DOI: 10.5061/dryad.22t16
title: Data from: Fine nurse variations explain discrepancies in the stress-interaction relationship in alpine regions

description: Despite a large consensus on increasing facilitation among plants with
 increasing stress in alpine regions, a number of different outcomes of
 interaction have been observed, which impedes the generalisation of the
 ‘stress-gradient hypothesis’ (SGH). With the aim to reconcile the
 different viewpoints on the stress-interaction relationship in alpine
 environments we hypothesized that fine nurse variations within a single
 life form (cushion) may explain this pattern variability To test this
 hypothesis, we compared the magnitude of the stress-interaction
 relationship in a single study area with that observed in existing studies
 involving cushions, worldwide. We characterized the nurse effects of
 cushions on the whole plant community at inter-specific, intra-specific
 and intra-individual levels along a stress gradient in the dry, alpine
 tropics of Bolivia (4400 m, 4700 m and 4900 m a.s.l). Using a relative
 index of interaction (RII) we included our data in a meta-analysis on the
 nurse effects of cushions along alpine gradients, worldwide. At
 inter-specific level, the loose cushion Pycnophyllum was a better nurse
 than the compact Azorella compacta. However, at intra-individual level
 facilitation was higher at the periphery than at the centre of cushions,
 exceeding in magnitude the variation observed at inter-specific level.
 This pattern was associated with higher minimum temperature and lower
 mortality at the periphery of cushions. The net effects of cushions on
 plant communities became more positive at higher elevation, corroborating
 the SGH. Within our single site in Bolivia, fine morphological nurse
 variations captured a similar variability in the stress-interaction
 relationship as that observed in a subset of studies on cushions on a
 worldwide scale. This suggests that fine variations in nurse traits, in
 general those not considered in protocols dealing with facilitation or in
 restoration/conservation management plans, explain in part the current
 discrepancies among SGH studies in alpine regions.
description: Data 1. Effects of the
 intra-individual variable on the nurse effects of cushions
 plantsData 1. Relative
 interaction indices (RII) between the nurse cushions Azorella compacta and
 Pycnophyllum spp. and the neighbouring plant communities. Each line
 represents an interaction between one individual cushion and one
 associated species, either at the centre of at the periphery of cushions
 (variable intra-individual). Data shown at three
 elevations.Data1_RII
 intraindividual.xlsxData 2. The effects of
 inter-specific variations in nurses on the outcome of
 interactionsData 2. The effects of
 inter-specific variations in nurses on the outcome of interactions with
 other plants in the Sajama National Park, Bolivia. Each line represents an
 interaction between one individual cushion and one associated species,
 through the Relative interaction index (RII). RII not shown when null
 values.Data2_interspecific.xlsxData 3. The effects of intra-specific variations in the nurse Azorella compacta on the outcome of interactionsData 3. The effects of intra-specific variations in the nurse Azorella compacta on the outcome of interactions with other plants in the Sajama National Park, Bolivia. Intra-specific variable hase two modalities : complex shape and hemispheric shape. Each line represents an interaction between one individual cushion and one associated species, through the Relative Interaction Index (RII). RII not shown when null values.Data3_intraspecific.xlsxData 4. Effects of intra-individual variations on the relative mortalities of the nurse cushionsData 4. Effects of intra-individual variations (centre vs. periphery) on the relative mortalities of the nurse cushions Azorella compacta and Pycnophyllum spp. Data available only at 4900 m.Data4_mortality.xlsxData 5. Minimum temperature in cushions.Data 5. Daily minimum temperature in the nurse cushions Azorella compacta and Pycnophyllum spp. at different elevations. Data provided (1) at the surface of cushions and (2) 1.5 cm belowground. Additional treatment: location on cushions.Data5_temperature.xlsxData 6. Compaction of cushions (KPa)Data 6. Compaction in nurse cushions at site 4900 m, along with the variables inter-specific, intra-specific and intra-individual.Data6_cushoin compaction.xlsxData 7. Additional cushion's parametersData 7. Cushion's parameters along the elevation gradient for two taxas, Azorella compacta and Pycnophyllum spp.: relative mortality, surface area and height.Data7_cushion parameters.xlsx