Masters Theses

Date of Award

8-1979

Degree Type

Thesis

Degree Name

Master of Science

Major

Ecology and Evolutionary Biology

Major Professor

H.R. DeSelm

Committee Members

Edward R. Buckner, J. Rennie

Abstract

High elevation fir and spruce-fir forests of the Southern Appalachians were sampled in the Black Mountains, North Carolina and in the Great Smoky Mountains, Tennessee and North Carolina. Both absolute and relative data were collected on the composition of the overstory and understory strata; the ground cover stratum was sampled for relative data. Both stands infested by the balsam woolly aphid and un-infested stands were sampled to determine the effects of the opened canopy caused by the death of Fraser fir on the population dynamics of these boreal ecosystems. Comparison of stand composition and use of correlation and regression analysis revealed trends in changes.

Overstory density in un-infested fir and spruce-fir forests at 6000 feet elevation or above averaged 354.7 stems per acre with a basal area total of 205.6 square feet per acre. In lower elevation un-infested stands overstory density averaged 280.4 stems per acre and basal area averaged 232 square feet per acre. Those stands infested by the balsam woolly aphid displayed decreasing overstory densities and basal areas in response to Fraser fir death.

Sapling densities are believed to have varied more as a result of sampling error than in response to fir death. Un-infested stands at or above 6000 feet elevation averaged 119.9 sapling stems per acre (77.3% fir) , lower elevation stands averaged 168.6 stems per acre (67.4% fir).

Stems less than one inch DBH and more than two feet tall exhibited the greatest response to aphid-caused Fraser fir death. These stems averaged 1110.5 stems per acre (50.2% fir) in the high elevation un-infested stands, 2828.3 stems per acre (24.1% fir) in the lower elevation stands sampled and 6238.5 stems per acre (18.8% fir) in the stands with the longest period of time since the death of fir occurred. Not only did the total sub-sapling density increase significantly in those stands infested by the balsam woolly aphid, but the relative composition of this stratum changed drastically also. As demonstrated by simple comparison of stand composition and by correlation and regression analyses, the densities of thorn-less blackberry (Rubus canadensis), red raspberry (Rubus idaeus var. canadensis) and Fraser fir increased significantly in response to overstory fir death. However, the densities of mountain cranberry (Vaccinium erythrocarpum) and hobblebush (Viburnum alnifolium) decreased.

Changes in the composition of the ground cover layer in response to the death of fir were also significant. Oxalis acetosella cover and total moss cover decreased as the canopy opened due to the death of fir.

Based on regression analysis results, the amount of aphid-caused fir death was a good predictor of increased densities of thornless blackberry and subsapling fir. Increased fir death was a predictor of less mountain cranberry and hobblebush densities.

Correlation of site and vegetation variables revealed that Oxalis acetosella and thornless blackberry increased toward dry sites and toward increased exposed surface rock. Pteridophyte cover increased toward mesic sites and as surface rock cover decreased.

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