Date of Graduation

2016

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Forest Resource Management

Committee Chair

William L MacDonald

Committee Co-Chair

John R Brooks

Committee Member

Jennifer L Koch

Committee Member

Daniel G Panaccione

Committee Member

Daniel B Twardus

Committee Member

Park Yong-Lak

Abstract

American beech have long been observed to escape both signs and symptoms of beech bark disease (BBD). Some may be resistant to Cryptococcus fagisuga (beech scale), a primary component of the BBD complex; research indicates about 1-2% of American beech inherit resistance to beech scale. At the landscape level a variety of environmental factors may induce ecological resistance, a transient condition allowing potentially susceptible individuals to remain disease-free. This project investigated factors that may contribute to ecological resistance, focusing on biotic and abiotic stand characteristics and their relation to BBD incidence and severity. Plots were established at fifteen sites in the Appalachian region; overall, 3,142 beech were evaluated for disease incidence and severity on 102 plots. Over 100 parameters were generated from sampling and compared with Cryptococcus infestation or Neonectria infection. Correlation was used to characterize relationships between recorded parameters and scale infestation or Neonectria infection. Principal Component Analysis identified four important Principal Components (latent variables) composed of recorded parameters. Principal Component 1 (PC1) explained 9.39% of variation in the data; PC2 explained 6.40% of variation; PC3 explained 5.51% of variation; PC4 explained 4.58% of variation. Stepwise multiple regression analyses used Cryptococcus infestation, Neonectria infection, and Principal Components (latent variables) as predictors for the responses Cryptococcus infestation or Neonectria infection. Principal Component 1 (p = 0.0014) and PC4 (p = 0.0015) were significant for Cryptococcus infestation. The interactions of Cryptococcus infestation, PC1, and PC4 (p = 0.0147) and Cryptococcus infestation, PC1, PC3, and PC4 (p = 0.006) were significant for Neonectria infection. Spatial analyses indicate there is spatial dependence for infestation at Blackwater Falls, WV (variability explained = 79.2%) and Great Smoky Mountains National Park, TN (variability explained = 52.9%); and for infection at Allegheny National Forest, PA (variability explained = 68.6%) and Cranberry Wilderness, WV (variability explained = 60.9%). This spatial dependence can partially be explained by inherited resistance and parameters composing significant latent variables. Finally, unusual blocky cankers regularly observed on beech but lacking viable Neonectria perithecia were sampled. Fusarium spp. were isolated from 85% of blocky cankers sampled; Fusarium colonies easily outcompeted and grew over Neonectria colonies when paired in culture and were statistically larger (p < 0.005). Overall, this investigation supports observations that some beech trees remain disease-free by some mechanism other than inherited resistance, and numerous factors were identified that potentially influence dispersal and survival of BBD causal agents.

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