Date of Award
Doctor of Philosophy
Natural Resource Ecology and Management
Janette R. Thompson
The landscape of the Midwest has been heavily altered by human land use, and remaining natural areas are under pressure from expanding agricultural and urban lands that surround them. Remnant natural areas, such as forests, may also be degraded by past or proximate land use, leading to loss of ecosystem services such as biodiversity and nutrient capture. Within hardwood forest ecosystems, the herbaceous layer is important for biodiversity and nutrient cycling, and is especially sensitive to disturbance. Previous research indicated that herbaceous plant community composition may shift due to human impacts, resulting in loss of specialist perennials and greater prevalence of non-native and generalist species. It has also been documented that preserved herbaceous plant communities had greater biomass and nutrient capture than those subjected to intense human disturbance. Taken together, earlier work pointed toward the opportunity for an integrated approach to assessment, restoration, and outreach to understand and improve the functional role of herbaceous flora in forests that have been subjected to different land uses. First, this work focused on identification and validation of a simple metric to describe floristic quality of forest herbaceous plant communities, the mean coefficient of conservatism (mean CC). Using plant life history characteristics (annual, biennial, fern, exotic, closed-canopy specialist, and moist-site specialist) and a robust data set from 126 plots in forests under five land uses (secondary, urban, grazed, managed for timber harvest, and preserved), an independent index of disturbance was developed and then used to validate mean CC. The disturbance index confirmed mean CC as a valid measure to assess floristic quality that could be recommended to forest landowners and managers as a way to quickly and easily determine conservation priorities, monitor land use impacts and assess restoration efforts. Second, this research investigated the effect of herbaceous community composition on terrestrial nutrient capture and linkages to surface water quality. Above- and below-ground herbaceous plant tissue, soil, and in-stream water samples were collected from forest areas (under urban, agricultural, and preserved land uses) and embedded streams, and measured to determine biomass and concentrations/quantities of nitrogen and phosphorus. Herbaceous flora under urban and agricultural land uses had more generalist species, lower quantities of nutrients stored in plant biomass, and higher concentrations of nutrients present in stream water. To further elucidate the role of herbaceous biomass in nutrient capture, an additional study focused on four spring-growing species that produce large quantities of plant tissue. Nutrient captured in quadrats dominated by a single species exceeded nutrient capture from quadrats in compositionally diverse herbaceous layers for three of the four species examined. Planting trials of a set of functionally important species also demonstrated the likelihood of persistence and recruitment in restoration plantings. Finally, collaborative learning workshops were conducted with forest land owners and forest managers to support the integration of understory restoration with other forest management goals. Land owners and land managers discussed barriers to effective forest management, and indicated plans to engage in invasive species control, timber stand management, and/or restoration and planting efforts as a result of collaborative interactions. Assessment of workshop activities and outcomes pointed to the importance of close integration of ecological and social system components to support restoration of ecosystem function at a landscape scale.
Michaeleen E. Gerken Golay
Gerken Golay, Michaeleen E., "Assessing the composition and function of hardwood forest herbaceous flora: implications and applications for forest restoration" (2013). Graduate Theses and Dissertations. 13031.