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Climate control on plant performance across an Andean altitudinal gradient

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Climate control on plant performance across an Andean altitudinal gradient
Rapp, Joshua Matthew
Understanding the response of species and ecosystems to climate change is one of the most pressing challenges of biology. The use of altitudinal gradients as 'natural experiments' to test the influence of climate on species distributions and performance has a long history in ecology and biogeography. This approach is a powerful way to gain insight into how species and ecosystems respond to warming, since unlike latitudinal gradients, temperature change across altitudinal gradients is not associated with changes in sun angle or day length. The studies included here describe the microclimate along a 3900 meter altitudinal gradient in the eastern Andes of southern Peru, and examine the demographic performance of vascular epiphyte and canopy tree species to this climatic gradient. An expected step change in climatic variables near putative 'cloud base' was not observed, contrasting with rapid changes in net primary productivity, soil properties, and bryophytic epiphyte biomass observed between 1500 and 1800 meters altitude. Vascular epiphyte species transplanted down slope across this gradient exhibited lower ramet survival and negative turnover at lower altitude, but reciprocal transplants revealed no clear trends in altered community composition. Lower altitude individuals appeared to be more resistant to drought than those from higher altitudes, regardless of the altitude where they were transplanted. While precipitation has the greatest seasonal variability of any of the microclimate variables considered here, with a peak in January and February and a minimum in June and July, seasonal patterns of cloudiness and the altitudinal decrease of temperature (mean lapse rate: 5.2ºC/km) appear more important in determining tree growth. Insolation, which is controlled largely by cloudiness in these tropical latitudes, peaked from September to December, and was associated with a seasonal peak in tree diameter growth rate, suggesting that forests on the eastern slope of the Andes may be light limited. Most species had similar growth phenology, suggesting they responded to the same environmental forcing. Within Weinmannia, a genus of canopy trees common in Andean cloud forests, species growing at lower altitude had higher mean diameter growth rates than high altitude species. Within species, however, diameter growth did not consistently decrease with altitude, and growth was significantly positively correlated with altitude in some species. This suggests that the observed positive relationship between temperature and productivity in the wet tropics is due to species compositional turn-over rather than a direct physiological control of temperature on growth. Together, these studies demonstrate the importance of both the temperature gradient and the cloud regime in controlling species performance in the eastern tropical Andes. Increasing temperature and a rising cloud deck are expected to drive changes in species performance and distributions. Species range shifts are likely to be limited by dispersal and because canopy trees are slow growing and long lived. This may constrain the ecosystem response to climate change, since ecosystem productivity is determined in part by the species composition of the community.
elevation gradient
reciprocal transplant
tropical rainforest
Silman, Miles R (committee chair)
Clark, James S (committee member)
Kron, Kathleen A (committee member)
Smith, William K (committee member)
Zeyl, Clifford (committee member)
2011-02-16T21:42:35Z (accessioned)
2011-12-01T09:30:36Z (available)
2010 (issued)
Biology (discipline)
2011-12-01 (terms)
http://hdl.handle.net/10339/30425 (uri)
en (iso)
Wake Forest University

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