Soil pH, topography and forest vegetation in the central Ozarks

In a detrended correspondence analysis (DCA) ordination, 81 forested sites in the southern Missouri Ozarks fell into three different groups. Groups I and II were upland, and Group III consisted of 17 bottomland stands with high importance of Platanus occidentalis. In Group I (34 upland stands), Quercus alba, Q. velutina, Q. rubra and Carya texana codominated in various combinations, but Q. velutina reached higher importance percentage (I.V.) at higher elevation above the streams and on more acid soils, whereas Q. alba was most important at lesser heights above the streams and on less acid soils. Pinus echinata and Q. stellata were concentrated at opposite ends of a DCA ordination of Group I, with Q. stellata I.V. highest on southern and western aspects and ridgetops and with P. echinata on various aspects. Quercus and Carya were reproducing well in all Group I stands and Acer saccharum in only a few. In Group II (30 upland stands generally with higher pH than Group I stands), a DCA ordination revealed a vegetational gradient correlated with aspect, with Juniperus virginiana stands on southern and western aspects at one end and stands with Tilia americana at the other end. Quercus muehlenbergii decreased in importance from the Juniperus end toward the Tilia end, whereas Acer saccharum increased over the same gradient. High abundance of Fraxinus americana and Ulmus rubra occurred where Acer saccharum was abundant. Quercus rubra, the only species important in both Group I and Group II, was abundant all across the Group II ordination, but was most important toward the Tilia end. Quercus spp. were not reproducing well in Group II stands, whereas Acer saccharum was, even in stands at the Juniperus end of the ordination. The differential reproduction of Quercus spp. vs. Acer saccharum on more acid vs. less acid to basic soils suggests that not only present composition but also potential (sapling layer) vegetation is related to soil pH.