During the 2011-2017 drought, bark beetles killed millions of trees across California burrowing through their bark and laying their eggs in the trees’ cambium. Warming caused by climate change has helped these beetle populations survive through the winter and quickly reach maturity. This warming, coupled with drought, has created the perfect environment for these beetles to thrive, since they are most likely to attack drought-stressed trees. The red turpentine beetle (Dendroctonus valens) infests pines native to the Eastern Sierra. Typically, unlike other Dendroctonus species, red turpentine beetles do not kill their host trees which gives us a unique opportunity to use dendrochronology to study past outbreaks in a monospecific Pinus jeffreyi stand. At our study site, we investigated the spatial scale of the Dendroctonus valens infestation as well as the interacting causes of tree mortality, including fire intensity and tree size. We used tree survey data collected from Indiana Summit (37° 48′ 13.2″ N, 118° 54′ 16.2″ W) and O’Harrell Canyon (37° 45′ 54.2″ N, 118° 44′ 07.8″ W) in 2018, and a dendrochronological reconstruction of the two stands using 129 Pinus jeffreyi cores collected in 2018 and 2019 to analyze the effects causes of mortality and decreased growth rates in this stand.
Results/Conclusions
Evidence of red turpentine beetle was found in trees at both Indiana Summit and O’Harrell Canyon. The percentage of trees with beetles at each site was 4.03% (N=541) at Indiana Summit and 1.99% (N=251) at O’Harrell Canyon. At Indiana Summit 9.73% (N=185) of dead trees had evidence of beetle infestation, while none of dead trees (N=20) had evidence of beetle infestation at O’Harrell Canyon. We used a logistic regression to determine traits that predict tree mortality in this system. We found that smaller trees’ DBH (p = 2e-16), larger scorch heights (p = 7.24e-12), and evidence of beetle infestation (p = 0.00266) were all significant predictors of tree mortality. The joint effect of scorch height and beetle presence was marginally significant as a predictor of tree mortality (p = 0.09058). This suggests that there are likely other variables that predict tree mortality in combination with beetles, tree size, and fire intensity, such as competition amongst trees. Further dendrochronological analysis will be done in order to assess the temporal aspect of beetle infestations in this stand.