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The grass ceiling: Recruitment limitation above timberline may limit the adaption ability of tropical montane cloud forest to global climate change

Thursday, 27 June 2013: 09:45
Americas B-C (Herradura San Jose)
Evan Rehm , Biological Sciences, Florida International University
Kenneth J Feeley , Biological Sciences, Florida International University
As global temperatures rise, climatic conditions suitable to tropical montane plant species will be displaced towards higher elevations. Plants are predicted to experience range contractions and elevated extinction risks unless they shift distributions upslope to remain within their thermal niches. In the Andes, grasslands (puna) above high-elevation timberlines are one possible area where montane plant species may expand their ranges with warming. However, there is strong evidence that temperature and intense UV solar radiation limit tree recruitment at tropical timberlines. As such, our goal was to experimentally test the effects of temperature and shading on tree seedling survival in the puna. In Manu National Park, Peru seedlings of timberline species were translocated to 5 locations (~3500m) and monitored for 1 year under the following treatments; control, open puna, shading, warming, and shading + warming. Downslope warming significantly decreased seedling survival (30% survival) when compared to controls (67% survival; pairwise proportion test) and seedlings transplanted into all other treatments. Seedlings planted in shading, shading + warming, and open puna treatments had similar survival to those of the control. With increasing global temperatures, freezing events should be ameliorated, allowing for more tree recruitment above timberline, yet our data show that warming actually decreases seedling survival. Conversely, seedlings in the open puna treatment experienced more severe and frequent frost occurrences relative to the control yet showed similar survival rates. Surprisingly, shading treatments did not significantly increase survival in the open puna suggesting that intense UV radiation above timberline does not prevent tree recruitment. Warming may actually have a negative effect on seedling survival in the puna, which could have dramatic impacts on global diversity as cloud forest species seek cooler refugia above timberline in response to increasing global temperatures.