Thinning and Urea Fertilization Effects on Emerging Grand Fir (Abies Grandis) Foliage and Growth of Western Spruce Budworm (Choristoneura Occidentalis) Larvae
Thinning and Urea Fertilization Effects on Emerging Grand Fir (Abies Grandis) Foliage and Growth of Western Spruce Budworm (Choristoneura Occidentalis) Larvae

Author: Thomas J. Savage

Publisher:

Published: 1987

Total Pages: 82

ISBN-13:

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The objective of this study was to determine how the balance of carbon to nitrogen in a grand fir ecosystem affects the chemistry of emerging grand fir foliage and the growth of western spruce budworm larvae. Forest plots in the grand fir zone of eastern Oregon were thinned, thinned and fertilized, fertilized without thinning, or left as a control to determine how increased nitrogen availability alters the efficacy of carbon-based chemical defenses at different light levels. Thinning did not significantly alter any of the foliar chemical fractions measured while fertilization increased the concentration of foliar nitrogen and free amino acids. Thinning increased tree vigor (g wood produced per m2 foliage), but fertilization only increased vigor in the thinned plots. Fertilization increased the weights of western spruce budworm pupae; thinning had no effect. Male and female pupal weights correlated with foliar free amino acid concentration and the ratios of foliar free amino acids to foliar nitrogen, available carbohydrates, and lignin, but stepwise regression analysis showed that foliar free amino acid concentration alone explained most of the variation in pupal weights. The correlation of foliar free amino acid concentration with male and female pupal weights, and the lack of correlation of any indices of carbohydrate availability suggest that changes in available nitrogen rather than changes in the carbon/nitrogen balance were associated with changes in larval growth. This can be attributed to either a lack of defensive capability in the emerging foliage or a failure to measure or manipulate the variables responsible for controlling foliar defense. However, larval growth is only one aspect of plant susceptibility to insects; changing the carbon/nitrogen balance in the grand fir ecosystem may ultimately affect the susceptibility of grand fir to western spruce budworm by changing the balance between plant growth and levels of plant herbivory.

The Influence of Induced Host Moisture Stress on the Growth and Development of Western Spruce Budworm and Armillaria Ostoyae on Grand Fir Seedlings
The Influence of Induced Host Moisture Stress on the Growth and Development of Western Spruce Budworm and Armillaria Ostoyae on Grand Fir Seedlings

Author: Catherine G. Parks

Publisher:

Published: 1993

Total Pages: 308

ISBN-13:

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This greenhouse study evaluates the influence of separately and simultaneously imposed water stress, western spruce budworm (Choristorneura occidentalis Freeman) defoliation, and inoculation with the root pathogen, Armillaria ostoyae (Romagn.) Herink, on the growth and biochemical features of Abies .grandis (Dougl.) Lindi. Seedling biomass, plant moisture status, bud phenology, and allocation patterns of phenolics, carbohydrates, and key nutrients (nitrogen, phosphorus, potassium and sulfur) are reported. Hypotheses are developed and tested on the impacts of water-stress, defoliation, and root inoculation, on western spruce budworm growth and development, and Armillaria ostoyae-caused mortality and infection. Western spruce budworm larvae fed on water-stressed seedlings had higher survival rates, grew faster, and produced larger pupae than those fed on well-watered seedlings. There is no clear reason for the positive insect response, but changes in foliage nutrient patterns and phenolic chemistry are indicated. Insect caused defoliation has been earlier reported to enhance successful colonization of Armillaria spp. on deciduous trees in the forests of the northeastern United States. The positive response of the fungus was attributed to a weakened tree condition. Conversely, although this study conclusively found water-limited trees to have increased susceptibility to A. ostoyae, defoliation significantly lowered Armillaria-caused infection and mortality. The decline in infection success is attributed to defoliation-caused reduction in plant water stress and an alteration of root carbohydrate chemistry. One and/or two years of defoliation did not appear to weaken the physiological condition of seedlings. Conversely, water-stressed seedlings that were also defoliated produced more buds, had an earlier bud phenology, contained higher total reserve carbohydrates, and had little Armillaria-caused mortality. The study suggests that during drought, short-term defoliation may be beneficial to grand fir and its associated forest community. Also, the additive effects of simultaneously occurring A. ostoyae and western spruce budworm may not be as severe as conventionally believed. Ecological and forest management implications are explored.