Abstract
The high diversity and abundance of vascular epiphytes in tropical montane cloud forest is associated with frequent cloud immersion, which is thought to protect plants from drought stress. Increasing temperature and rising cloud bases associated with climate change may increase epiphyte drought stress, leading to species and biomass loss. We tested the hypothesis that warmer and drier conditions associated with a lifting cloud base will lead to increased mortality and/or decreased recruitment of epiphyte ramets, altering species composition in epiphyte mats. By using a reciprocal transplant design, where epiphyte mats were transplanted across an altitudinal gradient of increasing cloud immersion, we differentiated between the effects of warmer and drier conditions from the more general prediction of niche theory that transplanting epiphytes in any direction away from their home elevation should result in reduced performance. Ramet mortality increased, recruitment decreased, and population size declined for epiphytes in mats transplanted down slope from the highest elevation, into warmer and drier conditions, but epiphytes from lower elevations showed greater resistance to drought in all treatments. Epiphyte community composition changed with elevation, but over the timescale of the experiment there were no consistent changes in species composition. Our results suggest some epiphytes may show resistance to climate change depending on the environmental context, although if climate change results in consistently drier conditions and higher cloud bases, biomass loss and shifting species composition in epiphyte communities is likely.
Highlights
Tropical montane forests, often referred to as cloud forests, harbor high species diversity, provide water and protect water quality for numerous people in tropical countries, and are under particular threat from climate change[1,2,3]
Greater epiphyte resistance to drought in this part of the Andes compared to previous studies may indicate that even seemingly benign dry seasons or dry periods can be important for structuring epiphyte communities, with potential implications for larger scale patterns of diversity
While epiphyte response to global climate change on tropical mountains is discussed in the literature[18,19,29,38], tropical mountains and their climates are highly heterogeneous, and predictions may defy all but the broadest generalizations
Summary
Tropical montane forests, often referred to as cloud forests, harbor high species diversity, provide water and protect water quality for numerous people in tropical countries, and are under particular threat from climate change[1,2,3]. Most cloud forest regions of the world, including the tropical Andes, are considered hotspots of biological diversity[4], and plant species endemism often reaches high levels within cloud forest[5,6]. Cloud immersion is important for many epiphyte species to maintain a positive water balance and avoid desiccation[17]. Because of their sensitivity to moisture levels, epiphytes are considered indicator species in cloud forests for changing water balance conditions[18], those in the wet tropics[19]
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