High-resolution time series of vessel density in Kenyan mangrove trees reveal a link with climate.

Tropical trees are often excluded from dendrochronological investigations because of a lack of distinct growth ring boundaries, causing a gap in paleoclimate reconstructions from tropical regions. The potential use of time series of vessel features (density, diameter, surface area and hydraulic conductivity) combined with spectral analysis as a proxy for environmental conditions in the mangrove Rhizophora mucronata was investigated. Intra-annual differences in the vessel features revealed a trade-off between hydraulic efficiency (large vessels) during the rainy season and hydraulic safety (small, more numerous vessels) during the dry season. In addition to the earlywood-latewood variations, a semiannual signal was discovered in the vessel density and diameters after Fourier transformation. The similarity in the Fourier spectra of the vessel features and the climate data, in particular mean relative humidity and precipitation, provides strong evidence for a climatic driving force for the intra-annual variability of the vessel features. The high-resolution approach used in this study, in combination with spectral analysis, may have great potential for the study of climate variability in tropical regions.