Abstract

The frequency, magnitude, and size of forest disturbances are increasing globally. Much recent research has focused on how the occurrence of one disturbance may affect susceptibility to subsequent disturbances. While much has been learned about such linked disturbances, the strength of the interactions is likely to be contingent on the severity of disturbances as well as climatic conditions, both of which can affect disturbance intensity and tree resistance to disturbances. Subalpine forests in western Colorado were affected by extensive and severe wildfires in the late 19th century and an extensive and severe outbreak of spruce beetle (Dendroctonus rufipennis) in the 1940s. Previous research found that most, but not all, of the stands that burned and established following the late 19th century fires were not susceptible to the 1940s outbreak as beetles preferentially attack larger trees and stands in advanced stages of development. However, previous research also left open the possibility that some stands that burned and established following the 19th century fires may have been attacked during the 1940s outbreak. Understanding how strongly stand structure, as shaped by disturbances of varying severity, affected susceptibility to past outbreaks is important to provide a baseline for assessing the degree to which recent climate change may be relaxing the preferences of beetles for larger trees and for stands in latter stages of structural development and thereby changing the nature of linked disturbances. Here, dendroecological methods were used to study disturbance history and tree age of stands in the White River National Forest in Western Colorado that were identified in historical documents or remotely-sensed images as having burned in the 19th century and having been attacked by spruce beetle in the 1940s. Dendroecological reconstructions indicate that in young post-fire stands only old remnant trees that survived the otherwise stand-replacing fires were killed in the 1940s outbreak. No young post-fire trees (< ca. 128 years) were susceptible to the 1940s outbreak, implying that under the relatively cool and wet conditions of the mid-20th century, susceptibility to and spatial patterns of spruce beetle outbreak were most likely controlled by variations in severity of prior disturbance by fire. This study provides a baseline for comparing linked disturbances under the relatively warmer and drier conditions of recent (e.g. post-1990) outbreaks in order to assess how climate mitigates the degree to which pre-disturbance history and structure affect susceptibility to disturbances.

Highlights

  • Disturbances such as wildfires and insect outbreaks are key drivers of the spatiotemporal patterns and processes of forest ecosystems

  • No young post-fire trees (< ca. 128 years) were susceptible to the 1940s outbreak, implying that under the relatively cool and wet conditions of the mid-20th century, susceptibility to and spatial patterns of spruce beetle outbreak were most likely controlled by variations in severity of prior disturbance by fire

  • Because the importance of pre-disturbance vegetation conditions on susceptibility to disturbances is theoretically expected to decrease as the intensity of subsequent disturbance increases, the strength of interactions among disturbances is likely to change as climatically-driven disturbances become more intense under climate change

Read more

Summary

Introduction

Disturbances such as wildfires and insect outbreaks are key drivers of the spatiotemporal patterns and processes of forest ecosystems. Because the importance of pre-disturbance vegetation conditions on susceptibility to disturbances is theoretically expected to decrease as the intensity of subsequent disturbance increases, the strength of interactions among disturbances is likely to change as climatically-driven disturbances become more intense under climate change. To assess such potential climatically-driven changes in disturbance interactions it is important to establish a clear baseline of how disturbances have interacted under less extreme climatic conditions. To provide baseline comparisons with disturbance interactions occurring under the warmer, drier climate of the early 21st century in western Colorado [8,9], here we assess how variability in high-severity fires affected susceptibility to an outbreak of spruce beetle (Dendroctonus rufipennis) in the 1940s in western Colorado

Methods
Results
Discussion
Conclusion

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.