High Plain Of Bogota Research Articles

Successional Position of Dry Andean Dwarf Forest Species as a Basis for Restoration Trials

The successional affinity of nine woody species was inferred from the structure, diversity and disturbance history of the vegetation where these occurred. This was done in order to obtain a basis for a restoration experiment, currently in execution, in the dry Andean dwarf forest zone on the edge of the High Plain of Bogota (Colombia), at 2600–2950 m.a.s.l. We laid out 101 relevees in grassland and shrubland types in different stages of recovery, and in relatively little disturbed endemic Condalia thomasiana dwarf forest. The disturbance history of sites over the last ~60 years was inferred from aerial photograph series (1941–1991). CCA and logistic regression were applied to relate species composition to diversity, environment and disturbance history. All species showed a preference for certain structural groups. Also, a clear relation between species occurrence and vegetation diversity was found. Baccharis macrantha, and Dalea coerulea appeared relatively tolerant to grazing, while the remaining seven species reacted negatively. Soil clay content, base availability and organic carbon content was also an important factor for occurrence of each species. Invasion of grasslands by woody species is pioneered by Baccharis macrantha and followed by Dodonaea viscosa. Dalea coerulea was predominantly found on truncated clayey soils, which will probably not support Condalia dwarf forest. The hypothesized classification of the nine planted species to either pioneers or late-successional was fine-tuned. This exploratory study will be of use in the set-up of future succession-based restoration experiments, and for converting exotics afforestations to natural vegetation.

The Plio-Pleistocene climatic record of the tropical Andes

Sequences of lake sediments on the high plains of the Colombian Cordillera Oriental (at an altitude of c. 2500 m) represent some 5 or 6 Ma. The last glacial–interglacial cycle is well documented in the sediments of Lake Fuquene; very long sequences (up to 350-m long cores) were collected in the high plain of Bogota, representing more than 3.5 Ma. Pollen diagrams are now available, covering that time and representing the longest known continuous terrestrial record available. They were dated using potassium-argon and fission track methods on material from intercalated volcanic ash layers. The pollen diagrams can be interpreted in terms of shifting vegetation zones, and these in turn enable us to draw approximate temperature and humidity curves. The temperature curve for the last 3.5 Ma can be correlated with deep-sea curves (oxygen isotopes, temperature). An important change in rhythm and intensity seems to take place at approximately 3.1 Ma and a cold period that should correspond in time with the Pre-Tiglian of Western Europe is conspicuous.