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

Abstract

In the Rio Ranchería 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 patches 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 Ranchería 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 Ranchería 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 Ranchería watershed have suffered permanent damage. The savannas of this region are likely to remain unless fire is suppressed and soil restoration practices implemented.

Pollen-based biome reconstructions for Latin America at 0, 6000 and 18 000 radiocarbon years ago

“…The extent to which lapserate changes can be used to explain spatially different signals from the data must be used with caution, particularly as most palaeoclimatic reconstructions have been carried out with some kind of modern analogue approach (Farrera et al, 1999). These reconstructions commonly do not take into account non-climatic parameters which would impact on vegetation composition and distribution such as volcanic activity (Kuhry, 1988), fire (Cavelier et al, 1998;Rull, 1999), UV-B insolation (Flenley, 1998) or atmospheric composition, in particular changing CO 2 levels (Woodward and Bond, 2004). For example, concentrations of CO 2 reduced to glacial levels (200 ppmV) have been shown to have a very significant impact on tropical vegetation (Jolly and Haxeltine, 1997;Boom et al, 2002;Marchant et al, 2002b;Wu et al, 2007a, b).…”

Museum collections indicate bird defaunation in a biodiversity hotspot

“…The savannization of moist forests in Colombia has been previously suggested due to deforestation and land practices (Cavelier et al 1998). This suggestion linked human induced-fire damaging soils dating as far as Pre-Columbian times.…”

Resilience of Amazonian forests : the roles of fire, flooding and climate

“…In fact, rare studies across the tropics have demonstrated forest savannization. In South America, centuries of land-use with fire and cattle allowed soils of moist tropical forests to erode intensely, favouring the colonization of savanna trees (Cavelier et al 1998). This suggests that chronic perturbations that allow resource conditions to degrade (Shakesby and Doerr 2006) may lead to savannization, if savanna trees are able to disperse into disturbed sites.…”

“…Jakovac et al (2014), have shown for instance that forest recovery slows down after repeated cycles of shifting cultivation in the Amazon forest. Although forest recovery in tropical systems seem to slow down with drought and repeated disturbances, evidence of forest savannization is rare (Cavelier et al 1998), suggesting a high capacity to persist in the forest state.…”