, Volume 19, Issue 8, pp 1478–1490 | Cite as

Litter Chemistry, Community Shift, and Non-additive Effects Drive Litter Decomposition Changes Following Invasion by a Generalist Pathogen



Forest pathogens have strong potential to shape ecosystem function by altering litterfall, microclimate, and changing community structure. We quantified changes in litter decomposition from a set of distinct diseases caused by Phytophthora ramorum, an exotic generalist pathogen. Phytophthora ramorum causes leaf blight and increased litterfall %N, but no mortality on California bay laurel (Umbellularia californica), a common overstory tree that accumulates high levels of infection. Lethal twig and bole cankers on tanoak (Notholithocarpus densiflorus) lead to the disease sudden oak death which creates canopy openings and alters litterfall in mixed-species forests dominated by redwood (Sequoia sempervirens) which is minimally susceptible. Species identity had the greatest effect on mass loss and N dynamics with the most rapid rates in bay laurel, slowest in redwood, and intermediate in tanoak. Decomposing litter from infected sources had increased N accumulation, and although these changes were of lower magnitude relative to species identity, the region-scale invasion of P. ramorum suggests that this effect could occur over an extensive area. Canopy mortality was a significant and slowing influence on litter N dynamics in all species and also dampened non-additive effects within mixed litter bags. Redwood—the lowest quality litter—demonstrated non-additive interactions with consistently lower C:N when decomposed in mixed litter bags, but this effect did not alter the entire mixture. Mortality and subsequent changes in community composition have the greatest magnitude effects on litter decomposition for sudden oak death, but our study implies that different and sometimes cryptic mechanisms will drive decomposition changes for other forest diseases.


Phytophthora ramorum sudden oak death tanoak California bay laurel tree mortality forest disease ecosystem function carbon nitrogen 



We thank H. Mehl and C. Shoemaker for their field and laboratory support of this research. We thank J. Ashander and S. Ibanez for feedback on the statistical analysis and Gary Lovett and two anonymous reviewers for helpful comments on earlier versions of this manuscript. We are grateful to the California State Parks and the Marin Municipal Water District for facilitating this research on their lands. This work was funded by NSF Grant DEB EF-0622770 as part of the joint NSF-NIH Ecology of Infectious Disease program, the Gordon and Betty Moore Foundation, and the USDA Forest Service Pacific Southwest Research Station.

Supplementary material

10021_2016_17_MOESM1_ESM.pdf (557 kb)
Supplementary material 1 (PDF 557 kb)


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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  1. 1.Department of Plant PathologyUniversity of CaliforniaDavisUSA

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