Michael Wille

Distribution and Ecology of Parent Taxa of Pollen Lodged Within the Latin American Pollen Database.

The cornerstone of palaeoecological research, concerned with vegetation dynamics over the recent geological past, is a good understanding of the present-day ecology and distribution of the taxa. This is particularly necessary in areas of high floral diversity such as Latin America. Vegetation reconstructions, based on numerous pollen records, now exist with respect to all major vegetation associations from Latin America. With this ever-increasing number of sedimentary records becoming available, there is a need to collate this information and to provide information concerning ecology and distribution of the taxa concerned. The existing Latin American Pollen Database (LAPD) meets the first of these needs. Information concerning the ecology and distribution of the parent taxa responsible for producing the pollen, presently lodged within the LAPD, is the focus of this paper. The ‘dictionary’ describes the ecology and distribution of the parent taxa responsible for producing pollen identified within sedimentary records. These descriptions are based on a wide range of literature and extensive discussions with members of the palaeoecological community working in different parts of Latin America investigating a range of different vegetation types.

Mid- to Late-Holocene pollen-based biome reconstructions for Colombia

Abstract The assignment of Colombian pollen data to biomes allows the data to be synthesised at 10 ‘time windows’ from the present-day to 6000 radiocarbon years before present (BP). The modern reconstructed biomes are compared to a map of modern potential vegetation to check the applicability of the method and the a priori assignment of pollen taxa to plant functional types and ultimately biomes. The reconstructed modern biomes are successful in describing the composition and distribution of modern vegetation. In particular, altitudinal variations in vegetation within the northern Andean Cordilleras are well described. At 6000 BP the biomes are mainly characteristic of warmer environmental conditions relative to those of the present-day. This trend continues until between 4000 and 3000 BP when there is a shift to more mesic vegetation that is thought to equate to an increase in precipitation levels. The period between 2500 and 1000 BP represents little or no change in biome assignment and is interpreted as a period of environmental stability. The influence attributed to human-induced impact on the vegetation is recorded from 5000 BP, but is particularly important from 2000 BP. The extent of this impact increases over the Late-Holocene period, and is recorded at increasingly high altitudes. Despite these changes, a number of sites do not change their biome assignment throughout the analysis. This asynchronous vegetation response is discussed within the context of site location, non-linear response of vegetation to Late-Holocene environmental change, regionally differential signals, localised human impact and methodological artefacts.

Upper forest line reconstruction in a deforested area in northern Ecuador based on pollen and vegetation analysis

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 paramo documents altitudinal migrations and the composition of the upper forest line prior to deforestation. Four successive radiocarbon dates of 293 ± 41 14 C y BP, 498 ± 40 14 C y BP, 626 ± 33 14 C y BP, and 729 ± 44 14 C 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.

Environmental change in the Colombian subandean forest belt from 8 pollen records: the last 50 kyr

Abstract. We present a reconstruction of forest history and climatic change based on 11 pollen records from eight sites, all located in the lower montane forest belt of the northern Andes in Colombia. We compared records from the Popayán area in southern Colobia, Timbio (1750 m), Genagra (1750 m) and Pitalito (1300 m) and the new Piagua (1700 m) record with the records from Lusitania (1500 m), Libano (1820 m), Pedro Palo (2000 m) and Ubaqué (2000 m) from Central Colombia. The changes of the altitudinal position of the lower/upper montane (= subandean/Andean, S/At) forest belt transition were used to estimate temperature change for the last 50 kyr. We infer a Last Glacial Maximum (LGM) temperature drop of 6°–7°C at 1700 m, and a steeper LGM lapse rate of 0.76°C/100 m compared to today (ca. 0.6°C/100 m). Around 50 uncal. kyr B.P. the temperature at 1700 m was ca. 3°C lower than today. Until 20 uncal. kyr B.P. the temperature oscillated and gradually decreased. During the LGM, temperature was down to ca. 6°–7°C lower than today. After the LGM, temperature increased and ca. 14 uncal. kyr B.P. it was 2°–3°C lower than today (S/At at ca. 1800 m, 500 m below present elevation; Susacá interstadial). An unquantified cooling (Ciega stadial) followed. During ca. 12.3–11.7 uncal. kyr B.P. the S/At shifted upslope to 2100 m indicating a temperature of 1°–2°C cooler than today (Guantiva interstadial). From 11.7–10.9 uncal. kyr B.P. the S/At was at 1800 m indicating that the temperature was ca. 3°C lower than today and wet conditions prevailed (partly coinciding with the El Abra stadial). The period 10.9–9 uncal. kyr B.P. was also cool, but drier. During 9–7.5 uncal. kyr B.P. temperature was ca. 1°C warmer relative to today (mid Holocene hypsithermal). During the last 5 kyr the presence of cultivated plants demonstates human colonization of the lower montane zone in Colombia.

