Cloud Forest Tree Growth Responses to Climate and Drought Vary by Island and Species in the Macaronesian Region

AimMacaronesian cloud forests are insular ecosystems subjected to local environmental variability, but the responses of their tree species to climate variations have never been studied. Our aim was to assess how the variation in environmental conditions associated with the geographical location of several islands in three Macaronesian archipelagos affects the growth patterns and drought-resistance of the dominant cloud forests trees.LocationAzores, Madeira and Canary archipelagos. Portugal and Spain.TaxonLauraceae, Aquifoliaceae, Clethraceae, Oleaceae, Rosaceae and Cupressaceae.MethodsWe assessed variations in the radial growth response of 10 cloud forest tree species from 18 populations on 5 islands along a geographical gradient in Macaronesia. We quantified the influence of local climatic variables and North Atlantic Oscillation (NAO) and East Atlantic Pattern (EA) circulation patterns on tree growth and how drought events affected to the resistance, recovery and resilience indices estimated for these species.ResultsTrees from the same island showed similar growth patterns, particularly in islands with marked hydric stress. In Madeira and the Canary Islands, radial growth was mainly determined by water availability, winter NAO negatively affected growth and droughts caused abrupt narrow growth-ring width. In the Azores, the effect of the EA was positive, as it increased temperature and relative humidity and promoted growth. Trees from wetter environments demonstrated higher growth resistance to drought, while trees from drier sites showed faster growth recovery after drought events.Main ConclusionsHomogeneous growth patterns among species from the same island suggested that the radial growth of trees in cloud forests is mostly determined by local environmental conditions, which are more important for their growth than phenotypic traits. The variability in water availability determined by a latitudinal geographical gradient throughout the Macaronesian region influenced both the climatic response of the trees and their resilience to drought.