Abstract
Tree growth and hydrologic patterns in three forested mitigation wetlands in Central Ohio were compared with a reference forested wetland and with previous data collected at these wetlands. Trees in two of these forested wetlands had been planted around deep water basins, while the other two wetlands, including a reference wetland, had established forests around vernal pools. Hydroperiod and precipitation data were used to quantify aspects of the hydrology of these wetlands and to create a vernal pool model. Tree growth, survival and recruitment data were used to assess the persistence of the trees and their productivity and to validate a previously created tree growth model. Groundwater and surface water fluctuations in these wetlands reflect different water sources, their connectivity to those sources and the size of their watershed. The two planted sites received their primary water sources from streams but their hydrographs were decidedly different. One site is connected to a stream with a large watershed, but the site is separated from the streamfiow by an inlet weir until the stream floods over the weir, which only occurs several times a year. Vernal pools at two of the wetland sites received their primary water from precipitation, but the mean depth and duration of inundation of vernal pools was significantly higher at the created vernal pool site than at the natural vernal pool site. Trees at the planted sites had significantly higher growth in DBH per year than the established sites. However, the established forest sites had significantly larger trees and, as a result, significantly higher basal area growth per year than the planted sites. Total basal area of the reference site was 38 mø/ha while at the planted sites it was around 2 mø/ha. Diversity and species richness was highest at the reference site (H' = 2.7, richness = 29) while the planted sites averaged H' of 2.05 and richness of 12.5. Tree species response to elevation varied according to site. The established sites, with larger and flood tolerant trees at lower elevations, exhibited greater growth there, while the planted sites showed the highest growth at mid-elevations. Fraxinuspennsylvanica exhibited the greatest growth in DBHJyr and basal area/yr at 0.9 cm/yr and 11.5 cmø/yr, respectively. The most dominant species at the planted sites was Acer saccharinum and the tree growth model predicted its growth within 10%. Using this model it was estimated that Acer saccharinum trees would need 44 years to meet the reference site's average DBH. Quercus palustris was the planted species with the lowest mortality at both sites. Volunteer trees made up 60% of the trees at the planted sites. Planting did speed up growth as the mean DBH of planted Fraxinus pennsylvanica was 13.0 cm while volunteer trees' was 2.6 cm. The three created sites each exemplified a property that enhanced tree growth, density or productivity. The site with the greatest hydrologic pulsing produced the greatest growth in DBH/yr; the site closest to an existing bottomland forest had the greatest tree density, volunteer tree DBH and height; and the site created in an existing forest generated the highest basal area increase per year.