Microenvironments for Forest-Farming of Medicinal Herbs in Varying Forest Structures of the Midwestern USA

Abstract

ABSTRACT To examine the potential for forest-farming production of medicinal plants in the temperate hardwood forests of the eastern US, forest floor microenvironments were examined in a chronosequence of even-aged forests and in canopy gaps of an uneven-aged forest in the midwestern US. Measurements of light, air and soil temperature, relative humidity, and vapor pressure deficit were taken on a diurnal basis several times each month during the growing season. In canopy gaps, measurements were taken along transects from the gap center into interior forest cover. Results showed that all of the microenvironmental variables are influenced by stand structure and age and thus influence the growth environment for forest-farming production. Soil and air temperatures were the most stable parameters with greater diurnal variation in air temperatures, relative humidity, and vapor pressure deficits. Light was the most variable parameter measured in both forest structures, ranging from near full sunlight in canopy gaps to less than 2% of full sunlight under the canopies of older forests. Spatial variability of light was very high in uneven-aged forest, and interior conditions were found beyond 8 m from a gap center. Temporal variability in both forest structures was also significant, with daily and seasonal patterns for most microenvironmental variables. Significant interactions among structural, spatial, and temporal variables precluded simple summarization of main parameter effects. With both even and uneven-aged stand structures, silvicultural manipulation would likely be needed to optimize conditions for a range of understory plants that could be produced on a commercial basis. However, the different structures imply different treatments and intensities of treatment, with scheduling being a function of the microenvironmental requirements of specific forest-farming crops.