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1. Colonisation of the alpine tundra by trees: alpine neighbours assist late-seral but not early-seral conifer seedlings

   https://doi.org/10.1080/17550874.2020.1762134  

   Jabis, Meredith D.; Germino, Matthew J.; Kueppers, Lara M. (January 2020, Plant Ecology & Diversity)

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2. Compositional shifts of alpine plant communities across the high Andes

   https://doi.org/10.1111/geb.13721  

   Cuesta, F; Carilla, J; LLambí, L D; Muriel, P; Lencinas, M V; Meneses, R I; Feeley, K J; Pauli, H; Aguirre, N; Beck, S; et al (September 2023, Global Ecology and Biogeography)

   Abstract AimClimate change is transforming mountain summit plant communities worldwide, but we know little about such changes in the High Andes. Understanding large‐scale patterns of vegetation changes across the Andes, and the factors driving these changes, is fundamental to predicting the effects of global warming. We assessed trends in vegetation cover, species richness (SR) and community‐level thermal niches (CTN) and tested whether they are explained by summits' climatic conditions and soil temperature trends. LocationHigh Andes. Time periodBetween 2011/2012 and 2017/2019. Major taxa studiedVascular plants. MethodsUsing permanent vegetation plots placed on 45 mountain summits and soil temperature loggers situated along a ~6800 km N‐S gradient, we measured species and their relative percentage cover and estimated CTN in two surveys (intervals between 5 and 8 years). We then estimated the annual rate of changes for the three variables and used generalized linear models to assess their relationship with annual precipitation, the minimum air temperatures of each summit and rates of change in the locally recorded soil temperatures. ResultsOver time, there was an average loss of vegetation cover (mean = −0.26%/yr), and a gain in SR across summits (mean = 0.38 species m²/yr), but most summits had significant increases in SR and vegetation cover. Changes in SR were positively related to minimum air temperature and soil temperature rate of change. Most plant communities experienced shifts in their composition by including greater abundances of species with broader thermal niches and higher optima. However, the measured changes in soil temperature did not explain the observed changes in CTN. Main conclusionsHigh Andean vegetation is changing in cover and SR and is shifting towards species with wider thermal niche breadths. The weak relationship with soil temperature trends could have resulted from the short study period that only marginally captures changes in vegetation through time. 

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3. On the Use of “Alpine” for High-Elevation Tropical Environments

   https://doi.org/10.1659/mrd.2022.00024  

   Suárez, Esteban; Encalada, Andrea C.; Chimbolema, Segundo; Jaramillo, Ricardo; Hofstede, Robert; Riveros-Iregui, Diego (February 2023, Mountain Research and Development)
4. Area, environmental heterogeneity, scale and the conservation of alpine diversity

   https://doi.org/10.1111/jbi.14573  

   Malanson, George P.; Testolin, Riccardo; Pansing, Elizabeth R.; Jiménez‐Alfaro, Borja (February 2023, Journal of Biogeography)

   Abstract AimArea and environmental heterogeneity together explain most patterns of species diversity but disentangling their relative importance has been difficult. Here, we empirically examined this relationship and parsed their relative importance, and that of the heterogeneity—effective area trade‐off, at different spatial scales and in different spatial representations in simulations. LocationAlpine grasslands of 23 mountain ranges of southern and central Europe. TaxonVascular plants. MethodsWe developed metrics of climatic and edaphic heterogeneity, using principal components analyses and the shoelace algorithm, and added elevation range. We applied commonality analysis to partition the unique and shared explanation of the observed vascular plant species richness among selected metrics. A simulation was developed to separate the relative importance of area and heterogeneity at different extents and representations of spatial nestedness, and the heterogeneity—effective area trade‐off was evaluated by altering spatial discreteness. ResultsThe explanation of the observed regional richness was shared by area and heterogeneity. The simulation revealed that heterogeneity was consistently more important, but less so among smaller areas. This qualitative pattern was maintained regardless of whether and how nestedness was represented. The heterogeneity–effective area trade‐off occurred in a few simulations of more discrete habitats. Main ConclusionsScale dependence may account for discrepancies among past empirical studies wherein environmental heterogeneity has usually outweighed area in the explanation of species richness; and it is not affected by nestedness. The potential heterogeneity–effective area trade‐off may be limited to locations where the environmental heterogeneity is quite discrete or if the added environment is beyond the niches of any species in the potential pool. The significant importance of area per se in small territories indicates that microrefugia, even with an unlikely full range of heterogeneity, will suffer local extinctions in the face of climate change. 

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5. Thermodynamic basis for the demarcation of Arctic and alpine treelines

   https://doi.org/10.1038/s41598-022-16462-2  

   Martin, Meredith Richardson; Kumar, Praveen; Sonnentag, Oliver; Marsh, Philip (July 2022, Scientific Reports)

   Abstract At the edge of alpine and Arctic ecosystems all over the world, a transition zone exists beyond which it is either infeasible or unfavorable for trees to exist, colloquially identified as the treeline. We explore the possibility of a thermodynamic basis behind this demarcation in vegetation by considering ecosystems as open systems driven by thermodynamic advantage—defined by vegetation’s ability to dissipate heat from the earth’s surface to the air above the canopy. To deduce whether forests would be more thermodynamically advantageous than existing ecosystems beyond treelines, we construct and examine counterfactual scenarios in which trees exist beyond a treeline instead of the existing alpine meadow or Arctic tundra. Meteorological data from the Italian Alps, United States Rocky Mountains, and Western Canadian Taiga-Tundra are used as forcing for model computation of ecosystem work and temperature gradients at sites on both sides of each treeline with and without trees. Model results indicate that the alpine sites do not support trees beyond the treeline, as their presence would result in excessive CO$$_2$$ ${}_2$loss and extended periods of snowpack due to temperature inversions (i.e., positive temperature gradient from the earth surface to the atmosphere). Further, both Arctic and alpine sites exhibit negative work resulting in positive feedback between vegetation heat dissipation and temperature gradient, thereby extending the duration of temperature inversions. These conditions demonstrate thermodynamic infeasibility associated with the counterfactual scenario of trees existing beyond a treeline. Thus, we conclude that, in addition to resource constraints, a treeline is an outcome of an ecosystem’s ability to self-organize towards the most advantageous vegetation structure facilitated by thermodynamic feasibility. 

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