This poster presents the integrated design of three studies investigating relationships between stand structure and development and the spread and incidence of Phytopthora ramorum (causal agent of sudden oak death) in tanoak (Lithocarpus densiflorus) / redwood (Sequoia sempervirens) stands. These three studies include a spatial analysis study to explore spatial patterns of stems with stem mortality and disease symptoms, a stand development study to reconstruct height and diameter development of stands under various levels of infections, and a thinning/burning study to assess the effect of fire and alterations in stand structure on disease spread. Our studies encompass eight 1 ha plots, four on Marin Municipal Watershed lands and three on Jackson Demonstration State Forest (Mendocino County). We present the research methods of the three studies, display a diagram illustrating the design of our plots and discuss the benefits of our coordinated research design.
The primary objective of the first study is to determine the relationship of spatial pattern of individual stems to patterns of disease spread. Spatial analysis plots, with a minimum of 300 trees, are installed, with all trees tagged and mapped. Species, height, crown class and diameter are recorded. The data include recently killed trees and records of SOD symptoms. Plots are being re-visited regularly to assess changes in disease incidence and spread over time.
The second study involves the reconstruction of individual tree height and diameter development in stands under various levels of infection. Smaller circular reconstruction plots, ranging in size from 0.10 to 0.25 ha., are established within or adjacent to the spatial analysis plots. A subsample of 5-10 trees on each plot are selected for more intensive sampling, which includes either coring all trees in three locations, measurements of crown radii and tree vigor, or stem analysis of selected trees to reconstruct past growth.
The third study will implement thinning and burning treatments to assess the effect of alterations in stand structure on disease spread. These plots, at least one-hectare in size, will be separate from those previously described, and will be established beginning in 2003. Smaller plots will be established within the thinning and burning treatments to evaluate the effects of changing density and species composition.
These three studies will provide valuable information on the incidence and spread of sudden oak death in redwood/tanoak forest stands. Spatial patterning can be a valuable resource for predicting and mitigating effects of disease, while information on stand development patterns provides the necessary background information for developing management tools. Finally, information on thinning and burning treatments and their effect on sudden oak death may lead to the development of new management approaches for treating both infected forests and forests threatened by infection.
