Format: ORAL

Francisco Cuesta1,Julieta. Carilla2, Luis. D. LLamb3,4, P. Muriel5,Mara. V. Lencinas6, R. I. Meneses7, Kenneth. J. Feeley8, H. Pauli9,10, N. Aguirre11, S. Beck12, A. Bernardi1,5, S. Cuello2, S. A. Duchicela1,13, P. Eguiguren11, L. E. Gamez3, S. Halloy14, L. Hudson15, R. Jaramillo5, P. L. Peri16, L. A. Ramrez3, P. Rosero-Aazco1, N. Thompson12, K. Yager17, C. Tovar15

1 Grupo de Investigación en Biodiversidad Medio Ambiente y Salud - BIOMAS, Universidad de las Américas, Quito, Ecuador 2 Instituto de Ecología Regional (IER), Universidad Nacional de Tucumán (UNT) - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Tucumán, Argentina 3 Instituto de Ciencias Ambientales y Ecológicas, Universidad de Los Andes, Mérida, Venezuela 4 Consorcio para el Desarrollo Sostenible de la Ecorregión Andina (CONDESAN), Lima, Peru 5 Laboratorio de Ecofisiología, Escuela de Ciencias Biológicas, Pontificia Universidad Católica del Ecuador, Quito, Ecuador 6 Centro Austral de Investigaciones Científicas (CADIC), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Tierra del Fuego, Argentina 7 Instituto de Investigaciones Arqueológicas y Museo, Universidad Católica del Norte, San Pedro de Atacama, Chile 8 Biology Department, University of Miami, Coral Gables, Florida, USA 9 Institute for Interdisciplinary Mountain Research, Austrian Academy of Sciences, Vienna, Austria 10 Department of Integrative Biology and Biodiversity Research, University of Natural Resources and Life Sciences, Vienna, Austria 11 Carrera de Ingeniería Forestal, Centro de Investigaciones Tropicales del Ambiente y Biodiversidad (CITAB), Universidad Nacional de Loja, Loja, Ecuador 12 Herbario Nacional de Bolivia, Museo Nacional de Historia Natural - Instituto de Ecología (UMSA), La Paz, Bolivia 13 Department of Geography and the Environment, University of Texas at Austin, Austin, Texas, USA 14 Ministry for Primary Industries, Wellington, New Zealand 15 Jodrell Laboratory, Royal Botanical Gardens Kew, Surrey, UK 16 Instituto Nacional de Tecnología Agropecuaria (INTA), Universidad Nacional de la Patagonia Austral (UNPA), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Santa Cruz, Argentina 17 School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York, USA

Aim: Climate change is transforming mountain summit plant communities worldwide,but we know little about such changes in the High Andes. Understanding large-scalepatterns 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 testedwhether they are explained by summits climatic conditions and soil temperature trends. Methods: Between 2012 and 2017/2019, using permanent vegetation plots placed on 45 mountain summits and soiltemperature loggers situated along a~6800kmN-S gradient, we measured species andtheir relative percentage cover and estimated CTN in two surveys (intervals between 5 and 8years). We then estimated the annual rate of changes for the three variables andused generalized linear models to assess their relationship with annual precipitation, theminimum air temperatures of each summit and rates of change in the locally recordedsoil temperatures. Results: Over 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 summitshad significant increases in SR and vegetation cover. Changes in SR were positivelyrelated to minimum air temperature and soil temperature rate of change. Most plantcommunities experienced shifts in their composition by including greater abundancesof species with broader thermal niches and higher optima. However, the measuredchanges in soil temperature did not explain the observed changes in CTN. Main conclusions: High Andean vegetation is changing in cover and SR and is shiftingtowards species with wider thermal niche breadths.The weak relationship with soiltemperature trends could have resulted from the short study period that only margin- ally captures changesin vegetation through time.