Pollen records from lacustrine sediments of deep basins in the Colombian Andes provide records of vegetation history, the development of the floristic composition of biomes, and climate variation with increasing temporal resolution. Local differences in the altitudinal distribution of present–day vegetation belts in four Colombian Cordilleras are presented. Operating mechanisms during Quaternary Ice–Age cycles that stimulated speciation are discussed by considering endemism in the asteraceous genera Espeletia , Espeletiopsis and Coespeletia . The floristically diverse lower montane forest belt (1000–2300 m) was compressed by ca . 55% during the last glacial maximum (LGM) (20 ka), and occupied the slopes between 800 m and 1400 m during that period. Under low LGM atmospheric p _{CO 2} values, C ₄ –dominated vegetation, now occurring below 2200 m, expanded up to ca. 3500 m. Present–day C ₃ –dominated paramo vegetation is therefore not an analogue for past C ₄ –dominated vegetation (with abundant Sporobolus lasiophyllus ). Quercus immigrated into Colombia 478 ka and formed an extensive zonal forest from 330 ka when former Podocarpus –dominated forest was replaced by zonal forest with Quercus and Weinmannia . During the last glacial cycle the ecological tolerance of Quercus may have increased. In the ecotone forests Quercus was rapidly and massively replaced by Polylepis between 45 and 30 ka illustrating complex forest dynamics in the tropical Andes.

Plant microfossil and macrofossil associations obtained from six dated sections from the area of the basin of Bogotá (2550 m, Eastern Cordillera, Colombia) show the evolution of the late Neogene Andean montane forest, triggered by the Andean orogeny. Progressive adaptation of warm tropical taxa to cool montane conditions, evolution of new neotropical montane taxa, and immigration of temperate Laurasian, Holarctic, and Austral-Antarctic elements gave shape to the present-day montane forest. Vegetational characteristics inferred from fossil plant associations reveal the altitude at the time of deposition. Neogene forests are floristically compared with contemporary forests at comparable altitudinal intervals in the surroundings of the Bogotá basin; however, the absence of taxa that had not yet arrived, or evolved, is most salient and shows that non-analogue plant communities are common. The main phases of montane forest development are: (1) pre-uplift phase of the late Miocene with abundant lowland... Resumen Los microfósiles de plantas y asociaciones de macrofósiles obtenidos de seis secciones fechadas del área de la cuenca de Bogotá (2550 m, Cordillera Oriental, Colombia) demuestran la evolución del bosque andino del Neógeno tardío, accionado por la orogenia andina. La adaptación progresiva de taxones tropicales calidos hacia las condiciones frías montanas, la evolución de nuevos taxones neotropicales montanos y la migración de elementos templados laurásicos, holárticos y austral-antárticos dieron forma al bosque montano actual. Las características de la vegetación deducidas de las asociaciones de plantas fósiles revelan la altitud al momento de los depósitos. Los bosques neógenos se comparan florísticamente con bosques contemporáneos a intervalos altitudinales comparables en los alrededores de la cuenca de Bogotá; sin embargo, la ausencia de taxones que todavía no habían llegado, o desarrollado, es sobresaliente y demuestra que las comunidades de plantas no análogas son comunes. Las fases principale...

An improved understanding of present-day climate variability and change relies on high-quality data sets from the past 2 millennia. Global efforts to model regional climate modes are in the process of being validated against, and integrated with, records of past vegetation change. For South America, however, the full potential of vegetation records for evaluating and improving climate models has hitherto not been sufficiently acknowledged due to an absence of information on the spatial and temporal coverage of study sites. This paper therefore serves as a guide to high-quality pollen records that capture environmental variability during the last 2 millennia. We identify 60 vegetation (pollen) records from across South America which satisfy geochronological requirements set out for climate modelling, and we discuss their sensitivity to the spatial signature of climate modes throughout the continent. Diverse patterns of vegetation response to climate change are observed, with more similar patterns of change in the lowlands and varying intensity and direction of responses in the highlands. Pollen records display local-scale responses to climate modes; thus, it is necessary to understand how vegetation–climate interactions might diverge under variable settings. We provide a qualitative translation from pollen metrics to climate variables. Additionally, pollen is an excellent indicator of human impact through time. We discuss evidence for human land use in pollen records and provide an overview considered useful for archaeological hypothesis testing and important in distinguishing natural from anthropogenically driven vegetation change. We stress the need for the palynological community to be more familiar with climate variability patterns to correctly attribute the potential causes of observed vegetation dynamics. This manuscript forms part of the wider LOng-Term multi-proxy climate REconstructions and Dynamics in South America – 2k initiative that provides the ideal framework for the integration of the various palaeoclimatic subdisciplines and palaeo-science, thereby jump-starting and fostering multidisciplinary research into environmental change on centennial and millennial timescales.

Pollen analysis of a 150-cm-long core from Pantano de Pecho (0°20′S, 78°37′W) at 3870 m altitude in the Ecuadorian páramo documents altitudinal migrations and the composition of the upper forest line prior to deforestation. Four successive radiocarbon dates of 293 ± 41 ¹⁴C y BP, 498 ± 40 ¹⁴C y BP, 626 ± 33 ¹⁴C y BP, and 729 ± 44 ¹⁴C y BP show that the record includes the last c. 730 radiocarbon y, corresponding to the last c. 660 calendar years (cal y BP). The natural upper forest line was at a minimum altitude of 3400-3500 m between c. AD 1290 to 1315 (zone 1), from c. AD 1315 to 1350 at 3500-3600 m (zone 2), from c. AD 1350 to 1640 at 3600-3700 m (zone 3), from c. AD 1640 to c. 1765 at 3750 m (zone 4), and from c. AD 1765 to the present at 3700-3650 m (zone 5). The most important taxa were Alnus, Hedyosmum, Miconia, other Melastomataceae, Gunnera and Solanaceae. Since c. AD 1350 Podocarpus was continuously present with low abundance, but possibly not close to the upper forest line. Rarer elements of the upper montane forest were Dodonaea, Myrsine, Weinmannia, Myrica, Myrtaceae, Sapium, Juglans, Piper, Euphorbiaceae and Rubiaceae. Human disturbance and deforestation are shown by the presence of Rumex, Spermacoce pollen and charcoal particles. We surveyed the vegetation composition from isolated forest patches located between 3650 m and 4300 m. TWINSPAN analysis indicates forest patches up to 3950 m have a similar floristic composition to closed forest below the upper forest line. We argue that this apparent similarity does not necessarily mean that the slopes between 3750 and 3950 m were covered by closed forest in the past.