Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Resumen:

Tropical mountain forest in the Andes of southeastern Ecuador is regularly destroyed to gain pasture land by cultivating the C4 grass Setaria sphacelata. After recurrent burning of the pastures, the grass is partly outcompeted by the C3 southern bracken (Pteridium arachnoideum). This competition represents the problematic of pasture degradation and increasing deforestation, due to the necessity of new pasture land. Because no information on the growth potential of both species in the Andes of Ecuador is available, a growth simulation model has been improved and properly parameterized with field observations. The measured speciesand site-specific physiological and edaphic parameters are presented in this paper, as well as the model validation with field observations of leaf CO2 assimilation. The validation showed deviations of simulated from observed leaf net assimilation lower than 5% of the observed values. The validated model was run with a fully realistic meteorological forcing of the year 2008 (10 min time step). The main result points to slightly higher growth potential of Setaria with 5879 g m-2 a-1, based on an annual CO2 net assimilation rate of 217 mol CO2m-2 a-1. The calculated growth potential of bracken was 5554 g m-2 a-1, based on the CO2 net assimilation of 197 mol CO2m-2 a-1. In addition, it was shown that decreasing incoming solar radiation and low temperature are favourable weather conditions for bracken in contrary to the pasture grass Setaria.

Resumen:

Ecuadorian mountain rainforests are declining dramatically due to deforestation. Exploitation of remaining forests has led to low abundances of native, valuable timber species. Enrichment planting of selected native tree species into forest gaps is a strategy that may increase their abundance and maintain biodiversity. However, the development of successful planting strategies requires knowledge of environmental demands on, and ecological requirements of, native species during their establishment. This knowledge is currently lacking for midand latesuccessional species in Central American forests. Two deciduous, mid-successional (Cedrela montana, Tabebuia chrysantha) and two evergreen, late-successional native tree species (Nectandra membranacea, Podocarpus sprucei) were planted into felling gaps. Photosynthetic performance and growth in height of these species were assessed along light gradients during seedling establishment to test whether species-specific light responses were related to plant successional traits. Both mid-successional species benefited from higher light levels in gaps up to 30% canopy openness60. In larger gaps, C. montana exhibited a significant decline in growth. As expected, growth of the latesuccessional species was only marginally increased at higher light levels. Nevertheless, the photosynthetic apparatus of N. membranacea displayed rapid acclimation to higher light conditions in gaps. Plant response to felling gaps may not always be predicted based on successional status. Our results suggest that the four investigated species may coexist in the same gap by occupying different niches along light gradients. This arrangement may offer an ecological basis to increase the abundance of valuable timber species through enrichment planting in Ecuador mountain rainforests.