Aboveground Biomass and Soil Organic Matter as a

1. Aboveground Biomass and Soil Organic Matter as a Function of Planting Strategy and Water Depth in Six Experimental Wetland Cells After One Year of Planting Rachel Cohn, Gavin M. Platt, H. Siv Tang Systems Ecology (ENVS316) Research Project, Fall ‘04 Background • Soil Organic Matter: Although SOM was greater overall in deep areas, the differences among depths are not statistically significant. We found no statistically significant effects of either depth or planting strategy on SOM. Wetlands are crucial ecosystems that serve many purposes, including wildlife habitat, flood abatement, and nutrient filtration. Despite their importance, increased land-use in the U.S. has led to enormous reductions in wetland cover, with 97% lost in Ohio alone. Recent efforts to reverse this trend have left ecologists to the challenge of recreating wetlands with similar structure and function as natural wetlands. Ecologists have observed that restored wetlands often fall short of natural wetlands’ biotic structure, functioning, and stability (Zedler 2003). In collaboration with Oberlin College and Ohio State University, the Ecological Design Innovation Center (EDIC) has created an experimental wetland facility to study the effects of different planting strategies on wetland restoration. Its long-term goal: to develop improved restoration management practices in order to maximize desirable structural attributes such as species diversity and functional aspects such as carbon accumulation and nutrient retention. Two main factors that contribute to and reflect wetland function are aboveground biomass and soil organic matter (SOM). Aboveground biomass provides a direct measurement of net ecosystem productivity. SOM content reflects long-term storage of organic carbon and associated nutrients, and contributes to water holding capacity and cation exchange capacity (CEC). The results of previous studies suggest that biomass and SOM are thought to be controlled in part by water depth and species diversity (Callaway 2003, Weiher 2004). Effects of Planting Strategy and Depth on Soil Organic Matter 6.0 Picture 1. Harvesting biomass at the site. 4.0 A permanent grid was established in each cell for research purposes (Fig. 2). Aboveground biomass was harvested using cutters and a 1m x 1m square sampling device, constructed of PVC pipe (Pic. 1), within each of the six wetland cells at rows 7 (shallow) and 5 (deep). Soil cores were taken from each corner of the sampling unit, and water depth was assessed at the center. Shallow % SOM Deep 2.0 Figure 2. Sampling protocol in wetland cells. Row 1 is the deep end, row 8 the shallow end. The six locations where samples (and subsamples) were taken are located as indicated in the diagram. 0.0 Selective Natural Combined Planting Recruitment Treatment Type Figure 4. % SOM = [(ash-free dry weight)/(oven-dried weight)]*100%. Y-error bars represent standard error of the mean among replicates. Conclusions We used standard laboratory techniques to estimate the dry-weight of aboveground plant biomass and to determine soil organic matter. We used analysis of variance to determine whether there were differences as an effect of either planting treatment or depth. Even just one year after these wetlands were initiated, we found that plant biomass is already a function of depth (P=.04). However, we found no significant effect of planting with a high species diversity on biomass or SOM. Because the wetlands are only two years old, and the last planting and seeding occurred only one year ago, we are not able to make concrete conclusions about whether this pattern will remain true in the future. We anticipate that, as the wetland matures, SOM will increase because of an accumulation of dead plant matter due to slow decomposition. We also anticipate a significant difference between naturally recruited and planted cells as community composition in the planted cells stabilizes. Further research will be necessary to determine the longer term effects of planting strategy on ecosystem structure and function. Purpose • Our two primary goals were: • To determine whether restored wetlands initiated with high species diversity (both seeding and planting) differ from those allowed to naturally recruit. • 2) To determine whether biomass and SOM differ as a function of depth within the wetland cells. Picture 2. Incinerating soil to determine SOM. Findings • Plant Biomass: Our analyses indicate that depth had a significant effect on plant biomass in the planted cells and among all treatments, but not in the cells subject to natural recruitment: P=.01 (planted), P=.04 (combined). We did not find significant overall differences in biomass between planted and natural recruitment treatments (Fig. 3). Experimental System & Methods The wetland facility consists of six hydrologically isolated 1/2 acre cells which were constructed to have nearly identical dimensions, soil properties, and hydrological conditions. Cells were graded from a shallow, seasonally inundated south side to a permanently aquatic north side. Four of the cells were seeded and planted in fall of ’03 with species native to northeast Ohio to achieve a high level of species diversity. Two of the cells were not planted and were subjected to natural recruitment (Fig. 1). Effects of Planting Strategy and Depth on Plant Biomass References 0.6 Callaway, J.C., Sullivan G., and Zedler J.B. (2003). Species-rich plantings increase biomass and nitrogen accumulation in a wetland restoration experiment. Ecological Applications, 13 (6), 1626-1639. Weiher, E., Forbes S., Schauwecker, T., Grace, J.B. (2004). Multivariate control of plant species richness and community biomass in blackland prairie. Oikos, 106, 151-157. Zedler, J.B. (2003). Wetlands at your service: Reducing impacts of agriculture at the watershed scale. Frontiers in Ecology and the Environment, 1 (2), 65-72. 0.4 Shallow Biomass (kg/m2) Deep 0.2 0.0 Selective Natural Combined Planting Recruitment Treatment Type Figure 1. Diagram of planting regime of the experimental system at EDIC. Figure 3. Biomass = oven-dried weight in kg/m2. Y-error bars represent standard error of the mean.