Population dynamics of overcup oak (Quercus lyrata) in a seasonally flooded karst depression

This study examined the environmental factors that control recruitment patt erns within a population of overcup oak (Quercus lyrata Walt.) in a seasona lly flooded karst depression located in southeastern Tennessee. The populat ion was censused using 240 plots in which demographic and environmental var iables were measured in 1997 and all tagged individuals were re-censused in 1998. We hypothesized that seed and seedling distribution and abundance wo uld reflect adult canopy cover, whereas sapling recruitment would reflect f looding and light patterns superimposed upon this original distribution. Th e initial spatial distribution of seeds on the forest floor of Sinking Pond in the fall was a reflection of seed rain directly beneath reproductive ad ults. However, immediately following this seed rain, the spatial pattern of viable seeds changed, reflecting factors associated with the microtopograp hy of the pond and litter depth. Light is an important factor in the distri bution and abundance of the larger (0.5-1.5 m) overcup oak saplings. The te mporal and spatial heterogeneity of light associated with treefall gaps and the spatial heterogeneity of microtopography (and its associated affect on the duration of inundation and litter depth) act as a filter, resulting in the differential survival of discrete clumps of saplings. This dynamic has resulted in even-aged clumps of overcup oak adults within the population. Sites currently favorable to survival of adult trees were shown to be unfav orable to juveniles, resulting in a spatial segregation of seedling and sap lings from the parent population. Our data indicate that there are no indiv iduals in the sub-canopy or canopy that are less than 40 years old, and tha t saplings are currently unable to reach the sub-canopy adult state. Theref ore, it appears that this population is currently experiencing a lack of re cruitment into the canopy. We found no evidence to suggest that such recrui tment gaps are a repeated phenomenon in the population. Therefore, we propo se that this population may now be experiencing not just a gap in recruitme nt, but perhaps a regeneration failure. We propose that the flooding durati on in Sinking Pond has increased within the last 50 years, to the point whe re it has become the primary factor limiting recruitment in this population . We conclude, therefore, that light as a factor in regeneration increases in its importance in response to the severity of flooding only up to a poin t, beyond which flooding becomes the overriding factor controlling regenera tion.