The savannization of moist forests in the Sierra Nevada de Santa Marta, Colombia

In the Rio Rancheria watershed of the Sierra Nevada de Santa Marta, between 500 and 1500 m, savanna vegetation is interspersed with moist forests. The savannas are composed of native savanna grasses like Aristida adscensionis L., Arundinella sp., Panicum olyroides Kunth, and Schyzachyrium microstachyum (Desv.) Roseng., Arrill & Izag and the African Melinis minutiflora P. Beauv. There is also Curatella americana L. and Byrsonima crassifolia (L.) H.B.K., two typical tree species of the neotropical savannas. Although moist forest patches occur more often on lower slopes and narrow valley bottoms, they can also be found on mid- and upper-slopes and less often on ridges. Thus? these forest patches are not gallery forests as are found throughout the neotropics, but the result of deforestation and fractionation of a continuous forest. A comparison of soil profiles between the savannas and remnant forest parches on the same slope, showed the disappearance of the A and B horizons (approx, 50 cm) under savanna vegetation. The sharp difference between the savanna and forest soils at the Rio Rancheria does not appear to be due to a change in soil water status along a toposequence or differences in the underlying bedrock. We hypothesize that the savannas of the Rio Rancheria watershed, are the result of deforestation and land practices on infertile soils derived from granite. The savannization process was likely initiated by Amerindians by means of the frequent use of fire or clearing lands for the cultivation of maize. The introduction of cattle by Spaniards (c. 1530) and the frequent use of fire to maintain grazing fields, contributed to further degradation of the habitat. While some tropical landscapes recovered their forest cover when human pressure was removed approximately 500 years ago, areas such as the Rio Rancheria watershed have suffered permanent damage. The savannas of this region are likely to remain unless fire is suppressed and soil restoration practices implemented.