Pecan tree rings as intrinsic and extrinsic indicators of environment

Abstract

Pecan (Carya illinoensis) tree rings are climate sensitive and correspond favorably with published post oak tree ring chronologies from adjacent locations. A pecan dendroecological model was built from monthly climatering index correlations. significant climate intervals and factors that influenced pecan ring width were obtained by iteratively combining strong correlations. They, along with previous ring width, were incorporated into the dendroecological model. Ring width of the previous year, rainfall from October and November of the previous year (lagged fall) and the mean temperature of April, May, and June of the ring year (spring) were correlated with current year pecan ring width. The regression model explained 70% of the variation. Correlation of yield and ring width indicated that ring widths were positively correlated to yield, but negatively correlated to previous yields. When added to the pecan dendroecological model, yields and previous yields were insignificant compared to other factors in the model. Yield did not appreciably affect ring width and indicated that ring width reduction associated with-masting (used as an index of resource depletion) did not occur in pecan. Pecan masting was analyzed according to a conceptual model of masting. This model involved the interaction of an intrinsic cycle inherent to the tree with extrinsic climatic factors which then determined the final amplitude of the yield at masting. The intrinsic cycle of pecan from individual tree orchard yield data was biennial. Extrinsic climatic factors were obtained from monthly climate correlations with mean orchard yields. Correlations were examined to determine climatic influences on yield. Temperature of the previous fall (October and November) and summer temperature (June, July and August) influenced yield. Pecan yield and masting cycles cannot be analyzed only from the perspective of an intrinsic cycle. Geographic units used for mast analysis should correspond to homogenous geoclimatic regions.