EFFECTS OF COMPENSATORY GROWTH ON POPULATIONPROCESSES: A SIMULATION STUDY

Abstract

The spatial extent of the canopy or root system of a plant is often used as an index of its potential to acquire resources, such as water and nutrients. This has given rise to the area of influence (AOI) and neighborhood concepts for quantifying competitive interactions between neighboring plants. Both are based on a circle of fixed radius centered on a plant, which presupposes that two plants in close proximity are always strong competitors. There is evidence that this is not always the case. In this paper, we present a simple model of plant population dynamics that extends the concept of AOI by considering “compensatory” growth of root systems. The ability of a plant to grow roots into soil zones free of neighbors in response to competitive pressures is expressed by the value of a single parameter, λ. Effects on population attributes resulting from competition in plants with compensatory growth are compared with populations with noncompensatory growth. Simulations show that compensatory plants are better able to utilize available space, have greater biomass, and outcompete noncompensatory plants. The change from a clumped to a regular distribution of individuals due to density-dependent mortality is delayed in noncompensatory plants. These theoretical results suggest that growth plasticity and the resulting asymmetry in space acquisition may play an important role in plant population dynamics.