A note on terminology

When we talk about ecosystems we need to define the quantities of which they are made. We will refer to concrete, measured or calculated quantities, as stocks of elements. When we talk about these quantities in more abstract terms we use the terms pools or compartments. The movements of matter between pools will interchangeably be called flows or fluxes. The transfer of energy between compartments was previously a key study area in ecology. Today we stress movements of individual elements, in particular carbon, as this approach provides insights into more aspects of ecosystems functionality. Amounts of elements can be expressed either by mass or by number of moles. We will follow the convention in terrestrial ecosystem ecology and use mass units, unless otherwise stated, rather than the molar units that are common in aquatic ecology. The typical units are kg m−2 and Mg ha−1 (1 kg m−2 = 10 Mg ha−1) for stocks, and flows are per year or per day. Mass can also be expressed as dry weight (dw), when all water has been removed, or fresh weight (fw), when the sample is at its ambient water content. Dry weight is often replaced by its carbon content; if no measurements are available a carbon content of 50% can be assumed.

Understanding processes