The effect of different proportions of canopy opening on the carbon cycle a Central Amazonian secondary forest

Abstract

The purpose of this study was to determine the effect of different proportions of canopy opening on the carbon cycle of a 10-year-old Cecropia-dominated secondary forest of central Amazonia. Proportions removed were 20,30, 80, and 100% of the total tree basal area in 10 30 x 30 experimental plots. The understory was left intact.First, a model describing carbon flow in the secondary forest system was created to simulate the effect of canopy removal on carbon cycling and to identify important parameters and processes affected by canopy opening. Based on a preliminary sensitivity analysis, environmental parameters (light availability, temperature, soil moisture and available phosphorus) and rates (growth, mortality, herbivory, litterfall, decomposition) influencing carbon uptake and flow were selected for field experimentation and quantification. Prior to implementing the canopy removal experiment in the field, some important carbon stocks were estimated. Finally, the results from simulations and field experiments were compared to evaluate the predictive ability of the model. Canopy removal increased air temperature, soil moisture, and light available to understory seedlings and saplings. As expected, there was less litter input and (non-significantly) slower decomposition of leaf litter in relatively opon plots than in the control. Primary productivity was almost three times higher in 50% removal plots than in controls, and not significantly lower than at higher amounts of opening. Of two economically valuable species transpanted, one (Paullinia cupana) did not grow well in the second-growth, while the other (hevea brasiliensis) grew well under any amount of canopy cover and survived better under 20% canopy removal. These differences in growth and suvival indicate that species selection is an important factor to be considered in the management of tall secondary forests. Model simulations and field experiment results both suggested that intermediate amounts of canopy removal increase plant growth without losing the benefits os canopy cover. Cultivation within tall secondary forests seems to offer a viable alternative to non-forest production systems. Canopy removal is an effective low-cost way of accelerating plant growth in secondary forest. It could be used cultivating economically important species or speeding the natural regeneration process.