RAIN-FOREST ON MARACA ISLAND, RORAIMA, BRAZIL - SOIL AND LITTER PROCESS RESPONSE TO ARTIFICIAL GAPS

Artificial canopy gaps were made by felling trees in rain forest on Ma raca Island. There were three replicates of each gap size; small (c. 4 0 m(2)), medium (c. 150 m(2)), large (c. 350 m(2)), very large (c. 250 0 m(2)), and unfelled forest controls (2500 m(2)). Changes in microcli mate, soil chemistry, and soil biological processes including decompos ition were measured for up to 12 months. Higher maximum and lower mini mum air temperatures occurred with increasing gap size but there was l ittle consistent effect of gap size on soil chemistry, Microbial bioma ss, soil respiration, and nitrogen mineralization and nitrification we re investigated in medium gaps, No differences were found between the gaps and the unfelled forest, and all had their lowest values in the d ry season. Within the medium gaps higher values for these variables oc curred in the 'under crown' position (where the crowns of the felled t rees had fallen under the surrounding canopy), Three litter-bag decomp osition experiments were made over 217 d, No relationship was found be tween decomposition and nutrient release rates and size of gap or posi tion within it and no clear trend was found with position along a cent ral trunk within a Sap, but a higher weight loss and nutrient release occurred under the crowns of fallen trees, It is concluded that decomp osition and nutrient release rates are not influenced in a consistent way by gap size, It may be that small areas of high nutrient release c an be caused by the local addition of large quantities of substrate, e ven though process rates remain unaltered. Because large additions of readily decomposable substrate are most likely to occur under a closed canopy, there is no support from the Maraca data that growth response s to gaps will involve an interaction between enhanced nutrient supply and increased light. (C) 1998 Elsevier Science B.V.