Relationships Between Ring-Width Variation and Soil Nutrient Availability at the Tree Scale

Abstract

Within the framework of the linear aggregate model of dendrochronology, the potential role of soil nutrient availability in explaining multi-decadal variation in radial growth at the tree level was studied in the central Spanish Pyrenees. Increment cores were collected from 20 mature Pinus uncinata Ram. and analyzed dendrochronologically. One ion-exchange resin capsule was buried within the root zone of each sampled tree for just over eight months. The resins were chemically extracted and measured for NH₄, NO PO₄, Ca, and K. Statistical relationships between indexed tree growth and soil nutrient availability were determined with regression analysis and bivariate plots. The single most important soil nutrient with respect to decadal-scale dendrochronological tree-growth variables in this study was N in the form NO which explained 22% of variation of trend in growth since 1950. The 20 values of NO₃ availability fell into two subgroups, one of trees with relatively higher NO₃ availability and the other with lower NO₃ availability. When the tree-growth data were grouped based on NO₃ availability, the two resultant index chronologies had different low-frequency features since 1950. Trees with low NO₃ availability have been growing as expected based on past growth, but trees with high NO availability have been growing better than expected. Measuring and analyzing soil nutrient availability at the tree level might enhance environmental applications of dendrochronological research. With soils information at this spatial scale, it is possible to distinguish between subgroups of trees within a tree-ring site and thereby construct subchronologies that differ significantly, especially for variation at the decadal scale. Subsite-chronologies may then lead to different and presumably more informative environmental interpretations relative to those based on a full-site chronology.