New insights into paleoenvironmental changes in Laguna Potrok Aike, southern Patagonia, since the Late Pleistocene: The PASADO multiproxy record

A series of long sediment cores was retrieved from Laguna Potrok Aike, Southern Patagonia, within the framework of PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Project), an ICDP (International Continental Scientific Drilling Program) lake drilling project. This maar lake, located at 52°S, 70°W in the Province of Santa Cruz (Argentina), in the southernmost continental area of the world, is one of the few permanent lakes in the region, providing a unique continuous paleoclimatic and paleoecological lacustrine record for the last glacial cycle. Previous multiproxy studies of this site have characterized the environmental history of these dry lands in the Patagonian Steppe for the last 16 cal. ka BP. This new series of sediment cores provides a much longer record of climate variability in Southern Patagonia since 51.3 cal. ka BP. Using a multiproxy strategy, a set of samples (mostly from core catcher material) was analyzed for physical properties, rock magnetism, geochemistry, CNS elemental analysis, stable isotopes, pollen and diatoms. This preliminary multiproxy limnogeological interpretation sheds new light on the regional Pleistocene and Holocene environmental history, revealing lake-level variations through time and identifying time windows of interest where higher resolution analyses will be carried out.

Submillennium-scale migrations of the rainforest-savanna boundary in Colombia: 14C wiggle-matching and pollen analysis of core Las Margaritas

Abstract We present the 11 150-cal-yr-long pollen record Laguna Las Margaritas (3°23′N, 73°26′W; 290 m altitude), located at a site sensitive to climatic change near the transition from the Amazonian rainforest to the savanna of the Llanos Orientales in Colombia. In the 10-m-long core nine AMS 14 C bulk samples show ages from 9760±60 to 854±36 BP and provide initial time control. Thirty-one additional AMS 14 C samples of selected macrofossils provide time control from 6250 to 4050 cal BP; for this interval precise time control was obtained by 14 C wiggle-match dating. From 11 150 to 9100 cal BP, grass savanna dominated the landscape while gallery forest along the drainage system was poorly developed. Water availability was lower than today and the length of the dry season longer. From 9100 to 7330 cal BP gallery forest expanded pointing to wetter conditions. From 7330 to 5430 cal BP savanna was increasingly replaced by forest, but with alternating abundance of both vegetation types. From 5430 to 2500 cal BP forest and wooded savanna dominated the western Llanos Orientales suggesting high precipitation rates. Expansion of Mauritia palm forest at 2500 cal BP reflects increasing water availability and stagnant water environments. Increasing savanna between 2500 and 1000 cal BP may represent a combined natural and anthropogenic signal. Development from open savanna to forest during the Middle Holocene is synchronous with a decreasing caloric seasonality, and a southward migration of the Intertropical Convergence Zone, suggesting that the large-scale climatic and vegetational change in the Colombian savannas is precession-forced. High-frequent migration of the savanna–rainforest boundary started around 6000 cal BP and continued at least to 3000 cal BP. Precipitation regimes in northwest and northeast South America seem opposite: dry conditions in the Colombian savanna area seem to reflect a La Nina setting of the climate system; wet conditions reflect an El Nino setting. Δ 14 C fluctuations reflect changes of solar activity and we tested the hypothesis that Δ 14 C fluctuations correspond to climatic and vegetational change. For the interval 6250 to 4050 cal BP, we applied 14 C wiggle-match dating (WMD), i.e. matching a series of radiocarbon ages in 14 C BP from the sediment, with the dendrochronology-based calibration curve, and we also wiggle-matched the pollen record vs. the Δ 14 C record. In this first attempt in a neotropical ecosystem, we could not find unambiguous support that changes in solar activity did trigger climatic and vegetational change in the savannas of the Llanos Orientales.

Intensified Southern Hemisphere Westerlies regulated atmospheric CO2 during the last deglaciation

The causes for the rise of atmospheric CO 2 during the last deglaciation are complex and remain a matter of controversial scientific discussion. One hypothesis explains this phenomenon with CO 2 release from the deep ocean. A change in atmosphere-ocean interaction induced by a shift or intensification of Southern Hemisphere Westerlies (SHW) could have stimulated this process. Here this hypothesis is tested using oxygen isotope ratios of aquatic cellulose from Patagonian lacustrine sediments as west-wind proxy. Our record indicates maximum SHW strength at 52°S between 13.4 and 11.3 calibrated kyr B.P. This is in agreement with an increase in zonal wind strength extending to the southern mid-latitudes during the Younger Dryas chronozone triggering the final CO 2 increase. Comparison with other Southern Hemisphere records implies southward migration of strengthened SHW at that time, leading to interglacial CO 2 levels and hence terminating the Last Glacial.

Vegetation disturbance and human population in Colombia – a regional reconstruction

Palaeoecologists using pollen to map vegetation since the last ice age have noted numerous changes – which they feel increasingly obliged to blame on humans. These changes, such as deforestation or the dominance of certain plants, may happen suddenly or take place over thousands of years. The authors study the pollen record in Colombia, identify plants diagnostic of cultivation or disturbed ground (“degraded vegetation”) and use them to map human activities by proxy. They show how the people move and the landscape changes between 5000 BP and the present day, from the coast inland, and from the lowlands up into the Andes.