Snow cover variables (snow cover frequency and snow disappearance date), along with elevation, were shown to be secondary but significantly influential explanatory variables for revegetation in the Oregon and Washington Cascades. Summer precipitation consistently appeared as the most important variable driving post‐fire revegetation across all four subregions. To assess the importance of snow cover for revegetation compared to other climatic, topographic, and burn severity‐related variables, binary regression tree models were constructed for the dominant pre‐fire conifer species within each of the four PNW subregions. We analyzed 24 high severity wildfires across four distinct PNW mountainous subregions, examining snow‐vegetation relationships for two years pre‐fire and four years post‐fire. Documented climate warming trends across the PNW include increasing wildfire frequency and severity and an increasingly ephemeral snowpack, especially at moderate elevations. Isolating patterns and drivers of evergreen recovery from deciduous recovery will enable improved characterization of forest ecological condition across large spatial scales.įorested, mountain landscapes in the Pacific Northwest (PNW) are changing at an unprecedented rate, largely due to shifts in the regional climate regime. This study is the most extensive effort, to date, to track postfire forest recovery across the western United States. SCS NDVI recovery rates were best explained by aridity and growing degree days. GS rates of NDVI recovery were best predicted by burn severity and anomalies in postfire maximum temperature. We found plots with conifer saplings had significantly higher SCS NDVI recovery rates relative to plots without conifer saplings, while plots with ≥50% grass/forbs/shrubs cover had significantly higher GS NDVI recovery rates relative to plots with <50%. Points were partitioned into faster and slower rates of NDVI recovery using thresholds derived from field plot data (n = 230) and their associated rates of NDVI recovery. Rates of postfire NDVI recovery were calculated for both the GS and SCS for more than 12,500 burned points across the western United States.
We sought to (1) characterize patterns in the rate of postfire, dual-season Normalized Difference Vegetation Index (NDVI) across the region, (2) relate remotely sensed patterns to field-measured patterns of re-vegetation, and (3) identify seasonally specific drivers of postfire rates of NDVI recovery.
In this analysis, we used Landsat imagery collected when snow cover (SCS) was present, in combination with growing season (GS) imagery, to distinguish evergreen vegetation from deciduous vegetation. However, information characterizing postfire recovery patterns and their drivers are lacking over large spatial extents. Postfire shifts in vegetation composition will have broad ecological impacts.
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