Tree rings in the tropics?

Sampling of Hymenaea courbaril with a motorized corer in Southern Amazon. ©Peter Groenendijk

Do tropical trees also produce growth rings?
Since more than a century we know some of them do. Just like temperate and boreal trees. Yet, studies on tropical tree rings have been scarce because year-long warm conditions were thought to prevent ring formation. That was incorrect! Instead of cold conditions during winter, growth in tropical trees stops during unfavourable periods due to other limiting environmental factors: water shortage during the dry season, root anoxia in flooded forests, etc. For a large group of species and a large proportion of tropical vegetations this leads to the formation of ring boundaries. We now know that several hundreds of tropical tree species form annual growth rings.

From rings to chronology
Growth rings – whether from boreal, temperate or tropical trees – store valuable information on the growing conditions, physiology and growth rate of trees. They can be counted to determine tree age (and find out that most tropical trees do not get older than two centuries). They can be measured to check whether growth during wetter or cooler years is stimulated, or whether large trees grow faster than smaller ones. The width of a ring depends on many factors: tree age, tree size, temperature, shade, rainfall, etc. In dendrochronology, we are mostly interested in the effect of climatic variation between years on tree growth, and we try to isolate that effect from others by a statistical procedure called detrending. Detrended tree-ring series can then be averaged across all trees in a population. The resulting chronology contains the population-level growth fluctuations and can be used to check how sensitive growth is to climatic variation.

The tropical tree ring (TTR) network aims to unite data from tree-ring studies across the tropics. We conduct meta-analyses and reviews to better understand how tropical trees respond to current and future climatic conditions.
At this moment, we have more than 100 collaborators in our network, with over 450 ring-width chronologies from 30+ countries from all tropical continents, and covering more than 85 tree species. See map here.