John Kabrick

Ecology and silviculture of hardwood – softwood mixtures. Naturally occurring mixtures of hardwoods and softwoods, or “mixedwoods”, are found throughout the temperate region of the United States, Canada, and elsewhere in the world. They are compositionally diverse and appear to have originated from a complex array of natural disturbances or past harvesting. Contemporary mixedwood stands can be difficult to regenerate and manage because individual species of these mixtures have differing shade tolerances, growth rates, longevities, phenology, and crown and root structure. Consequently, they often cannot be sustained without deliberate silvicultural efforts to regenerate and recruit desirable species. Despite the difficulties, foresters are interested in managing hardwood–softwood mixtures because of the many benefits that they are perceived to confer including increased resistance to pests and diseases, improved habitat diversity, enhanced climate change resilience and adaptability, and increased diversity of forest products. My research includes (1) evaluating the benefits of mixtures relative to their hardwood or softwood analogs in terms of resilience to insect pests and diseases, climate change, and other disturbances; (2) developing and testing silvicultural practices for sustainably managing the various mixtures in the eastern United States and Canada, particularly for shortleaf pine and oak mixtures; and (3) engaging with managers and fellow scientists to share local and broader-scale findings related to the benefits and silviculture of mixedwood types.

Composition, structure, and silviculture of woodlands and other open forests. Much is known about the composition and structure of forests and silvicultural methods for regenerating and tending forests have been widely studied. However, the composition, structure, and in particular, the silviculture of woodlands and other disturbance-dependent open forests has received little attention. My research includes (1) developing meaningful density and size distribution metrics and targets for woodlands and savannas; (2) experimentally examining the effects of prescribed burning and thinning for meeting compositional and structural targets; and (3) developing a conceptual framework and sets of tools based on fundamental silvicultural principles.

Dynamic soil properties for sustainable forest management. Sustainable forest management requires ensuring that soil physical properties are protected, and soil carbon and nutrient supplies are not depleted through harvesting, prescribed burning, and related management activities. I am currently working on several projects that are focused on the effects of management on soils. This includes examining the effects of timber harvesting and prescribed burning on soil carbon, nutrients, and physical properties including aggregate stability, bulk density, and porosity. I am a team member of the Long-Term Soil Productivity network to examine the effects of organic matter removal and soil compaction on sustained forest growth and productivity. Along with colleagues in the Natural Resources Conservation Service, I am establishing baseline information about soil health metrics in native forests so that the effects of past and present land used can be evaluated. I am working with a team of scientists to mitigate compaction in log landings with subsoiling treatments and biochar applications, ultimately to establish pollinator habitat. I am quantifying the role of soil temperature and mositure on soil organic matter decomposition, and for bottomland tree root growth and flood tolerance in managed wetlands. Recently I began working with scientists and managers in the Forest Service and other agencies to provide more access to soil moisture and temperature data for making management decisions. 

Important research included examining the relationship between site factors and oak decline and mortality, quantifying the cumulative effects of even-aged, uneven-aged, and no-harvest management on forest vegetation and wildlife species, developing methods for the natural and artificial regeneration of bottomland forests, and evaluating the flood tolerance of bottomland hardwoods.

I am interested in developing and evaluating silvicultural systems for sustaining native flora and fauna communities in balance with traditional forest commodities. This includes quantifying the roles of disturbances (harvests and fire) and environmental conditions for creating and maintaining various forest and woodland structures over space and time. Of particular interest are the interactions between the physical environment (e.g., geological parent material, landform position/aspect, soils, and hydrology) and forest vegetation. I also have interests in examining the long-term consequences of forest management on the soil's ability to store carbon and to supply nutrients and water, and using models for evaluating silvicultural approaches for positioning forests and woodlands for projected changing conditions.

Forest management is becoming more challenging because of the combination of changing societal expectations and evolving ecological perspectives. Consequently, public forest land management agencies are increasingly setting more complex objectives emphasizing more wholistic, system-level forest management including restoring and sustaining native forest and woodland communities. Moreover, private forest land owners are shifting their priorities to emphasize non-commodity forest values such as wildlife habitat. These changing expectations and evolving perspectives require developing and evaluating new management methods based upon basic silvicultural and ecological principles.