Products and services from ecosystems are inherent to sustaining life on this planet. Forest ecosystems, in particular, provide a suite of products and services that sustain life for humans and other species. In addition to the obvious products such as wood for building houses, and firewood for heating homes, nontimber forest products are also an economic commodity that benefits many communities. Mushrooms, greens, biochemicals, charcoal, fruits, roots, and tree bark (e.g., cork) all contribute to local economies. In addition, most metropolitan areas of the world receive their drinking water from watersheds that have forested headwaters. Carbon sequestration, shade, and game species harvested for subsistence food are also derived from forests by communities around the world. And the intrinsic beauty of forests attracts hikers, artists, musicians, philosophers, and many others to seek inspiration and solace in forests. And, of course, habitat for many species of biodiversity, including humans, can be found in forested ecosystems.
All of these ecosystem services are valued and are reasons why many people in our societies wish to ensure that forests are protected or managed sustainably. But sustainability is a tricky thing to define. It reflects a suite of societal values such as those listed earlier, and it necessarily implies a time frame. For how long will we be able to sustain these values? Species go extinct. Climate changes. Forests burn and regrow. And throughout these disturbances and other changes that occur in forests, habitat for species is destroyed and regrows, or it may be eliminated or appear in a place where it never occurred before. The one thing that is constant about our environment is change, and the way that species, including humans, have persisted in the face of those changes is through maintaining the genetic diversity and behavioral flexibility to allow some members of each species to persist.