Variation of the treefall gap regime in a bottomland hardwood forest: Relationships with microtopography

Treefall gaps, formed as a result of small-scale disturbances, allow seedling recruitment and growth in forests where large-scale disturbances are infrequent. Many factors contribute to gap regime heterogeneity within and among forest stands, including wind and fire patterns, stand age, stand composition, and site hydrology. While there is evidence suggesting that topography can also affect gap formation, most studies have examined gaps in steep terrain rather than in relatively level terrain such as bottomland hardwood forests. This study examined the treefall gap regime among three microtopographical classes - ridge, slope, and bowl - in a bottomland hardwood stand in the Big Thicket region of east Texas. The null hypothesis that the gap regime does not vary among microtopographical positions was tested. Using point sampling, microtopographic variation was estimated throughout the site. Line intersect sampling was used to select gaps for measurement of gap frequency, area, fraction (percent cover) and abundance (density) within the study area. While gap area and frequency did not vary among microtopographical classes, fraction and abundance differed significantly. Ridges contained the highest fraction and highest abundance compared to slopes and bowls. Based on these findings, the null hypothesis was rejected and we concluded that microtopography affects at least some aspects of the gap regime in this bottomland hardwood forest.