Quantifying succession and ecosystem service recovery in California’s altered wildfire regime

Abstract:

Wildfire has the potential to greatly modify the short- and long-term fluxes of greenhouse gases between the land surface and the atmosphere, impacting the provisioning of ecosystem services from natural lands upon which society relies. California is at the epicenter of these challenges – experiencing 15 of its 20 largest recorded fires in the last two decades. While historically low-intensity, frequent fires in California’s dry forests may have been nearly in equilibrium with climate, contemporary perturbations could result in wildfire emissions that are not fully compensated for by regeneration, posing new challenges in accounting for net fire and land sector carbon emissions.

To understand the complete biogeochemical impacts of a changing fire regime, and the net benefit of management strategies that avoid or lessen the severity of wildfires, we need to better characterize the multi-decadal regeneration of ecosystem services after fire. Here we quantify the impacts on carbon uptake associated with larger, more severe fires in California. We apply a chronosequence of more than three decades of medium-resolution remote sensing vegetation indices to ask: 1) What is the magnitude and spatial arrangement of primary productivity changes associated with fires in California? and 2) How long does it take for burned areas to recover carbon uptake capacity?

Across more than 2000 forest fires that occurred over the last four decades, we find significant changes in important ecosystem services and recovery trends. Changes in gross primary productivity, derived by scaling Landsat near infrared reflectance with eddy covariance tower measurements, indicate that the average fire area’s productivity is reduced by ~6% the year following fire, with mean recovery to pre-fire conditions occurring after a quarter decade. The highest severity and largest fires led to a 31% and 21% productivity deficit in the first year after fire, and recovered at different rates. Understanding how disturbances like fire influence the state’s ability to take up CO₂ in natural and working lands will be paramount to weighing the costs and benefits associated with fire management strategies like fuels reduction, and constraining the potential for meaningful carbon sequestration in natural and working lands in the decades ahead.