Documenting Natural and Human-Caused Plant Invasions Using Paleoecological Methods

Abstract

Paleoecologists and ecologists are concerned with ecological dynamics, but typically at different temporal, spatial, and taxonomic scales. A key interest for both groups is documentation of species invasions and assessment of their causes and consequences. However, the termsinvasionandinvaderhave different connotations for each group owing to a differential in scale. Ecologists tend to view invasion as the introduction and expansion of a nonindigenous (NI) species within a region, typically occurring rapidly (10’ to 10²years) against a backdrop of constant climate and moderate-to-intense landscape disturbance related to human activities (e.g., Elton 1958; Mooney and Drake 1986). In contrast, paleo-ecologists perceive invasions as spatial and population expansions of species related ultimately to secular changes in climate and other environmental factors. These “natural” invasions occur over longer time spans (10²to 10⁶years) and are typically detected at broad spatial scales (10’ to 10⁴km) (e.g., Huntley and Webb 1988). Environmental changes, usually substantial at these time scales, mediate the ecological processes underlying the invasions (MacDonald 1993; Webb 1986).