Effects of Rock and Shrub Coverage on the Longleaf Pine (Pinus palustris) at Oak Mountain State Park, Pelham, Alabama

This study was designed to achieve a better understanding of the relationship between rock and shrub cover and longleaf pine (Pinus palustris) communities. Longleaf pine once covered much of the southeastern United States, but widespread harvesting, land development and fire suppression have led to a major decrease in the extent of this ecosystem. The longleaf community has declined to less than 3% of its former range, now covering less than 1.2 million hectares. Longleaf pine communities are dependent upon fire to promote regeneration of longleaf seedlings by reducing competition. In our study, both rock and shrub cover are important ecological factors to understand in the longleaf community because of how they relate to fire. Due to the suppression of fire, longleaf pine communities are met with increasing competition from shrubs in the seedling and adult stages. Rock coverage could possibly act as a fire surrogate because there is less soil for trees to root, lower soil moisture, and lower nutrient levels, which may help to reduce competition. To study these relationships, 26 plots were surveyed in Oak Mountain State Park, Pelham, Alabama, which contains a very important type of longleaf community: the mountain longleaf pine. We set up the plots in two distinct areas of the park: 13 plots in the foothills (the low hills or mountains at the bottom of Double Oak Mountain), and 13 plots in the ridge (south-east facing slope of Double Oak Mountain). We used a line transect method to determine rock and shrub cover for each zone and compare it to small (height 1.3 m) longleaf pine growth using Mann-Whitney tests and regressions. Shrub cover was divided into highbush blueberry (Vaccinium arboretum) and lowbush blueberry (Vaccinium pallidum). We found a significant positive correlation in the ridge between lowbush blueberry coverage and large longleaf pine stems, and between rock coverage and basal diameter for small longleaf pine stems. All lowbush blueberry regressions in the ridge were positively correlated while all regressions involving highbush blueberry in the ridge were found to have negative correlations. There were no significant regressions in the foothills and no clear pattern with regard to the directionality of the relationships. We concluded that lowbush blueberry may be positively correlated with longleaf pine in the ridge because they are both dependent on fire and the ridge community has been burned more recently. Highbush blueberry may be negatively correlated with longleaf pine in the ridge because it is significantly larger than lowbush and may be competing with longleaf pine for light and nutrients. We concluded that increasing rock coverage in the ridge results in increasing basal diameter for small longleaf stems possibly due to a lack of nutrients and water in the ridge, which may cause small longleaf stems to grow in girth before growing in height to adapt in the harsh conditions. However, none of these relationships were found in the foothill community. Therefore, our main conclusion was the difference between the ridge and foothill communities and how these communities have very different ecological relationships.