Effects of fire on vegetation in the Big Thicket of southeastern Texas, United States of America
Harcombe, Paul A.
Doctor of Philosophy
This study shows that fire had a strong short-term effect on the small-sized individuals in the understory of two dry upland vegetation types, sandhill and upland pine. Large trees were less affected than saplings and small trees. The changes in these types were mainly structural rather than compositional. The influence of fire diminished toward the wet end of the vegetation gradient. Post-fire recruitment via resprouting and germination from seeds was rapid. The interaction of fire and vegetation type was apparent in the comparison of the two dry upland types with slope types. Simulation of fuel and fire provided additional, although not very strong, support for the existence of differences in fire behavior corresponding to an environmental gradient from dry upland forests to mesic and wet slope forests. Ordination using pre- and post-fire data suggests that fire had limited effects on current vegetation patterns and there was no indication that any present pre-fire type would be converted to another type. Furthermore, there were no clear convergent or divergent patterns in overall vegetation change; hence it was difficult to predict long-term changes. An eight-year record of vegetation change at a tornado damaged savanna site in Hickory Creek Unit demonstrates that the tornado had resulted in the succession of the vegetation toward a midslope forest, but two prescribed fires partially reversed such a trend. Phytolith analysis revealed that upland pine and some upperslope forests had abundant grass phytoliths. This indicates that these types had a grass component in the past under an open canopy which might have disappeared as a result of fire suppression, logging, and encroachment of shrubs and hardwoods.
Ecology; Forestry; Wildlife management; Agriculture; Biology