DOI: 10.5061/dryad.ks97h
title: Data from: Mediterranean and temperate treelines are controlled by different environmental drivers

description: 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, Nothofagus
 pumilio) and in Spain (36ºN, Pinus sylvestris, 42ºN, P. uncinata). Samples
 for NSC were taken at the onset of summer and autumn, which represent
 periods of contrasting drought intensities in Mediterranean regions. Tree
 growth decreased significantly with elevation in temperate treelines but
 not in Mediterranean treelines. In Mediterranean treelines, new twig NSC
 concentrations increased significantly with elevation in the early summer
 but not in the early autumn. In temperate treelines, in contrast, no
 elevational or seasonal variation (or interaction between them) was
 observed in new twig NSC concentrations. The NSC concentrations of the
 branches and stems from both climates showed no elevational trends. The
 soluble sugars’ NSC fraction increased over the season in Mediterranean
 treelines and decreased in temperate treelines. Synthesis. Although we
 found support for the growth limitation hypothesis (GLH) in temperate and
 Mediterranean treelines, our study shows that the tree growth and C
 balance in Mediterranean treelines are not controlled by low temperature
 alone. We suggest that environmental factors other than temperature
 explain the lower global elevation of Mediterranean treelines when
 compared to temperate treelines.
description: Growth and carbohydrates
 in temperate and Mediterranean treelinesThe file contains two
 sheets: 1. NSC shows total soluble carbohydrate, starch, and non
 structural carbohydrates concentrations per mass unit (col I, J, K,
 respectively) and per volume unit (N, O, P, respectively) in three tissues
 (col D, new developing twings, stem sapwood, and branches) in early summer
 and early autumn (col E, spring and autumn, respectively) 6-8 adult trees
 of different species (lenga: Nothofagus pumilio, frangel: Kageneckia
 angustifolia, uncinata: Pinus uncinata, sylvestris: Pinus sylvestris) at
 three elevations (treeline, intermediate named as "inter", and
 closed or montane forest named as "low") of altitudinal
 gradients sampled in four locations of Chile (termas: Termas de Chillán,
 antillanca: Antillanca area within Puyehue National Park, castillo: Cerro
 Castillo Natural Reserve, in Patagonia, and farellones: Farellones in
 Central Chile) and Spain (pyrenees: Sierra de Cutas area in Spanish
 Central Pyrenees, and sierra: Sierra Nevada). First col indicates the
 climate for each location. 2. BAI refers to mean annual basal area
 increment of the last 10 years in 6-8 adult trees of different species
 (lenga: Nothofagus pumilio, frangel: Kageneckia angustifolia, uncinata:
 Pinus uncinata, sylvestris: Pinus sylvestris) at three elevations
 (treeline, intermediate named as "inter", and closed or montane
 forest named as "low") of altitudinal gradients sampled in four
 locations of Chile (termas: Termas de Chillán, antillanca: Antillanca area
 within Puyehue National Park, castillo: Cerro Castillo Natural Reserve, in
 Patagonia, and farellones: Farellones in Central Chile) and Spain
 (pyrenees: Sierra de Cutas area in Spanish Central Pyrenees, and sierra:
 Sierra Nevada). First col indicates the climate for each
 location.mediterranean_nsc_dryad.xlsx