Therefore, the impact of humans on ecosystems is a central theme in Biogeography. Species richness is the number of species per unit area of ground. Biomass consists of all physical components of vegetation . Productivity is the amount of biomass that accumulates by photosynthesis in a given region in a given time. Structure refers to the way the biomass is arranged into vertical and horizontal layers.
Composition refers to the actual species of organisms that comprise and ecosystem.
We've only identified up to about 1.7 million species of living things, a small proportion of the total amount. Total estimated amount of species may be over 100 million , with up to 80 million represented by arthropods, and about 30 million represented by insects alone. This includes about 3000 bacteria, and 69000 fungi species. Complicating this are extinctions . Loss of species from rainforests alone amount to 6000 species per year, or about 17 species per day.