A reconstruction of Colombian biomes derived from modem pollen data along an altitude gradient

Biomes are reconstructed in Colombia from modem (core-top) pollen data deri ved from 22 sites along an altitudinal gradient (2000-4100 in) that encompa sses the tree line. The 'biomization' methodology is described in a stepwis e manner that details the reconstruction of vegetation along an altitudinal gradient. In the majority of the cases, the results are comparable to site -specific descriptions of the vegetation. At altitudes between 2000 and 300 0 in, cool mixed forest and cool evergreen forest biomes are important. Bet ween 3000 and 3700 in the cool grassland/shrub biome is dominant. Above 370 0 m, the affinity score to arboreal biomes is low with a concomitant increa sed affinity to the cool grassland biome that co-dominates along with the c ool grassland/shrub biome. Hence, the technique is shown successful at reco nstructing modem vegetation, this is particularly so when affinity scores t o the range of biomes, rather the single most dominant biome, are used to d escribe vegetation composition. The results are able to delimit the altitud inally-induced changes in vegetation, from Andean forest associations, open forest and shrub grassland complex through to high altitude grasslands. Ho wever, this ability of the modern pollen data to predict the potential vege tation, via the biomization technique, is complicated by several site-speci fic factors that impact on the vegetation. Of particular importance are loc alised environmental conditions, particularly moisture regime. An additiona l area of interest is the impact that human activity has had on the vegetat ion. By manipulation of the input matrices, which are assigned a priori, an d consultation of the range of biome affinity scores, it is possible to ide ntify which sites reflect an anthropogenic signal and how this is manifeste d within the pollen data. By investigating the range of affinity scores, th ese factors can be identified and the relatively subtle changes in reconstr ucted vegetation determined, in particular, how the composition and quantit y of the arboreal component changes about the tree line. The results are di scussed in the context of using tree line position, and altitudinally-induc ed floristic changes, for palaeoclimatic reconstruction. (C) 2001 Elsevier Science B.V. All rights reserved.