Nutrient Availability in Tropical Rain Forests: The Paradigm of Phosphorus Limitation

Abstract

Tree-ring studies provide important contributions to understanding the climate sensitivity of tropical trees and the effects of global change on tropical forests. This chapter reviews recent advances in tropical tree-ring research. In tropical lowlands, tree ring formation is mainly driven by seasonal variation in precipitation or flooding, and not in temperature. Annual ring formation has now been confirmed for 230 tropical tree species across continents and climate zones. Tree-ring studies indicate that lifespans of tropical tree species average c. 200 years and only few species live >500 years; these values are considerably lower than those based on indirect age estimates. Size-age trajectories show large and persis- tent growth variation among trees of the same species, due to variation in light, water and nutrient availability. Climate-growth analyses suggest that tropical tree growth is moderately sensitive to rainfall (dry years reduce growth) and temperature (hot years reduce growth). Tree-ring studies can assist in evaluating the effects of gradual changes in climatic conditions on tree growth and physiology but this requires that sampling biases are dealt with and ontogenetic changes are disen- tangled from temporal changes. This remains challenging, but studies have reported increases in intrinsic water use efficiency based on δ13C measurements in tree rings, most likely due to increasing atmospheric CO2. We conclude that tree-ring studies offer important insights to global change effects on tropical trees and will increasingly do so as new techniques become available and research efforts intensify.