Species-specific growth responses to climate variability for cerrado trees of southern Brazil

Tree growth in tropical forests and savanna has been shown to be sensitive to annual variations in rainfall, especially during anomalously dry years such as those that occur during El Niño. We measured variations in stem growth increment for 33 different tree species growing in upland and seasonally flooded (hyperseasonal) forests and woodlands of the Brazilian savanna (cerrado) located in the Cuiaba Basin and Northern Pantanal of Mato Grosso, Brazil. Measurements of tree growth were made on 434 trees using plastic, spring-loaded dendrometer bands between 2015 and 2018, which encompassed the 2015-16 El Niño-La Niña cycle that was one of the most intense on record for the region. Cluster analysis was used to determine if patterns in the tree growth response to rainfall variation could be predicted from phenological and/or habitat traits. Annual rates of stem growth varied substantially between species, and according to the literature, trees with high growth rates were associated more with secondary habitats while trees with slower growth rates were associated more with primary forests and woodlands. In addition, none of the fast growing trees were evergreen while an equal proportion of trees with slower growth rates were evergreen or deciduous. Stem growth rates were significantly lower in 2015-16, during the hot, dry El Niño, and highest in the following year, during the cooler, wetter La Niña, and annual variations in stem growth were significantly positively correlated with annual rainfall. To better quantify the species growth response to annual rainfall we calculated the slope of the regression between stem growth (y-axis) and annual precipitation (x-axis) for each species. Cluster analysis revealed five groups of trees with significantly different growth responses to precipitation, while for the Pantanal, cluster analysis identified three groups of trees with significantly different growth responses to rainfall, and in general, tree species that grew more rapidly also had a higher stem growth response to variations in rainfall. These data indicate that interannual variations in rainfall affect the growth of tropical forest and woodland trees differently, and that differences in the species growth response to rainfall may be driven in part by the phenological and habitat traits of the different species. These species-specific responses will presumably feed-back on community diversity and productivity as climate change ensues.