Transcript Slide 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
2) 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.
Background
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.
Effects of Planting Strategy and Depth
on Soil Organic Matter
6.0
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).
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.
% SOM
Picture 1. Harvesting biomass at the site.
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.
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).
Cell I
Cell II
Natural
Recruitment
Planted and
Seeded
Cell III
Cell IV
Planted and
Natural
Seeded
Recruitment
Cell V
Cell VI
Planted and
Seeded
Planted and
Seeded
Figure 1. Diagram of planting regime of the experimental system at EDIC.
North (Deep)
Picture 2. Incinerating soil to determine SOM.
Findings
1) 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).
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0.0
Selective
Planting
Natural
Recruitment
Combined
Conclusions
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.
Effects of Planting Strategy and Depth on Plant Biomass
References
0.6
0.4
Shallow
Deep
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.
0.2
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.
0.0
Selective
Planting
South (Shallow)
Deep
Figure 4. % SOM = [(ash-free dry weight)/(oven-dried weight)]*100%. Y-error bars represent
standard error of the mean among replicates.
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.
Biomass (kg/m2)
Experimental System & Methods
Shallow
Treatment Type
Purpose
Our two primary goals were:
1) 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.
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Natural
Recruitment
Combined
Treatment Type
Figure 3. Biomass = oven-dried weight in kg/m2. Y-error bars represent standard error of the mean.
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.