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Evaluating spatial patterns of drought-induced tree mortality in a coastal California pine forest

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Title Evaluating spatial patterns of drought-induced tree mortality in a coastal California pine forest
Names Baguskas, Sara A. (creator)
Peterson, Seth H. (creator)
Bookhagen, Bodo (creator)
Still, Christopher J. (creator)
Date Issued 2014-03 (iso8601)
Note This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/forest-ecology-and-management/.
Abstract In a coastal, fog-influenced forest on Santa Cruz Island in southern California, we
observed mortality of Bishop pine (Pinus muricata D.Don) trees following a brief (2 year), yet
intense, drought. While anecdotal evidence indicates that drought-induced Bishop pine mortality
has occurred in the past in the stand we studied, this is the first attempt to capture the spatial
distribution of mortality, and begin to understand the environmental drivers underlying these
events. We used high spatial resolution remote sensing data to quantify the spatial extent of tree
mortality using a 1 m true color aerial photograph and a 1 m LiDAR digital elevation model. We
found the highest density of dead trees in the drier, more inland margins of the forest stand. We
used the Random Forest decision tree algorithm to test which environmental variables (e.g.,
summertime cloud frequency, solar insolation, and geomorphic attributes) would best separate
live and dead tree populations. We also included tree height as a variable in our analysis, which

we used as a proxy for overall tree 24 size and potential rooting distribution. Based on the Random
Forest analysis, we generated a map of the probability of survival. We found tree survivorship
after drought was best explained by the frequency of summertime clouds, elevation, and tree
height. Specifically, survivorship was greatest for larger trees (~8-10 m tall) in more foggy parts
of the stand located at moderate elevation. We found that probability of survival was lowest at
the inland extent of the stand where trees occur at the upper limit of their elevation range (~400
m). The coexistence of these main factors with other landscape variables help identify areas of
suitable habitat for Bishop pines across the stand, and extend our understanding of this species’
distribution.
Genre Article
Topic Tree mortality
Identifier Baguskas, S. A., Peterson, S. H., Bookhagen, B., & Still, C. J. (2014). Evaluating spatial patterns of drought-induced tree mortality in a coastal California pine forest. Forest Ecology and Management, 315, 43-53. doi:10.1016/j.foreco.2013.12.020

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