DENDROECOLOGICAL AND ECOPHYSIOLOGICAL ANALYSIS OF GAP ENVIRONMENTS INMIXED-OAK UNDERSTOREYS OF NORTHERN VIRGINIA

1. Ecophysiological, morphological and dendroecological attributes wer e examined in species growing in understorey and newly formed gap envi ronments in mixed-Quercus forests of northern Virginia. 2. Gap environ ments were characterized by higher photosynthetic photon flux density (PPFD) but were not different from non-gap control plots in their soil moisture, predawn leaf water potential (Psi), leaf temperature or lea f to air vapour pressure deficit (VPD). In addition, few significant d ifferences existed between regeneration responses at gap and control s ites. 3. Plants in gaps experienced higher rates of net photosynthesis (A) and leaf conductance to water vapour diffusion (g(WV)) than contr ol plants, although parameters did not differ between early vs late su ccessional species. Gap plants also produced leaves with smaller leaf area and greater leaf thickness, leaf mass per area (LMA) and stomatal density than control plants. 4. All gap species experienced accelerat ed height growth compared to non-gap plants, with early successional S assafras albidum (Sassafras) and Liquidambar styraciflua (Sweetgum) ex hibiting the highest rates. In contrast, average radial growth in smal l, understorey trees was not significantly different between habitat t ype, although Quercus alba (White Oak) did respond significantly to th e most recent gaps. 5. Many small trees (6-12 cm d.b.h.) were surprisi ngly old - up to 100 years in age. Despite severe suppression periods in these trees, they experienced release events during their lifetime, although not necessarily to the most recent gaps. This may partially explain the lack of correlation between ecophysiological and growth pa rameters.