A periodic table for ecology? A chemist's view of plant functional types



Abstract. A functional type approach, in which the complexity found in nature is reduced by grouping organisms that are functionally similar into a single classification, is being promoted in global change research. This paper examines a proposed analogy between this functional type approach in global change ecology and the periodic table of the elements in chemistry. When applied to a ‘bottom-up’ approach for defining functional types in ecology, in which large numbers of organisms are classified into smaller groups based on similarity of certain functions, the analogy fails. Ecological functions are not simple attributes of a biological entity, as electronic structure is for a chemical element, but are themselves complex chemical and physical systems that often interact strongly with the environment. The analogy to the periodic table may be of some use as an organizing tool in a ‘top-down’ approach in which a modelling context is used to define the number of ‘elements’ and their properties. This will be elaborated for plant functional types. Each PFT is assigned characteristics that allow its response to the driving forces of change, e.g. temperature, precipitation, soil nutrients, disturbance, to be predicted. ‘Rules of combination’ determine how the mix of PFTs in a particular ecosystem changes to form different ecosystems, which would correspond in the analogy to chemical compounds. However, these requirements present significant challenges to the usefulness of the analogy, even as an organizing tool in the ‘top-down’ approach.