DISTRIBUTION OF PTERIDOPHYTA AND MELASTOMATACEAE ALONG AN EDAPHIC GRADIENT IN AN AMAZONIAN RAIN-FOREST

Pteridophyta and Melastomataceae were studied in an area of non-floode d (tierra firme) rain forest in Peruvian Amazonia, close to the villag e of Mishana (River Nanay, in the vicinity of Iquitos City). The gener al objective of the study was to establish a method for rapidly docume nting changes in the floristic composition among and within rain fores ts in geologically different areas. More specifically, the changes in the plant communities were documented along an edaphic and topographic gradient from clay soil on level ground to quartzitic sand on a hill top. Two 5-m-wide, parallel transects were established 50 m apart. A t otal of 40 species of pteridophytes were found; 18 of these were confi ned to clayey soil and 11 to sandy soil. The total number of Melastoma taceae on the transects was 22, and 14 of these were confined to claye y soil while only two were confined to sandy soil. Further differences in the abundance of many species correlated with drainage conditions and the accumulation of organic matter on the soil surface. Cluster an alyses were made using both edaphic and floristic criteria, and in all cases the transects could be divided into distinct sections. Both tra nsects gave rather similar results. and therefore it was concluded tha t the chosen transect width was sufficient to document the prevalent f loristic patterns.