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Organic-rich layers intercalated in a Late Pliocene fluvial-lacustrine sediment sequence located at 2650 m elevation in the Guasca Valley (high plain of Bogota, Cordillera Oriental, Colombia) were analysed for plant micro- and macrofossils. Paleoenvironmental reconstructions indicate that a subandean forest (lower montane), at present found from 1000–2300 m alt., was prevalent in the area at that time. This subandean forest showed marked changes in its floristic composition. Several recorded forest taxa, such as Alchornea, Eugenia, Ilex, Myrica, Myrsine, are adapted to disturbance. Alternation of aquatic and paludal environments based on lithology and paleovegetation, shows that local conditions in the marginal areas of the basin were affected by major water level fluctuations. These dynamic conditions were most probably associated with the initial stage of development of the large tectonic-sedimentary basin of Bogota near the end of the final uplift of the Cordillera Oriental. Sixty-three plant macrofossil types were recognized new for the study area, including leaves, fruits, seeds and bryophytes, and are described and illustrated.

The El Abra stadial is a climatic cooling event defined in the Eastern Cordillera of Colombia, which corresponds both in timing and intensity to the Younger Dryas climatic oscillation of the northern North Atlantic region. The stadial was preceded by the relatively warm Guantiva interstadial and followed by the warm Holocene. Colder climatic conditions during the El Abra stadial caused a 400 m lowering of the upper Andean forest limit below its altitudinal location during the preceding Guantiva interstadial. Translated in temperature change, this represents a drop in mean annual temperature of approximately 2 to 3°C. The lowering of the upper forest limit and inferred temperature change for the El Abra stadial, compared to Late Holocene conditions, are in the order of 600 m and 4°C, respectively. The transition of the Guantiva interstadial to the El Abra stadial has been radiocarbon dated at 11,210 ± 90 BP and 10,820 ± 60 BP. Climatic warming may have started shortly after 10,380 ± 90 BP, and near present-day temperatures were reached at least as early as 8920 ± 100 BP. Maximum cooling was probably attained between 10,800 BP and 10,300 BP. Further (AMS) radiocarbon dating is planned to establish more exactly the timing of the El Abra stadial. A glacial advance of El Abra age, the Bocatoma stade, has been recognized in the highest part of the Colombian Eastern Cordillera, the Sierra Nevada del Cocuy. During this advance, glaciers extended some 700 m lower than at present. A climatic cooling event of El Abra age, associated with shifts of the upper Andean forest limit and glacial advances, has also been recognized in other parts of Andean Colombia, including the Central Cordillera and the Sierra Nevada de Santa Marta.

A palynological and macrobotanical study was made of a 40 cm long peaty clay layer (SUBA 39 section) intercalated in fluvial deposits of Pliocene age from the Subachoque Valley, located at the northwestern border of the high plain of Bogota in the Cordillera Oriental of Colombia at an elevation of 2820 m above sea level. This has permitted a detailed reconstruction of the former regional and local vegetation cover. The regional one consisted of an admixture of lower tropical, subandean and Andean forest elements that most probably developed in a tropical lowland environment. Few local vegetation elements have been found; only ferns were abundant along the shores of the former closed river branch. This reconstruction represents one of the vegetation types that existed at the beginning of the final upheaval of the northern Andes. All macrofossil types (cuticular remains, fruits, seeds, etc.) and some newly recognized microfossil types (pollen, fungal spores, etc.) found in the SUBA 39 section, are briefly described and illustrated.

The influence of volcanic activity and climatic change upon regional and local vegetation developments during the last 5800 years in the area of the El Bosque mire has been traced through examination of a peat section collected from this mire, located ca. 4°45′N, 75°27′W, at an elevation of 3650 m, in the Cordillera Central of Colombia. The 11 m long peat section was examined for all kinds of microfossils and macroscopical plant remains. At approximately 5800 yr B.P. a lava flow of the Nevado Santa Isabel volcano obstructed the El Bosque depression, resulting in the formation of an area of impeded drainage in which a mire vegetation developed. The former vegetation in the surroundings of the depression was seriously affected by the eruptive phase and was mainly replaced by pioneer grasslands. After about 125 years forest vegetation re-appeared. From ca. 5675 to 2160 yr B.P. the vegetation surrounding the mire consisted mainly of a dense high-Andean dwarf forest of Polylepis . The stands of vegetation at the boring site itself developed from an aquatic vegetation in small pools with Azolla and Drepanocladus to relatively drier vegetation types with Carex, Disterigma and Campylopus . During this period regional and local vegetation types were little affected by volcanism, with the exception of an interval between ca. 3900 and 3300 yr B.P. From ca. 2160 yr B.P. onwards the influence of volcanic activity upon the vegetation cover in the El Bosque area increased, Polylepis dwarf forest being replaced by a more open type of high-Andean forest. Disturbances due to volcanic activity also resulted in consecutive vegetational successions in the mire. Although volcanic activity has been the main factor to which changes in the regional vegetation types can be attributed, a more or less gradual lowering of the forest line as a result of a slight deterioration of the climate during the late Holocene can also be deduced from the El Bosque pollen diagrams.

The results of a palynological study of a 13 m deep bore hole of lake deposits from the Paramo de Agua Blanca, Colombian Eastern Cordillera (5°N; elev. 3250 m) are reported. By means of 14 C dates and an indirect dating method based on pollen densities, it was possible to provide the pollen diagram with an approximate time-scale. The section, representing some 465,000 years, gives a continuous record of the Middle and Late Pleistocene and Holocene vegetational and climatic sequences. The sequence of glacial and interglacial periods in combination with their age and duration according to the indirect time determinations could be tentatively correlated with the European chronostratigraphic sequence.

A section representing the closing phase of the Atlantic and the Early Subboreal was examined at centimeter intervals for all kind of micro- and macrofossils. The section was taken on the slope of a Pleistocene coversand ridge in the SE margin of the Amtsven (northwest Germany). During the Atlantic large areas of forest were replaced by raised-bog vegetation. In the Late Atlantic and the Early Subboreal the area surrounding the coversand ridge became gradually wetter due to a rising water-table resulting from an approaching and ultimately transgressing bog. Locally, a Quercus-Tilia forest persisted till the Early Subboreal on account of its more elevated situation on the coversand ridge, but when the water table continued to rise the Quercus-Tilia forest gradually developed, within a time-span of about 400 yrs., into a raised bog through various successive vegetational phases.