Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

G. Bruce Williamson

Abstract

The influence of fire on turkey oak (Quercus laevis Walt.) and sand live oak (Q. geminata Small) populations was examined in experimental fires in sandhills near Tampa. Turkey oak crown survival was positively related to oak dbh, distance to the nearest longleaf pine (Pinus palustris Mill.), and dbh of the nearest pine. The pyrogenic litter of pines adversely affected survival of small turkey oaks within 10-20 m of the nearest pine, depending on fire severity. Resprouting of crown-killed turkey oaks was inversely related to oak dbh and, in one field, distance to the nearest pine. Poor resprouting away from pines was associated with delayed crown mortality and incomplete release from apical dominance. Turkey oaks were weakly clumped to randomly distributed at most scales in unburned fields. Four-year changes in a plot unburned for $>$21-25 yr suggested that as stands mature, trees become more randomly distributed. Initial fires reduced turkey oak densities by 41-57% and (1) reduced the scale of maximal clumping, (2) increased clumping intensity, and (3) created large-scale randomness and uniformity. Patchiness of surviving trees was probably related to spatial variation in fire intensity, particularly with distance from pines. Repeated fires increased clumping intensity and gradually eroded large-scale randomness and uniformity, with most trees surviving only in a few isolated patches. Mainly small sand live oaks ($<$10 cm dbh) were killed by initial fires, and subsequently larger trees were lost only very slowly from repeated annual and biennial fires. Although fuel characteristics within sand live oak groves display fire-retarding characteristics, fire mortality was mainly dependent on the size of individual trees, and not with grove size or location of trees within a grove. Trees suffered high crown mortality from intense fires occurring near longleaf pines, although mortality rates tapered off rapidly beyond the perimeter of the pine's crown. Age-class structures of groves recovering from fire suggested that even-aged cohorts of resprouts develop after some fires, but new sprouts are also produced annually as part of normal clonal growth and expansion. Sand live oaks are well adapted to sandhill as well as less frequently burned scrub and hammock communities.

Pages

139

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