Modeling and Mapping Oak Advance Reproduction Density Using Soil and Site Variables

Regenerating oaks (Quercus spp.) has remained a widespread and persistent problem throughout their natural range. Research shows that abundant oak advance reproduction is crucial for success. Although it is recognized that oak advance reproduction accumulation is inversely related to site quality, there has been little effort to model oak advance reproduction density as a function of measured levels of light, water, or nutrient supply. The objective of this study was to determine whether oak advance reproduction could be modeled and mapped with site variables. The study was conducted on the Sinkin Experimental Forest in southeastern Missouri in 20 5-ha experimental units. Vegetation and site data were collected in 120 0.5-ha circular plots with nested subplots for the inventory of the midstory (0.01 ha) and reproduction (0.004 ha). Site variables included soil available water capacity, pH, photosynthetically active radiation in the understory, forest stocking, terrain shape, and slope-aspect. Oak advance reproduction abundance was related to soil acidity and available water capacity and to other site information such as slope-aspect. Models for the red oak group species generally exhibited better fit than those for the white oaks. There also was evidence that estimates of soil acidity and available water capacity can be obtained from the SSURGO database and used in these oak advance reproduction models along with other site information to generate maps of estimated oak reproduction densities. These maps could be used for planning silvicultural interventions to increase the abundance and size of oak advance reproduction before forest regeneration.