Tree Diameter Distributions and Replacement Processes in Southeast Texas Forests

Fifteen forest stands were sampled along a moisture gradient in southeast Texas to examine size class distributions of species. Important tree species (> 10 percent relative basal area) were generally poorly represented as saplings in mesic and wet forests but not in dry forests. A given dominant species tended to show greater reproductive failure (i.e., poorer representation of saplings) in wet than in mesic forests. Understory shrub species were well represented over the range of sapling sizes (1-10 cm) so that whole stand size class distributions showed no underrepresentation of smaller stems. Underrepresentation of saplings of important canopy trees is probably the result of mortality, and possibly also periodic seed set in Fagus grandifolia . Increased mortality of saplings from dry to wet forests is explained in terms of increased competition from both overstory and understory species. The underrepresentation is marked enough to raise questions concerning the long-term stability of these forests. It is postulated that replacement of overstory trees by saplings occurs following disturbance when sapling mortality is relaxed. Multiple-tree canopy gaps may be most important in allowing replacement in southeast Texas forests. Forest Sci. 24:153-166.