Ecosystem functions are hard to see in action. But without the part of the carbon cycle where small invertebrates, fungi, and microorganisms work to break down wood fiber, the downed logs in an ancient forest would never decay. Natural disturbances also play a role. Wildfires release nutrients to the soil, weed out weak trees, and reset the successional clock. The energy of falling water creates spawning beds for salmon even while it carves a mountain's bones.
Plants breathe oxygen into the atmosphere.
Ecological processes create landscapes and diverse environmental conditions out of life itself. Ecosystem components, structures, and functions are all interdependent. To understand biodiversity, one has to think like a mountain and consider not only the biotic elements of plants, animals, and other living beings, but also the patterns and processes that shape volcanoes and forests. More useful than a definition, perhaps, would be a characterization of biodiversity that identifies the major components at several levels of organization. Composition has to do with the identity and variety of elements in a collection, and includes species lists and measures of species diversity and genetic diversity.