Tree growth response to fuel reduction treatments along a topographic moisture gradient in mixed-oak forests of Ohio, U.S.A.

Abstract

This study examined the effect of the soil moisture gradient on tree growth response to prescribed fire and thinning in oak-dominated forests of Ohio. Six hundred and ninety-six increment cores (348 trees, five species) were collected from eighty 0.1 ha plots distributed across four treatments (control, thin, burn, thin + burn) in two sites. Ring widths were converted to basal area increments (BAIs). A water balance approach based on geographic information systems (GIS) was used to assess the potential evapotranspiration (PET) and moisture deficit for each tree, along with a long-term integrated moisture index, also based on GIS. The moisture gradients varied considerably across the landscape, with the highest PET and moisture deficit on ridges and south-facing slopes. This variation influenced the BAI of the studied species, but more strongly in the control stands than in the managed stands, where treatment effects became the main drivers of growth. Oaks exhibited greater BAI on sites with intermediate moisture demand or stress, whereas the non-oaks had greater BAI on more mesic sites. Moisture deficit and PET also interacted to influence BAI of yellow-poplar (Liriodendron tulipifera L.) and white oak (Quercus alba L.), particularly in the control. These results demonstrate the strong regulatory effect of the topographically controlled soil moisture gradient on tree growth in mixed-oak (Quercus spp.) forests, which can be explored to better understand community response to prescribed fire and thinning treatments.