Climate signals in tree rings of Paubrasilia echinata (Leguminosae-Caesalpinioidea) from the Atlantic Forest of Brazil

Abstract

Key message Tree-ring chronologies were built for wild and cultivated Paubrasilia echinata, a presently endangered species. Significantly P. echinata showed measurably different growth patterns related to the environment where wild and cultivated trees have grown. Paubrasilia echinata once grew so abundantly along the tropical coast of South America that the names given to the tree by early Europeans colonists-Bresil, Brasil, Brazil-became synonymous with an entire geography. Today, despite restoration and protection efforts, the species remains under threat of extinction throughout Brazil's Atlantic Forest. Considering the past overexploitation and ongoing climate changes, the future of P. echinata significantly depends upon human understanding of the species' growth dynamics and growth-climate relations. Therefore, this work aims to: (1) demonstrate the feasibility of calendar dating P. echinata tree rings; (2) build chronologies by analyzing its growth rings; and (3) establish with detail the specific influence of climate on annual radial xylem production. Differences in vessel and axial parenchyma frequency, local distended rays and marginal parenchyma were the wood anatomical markers used to distinguish boundaries between adjacent rings so that dendrochronological methods could be applied. For climate-growth responses, we developed tree-ring width chronologies from wild and cultivated trees. Results revealed that seasonal rainfall is the most important factor influencing P. echinata growth. More specifically, positive correlation was observed between the tree-ring chronology of wild trees and precipitation during the rainy months of the growing season, while the tree-ring chronology of cultivated trees correlated negatively with precipitation in months before the growth period. Wild trees showed increment growth rates lower than planted trees. Rainfall's observed effect on P. echinata is, of course, not surprising. However, our results contribute a detailed quantitative record of that effect, which expands the body of ecological knowledge regarding P. echinata necessary for ongoing conservation efforts under current and future human-caused climate change.

Key message Tree-ring chronologies were built for wild and cultivated Paubrasilia echinata, a presently endangered species. Significantly P. echinata showed measurably different growth patterns related to the environment where wild and cultivated trees have grown. Paubrasilia echinata once grew so abundantly along the tropical coast of South America that the names given to the tree by early Europeans colonists-Bresil, Brasil, Brazil-became synonymous with an entire geography. Today, despite restoration and protection efforts, the species remains under threat of extinction throughout Brazil's Atlantic Forest. Considering the past overexploitation and ongoing climate changes, the future of P. echinata significantly depends upon human understanding of the species' growth dynamics and growth-climate relations. Therefore, this work aims to: (1) demonstrate the feasibility of calendar dating P. echinata tree rings; (2) build chronologies by analyzing its growth rings; and (3) establish with detail the specific influence of climate on annual radial xylem production. Differences in vessel and axial parenchyma frequency, local distended rays and marginal parenchyma were the wood anatomical markers used to distinguish boundaries between adjacent rings so that dendrochronological methods could be applied. For climate-growth responses, we developed tree-ring width chronologies from wild and cultivated trees. Results revealed that seasonal rainfall is the most important factor influencing P. echinata growth. More specifically, positive correlation was observed between the tree-ring chronology of wild trees and precipitation during the rainy months of the growing season, while the tree-ring chronology of cultivated trees correlated negatively with precipitation in months before the growth period. Wild trees showed increment growth rates lower than planted trees. Rainfall's observed effect on P. echinata is, of course, not surprising. However, our results contribute a detailed quantitative record of that effect, which expands the body of ecological knowledge regarding P. echinata necessary for ongoing conservation efforts under current and future human-caused climate change.