Changes of seasonally dry forest in the Colombian Patía Valley during the early and middle Holocene and the development of a dry climatic record for the northernmost Andes

A 450 cm long sediment core was collected from a swamp in the dry forest ecosystem of the Patía Valley in Colombia (02°02′ N, 77° W at 750 m elevation). This core (Potrerillo-2) was analysed using pollen, lithostratigraphy and radiocarbon dates and was correlated with an already existing dataset from Patía-1. Together these records show that dry forest existed in the Patía Valley since the early Holocene and that open vegetation and dry forest coexisted through time, but that during dry periods open vegetation dominated in the valley. The data also show that relatively humid and wet conditions were present at the Patía Valley from c. 9510 to 8600 cal yr BP, whereas between c. 8360 to 8260 cal yr BP dry conditions prevailed in the valley. The pollen record of Potrerillo-2 illustrates well the response – and high sensitivity – of dry forest ecosystems to changes in precipitation, which is mainly related with the mean position of the ITCZ.