PS 15-217 - The effect of multiple disturbance mechanisms on longleaf pine (Pinus palustris) seedling health and function

Abstract: The longleaf pine savanna ecosystem, while once extensive throughout the Southeast United States, has been reduced to 3% of its original range. This drastic range reduction is attributed to anthropogenic disturbances such as land use alteration, fire-suppression regimes, and exploitation of the ecosystem for its natural resources. In the recent decades, increasing interest in restoring this ecosystem has been hindered by a paucity of information relating to how many of its endemic species respond to stressors. To better assist the restoration efforts, additional understanding of the ways in which longleaf pine (Pinus palustris) seedlings respond to various pressures is of vital importance. The longleaf pine is the dominant and sometimes only tree species in the overstory; however, this pine goes through an extended grass stage where it remains in the understory competing with herbaceous plants. Through three independent greenhouse experiments, I aimed to determine the effects of trampling, understory raking, and nutrient and drought interactions on the water potential, biomass, and overall plant health of longleaf pine seedlings. Each greenhouse experiment used tree seedlings plugs in the grass stage. Plugs such as this are commonly used in restoration throughout the state.

Overall, we found that disturbance negatively impacted seedling health and growth. In the first experiment, I simulated trampling at two levels (low intensity and high intensity) to mimic deer presence, and in the second experiment, I simulated raking at two levels (low intensity and high intensity) to simulate the common practice of pine straw raking for sale. Preliminary results from both experiments suggest that high intensity disturbance has greater effect on longleaf pine seedling health than does low intensity disturbance, with low intensity treatments not being significantly different from the control. In the third experiment, I manipulated nutrient availability (no addition and nitrogen addition) and drought (adequate water and water stress). I found that drought has significant effects on the water potential of longleaf pine seedlings, and this effect is greater when nutrients are provided. Combined, this work shows that longleaf pine seedlings are negatively impacted by multiple types of environmental stressors, both natural and anthropogenic, particularly so at higher levels of disturbance and when stressors are combined. Stakeholders should account for multiple and high intensity stressors during restoration efforts in order to better facilitate the rehabilitation of longleaf pine savanna ecosystems.