COLOMBIA, LOCATED IN the northwest of South America, is a highly-diverse country in terms of environment and climate. Colombia is dominated by the Andes, where the tropical diurnal climate is characterized by small differences in monthly temperature (less than 3 degrees C), although daily fluctuations may be large (up to 20 degrees C), especially during dry seasons. Three Cordilleras of the northern Andes are described by approximately 22,966 ft. (7,000 m.) of altitudinal change; this altitudinal rise equates to a temperature change of nearly 30 degrees C, and results in a significant change in vegetation recorded over a relatively small area. For example, there are transitions from cool high-altitude grasslands, to temperate forests at mid-altitudes, and some of the most diverse tropical rainforests in the world within the Chocó Pacific region.

Away from the Andes, the extensive lowlands are also incredibly diverse, ranging from lowland rainforests in Amazonia, to extensive savannas of the Llanos Orientales. The diversity of lowland ecosystems is mirrored by the climate; precipitation is highest in the Chocó Pacific region, due to the proximity of the Pacific-based moisture source and the steeply-rising ground of the Western Cordillera. Within Andean Colombia, low rainfall is recorded within rain shadow areas of the inter-Andean plains.

Colombian paleoecological archives of vegetation change represent a remarkable record for Latin America and the wider tropics. The Colombian pollen data allows an understanding of regional environmental change and its impact on tropical vegetation composition and distribution that rivals the resolution commonly available from more temperate latitudes where Quaternary science research has a longer ancestry and wider research base.

For example, one record from the Funza sedimentary basin within the high plain of Bogotá (8,366 ft. or 2550 m.), situated on the eastern Cordillera of Colombia, is a 1,968 ft. (600 m.) sedimentary sequence that documents vegetation change over the past 3.5 million years, according to H. Hooghiemstra.

This exceptional record, possibly the best record of vegetation change in the world, has resulted as sediment infilling during the Quaternary was in balance with subsidence of the basin floor and Andean uplift, leading to a permanent lake environment. The record has shown that during interglacial periods, the upper forest limit of the northern Andes was located maximally between 11,155-11,483 ft. (3,400-3,500 m.). During glacial periods, the forest limits have been placed at approximately 6,562 ft. (2,000 m.), with the area surrounding the core site being characterized by an increase in grass-dominated communities.

The extensive paleoecological data from Colombia that cover all major ecosystem types and climatic zones have been used in several synthesis studies. The reconstructions successfully describe the composition and distribution of vegetation, and in particular, alti-tudinal shifts in vegetation associated with the northern Andean Cordilleras and transitions from Amazonian lowland rainforest to savanna, according to Rob Marchant, et al. Under climatic conditions of the last glacial period, montane vegetation types extended to low altitudes where there was a concentration of moist vegetation type and concomitant expansion of the savanna areas.

As climate ameliorated, the reverse situation occurred. For example, in the mid-Holocene, the vegetation is characteristic of warmer environmental conditions than those of the present day. This trend continues until between 4,000 and 3,000 years before the present era, when there is a shift to more mesic vegetation that is thought to reflect an increase in precipitation levels, according to Marchant and Hooghiemstra. The influence attributed to human-induced impact on the vegetation is recorded from 5,000 years before the present era, but is particularly important from 2,000 years before the present era. The extent of this impact increases over the late Holocene period, recorded at increasingly higher altitudes. Despite these changes, many sites do not change their vegetation, such as those with asynchronous vegetation response results from site location, non-linear response of vegetation to Late-Holocene environmental change, regionally differential signals, and localized human impacts.

See ALSO: Climatic Data, Nature of the Data; Paleoclimates; Plants.

BIBLIOGRAphY. H. Hooghiemstra, "Vegetational and Climatic History of the High Plain of Bogotá, Colombia: A Continuous Record of the Last 3.5 Million Years," Dis-sertationes Botanicae (v.79, 1984); R.A. Marchant et al., "Colombian Dry Moist Forest Transitions in the Llanos

Orientales—A Comparison of Model and Pollen-Based Biome Reconstructions," Palaeogeography, Palaeoclima-tology, Palaeoecology (v.234, 2006); R.A. Marchant and H. Hooghiemstra, "Rapid Environmental Change in Tropical Africa and Latin America about 4000 Years Before Present: A Review," Earth Science Reviews (v.66, 2004).

Rob Marchant University of York

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