Using Fire Return Interval Departure (FRID) Analysis to Map Spatial and Temporal Changes in Fire Frequency on National Forest Lands in California

摘要

In California, fire regimes and related ecosystem processes have been altered by land use practices associated with Euro-American settlement, and climate warming is exacerbating the magnitude and effects of these changes. Because of changing environmental baselines, restoration of narrowly defined historical conditions may no longer be an attainable or sustainable long-term management goal, but comparisons between historical and current fire regimes can assist managers in prioritizing areas for ecological restoration and other management actions. Fire return interval departure (FRID) analysis quantifies the difference between current and presettlement fire frequencies. We assessed FRID variability along geographic, climatic, and vegetation gradients in California on lands managed by the U.S. Department of Agriculture Forest Service and three forest-dominated national parks, using two types of FRID metrics: percent FRID (PFRID), and the NPS-FRID index. Much of northern California north of the Tehachapi Mountains has missed multiple fire cycles owing to fire suppression, while southern California is characterized by large areas burning at higher frequencies than under presettlement conditions. PFRID exhibited a unimodal (hump-shaped) relationship to elevation across our study area.