Study shows that heat and drought slow down tropical tree growth

^{Translation by Diana Taborda}

Cristina Nabais and Ana Carvalho, researchers at the Centre for Functional Ecology of the University of Coimbra, have participated in an international study that concluded that stem growth of tropical trees is reduced in years when the dry season is warmer and drier than normal.

This study, led by researchers of the University of Wageningen (the Netherlands), State University of Campinas – UNICAMP (Brazil) and the University of Arizona, (USA), has just been published in “Nature Geoscience”, (Nature Publishing Group) and is based on a new global network, created by the collaborators, of over 14,000 tree-ring data series from 350 locations across 30 tropical and sub-tropical countries.

The researchers found that “the effect of drier and hotter years is larger in more arid or warm regions. This suggests that climate change may increase the sensitivity of tropical trees to climatic fluctuations.”

According to the authors of the study, for a long time, ecologists "assumed that tropical trees did not produce growth rings due to the lack of cold winters in the tropics. In recent decades, however, the formation of growth rings has been proven for hundreds of tropical tree species".

According to Peter Groenendijk, UNICAMP co-author, “these (tropical) tree rings present a wealth of information on the growth history of trees. In this study, we have explored that potential. For the first time, we obtained a Pantropical picture of how tropical tree growth reacts to climate fluctuations”.

The results of this study help understand the large fluctuations in carbon uptake by tropical vegetation worldwide.

Cristina Nabais, faculty member of the Department of Life Sciences of the Faculty of Sciences and Technology of the University of Coimbra (FCTUC) and co-author of the study, stresses that "it is important to continue the sampling effort in tropical regions, extending the geographical coverage of the series of growth rings. Therefore, the dendrochronology laboratory of the Centre for Functional Ecology of the UC wants to continue to contribute to a greater knowledge of the growth dynamics of trees in tropical regions".

The authors were surprised by the finding that during the dry season, climate had a stronger effect on tree growth than the wet season. “A possible explanation is that water is available for a longer period of time during years with wetter or cooler dry seasons. Put simply, the growing season is longer. This then leads to more stem growth.”

They add that this study fills an important gap in tree-ring data. Along with the publication of the study, free access tree-ring data from more than 100 study locations have been uploaded to the global database for tree-ring data, the International Tree-ring Databank (ITRDB).

Global warming is expected to increase the temperature at the study sites by 0.5 degrees per decade in the future. The authors expect warming to aggravate the negative effects on tree growth of hotter and drier dry seasons. If slower growth increases the risk of tree death, tropical vegetation may more frequently become a source of CO2 instead of absorbing this greenhouse gas.

The scientific paper "Tropical tree growth driven by dry-season climate variability" is available at: https://doi.org/10.1038/s41561-022-00911-8.