Semester

Fall

Date of Graduation

2001

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Wood Science and Technology

Committee Chair

Ray R. Hicks, Jr.

Abstract

Stand dynamics and disturbance histories of five eastern, oak-dominated old-growth stands were investigated using ecological field sampling techniques, dendrochronologogical methods, and a review of historical resources of original forest composition and patterns of human and natural disturbance. Witness tree tallies from 18th century land surveys show that presettlement forests in the study areas were oak-dominated forests. Quercus alba was, at minimum, twice as abundant as Q. velutina, the second ranked species. Acer saccharum and Fagus grandifolia were among the top ten ranked species at each site; however their importance value was consistently less than one-third the value for Q. alba. Querus rubra, Q. prinus, Castanea dentata, and Acer rubrum were relatively minor components of presettlement forests, rarely ranked among the ten most abundant tree species.;On average, at least one canopy disturbance occurred on these study sites every three years; larger multiple-tree disturbances occurred every 17 years. Although there was some variation by site and by historical period, there has been little significant change in canopy disturbance rates for the 300-year period reviewed. A review of tree-ring chronologies yielded three growth strategies. For these oaks, the likelihood of originating in a large opening and achieving overstory status before canopy closure is about the same as the probability of requiring a major release, either from the understory or from a smaller gap that closed. Half of the cored trees established individually, and 30% attained overstory status individually, members of no identifiable cohort. The majority of multiple-tree events occurred in gaps <200 m2 in area. For trees that required a major canopy release, understory residence times averaged 89, 54, and 50 years for Quercus alba, Q. rubra, and Q. velutina, respectively. Although there is some historical precedence for these values, few contemporary second-growth forests contain understory oaks of this age, particularly Q. rubra. In view of the lack of change in canopy disturbance rates, these understory residence averages suggest that the level of understory shade, and by implication, the abundance of shade tolerant understory species, was considerably less in the period before 1900. This hypothesis is consistent with presettlement survey tree-tallies, the absence of shade tolerant species in the oldest cohorts, fire frequency data from other studies, and the fact that virtually no oaks that recruited after 1900 did so after a prolonged period in the shaded understory.

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