Short answers, pulled from the story.
Estimates range from 40 to 75 percent of all biotic species on Earth being indigenous to rainforests. Tropical rainforests alone may contain many millions of species of plants, insects, and microorganisms still undiscovered by science.
A tropical rainforest has four main layers: the emergent layer (trees reaching 45-80 metres), the canopy layer (30-45 metres, home to an estimated 50 percent of all plant species), the understory layer, and the forest floor, which receives only 2 percent of incoming sunlight.
Rapid bacterial decay prevents humus from accumulating, and the clay particles in tropical soils trap nutrients poorly. High rainfall washes nutrients away quickly, and high soil acidity reduces the gradient plants need to absorb what nutrients do exist.
Brazil holds the largest number of uncontacted tribes in the world. On the 18th of January 2007, FUNAI confirmed 67 uncontacted tribes in Brazil, surpassing New Guinea, which has an estimated 44 uncontacted groups in the province of Irian Jaya (West Papua) alone.
Dendronautics is the science of accessing tropical forest canopies using airships or similar aerial platforms. Systematic canopy exploration only began in the 1980s, when researchers also developed methods such as firing ropes into treetops using crossbows.
Almost 90 percent of West Africa's rainforest has been destroyed. Madagascar has lost two thirds of its original rainforest since humans arrived, and Amazon deforestation jumped 69 percent in 2008 compared to 2007, according to official Brazilian government data.