PLANT DIVERSITY, YIELD & STABILITY IN PERENNIAL BIOFUEL PLANTINGS
Along with researchers in the Great Lakes Bioenergy Research Center, I am examining the relationships between plant community composition and the consistency of yield in fields planted with several candidate bioenergy crops: switchgrass monocultures, mixtures of native C3 and C4 grasses, prairie, and an early successional field. Stabilization provided by tradeoffs between functional groups or species in response to environmental fluctuation may be an important benefit gained from plantings with many species. We are also interested in the effects of harvesting frequency and timing on plant community composition in prairies being harvested for biofuel. Ecological services such as pollination, carbon cycling and water retention depend in part on plant composition, thus managing the plant community via harvesting could enhance or decrease the provision of different services.
Recent publication: Stahlheber, K. A. et al. 2016. Balancing biofuel production and biodiversity: harvesting frequency effects on tallgrass prairie depend on plant community composition. Biomass and Bioenergy 92: 98-105.
INTRASPECIFIC TRAIT VARIATION IN SWITCHGRASS [Panicum virgatum]
Intraspecific variation is quite large in switchgrass, especially between the two major North American ecotypes: upland and lowland. They differ in productivity, chemical composition, stress tolerance and phenology, among other traits. In conjunction with undergraduate researchers and the Emery lab at University of Louisville, I am exploring above and belowground trait variation in twelve varieties of switchgrass planted in a common garden. We plan to relate these traits to patterns of productivity over the last five years and the impacts of intraspecific variation on belowground communities (primarily fungi & nematodes). We are also comparing the scale of variation between switchgrass varieties with variation between different species of grass. Just as species diversity can lead to enhanced stability, productivity, protection from weed invasion - among other services - genetic variation within switchgrass may be an important way to enhance 'monocultures' typically used for biofuel.
LINKING SWITCHGRASS [Panicum virgatum] PRODUCTION AND PERFORMANCE TO SOIL COMMUNITIES
In collaboration with Sarah Emery at University of Louisville, I am examining the responses of several varieties of switchgrass [Panicum virgatum] to drought stress and nitrogen fertilizer. By simultaneously measuring belowground communities, plant physiology and growth in fields subject to different fertilizer applications and precipitation treatments, we hope to understand how soil organisms might be affected by management and/or alter plant responses. In particular, we are documenting the abundance, diversity and composition of arbuscular mycorrhiazal fungi (AMF) and nematodes in soils using both morphological and next-generation sequencing methods. AMF in particular can help host plants in stressful environments by enhancing nutrient update and/or drought tolerance, but these mutualistic relationships may change when plants are fertilized.
GRAZING AND PLANT SPECIES DIVERSITY
Another research interest is the connection between domestic livestock grazing and the plant community. In California, grazing has been proposed as a way to control undesirable exotic species and enhance the presence native species. Impacts of grazing, however, might vary between different habitats or locations within a pasture, such as the understory of trees. My work is examining the impacts of cattle on the oak understory [Quercus spp.] compared to open grassland, where most research has demonstrated that grazing can enhance diversity (although this might primarily be an increase in non-native forb species). Native species in the understory may be more or less sensitive to grazing than those that are more common in the open, and the tendency of animals to cluster around shade could heighten the impacts of grazing under trees.
Recent Publication: Stahlheber, K. A. and C. M. D’Antonio. 2013. Managing plant composition with livestock: A meta-analysis of grazing in California Mediterranean grasslands. Biological Conservation 157: 300-308.
SAVANNA TREES AND PLANT COMMUNITY STRUCTURE
I am broadly interested in the influence of savanna oak trees [Quercus spp.] on plant community structure in California. During my dissertation I used observational and experimental approaches to assess local, landscape and regional-scale impacts of trees on plant diversity and species composition. Ongoing work in this area is examining how oak trees change litter decomposition and cycling relative to rates in open grassland.
Recent Publication: Stahlheber, K. A. 2016. The impacts of isolation, canopy size, and environmental conditions on patterns of understory species richness in an oak savanna. Plant Ecology.