Bark Beetle Study

Examining Bark Beetle Attack in Giant Sequoias

Ancient Forest Society is leading a two-year study examining bark beetle attack in giant sequoia trees in collaboration with scientists from Colorado State University. The study is funded by the CAL FIRE Forest Health Research Program and will take place in four different locations: Calaveras Big Trees State Park, Yosemite National Park, Sequoia National Park and Mountain Home Demonstration State Forest.

Giant sequoia is a globally unique species cherished for its size, beauty, cultural significance, and ecological importance. However, a native phloem-feeding bark beetle, Phloeosinus sp., appears to have played a role in the recent death of dozens of mature sequoia trees weakened by fire and drought. This poorly understood phenomenon has never previously been observed and suggests that beetle attack may pose a significant novel threat to these iconic trees. There is therefore an urgent need to increase our knowledge of the ecological and physiological mechanisms underpinning sequoia tree interactions with Phloeosinus beetles to develop effective conservation strategies for sequoia groves.

Our research team has worked to document beetle activity in sequoia tree crowns and understand the basic biology of Phloeosinus colonizing these trees. Over the past three years we have developed new knowledge of Phloeosinus ecology and distribution, including key details about the taxonomy and life history that are important for management. While we have been investigating giant sequoia-beetle interactions for several years, linking beetle biology with tree physiology and defenses is the next critical research step.

The primary goal of this project is to investigate fundamental interactions between beetle biology, tree ecophysiology, and defense against attack. We will combine ground and canopy surveys, measurements of tree water and carbon relations and defensive traits, and basic entomology experiments to describe Phloeosinus developmental thresholds, movement in the canopy, and responses to tree physiology in the context of environmental water stress. The study will monitor and compare the physiological status of healthy trees, trees that show signs of stress but live, and trees that die. We will also test whether drones can be used to evaluate beetle activity in sequoias by comparing in-crown observations by tree climbers with concurrent drone imagery.

The resulting datasets will enhance our understanding of sequoia tree response to beetle attack and be used to develop models to predict the probability of Phloeosinus occurrence in sequoia trees based on tree condition, location, and environmental conditions. Our integrated approach will provide novel insights into the relationships between giant sequoia trees and Phloeosinus beetles to inform management strategies aimed at conserving giant sequoia ecosystems in a changing climate.