At the broadest level, research conducted by my group addresses the roles of mechanisms that underlie ecological interactions at levels spanning the range from biochemistry to ecosystems. We are particularly interested in how plant chemistry influences: 1) interactions among plants, herbivores, and natural enemies, and 2) ecosystem dynamics such as decomposition and nutrient cycling. Other, nonchemically-oriented work addresses environmental impacts on trophic cascades and insect biodiversity. Our research focuses on northern temperate forest species (aspen, maple, birch) and western riparian species (cottonwood), although some studies address herbaceous systems. Our research is funded by multiple sources, principally NSF (Ecological Studies), DOE (Office of Biological and Environmental Research) and the University of Wisconsin (USDA-Hatch).
Current focal areas include:
1. Genetic and environmental
mediation of plant defense. 
This research seeks to explain how genetic, environmental, and ontogenetic factors shape the expression of defense traits (chemical resistance and tolerance) in trees, and how these in turn affect tree resistance to herbivore (insect and mammal) attack,
herbivore susceptibility to natural enemies, and ecosystem processes such as nutrient cycling. Our major experimental system consists of aspen (Populus tremuloides) and a variety of aspen-feeding animals (ranging from gypsy moths to elk).
The secondary metabolites of importance include phenolic glycosides and
proanthocyanidins (condensed tannins). Previous research assessed
the roles of genotype and resource availability with respect to short- and long-term
induced responses in aspen. Recent and future emphases address the costs
of defense (resistance and tolerance) in ontogenetic and evolutionary context.
Related research with colleagues at Northern Arizona University is evaluating how genetic and chemical variation in naturally occurring and synthetic hybrids of cottonwood species mediates ecological structure and function at population, community and ecosystem levels. The "extended phenotype" concept is a central theme of this research. Collaborative projects underway relate cottonwood chemistry to arthropod communities, mycorrhizal communities, mammalian foraging, and litter decomposition. For more information see The Cottonwood Ecology Group website.
2. Global environmental change
and plant-insect interactions. 
This research evaluates the consequences of global environmental changes
for plant growth, foliar chemistry, herbivore and natural enemy performance,
and insect biodiversity. Primary emphasis has been on enriched carbon
dioxide, although tropospheric ozone and enhanced ultraviolet radiation
are also of interest. Work is conducted in environmentally controlled
glasshouses and at a multi-institutional Free Air CO2
Enrichment facility (Aspen FACE) in northern Wisconsin. Experimental organisms include
herbaceous (e.g., clover) as well as woody (e.g., aspen, birch, maple,
oak) plant species, lepidopteran, coleopteran and homopteran folivores,
soil microarthropods, and natural enemies (virus, predators and parasitoids). Current work at Aspen FACE is addressing the effects of elevated CO2 and ozone on: 1) canopy insect biodiversity, 2) impacts of insects on primary production, and 3) insect-mediated organic substrate deposition and nutrient cycling.
For more information about the FACE facility, see the Aspen FACE homepage.
3. Genetic variation and ecosystem function. 
This research investigates how inter- and intraspecific genetic variation, resource availability, and herbivory interact to influence ecoystem function (leaf litter decomposition and nutrient cycling). Model systems include quaking aspen in Wisconsin and riparian cottonwoods in the Intermountain West (in collaboration with researchers at Northern Arizona University). A central focus of this research is to identify the relevance of intraspecific biodiversity and herbivory for the functioning of forest ecosystems.
