Shortleaf pine (Pinus echinata Mill.) has a wide ecological amplitude and is the most widely distributed southern pine in the U.S., ranging from Texas and Oklahoma in the west to New York in the northeast. It is most abundant in the Ouachita Mountains and Salem Plateaus eco-regions of Oklahoma, Arkansas (the ecological center of best development), and Missouri plus the Piedmont in the southeast. Although widely occurring, actual community composition and stand structure may vary, leading us to hypothesize that the forest communities where shortleaf pine occurs may differ between 10 major eco-regions in the eastern U.S. We used data from the USDA Forest Service, Forest Inventory and Analysis (FIA) program, to determine the extent and structure of present-day shortleaf pine communities, of which many are a result of timber cutting over the last century. To illustrate community differences between regions we used a modified version of Whittaker’s dominance-typing methodology to identify novel forest communities where shortleaf pine was dominant and also forest communities where shortleaf pine was co-dominant (second or third in stand dominance).
Results/Conclusions
Currently there are 96,624,080 ha (±307,200 C.I.) of forest land across the eastern U.S. within the range boundary of shortleaf pine. Only 9,651,874 (±61,736 C.I.) ha of this forest land contained at least 14 shortleaf pine trees per ha (TPH) that were ≥2.54 cm dbh (one tree sampled per sample unit [SU]). Shortleaf pine was dominant on 2,155,535 (±42,945 C.I.) ha of natural forest stands, with 70 percent of these west of the Mississippi River. The frequency of shortleaf-pine-dominated communities declined on a west to east gradient where eventually shortleaf pine made up a minor component of stand composition. Although there was little difference in stand structure between the east and west (basal area, density, quadratic mean diameter), community components differed. In the Ouachita Mountains eco-region, white oak (Quercus alba L.) and post oak (Q. stellata Wangenh.) were the common associates while in the Piedmont, sweetgum (Liquidambar styraciflua L.), Virginia pine (P. virginiana Mill.), yellow poplar (Liriodendron tulipifera L.), and red maple (Acer rubrum L.) were most common. Average species richness was also slightly higher in the east, 6.4 versus 4.5 tree species SU-1 indicating a stronger dominance factor in the west and an increasing richness gradient west to east.