At high elevations of the tropical Andes, the cloud forests give way to high elevation puna grasslands. We have a nice new paper out in Environmental Research Letters (led by Imma Oliveras), which examines for the first time the productivity of Andean montane grasslands (or puna) and compares it with adjoining tropical montane forests. We find that the grasslands are just as productive as the forests, but have have very different carbon cycling and turnover properties. Here is the abstract
We aim to assess net primary productivity (NPP) and carbon cycling in Andean tropical alpine grasslands (puna) and compare it with NPP of tropical montane cloud forests. We ask the following questions: (1) how do NPP and soil respiration of grasslands vary over the seasonal cycle? (2) how do burning and grazing affect puna productivity? (3) if the montane forest expands into the puna, what will be the resulting change in productivity? The study sites are located at the South-eastern Peruvian Andes; one grassland site and the forest sites are in Wayqecha biological station, and another grassland site in Manu National Park. At each grassland site, we selected a burnt and an unburnt area, installed unfenced and fenced transects in each area, and monitored above-ground productivity (NPPAG), below-ground productivity (NPPBG) and soil respiration (Rs) for 2 yr. In the forest, we monitored NPPAG, NPPBG and Rs for 2–4 yr. Grassland NPP varied between 4.6 ± 0.25 (disturbed areas) to 15.3 ± 0.9 Mg C ha−1 yr−1 (undisturbed areas) and cloud forest NPP was between 7.05 ± 0.39 and 8.0 ± 0.47 Mg C ha−1 yr−1, while soil carbon stocks were in the range of 126 ± 22 to 285 ± 31 Mg C ha−1. There were no significant differences on NPP between the puna and forest sites. The most undisturbed site had significantly higher NPP than other grassland sites, but no differences were found when relating grazing and fire at other sites. There were lower residence times of above-ground biomass compared to below-ground biomass. There was a strong seasonal signal on grassland NPPAG and NPPBG, with a shift on allocation at the beginning of the austral summer. High elevation tropical grasslands can be as productive as adjacent cloud forests, but have very different carbon cycling and retention properties than cloud forests.
The paper can be downloaded here:
Oliveras I, C Girardin, C E Doughty, N Cahuana, C E Arenas, V Oliver, W Huaraca Huasco and Y Malhi (2014) Andean grasslands are as productive as tropical cloud forests Environ. Res. Lett. 9, 115011 doi:10.1088/1748-9326/9/11/115011
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University