Stability of a Neotropical microrefugiumduring climatic instability

Abstract

The primary objectives of this study were (1) to assess, in the light of palaeoecological reconstruction, the climate stability hypothesis used by evolu-tionary biologists to explain high diversity in historically stable areas, and (2)to identify the response mechanisms of a tropical rain forest microrefugium toclimatic variability. Location North-eastern Brazil, Serra de Maranguape. Methods Vegetation and climatic changes were reconstructed using a pollenrecord in a sediment core from a forest hollow, and the chronology was basedon accelerator mass spectrometry radiocarbon analyses. Results Past vegetation dynamics consisted of three main forest types, shownby major compositional changes in rain forest assemblages between 5000 and1000 cal. yr bp . Dense ombrophilous forest was abruptly replaced by heliophil-ous early successional tree taxa at 4275 cal. yr bp . These early successional treetaxa were established over a period of c. 100 years, and their dominance lastedfor c. 750 years and was associated with dry conditions until 3525 cal. yr bp .Subsequently, the expansion of secondary successional tree taxa over a periodof c. 550 years enabled the recovery of ombrophilous forest. Main conclusions The vegetation changes in the Serra de Maranguape pro-vide evidence for the high sensitivity of this rain forest microrefugium to cli-matic variability on a multidecadal to millennial time-scale during the mid- tolate Holocene. Despite the substantial compositional and climatic changes, thismicrorefugium apparently was continuously forested and responded to climaticinstability by recruiting key species to its highly diverse stock. This evidencehelps to address the joint concerns of evolutionary biologists and palaeoecolo-gists regarding how forests can persist during periods of climatic variability by showing that some tropical regions can remain continuously forested despitereorganization during abrupt and short-term climatic changes