Decomposition and vegetation dynamics in a sand prairie encroached on by forest
Sand prairies are an increasingly rare ecosystem, characterized by grassland vegetation, high sand content, and low organic matter in the soil. Following a fire in the late 1960s, oak and jack pine trees (Quercus rubra and Pinus banksiana, respectively) have been encroaching on the Van Zelst prairie. Changes in plant community structure are expected to impact decomposition dynamics. This study measured how forest encroachment and restoration impacted decomposition and plant diversity in three locations, (1) native prairie, (2) restoration zones between prairie and forest, and (3) forest. The restoration zone was created three years ago when oak and jack pine trees were removed. I hypothesized that alteration of nutrient input by different vegetation and increased moisture retention by encroaching forest could increase enzyme activity rates in the forest compared to the native prairie. In addition, restoration plots would be intermediate to native and forest plots due to increased light but slow lichen recruitment. Each location has three 2 x 2 m2 plots. Activity for enzymes involved in carbon, nitrogen, and phosphorus activity was assayed in all plots at 0-15cm and 15-25cm below the surface in July 2014 and October 2014, and will continue. Vegetation surveys were completed at the same time as soil collection to determine lichen, grass, flower, and woody plant composition.
In July and October 2014, the plots in the native prairie were dominated by native and invasive wildflowers and grass (Carex spp., Schizachyrium scoparium, Hieracium aurantiacum, Daucus carota, Asclepias spp. and Aster spp.). About 25% of the native prairie plots were covered in lichens, primarily Cladonia. The restoration plots were characterized by 70% grasses, primarily Carex, 15-20% bare ground and less than 10% lichens and wildflowers. The forest floor coverage in the forested area was 50-60% grass, 40% Q. rubra and P. banksiana, and less than 10% lichens and wildflowers (primarily Cladonia and Asclepias, respectively). Plant species richness was greatest in the native prairie and lowest in the restoration plots, while evenness was greatest in the restoration plots. The activity for all enzymes in 2014 was lowest in the restoration plots. Phenol oxidase activity was greatest in forested plots than the native and restoration plots, likely due to more complex litter inputs. Phosphatase and beta-glucosidase activity were similar across plots and had the greatest activity of all enzymes. Restoration plots likely had the lowest enzyme activity due to the bare ground and lack of diverse vegetation.