Dead tree removal after drought mortality increases diversity at multiple scales.

Background/Question/Methods

: Climate change is increasing the severity and duration of drought in several arid and semi-arid regions globally requiring rapid adaptation to novel conditions. As land managers develop strategies to adapt, thye must be careful to a minimize the ecological impacts of new management approaches. Between 2014-2017, California experienced an exceptionally severe drought resulting in the mass mortality of over 100 million forest trees of Sierra Nevada. This widespread tree mortality elevates forest fuels increasing fire risk in an already fire-prone region. To adapt to climate-driven mortality, managers can cut and remove dead trees to reduce fuel loads. While selective harvesting is not a new strategy, the conditions created by severe drought mortality creates novel conditions to test for their ecological impacts, especially on understory plant diversity. In this study, we established 63 pairs of 400 m2 plots across a 200-mile span of Sierra Nevada to study the impacts of dead tree removal on plant diversity.

Results/Conclusions

: We found that local species density increases 16% after dead tree removal (p < 0.001) driven primarily by increases in forbs and shrubs. Plant evenness was not impacted by dead tree removal (p = 0.48). Across all plots we found 20% more species where dead trees were removed. Additionally, dead tree removal resulted in the increase in abundance of a suite of species and a corresponding loss for others. Overall, we concluded that dead tree removal does not negatively impact local diversity, and increases diversity across a larger scale, likely, by opening up microsites and changing local conditions that favor increased establishment of new species.