Impacts of insect-driven tree mortality on land-surface water and energy exchanges

Insect-driven forest disturbances are important contributors to tree mortality and biomass losses in temperate and boreal regions. With the rising temperatures and shifting precipitation patterns, insect induced tree mortality is expected to increase in many regions. Insect outbreaks not only influence tree cover and carbon stocks, but , through their impact on tree functioning, also influence land-atmosphere exchanges of water and energy, which in turn can impact atmospheric properties. While insect outbreaks can impact very large regions, most observational studies focus on small regions and individual events.

 

Here, we aim to provide an observation-based regional synthesis of the impact of insect-driven tree mortality on land-atmosphere water and energy exchanges, focusing on western USA. For this, we analyse satellite-based data (MODIS) on evapotranspiration (ET), albedo, land-surface temperature (LST) and snow cover for insect-affected regions between 2001-2022. Preliminary results indicate an increase in summer LST in areas affected by more severe insect-driven tree mortality, along with a decrease in ET, compared to the years before the mortality events. These differences can be partly explained by reduced snow cover in winter, which contributes to decreased winter albedo in insect-affected areas. These effects are not only limited to the outbreak event, but also show persistent trends in the subsequent years.