MSA - Ecology/Pathology
Hawkins, Ashley , Henkel, Terry W. .
Native fungal pathogens may facilitate persistence of Douglas fir in late-seral Abies concolor/Pseudotsuga menziesii forests of Northern California.
In native forests fungal and other biotic pathogens can accelerate tree decline and turnover rates, increase stand structural heterogeneity, and alter tree community composition. In northern California, white fir (Abies concolor) and Douglas fir (Pseudotsuga menziesii) are co-occurring coniferous canopy tree species that exhibit different degrees of shade tolerance and regenerative abilities following disturbance. In the absence of fire, the shade-tolerant A. concolor will eventually succeed the shade-intolerant P. menziesii. Initial field observations in the Six Rivers National Forest suggested that in late-seral stands of A. concolor/P. menziesii tree decline and mortality was accelerated in A. concolor. In this study, we asked whether native forest pathogens are having disproportional impacts on A. concolor. Biotic and abiotic agents of disturbance were sampled in late-seral A. concolor/P. menziesii stands in northwestern California to assess their roles in tree mortality, gap formation, and regeneration. In three study sites ranging from 4-10 ha we sampled relative abundances and size class distributions of A. concolor and P. menziesii, determined presence and impacts of pathogens including root, butt, and stem rot fungi and dwarf mistletoes, and estimated agents of mortality in dead trees. Canopy gaps occurring in the sites, along with an equivalent area of closed-canopy forest, were sampled for mode of death of the gapmaker trees and seedling/sapling regeneration of A. concolor and P. menziesii. Root rot fungi including Armillaria spp. and Inonotus dryadeus, in combination with windthrow, accounted for a significantly higher mortality and gap formation in A. concolor relative to P. menziesii. While both A. concolor and P. menziesii regenerated well in canopy gaps, under closed canopy A. concolor regenerated more than P. menziesii. The implications of selective mortality of A. concolor in these forests and resulting impacts on succession will be discussed.
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1 - Humboldt State University, Biological Sciences, Arcata, CA, 95521, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood B/Snowbird Center
Date: Tuesday, July 28th, 2009
Time: 4:45 PM