Landscape-scale variability of air and soil temperature related to tree growth in the treeline ecotone

Abstract

Treeline isotherms are used in comparative and modelling studies to predict treeline positions. However, how representative local short-term temperature records are for a given region remains poorly understood. Furthermore, the predictive value of on-site temperatures for explaining tree growth requires further validation. Here we present temperature records and tree growth datasets from treeline ecotone sites differing in elevation and slope direction in the High Sudetes (Czechia and Poland). The goal was to determine the spatial and temporal variability of soil and air temperatures and to describe the relationship of various temperature metrics with tree growth. Our results demonstrate that, because of spatial and temporal variability, major temperature metrics used in comparative studies should be provided with an uncertainty range between 0.6 and 0.8 K for seasonal mean soil and air temperature. While soil temperatures exhibit high spatial variability, air temperatures vary more with time. Elevation is the most important driver of temperature patterns in treeline ecotones. Differences related to slope direction were important mainly for soil temperatures in lower parts of treeline ecotones. Tree growth is tightly related to June–September air temperature, with a modulating role of the onset date of soil temperature-defined growing season. In this study, we describe patterns of temperature variation in the treeline ecotones of two mountain ranges and demonstrate the extremely strong dependence of tree stem growth on air temperature, with very limited remaining space for other potentially limiting factors.