Cultivars of Eastern Black Walnut Trees ( Juglans Nigra L.) Have Greater Nut Yields Than Native Trees at Similar Trunk Cross-Sectional Areas

Abstract

Orchard production of eastern black walnut ( Juglans nigraL.) cultivars may be the best way to stabilize the supply of nuts. The objective of this study was to determine if the relationship between trunk cross-sectional area (TCSA) and nut yield is different between cultivars of black walnut and native trees. Data were collected from 13 stands of black walnut (six stands of native trees and seven stands of cultivars) growing in open canopy or free-to-grow circumstances in the central United States for two consecutive years (2002-2003). The regression equations between two-year mean for nut yield per tree and trunk cross-sectional area (TCSA) were highly significant for data from native trees and cultivars of black walnut; however the slopes and Y-intercepts differed. For cultivars, the equation was: two-year mean yield (kg per tree) = 0.0071*(mean TCSA, cm ²) + 1.38. For native trees, the equation was: two-year mean yield (kg per tree) = 0.0049*(mean TCSA, cm ²) - 0.11. When various independent variables were assessed as predictors of two-year means for yield among the 13 stands, the regression equations generated by backward selection included two variables: 1) the tree stock type, i.e. cultivars versus native trees; 2) annual mean increase in TCSA. These analyses indicate that cultivars did differ from native trees in the relationship between TCSA and nut yield per tree.