Ecophysiology of Seedlings of Oaks and Red Maple Across a Topographic Gradient in Eastern Kentucky

Abstract

Abstract Throughout much of the eastern United States, oaks (Quercus spp.) are being replaced through natural succession by more shade-tolerant species. In Robinson Forest in eastern Kentucky, A. rubrum is numerically dominant in the understory and appears to be successionally replacing five oaks that occur at different topographic positions in upland forests. To help predict future succession, we compared A. rubrum and the five oaks in terms of patterns of gas exchange and water relations in understory seedlings subjected to artificial, saturating light levels. Physiological responses exhibited clear diurnal patterns, but were not strongly related to topography (mesic versus xeric aspects). Despite their different topographic distributions, oaks differed only minimally in responses. The lack of oak species and topographic effects on physiology may have stemmed from nonlimiting moisture conditions during the study. In contrast, A. rubrum exhibited very low A and gww and very high ψleaf compared to the oaks. Furthermore, in the oaks, A was controlled mainly by gwv, whereas in A. rubrum, ψleaf and Tleaf were more strongly correlated with A than was gwv probably reflecting relatively low dehydration tolerance in A. rubrum leaves. Future light regimes should be enhanced by gap-phase dynamics. Under these conditions, the higher photosynthetic capacity of oaks compared to A. rubrum may contribute to higher leaf carbon gain. On the other hand, abundant tall understory A. rubrum may continue preempting light from smaller oak juveniles, promoting eventual replacement of oaks by A. rubrum at Robinson Forest. For. Sci. 42(3):335-342.