Mediterranean and temperate treelines are controlled by different environmental drivers

The growth limitation hypothesis (GLH) is the most accepted explanation for treeline formation, but it has been scarcely examined in Mediterranean treelines, which are located at lower elevations than temperate treelines. The GLH states that low temperature is the ultimate environmental driver for treeline formation, constraining C-sinks (i.e. tissue formation) more than C-sources. The GLH predicts similar or increasing (but not decreasing) non-structural carbohydrate (NSC) concentrations with elevation throughout the course of the growing season. We hypothesized that elevational trends in growth and NSC in Mediterranean regions are not determined by only low temperature. We tested the GLH by examining the mean annual basal area and NSC concentrations in developing (new twigs) and ripened tissues (branch, stem) of trees growing at three elevations in three Mediterranean and three temperate treelines in the Chilean southern Andes (33ºS, Kageneckia angustifolia, 36ºS, 40ºS, and 46ºS, Noth...