Transferring site information for black walnut from native woodlands in southeastern Kansas USA to identify sites for agroforestry practices

Abstract

Black walnut (Juglans nigra) is an important tree species for temperate agroforestry in the United States for timber, nuts, wildlife, and abrasives. Predictions of forestland productivity are needed for proper species selection in tree planting. Potential productivity can be estimated for non-forested areas and agricultural croplands by relating site quality to site and soil characteristics. Our study measured the growth potential of black walnut in natural stands. We looked at over 210 stands on unglaciated soils in southeastern Kansas with the site index at 50 years ranging from 9.1 to 26.8 m. Numerous environmental factors were evaluated, including: site, soil chemical, and soil physical properties. These environmental factors were related to tree height at the standard age of 50 years. Simple correlation and multiple regression analyses were run with the site index using over 60 variables of soil and topographic characteristics. Understory competition had no effect on site index. Chemical characteristics had a slight effect on site index. We explained 73 % of the variation in site index with just two variables; depth to a restrictive layer (DRL) and soil type. DRL is a good predictor of walnut productivity.