Comparing burn severity and solar radiation exposure as control mechanisms on vegetation regrowth patterns following the 2017 Eagle Creek - Columbia River Gorge wildfire

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Diane Carrico, Environmental Science, Oregon State University, Corvallis, OR

Background/Question/Methods
The Eagle Creek Fire began on September 2, 2017 and was 100% contained on November 30, 2017. The fire included 48,861 acres of land dominated by evergreen forests, cost approximately $20 million in damages, and received limited post-fire rehabilitation interventions. The objective of this project is to compare burn severity and solar radiation exposure as control mechanisms on post-fire vegetation regrowth patterns within the burn zone. The time frame will span four (4) years from 2017 to 2020. Google Earth Engine will be used to analyze the Normalized Difference Vegetation Index (NDVI), Normalized Burn Ratio (NBR), and Continuous Heat-Insolation Load Index (CHILI) of the region. NDVI will be analyzed annually via remote sensing tools during the Summer months, CHILI data will be based upon a fixed position of the sun, and NBR data will be based upon pre and post fire imaging specific to this wildfire event.
Land features will be divided into Primary features with Secondary features comprising some smaller element of a Primary feature. The burned region was heavy along the north-northwest oriented primary valley west of Eagle Creek Trail, the slope east of the Eagle Creek Trail, and neighboring primary valleys southwest of this area. Primary ridgelines trend to more severe burns on eastern slopes relative to western slopes. The topography of the area is rugged and composed of a series of ridges and valleys that receive varied exposure to solar radiation. I hypothesize that vegetation recovery will be predominantly controlled by exposure to solar radiation while burn severity contributes to overall recovery to a lesser extent.
Results/Conclusions
The vegetation regrowth patterns on secondary features are predominantly oriented in a north versus south slope orientation rather than fixed upon an east versus west slope orientation. Regrowth on primary features are predominantly oriented in an east versus west orientation. NDVI values near -1 (indicative of water) appear on large swaths of some slopes. Primary north-south oriented valleys have low NDVI values (indicating reduced growth), but higher values on primary ridgelines. Regrowth on northern and southern secondary slopes are varied, based upon orientation alone, and defined by secondary ridgelines. Primary eastern slopes show more dominant regrowth than corresponding western slopes and appear defined by ridgelines. There is revegetation in most areas with the most prominent growth between 2018 and 2019. Cooler regions indicated in the CHILI data overarchingly align with low NDVI values and lack of regrowth.