What Are Ecosystem Services? Ecosystems are comprised of organisms and the physical environment that they inhabit. The continuous interactions among them create the conditions and processes through which natural ecosystems function. It is these conditions and processes that help to sustain life and enrich the planet's biological diversity. They also provide critical services, such as water purification, air cleansing and recycling, flood control, natural pest control, medicinal remedies and pollination, upon which human sustainability depends. Without these 'ecosystem services' and a whole host of others, human society could not be supported (7). Natural ecosystems seem to provide ecosystem services for free. As a result, it is easy and not uncommon to take these services for granted — at least until ecosystems stop providing them. When a large area of forest is clear-cut, for example, it may no longer be able to absorb sufficient amounts of water to prevent flooding and mudslides during periods of heavy rain. Because ecosystem services are often poorly understood, they also tend to be undervalued. Pollination is an example of an ecosystem service that is often overlooked.