Our study consists of 14 headwater wetlands dominated by black ash and located on the Ottawa National Forest in the western upper peninsula of Michigan. The wetlands range 0.25-1.4ha in size and are defined by spring inundation and saturation throughout the growing season. Each site receives water from the surrounding forested uplands with little to no flow enter through a defined channel, and most have a defined ephemeral channel draining the site during high water. Black ash accounts for 70-90% of the overstory basal area with the rest of the stand being composed of mainly red maple, yellow birch, northern white cedar, and balsam fir. The soils are primarily organic and the depth to mineral soil ranges from 0m to greater than 6m. In order to evaluate the impacts of EAB on black ash wetlands we simulated an infestation at each of our study sites by girdling or cutting and leaving on site all ash stems greater than 1" in diameter. The two simulation techniques are meant to simulate a stand soon after infestation peaks and a stand showing the long-term impacts of infestation.

Generalized hydrology of study wetlands

The 14 sites are divided into three study branches to enable us to address a wider range of research topics: ecological process sites, underplanting sites, and a paired watershed experiment. There are nine ecological process sites divided into three geographic blocks and each group contains a control, a girdle, and an ash cut wetland. At these sites we have been looking at how the removal of black ash from the landscape would affect carbon dioxide and methane efflux from soils and quantifying, for the first time in North America, the amount of these gases emitted directly from the trunks of wetland trees. We are classifying various components of the hydrology of these sites including water level changes, groundwater interactions, canopy transpiration, interception, and stemflow. In addition to measuring interception and stemflow we have estimated nitrogen input from rainfall interacting with the canopy and evaluated the availability and allocation of that nitrogen within the sites.

Three of the study wetlands were used to evaluate the species suitability and planting strategies that could be used to retain these sites as forested wetlands. Ten species were selected for planting within the study sites and plantings were arranged along stratified transects along the hydrologic gradient present within the sites. The plantings were arranged in pairs to evaluate the effect of microtopography on seedling survival and by planting in each treatment type we can compare the effectiveness of planting during different stages of infestation.

Seedling planting arrangement

Two of our study sites are grouped together in a paired watershed experiment. This type of experiment uses pre-treatment data from two sites with flumes installed at their outlets to relate the flow of water and nutrients from one wetland to the other. Following treatment at one of the two sites changes to that relationship can be studied and attributed to the treatment applied. The continuous record of water yield from a control and an ash-cut site, combined with regular water sampling allows us to calculate the amount of carbon and nitrogen being transported out of these sites. To help us understand the source of this carbon we are also studying the rates of decomposition of organic matter in the soil.