Demography of Nothofagus pumilio forests at the extremes of the altitudinal gradient in Southern Patagonia

ASCHERO, V.; SRUR, A.M; VILLALBA, R.

Los Reyunos, Mendoza

Conferencia; Inter-American Institute for Global Change Research Final Science Meeting, IAI CRN-CRA2047,; 2014

Inter-American Institute for Global Change

Temperature in the Southern Patagonian Andes has increased since the 1950's. Consequences ofhigher temperatures on tree demography are not easy to predict and different effects are expectedalong the altitudinal range of N. pumilio forests. For example, detrimental microclimatic conditionsfor seedling establishment are associated with increasing temperature at low altitude forests,particularly if drought episodes became more frequent. In contrast, higher temperature couldameliorate seedling establishment at high elevations in response to the temporal expansion of thegrowing season and the reduction of stress caused by heavy and long-lasting snow accumulation.To test for the hypothesis that recent climate changes in Southern Patagonia have influenced treedemography differentially along the altitudinal gradient, we are monitoring since 2012 theNothofagus pumilio vital rates at low and high elevations at El Chaltén, Santa Cruz, in the SouthernAndes of Argentina. Here, we present our first results about forest regeneration dynamics, treegrowth and mortality at the extremes of the altitudinal gradient. The number of new-born seedlingsgerminated between 2012-2014 was different in the altitudinal extremes. Density of new-bornseedlings at high-altitude forests was 13 times higher than at low altitudes. In contrast, mortality ofmarked seedlings was higher at low-altitude than at high-altitude forests. Consequently, seedlingdensity is lower at low-altitude than at high-altitude forests. Positive temporal trends in tree growthat high altitude forests in recent decades contrast with stable or decreasing trends at lowerelevations. Mortality of adult individuals (>5 cm DBH) was higher in lower-elevation than athigher-elevation forests. The registered patterns support the idea that recent climate change affecttree demography in different ways along the altitudinal range in mountain forest.