of nutrient availability and N and P co-limitation in driving post-fire successional trajectories in arctic tundra.