Not water, but the sunlight is the main factor in determining the growth of hundreds of species of trees in tropical forests. The change in the physiological characteristics of tree species explains how different species adapt within ecological niches, thus contributing to the enormous diversity that characterizes the tropical forests. This is the conclusion arrived at by the researchers at Wageningen University and the University of Utrecht in a publication which appeared a few days ago, the scientific journal PNAS.
Tropical forests are capable of supporting hundreds of species of trees on a few acres, but little is known about how this diversity has evolved. A study by Frank Stercke, Lourens Poorter and Lars Markesteijn (Wageningen University) and Schieving Feike (Utrecht University) indicates that the tested species responded differently to changes in the availability of electricity and water because they had different physiological characteristics. Most of the species occupied a specific niche that allows co-existence of all these species and biologically diverse forest.
To perform the study, the researchers measured a number of physiological properties such as leaf area, wood density, photosynthetic capacity, leaf water potential and drought resistance in tropical tree species in a Bolivian forest. They used a physiological model to calculate the speed at which the various species can grow when exposed to different combinations of water and light. The simulations show that variations in the production of leaf photosynthesis and the ability to allow the species to specialize for a variety of light niches. The sensitivity to drought in various species (and therefore the consumption of water) has measured variations, yes, but does not lead to specialization of the trees to dry or wet areas in the same forest.
The researchers conclude that even in relatively dry tropical forests, light is the driving force of niche specialization. This makes the sunlight more important than water.
The study is one of the first that uses physiological models to explain species richness present in a tropical forest. In the future, these models will also be used to examine the distribution of plant species in different climatic gradients.