topsoil of tropical rainforest

soil tree leaf forest woodland plant autumn flower wood wildlife nature garden track jungle branch trail trunk grass green topsoil tropical rainforest secondary bukit batok singapore hillside flat land asia landscape fertile fertility woods greenery brown young plants saplings growth new regenerating ground sediment clay silt dry dried porous permeable surface litter nutrient cycle carbon leaves natural branches decomposition sticks log shoots stones pebbles gravel rocks igneous sedimentary rock erosion weathering biological humid