Effects of dead tree removal on the resilience and successional trajectory of high-mortality forests
Primary Investigator: Rebecca Wayman
Project Partners: Jim Quinn, Ph.D.; Carrie Levine; Hugh Safford, Ph.D.
Institution: University of California, Davis
Project Type: Demonstration State Forests
Grant Award #8GG18801; 8GG20800
Amount awarded: $457,596
Award Date: September 2018
A recent severe native bark beetle epidemic in the Sierra Nevada resulted in widespread tree mortality on an unprecedented scale, yet the factors affecting ecosystem recovery from such a disturbance are not well understood. Resource managers are tasked with prioritizing limited funding for restoration treatments in preparation for or recovery from this and other disturbances. In an era of predicted increases in drought and temperature stress and related fire and insect disturbances, ecosystem resilience, or the ability of a system to recover from disturbance, is of central importance to such management decisions.
Our proposed study compares the post-disturbance management practice of dead tree removal to no treatment following severe drought and insect-induced tree mortality in the Sierra Nevada. We are evaluating effects on ecosystem resilience from four perspectives: 1) carbon balance, 2) tree regeneration and successional trajectories, 3) fuels and implications for future fire, and 4) understory plant communities. Ecosystem resilience can be defined differently depending on recovery goals, but our project aims to provide management with information key to assessing whether specific recovery goals are likely to be met under different post-disturbance management scenarios.
In 2020, we collected vegetation, fuels, and soils data on 90 paired plots (treated through dead tree removal and untreated) at Mountain Home Demonstration Sate Forest and on the Stanislaus, Sierra, and Sequoia National Forests. In 2021 we will conduct additional paired plot sampling. Our analyses will aim to answer the following questions:
1) Do treated and untreated stands have significantly different carbon balance in key carbon pools (live biomass, standing dead and downed wood, soil organic layer and mineral soil)? Do treated and untreated stands show different trajectories and rates of recovery from carbon source to carbon sink after disturbance?
2) Does the removal of standing dead trees, along with associated ground disturbance and increases in light levels, alter patterns of advanced (established pre-treatment) and/or post-treatment tree regeneration as compared to untreated stands, and do effects differ by species? Are shrub abundance and cover associated with differences in patterns of tree regeneration between treated and untreated stands?
3) How do treated and untreated stands differ in canopy and surface fuel loading?
4) Does the removal of standing dead trees, along with associated ground disturbance and increases in light levels, alter native and non-native understory plant species richness and diversity, composition, and cover as compared to untreated stands?
We hope to also answer these questions over the longer term by resampling our permanent plots on 5-year intervals if funding allows.