Graduate Thesis Or Dissertation

Pathological and ecological aspects of decline and mortality of Chamaecyparis nootkatensis in southeast Alaska

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  • Alaska-cedar (Chamaecvparis nootkatensIs (D. Don) Spach) is a valuable tree that is suffering from a serious decline and mortality of unknown cause throughout southeast Alaska. Epidemiological and pathological studies were initiated to determine if a pathogen is the primary cause of this problem. By examining old aerial photographs and by determining the approximate year of death of Alaska-cedar trees that are now in various stages of deterioration, I established that extensive mortality began about 100 years ago. In some areas, the boundary of mortality has advanced, but typically by not more than 100 m. Decline and mortality has apparently not spread to new areas, however, since all sites examined with dying cedars have at least sane of the original, 100 year-old mortality present. Maps showing boundaries of mortality at seven sites were made from aerial photographs taken in 1927, 1948, 1965, and 1976 and were supplemented by ground surveys in 1982 and 1983. These data show that local spread has occurred along an ecological gradient from bogs to better drained forest types. Basal scars, common on Alaska-cedar trees in some stands, are caused primarily by brown bears (Ursus arctos), but are not associated with decline. Reproduction of Alaska-cedar from seeds is failing in most affected stands, but vegetative reproduction by the rooting of lower limbs is succeeding on bog and semi-bog forest types. Because crown symptoms suggest a possible root disease, root systems of 35 healthy and declining Alaska-cedar trees were excavated to study symptoms and to isolate fungi. Symptoms on declining trees included dead fine roots and necrotic lesions on coarse roots and tree boles. Necrotic lesions, similar to those on declining trees, were produced on healthy trees by mechanical wounding without inoculation. More than 50 taxa of fungi were isolated or collected from lesions and other symptomatic tissues; 37 were new reports on Alaska-cedar, but the 12 most common did not kill inoculated seedlings of Alaska-cedar. The possible roles of Armillaria sp., Phvtophthora sp., Cvlindrocarpon didvmum, Mycelium radicis atrovirens, vesicular-arbuscular mycorrhizae, Phloeosinus spp. (bark beetles), and nematodes in decline are discussed. Foliar and soil nutrient analyses support neither nutrient deficiencies nor mineral toxicities as causes of decline. In summary, epidemiological evidence and the lack of aggressive pathogens suggest that biotic agents are not responsible for Alaska-cedar decline and that some abiotic factor(s) is a more likely cause.
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