Late Holocene Colombian vegetation dynamics.

Using the biomisation method, Colombian pollen data are synthesised at ten 'time windows' from the present day to 6000 radiocarbon years before present (BP). The modern reconstructed biomes are compared to a map of modern potential vegetation to check the applicability of the method and the a priori assignment of pollen taxa to plant functional types and ultimately biomes. The reconstructed modern biomes are successful at describing the composition and distribution of modern vegetation, and in particular altitudinal shifts in vegetation associated with the northern Andean Cordilleras. At 6000 BP the biomes are mainly characteristic of warmer environmental conditions relative to those of the present day. This trend continues until between 4000 and 3000 BP when there is a shift to more mesic vegetation that is thought to equate to an increase in precipitation levels. The period between 2500 and 1000 BP represents little or no change in biome assignment and is interpreted as a period of environmental stability. The influence attributed to human-induced impact on the vegetation is recorded from 5000 BP, but is particularly important from 2000 BP. The extent of this impact increases over the late Holocene period, being recorded at increasingly high altitudes. Despite these changes, a number of sites do not change their biome assignment throughout the analysis. This asynchronous vegetation response is discussed within the context of site location, non-linear response of vegetation to Late Holocene environmental change, regionally differential signals, localised human impact and methodological artefacts