Spatial patterns in mesic savannas: the local facilitation limit and the role of demographic stochasticity

TL;DR

This paper presents a model for tree density dynamics in mesic savannas, highlighting the importance of long-range competition and fire as a facilitation mechanism, and examines the role of demographic stochasticity in pattern formation.

Contribution

It introduces a model that combines long-range competition and local fire facilitation, analyzing how demographic noise influences vegetation patterns in savannas.

Findings

Long-range competition is essential for pattern development.

Demographic noise produces irregular, realistic vegetation patterns.

Tree-grass coexistence persists under typical noise levels.

Abstract

We propose a model equation for the dynamics of tree density in mesic savannas. It considers long-range competition among trees and the effect of fire acting as a local facilitation mechanism. Despite short-range facilitation is taken to the local-range limit, the standard full spectrum of spatial structures obtained in general vegetation models is recovered. Long-range competition is thus the key ingredient for the development of patterns. The long time coexistence between trees and grass, and how fires affect the survival of trees as well as the maintenance of the patterns is studied. The influence of demographic noise is analyzed. The stochastic system, under the parameter constraints typical of mesic savannas, shows irregular patterns characteristics of realistic situations. The coexistence of trees and grass still remains at reasonable noise intensities.