Aboveground Biomass and Soil Organic Matter as aFunction of Planting Strategy and Water Depth in Six

Experimental Wetland Cells After One Year of Planting

Rachel Cohn, Gavin M. Platt, H. Siv TangSystems Ecology (ENVS316) Research Project, Fall ‘04

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).

Background

Purpose

Findings

Conclusions

References

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.

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).

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.

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.

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.

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.

Picture 1. Harvesting biomass at the site.

Picture 2. Incinerating soil to determine SOM.

Effects of Planting Strategy and Depth on Plant Biomass

0.0

0.2

0.4

0.6

SelectivePlanting

NaturalRecruitment

Combined

Treatment Type

Bio

ma

ss

(k

g/m

2 )

Shallow

Deep

Effects of Planting Strategy and Depthon Soil Organic Matter

0.0

2.0

4.0

6.0

SelectivePlanting

NaturalRecruitment

Combined

Treatment Type

% S

OM

Shallow

Deep

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).

Figure 3. Biomass = oven-dried weight in kg/m2. Y-error bars represent standard error of the mean.

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.

Figure 4. % SOM = [(ash-free dry weight)/(oven-dried weight)]*100%. Y-error bars represent

standard error of the mean among replicates.

Cell I Cell II Cell III Cell IV Cell V Cell VI North (Deep)

Natural Recruitment

Planted and Seeded

Planted and Seeded

Natural Recruitment

Planted and Seeded

Planted and Seeded

South (Shallow)

Figure 1. Diagram of planting regime of the experimental system at EDIC.