DOI: 10.5061/dryad.ff574
title: Data from: Competitor or facilitator? The ambiguous role of alpine grassland for the early establishment of tree seedlings at treeline

description: Alpine treelines are expected to move upslope with a warming climate.
 However, so far treelines have responded inconsistently and future shifts
 remain difficult to predict since many factors unrelated to temperature,
 such as biotic interactions, affect responses at the local scale.
 Especially during the earliest regeneration stages, trees can be strongly
 influenced by alpine vegetation via both competition and facilitation. We
 aimed to understand the relative importance of these two types of
 interaction in different vegetation structures for treeline regeneration
 dynamics. Effects of herbaceous alpine vegetation on seedling emergence
 and first-year performance were studied in a field experiment in the
 French Alps (2100 m a.s.l.) with five important European treeline tree
 species: Larix decidua, Picea abies, Pinus cembra, Pinus uncinata and
 Sorbus aucuparia. Total emergence and locally-germinated seedling survival
 were not affected, but for seedlings planted at two months of age,
 negative vegetation impacts dominated for all response parameters:
 first-year survival, growth and carbohydrate accumulation. However, in the
 winter half-year, evergreen tree seedlings increased carbohydrate reserves
 under the protection of senescent herbs. Also, responses of
 locally-germinated seedlings suggest facilitative vegetation effects in
 the first two months after emergence. Thus, the interaction switched
 between competition and facilitation according to ontogenetic stage and
 seasons. Still, the net outcome after one year was negative, but species
 differed in their susceptibilities. Because initial establishment is the
 first bottleneck determining whether treelines remain stable or move
 upslope, understanding establishment, including site-, life-stage and
 species-specific processes, is essential for understanding observed
 treeline spatial patterns and dynamics. When developing predictive models
 of treeline dynamics, all these ‘local’ aspects should be incorporated in
 addition to more global drivers like changes in temperature.
description: Seedling emergence and
 survival_Loranger2017Emergence and
 survival_Loranger2017.csv = Comma-delimited CSV. Emergence of tree
 seedlings from seeds and subsequent survival through the first growing
 season at alpine treeline elevation in the French Alps. Seeds were sown in
 autumn 2013 and emergence and survival/mortality were registered weekly
 throughout the growing season in 2014. Date = date of monitoring FreeDays
 = number of days after snowmelt Block = experimental block Treat =
 treatments: C = Control = bare-ground plots; Sh = shading = covered by
 shade roofs; V = full vegetation, V2 = intermediate vegetation. Species:
 Lar = Larix decidua; Pic = Picea abies; Sor = Sorbus aucuparia; Pinc =
 Pinus cembra; Pinu = Pinus uncinata Row = row in plot Sown = number of
 seeds sown Dead = number of dead seedlings Alive = number of surviving
 seedlings Germ_All = number of germinated seedlings (including
 subsequently dead ones)Emergence and
 survival_Loranger2017.csvCarbohydrates and
 Biomass_Loranger2017Carbohydrates and
 Biomass_Loranger2017.txt = Tab-delimited text file. Non-structural
 carbohydrate concentrations and biomass of plant parts (roots, stems,
 leaves) of tree seedlings at alpine treeline elevation in the French Alps.
 Seedlings were planted in spring 2013 and harvested in autumn 2013 and
 spring 2014. ID = Sample ID from carbohydrate extraction Season = sampling
 season: S13 = September 2013, M14 = May 2014 Block = experimental block
 Treat = treatments: C = Control = bare-ground plots; Sh = shading =
 covered by shade roofs; V = full vegetation, V2 = intermediate vegetation
 Species: Lar = Larix decidua; Pic = Picea abies; Sor = Sorbus aucuparia;
 Pin = Pinus cembra; Pinu = Pinus uncinata Ind = seedling number in the
 plot Part = seedling part: L = leaves, S = stem, R = roots MassSm = mass
 of extraction sample (mg) MassPt = mass of seedling part (mg) Glu =
 glucose concentration (mg/g) Fru = fructose concentration (mg/g) Sac =
 saccharose concentration (mg/g) Mal = maltose concentration (mg/g)
 Total_SC = total soluble sugar concentration (mg/g) Starch = starch
 concentration (mg/g) Total_NSC = total non-structural carb. Concentration
 (mg/g)Mortality_Loranger2017_13-14Mortality_Loranger2017_13-14.csv = Comma-delimited CSV. Seedling mortality in tree seedlings at alpine treeline elevation in the French Alps. Seedlings were planted in spring 2013 and mortality was registered in September 2013 and April-May 2014, after snowmelt. The first registration was April 16th in Block 1, in the other blocks the registration was later, as snow melted later. Season = grouping of data collections into two seasons: May14 = Spring (16 April to late May) 2014, Sept 13 = 2 Sept 2013 Block = experimental block Treat = treatments: C = Control = bare-ground plots; Sh = shading = covered by shade roofs; V = full vegetation, V2 = intermediate vegetation. Species: Lar = Larix decidua; Pic = Picea abies; Sor = Sorbus aucuparia; Pin = Pinus cembra; Pinu = Pinus uncinata Planted = number of seedlings planted DeadOn = number of dead seedlings not counting those damaged by breakage or herbivory DeadAl = number of dead seedlings