COS 130-5 - Relationship between canopy structure, microclimate, and Swiss needle cast disease severity among young and mature Douglas-fir forests

Thursday, August 10, 2017: 9:20 AM
D137, Oregon Convention Center
Yung-Hsiang Lan, Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR and David Shaw, Department of Forest Engineering, Resources, and Management, Oregon State University, Corvallis, OR

Swiss needle cast (SNC) is an endemic disease of Douglas-fir caused by Phaeocryptopus gaeumannii. The fungus infects newly emerged needles between May and August. As the fungus develops, the fruiting bodies (pseudothecia) block the stomata and inhibit gas exchange, reducing the photosynthesis rate in infected trees. The objective of this research is to verify if anecdotal observations that SNC is more severe in young trees than in mature trees is true, based on the relationship between canopy structure, microclimate, and P. gaeumannii behavior among different ages of Douglas-fir forests. We hypothesize that the complexity in mature forests contributes to different microclimates, a factor that may reduce needle infection.

Five study sites were selected in 2015 and 2 more were added in in 2016. In each site, 3 young trees (20-30 years old) and 3 mature trees (120- 450 years old) were climbed to sample needles from lower, middle, and upper canopy position. Severity of SNC was measured by counting the percent stomata occluded by pseudothecia on 2-yr-old needles. We also used leaf wetness sensors to record the moisture on needle surface on low-, mid- and top-canopy position, and measured the tree crown and branch characteristics of mature Douglas-fir trees.


Preliminary results from 2015 indicate that pseudothecia were generally present both on mature trees or young trees. However, in certain sites, the fungus presence was low on both mature and young trees probably because the climate is not suitable for the fungus development due to high altitude, dry summer and cold winter. In sites with P. gaeumannii present, severity of mature trees was 0-4%, and young stands were 5-50%. The fungus presence showed SNC is more severe in young trees than in mature trees. The meteorological and crown structure data were collected and 2016 SNC severity data and statistics will be analyzed along with vertical patterns of disease severity in young vs. mature/old trees.

This study will provide increased knowledge on SNC disease ecology in mature Pacific North West Douglas-fir forests. Studies of P. gaeumannii have previously only occurred in young stands. Knowledge of mature forests is necessary to understand the epidemiology of disease and due to management of older stands for endangered wildlife like the spotted owl and marbled murrelet.