ECOSTRESS And EMIT Applications In Thinned and Non-Thinned Semi-Arid Forests

Southwestern US forests are experiencing increasing wildfire activity and regional drought. To reduce the wildfire risks, land managers are implementing large-scale forest thinning treatments. We quantify the impacts of semi-arid ponderosa pine forest thinning treatment and regional drought on ECOSTRESS land surface temperature (LST) and evapotranspiration (ET) during spring seasons when the study region experiences a dry period and plant water stress is heightened. Our study period at a northern Arizona study site included an average precipitation year, 2019, followed by a regional drought period of 2020-2022, and a record winter snowfall year 2023. Our results demonstrate significant impacts from forest thinning, regional drought, and their interaction on ECOSTRESS LST data. Consistent with high-resolution UAV thermal images, ECOSTRESS LST indicate that the thinned forest had greater temperature (2-5°C greater mean LST) across years. During the regional drought period, ECOSTRESS LST increased in both thinned and non-thinned forests by up to 10°C and then declined in 2023. ECOSTRESS ET was similarly impacted by forest thinning and regional drought. Consistent with in situ ET measurements, ECOSTRESS ET was significantly greater in the non-thinned forest compared to the thinned forest across years, but significantly decreased during drought period in both forests. Our results indicate both ECOSTRESS LST and ET data are sensitive to regional drought and thinning impacts in semi-arid ponderosa pine forests. Our analysis of more recently launched EMIT hyperspectral-derived moisture indices indicate that EMIT trends are not consistent with ECOSTRESS ET data or ground-based hyperspectral-derived moisture indices.