Vegetation And Soil Characteristics Of Pine Plantations And Naturally Regenerated Hardwood Forests On The Hoosier National Forest

During the 1930s there was widespread erosion on farmland and subsequent land abandonment. As a result, Pinus strobus L. (white pine), P. resinosa Aiton (red pine), and P. echinata Mill. (shortleaf pine) were planted in the Midwest to prevent erosion and rehabilitate sites. These species were selected due to their wide availability at the time. Currently, it is the goal of the U.S. Forest Service to provide a more natural and sustainable landscape, in part by removing these non-native Pinus stands and by replacing them with native hardwood species. The ultimate success of hardwood restoration depends, in part, on the lasting influence of Pinus stands on the soil where they were planted. This is worthy of concern because species of the family Pinaceae have a noted impact on nutrient availability, organic matter cycling, soil acidity, and soil buffering capacity compared to mesophytic hardwood species. This study investigates the impact that Pinus plantations have had on soil and vegetation communities compared to hardwood stands. I sampled old-field sites on mesic ridges and bottoms in the Hoosier National Forest that were planted to P. echinata and P. strobus, or naturally regenerated to mixed hardwood species. I measured overstory and understory vegetation, including saplings, seedlings and herbaceous-layer species. I measured environmental variables including soil, litter depth, and canopy openness. Soils were sampled and analyzed for macronutrients, micronutrients, pH, organic matter, exchange capacity, and Al. I used Non-metric multidimensional scaling (NMS) ordination and two-way ANOVA with Tukey multiple comparisons post hoc tests (a = 0.05) to statistically analyze data. Species composition under Pinus stands was distinctly different from that of hardwood stands. Pinus stands had lower concentrations of organic matter (OM; -21%), total carbon (TC; -29%), total nitrogen (TN; -30%), manganese (Mn; -37%), calcium (Ca; -24%), Zinc (Zn; -13%), and boron (B; -24%). Pinus stands had 2-5 times greater litter depth and 17% greater concentrations of Al compared to naturally regenerated hardwoods. As a result, Pinus stands displayed lower herbaceous-layer cover, species richness, and diversity. Hardwood stands contained a greater number of plant functional groups and had greater cover of graminoids, perennials, invasive species, and other mesophytic woody species including Acer saccharum Marshall (sugar maple), Lindera benzoin L. (spicebush) and Cornus florida L. (flowering dogwood). Herbaceous functional groups were more dominant on bottoms, while seedlings and saplings were more dominant on ridges. Ridge hardwood stands contained more mesophytic woody species, whereas ridge P. echinata stands contained a greater density of understory Quercus spp. and Fagus grandifolia Ehrh. (American beech). Soil fertility proved to be a driving factor in understory communities in my study. Infertile soil with deep litter hosted lower plant cover, but a greater density of Quercus spp., whereas more nutrient rich soils hosted mesophytic species. Bottomland soil was better buffered, allowing Acer spp. to ascend to the overstory with Pinus. The result was that, in bottoms, Pinus did not have as large an impact on soil or vegetation communities, resulting in greater similarity to hardwood stands