Western Spruce Budworm Effects on Forest Resilience

Area of Science:

• Forestry
• Ecology
• Entomology

Background:

• Western spruce budworm (Choristoneura freemani) is a major forest pest in the western US.
• Northern New Mexico experienced severe outbreaks from the 1980s to 2010s, causing substantial tree mortality.
• Impacts on forest stand dynamics in the US Southwest remain understudied.

Purpose of the Study:

• To investigate the effects of western spruce budworm outbreaks on forest stand dynamics.
• To analyze impacts across elevational and defoliation intensity gradients.
• To inform forest management and resilience strategies in the US Southwest.

Main Methods:

• Studied stand conditions (size structure, species composition, damaging agents) along elevational and defoliation gradients.
• Assessed overstory and understory characteristics.
• Identified western spruce budworm as the primary damaging agent.

Main Results:

• Western spruce budworm caused mortality across all size classes, especially in spruce-fir stands.
• Spruce-fir stands exhibited unsustainable mortality rates and a shift towards non-host species.
• Mixed-conifer stands showed a transition to non-host species, potentially increasing resilience.

Conclusions:

• Spruce-fir stands face a potential lack of resilience due to high mortality and low regeneration.
• Mixed-conifer stands may have enhanced resilience to future western spruce budworm outbreaks.
• Understanding these dynamics is crucial for managing western US forests.