Doctoral Dissertations

Yao Yin

Date of Award

5-1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Botany

Major Professor

Frank McCormick

Committee Members

Clifford C. Amundsen, Hazel Delcourt, William R. Emanuel, William H. Martin

Abstract

This is a study of old-growth mixed mesophytic forests of Lilley Cornett Woods (LOW) in southeastern Kentucky. The study consists of four units: (i) a field investigation of seedlings and saplings under gap and closed canopy conditions; (ii) a projection, with the "Markov chain" model, of the future structure of canopy vegetation; (iii) a new formula for calculating canopy turnover time; and (iv) a gap model that simulates dynamics of mixed mesophytic forests in southeastern Kentucky. Sixty eight percent of all tree seedlings originate in gaps, although treefall gaps constitute only ≈10% of forest area. Gaps account for 30% of sample variance of seedling density, 48% of sample variance of sapling density, and 39% of sample variance of sapling height growth. Mortality rates of seedlings are significantly lower under gap conditions than under closed canopy conditions. Treefall gaps are necessary for saplings to grow to canopy height. These results indicate that gaps are primary regeneration sites of forests of LCW. The structure of sapling populations in gaps is indistinguishable from that beneath closed canopies. The structure of sapling populations do differ between different slope positions (lower, middle, and upper slopes). Effects of gap size, gap age, gap type (single-tree vs. multiple-tree gap), and tree fall type (uprooting, snap off, standing dead) upon seedlings and saplings were examined using variance analysis. Gap age and gap size significantly influence seedling and sapling densities and sapling height growth. Treefall type significantly influences sapling height growth. Gap type has no influence upon seedling and sapling densities or sapling height growth. Based on the structure of sapling populations, the current structure of canopy trees is likely to be maintained, according to the projection of the "Markov chain" model. Therefore, regeneration through treefall gaps is sufficient to maintain old-growth mixed mesophytic forests of LCW at an equilibrium state. Forests of LCW were compared to several forests in the eastern United States, with regard to turnover times. The formula used to calculate turnover time was derived from a formula which describes the relationship between gap area and gap age. Using existing data in the literature, turnover time of forests of LCW was estimated to be between 102 and 123 years. This is longer than turnover times of more southern forests in the southern Appalachians (≈36 to 106 years), but shorter than that of more northern forests in Ohio (≈133 years). A JABOWA-FORET type computer model (FOREK) was developed to simulate dynamics of mixed mesophytic forests in southeastern Kentucky. The model treats forest dynamics as a stochastic process determined by ecological characteristics of individual species, regional temperature and precipitation (the site factor), and shading and depletion of nutrients between neighboring trees (the microsite factor). A new approach to simulating spatial interactions between neighboring trees is used in the model. With this new approach, the model delineates a tree's neighborhood based on information on explicit horizontal dispersion of trees. Both spacing and height of neighboring trees are considered in determining shading and depletion of soil nutrients. The model has successfully predicted the historical structure of mixed mesophytic forests in southeastern Kentucky. Coefficient of percentage similarity between predicted and observed forest structure is 79%.

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