Global tree-ring analysis reveals rapid decrease in tropical tree longevity with temperature
- aInstitute of Biosciences, University of São Paulo, São Paulo, SP 05508-090, Brazil;
- bCluster of Ecology, Institute of Botany, São Paulo, SP 04301-902, Brazil;
- cSchool of Geography, University of Leeds, LS2 9JT Leeds, United Kingdom;
- dDepartment of Physical Geography, University of Passau, 94032 Passau, Germany;
- eInstituto de Geografía, Pontificia Universidad Católica de Valparaíso, 2390302 Valparaíso, Chile;
- fNational Institute of Amazonian Research, Manaus, AM 69067-375, Brazil
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Edited by Carlos A. Nobre, University of São Paulo, Sao José dos Campos, Brazil, and approved September 29, 2020 (received for review March 4, 2020)

Significance
This study highlights previously unknown patterns of tree longevity and growth across the world. Tree-ring data reveal a large-scale trade-off between tree longevity and growth, following global patterns of increasing forest productivity and biomass turnover rate from temperate to tropical regions. The oldest known trees live under dry conditions in temperate and boreal zones, while in the dry tropical lowlands, trees only reach relatively short lifespans. Longevity of tropical trees also sharply decreases above mean annual temperatures of 25.4 °C. Thus, predicted future changes in moisture availability and increases in temperature have the potential to reduce tree longevity in tropical lowlands impacting carbon stocks.
Abstract
Forests are the largest terrestrial biomass pool, with over half of this biomass stored in the highly productive tropical lowland forests. The future evolution of forest biomass depends critically on the response of tree longevity and growth rates to future climate. We present an analysis of the variation in tree longevity and growth rate using tree-ring data of 3,343 populations and 438 tree species and assess how climate controls growth and tree longevity across world biomes. Tropical trees grow, on average, two times faster compared to trees from temperate and boreal biomes and live significantly shorter, on average (186 ± 138 y compared to 322 ± 201 y outside the tropics). At the global scale, growth rates and longevity covary strongly with temperature. Within the warm tropical lowlands, where broadleaf species dominate the vegetation, we find consistent decreases in tree longevity with increasing aridity, as well as a pronounced reduction in longevity above mean annual temperatures of 25.4 °C. These independent effects of temperature and water availability on tree longevity in the tropics are consistent with theoretical predictions of increases in evaporative demands at the leaf level under a warmer and drier climate and could explain observed increases in tree mortality in tropical forests, including the Amazon, and shifts in forest composition in western Africa. Our results suggest that conditions supporting only lower tree longevity in the tropical lowlands are likely to expand under future drier and especially warmer climates.
Footnotes
- ↵1To whom correspondence may be addressed. Email: locosselli{at}yahoo.com.br or msbuck{at}usp.br.
Author contributions: G.M.L., R.J.W.B., S.K., and M.B. designed research; G.M.L., R.J.W.B., M.d.S.L., M.G., S.K., A.A.d.O., J.B., D.A., G.C., J.S., and M.B. performed research; G.M.L., R.J.W.B., M.d.S.L., S.K., A.A.d.O., and J.B. analyzed data; and G.M.L., R.J.W.B., M.d.S.L., M.G., S.K., A.A.d.O., J.B., D.A., G.C., J.S., and M.B. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2003873117/-/DCSupplemental.
Data Availability.
The dataset of tropical trees is available at Figshare (DOI: 10.6084/m9.figshare.13119842) together with the R codes for the two models and their respective diagnostics and results. The dataset from extropical trees is available at the International Tree-Ring Data Bank (ITRDB) (https://www.ncdc.noaa.gov/data-access/paleoclimatology-data/datasets/tree-ring). Refer to the SI Appendix for detailed information on ITRDB data used in this study.
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