A huge diversity of species occupy niches within a complex vertically-layered structure of plant forms. High productivity is fuelled by rapid-growing plants including buttressed trees, bamboos, epiphytes, lianas and ferns. Forest canopies sustain moist soils and abundant leaf litter decomposed by fungi and bacteria. High diversity of invertebrates at all levels of the forest supports diverse vertebrate life forms, particularly mammals and birds, which play critical roles in plant dispersal and pollination. Conditions near the equator are stable and humid year-round (up to 6000 mm rain per annum), but become more seasonal with mild winter frosts in the subtropics.