title: An individual-based forest model links canopy dynamics and shade tolerances along a soil moisture gradient.
abstract: Understanding how forested ecosystems respond to climatic changes is a challenging problem as forest self-organization occurs simultaneously across multiple scales. Here, we explore the hypothesis that soil water availability shapes above-ground competition and gap dynamics, and ultimately alters the dominance of shade tolerant and intolerant species along the moisture gradient. We adapt a spatially explicit individual-based model with simultaneous crown and root competitions. Simulations show that the transition from xeric to mesic soils is accompanied by an increase in shade-tolerant species similar to the patterns documented in the North American forests. This transition is accompanied by a change from water to sunlight competitions, and happens at three successive stages: (i) mostly water-limited parkland, (ii) simultaneously water- and sunlight-limited closed canopy forests featuring a very sparse understory, and (iii) mostly sunlight-limited forests with a populated understory. This pattern is caused by contrasting successional dynamics that favour either shade-tolerant or shade-intolerant species, depending on soil moisture and understory density. This work demonstrates that forest patterns along environmental gradients can emerge from spatial competition without physiological trade-offs between shade and growth tolerance. Mechanistic understanding of population processes involved in the forest-parkland-desert transition will improve our ability to explain species distributions and predict forest responses to climatic changes.
authors.affiliation: Department of Mathematics and Statistics , School of Art and Sciences, Washington State University , Vancouver, WA, USA.
authors.forename: Jean
authors.initials: J
authors.lastname: Liénard
authors.affiliation: Department of Mathematics and Statistics , School of Art and Sciences, Washington State University , Vancouver, WA, USA.
authors.forename: Nikolay
authors.initials: N
authors.lastname: Strigul
keywords: crown competition; forest succession; gap dynamics; individual-based forest model; moisture gradient; root competition; shade tolerance