Fine nurse variations explain discrepancies in the stress‐interaction relationship in alpine regions

Abstract

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

Nurse species and indirect facilitation through grazing drive plant community functional traits in tropical alpine peatlands

“…An important result of our study is that the identity of the nurse species, even when the species belong to the same life form, can generate different outcomes in terms of plant–plant interactions in grazed conditions. This corroborates the results of a recent study in the dry Central Andes with two different cushion species (Anthelme et al., ), in which the authors showed a different outcome in direct facilitation.…”

Vegetation trends over eleven years on mountain summits in NW Argentina

“…A total of 217 species are now listed for the area including 16 species not recorded in 2002. From the 14 new species reported in this study, six are probably new for the area, recorded at higher elevation than literature (e.g., Hypoxis decumbens, Sisyrinchium hypsophilum) and had been observed at lower elevation close to the area (e.g., Stevia chamedrensys), most of them are perennial herbs widely distributed in the Andes (Raimúndez & Ramirez, ), suggesting some upward movements, probably in response to short‐term climate variability, instead of long‐term trends, both important for modeling vegetation communities (Anthelme et al, ). In this study, vegetation variables were analyzed at a small spatial scale (1m 2 plot) which captured 78% (109 species) of the total richness recorded in the four summits (Table ).…”

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The role of nurse successional stages on species‐specific facilitation in drylands: Nurse traits and facilitation skills

“…This work shows that nurse successional stage could play a role in complex species‐specific interaction outcomes, which are frequently unpredictable (Anthelme, Meneses, Valero, Pozo, & Dangles, ). This might be due to differences in the way nurses from distinct successional stages alter conditions and available resources for the same target species (Diaz & Cabido, ).…”