Distribution of wetland tree species in relation to a flooding gradient and backwater versus streamside location in Arkansas, U.S.A.1

DALE, EDWARD E., JR. (Dept. of Biological Sciences, University of Arkansas, Fayetteville, AR 72601) and STEWART WARE (Dept. of Biology, College of William and Mary, Williamsburg, VA 23187-8795). Distribution of wetland tree species in relation to a flooding gradient and backwater versus streamside location in Arkansas, U.S.A. J. Torrey Bot. Soc. 131: 177-186. 2004.-Most of Arkansas is outside the normal geographic range of several bottomland hardwood species important in floodplain forests of the southeastern United States. Other species therefore occupy the portions of the flooding gradient normally filled by those missing species. Analysis of 45 non-quantitative elevational transects from slough edge or stream edge to upland sites and ordination of 58 quantitatively sampled bottomland stands were used to assess distribution of tree species along a flooding gradient and in relation to steamside vs. backwater habitats in southern and eastern Arkansas. Emphasis was on hardwood stands dominated by species other than the extremely flood-tolerant Taxodium distichum and streamside species Salix nigra. Flooding gradient rankings based on site dominance along the elevational transects could be assigned to 20 tree species. Across the ordination, three dominant oaks were arranged from drier to wetter sites in the order Quercus nigra, Q. phellos, and Q. lyrata. Despite a wide moisture tolerance, Liquidambar styraciflua was much more important toward the drier end of the ordination. Carya ovata was important in much wetter stands than would be predicted by the literature, and Quercus stellata and Q. texana (= Q. nuttallii) were most important near the middle rather than at the drier end of the ordination. Carya aquatica was the important hickory in the wetter half of the ordination, and occurred in both backwater and streamside stands. Celtis laevigata also reached high importance in both streamside and backwater sites, and its associates in those sites suggest that it has greater flood tolerance than indicated by the elevational transects. Taxa like Forestiera acuminata and Planera aquatica that typically occur as subcanopy species were dominant in some wet stands, presumably because timber harvest had removed most of the original canopy trees. Ulmus spp. and Fraxinus pennsylvanica occurred at moderate levels across all but the driest portion of the flooding gradient, but almost never dominated a stand, and surprisingly were rarely important in the same stands. The important southern bottomland forest species Quercus laurifolia, Fraxinus caroliniana, F. profunda, and Nyssa sylvatica var. biflora (= N. biflora) are among those absent from the study area, and several other such species were present but of very low importance (Quercus michauxii, Acer rubrum, Acer saccharinum, Betula nigra).