Lodgepole pine tree-ring growth, Δ13C and the inverse texture effect across a soil chronosequence in glacial till

Abstract

Our goal was to better understand tree growth and photosynthetic responses to variations in plant available water and elucidate the role of the inverse texture effect in snow dominated montane forests. We measured tree ring carbon isotope composition and annual growth over a 31-year record for lodgepole pine (Pinus contorta Douglas ex Loudon) growing on three different-aged glacial till surfaces in Wyoming, USA. Soils of different ages developed on till surfaces from three separate glaciation events were significantly different in clay content and distribution with depth; maximum clay content at depth ranged from 19 to 20% on the two youngest till surfaces, but was as high as 36% on the oldest till surface. Ring growth was lowest at the youngest till sites, and only on these coarse-textured soils was growth positively correlated with annual maximum snow water equivalent (SWEmax). Δ13C was highest for trees at these young till sites, suggesting that hydraulic conductivity and stomatal conductance is comparatively high during growth periods on these coarse-textured soils. Taken together, we found that age of glacial till and related soil texture differences strongly influenced tree-ring growth and Δ13C response of lodgepole pine to interannual variation in precipitation and drought severity, but responses did not support an inverse texture effect in these semi-arid forest systems.