Fifty-thousand-year vegetation and climate history of Noel Kempff Mercado National Park, Bolivian Amazon

Abstract

Pollen and charcoal records from two large, shallow lakes reveal that throughout most of the past 50,000 yr Noel Kempff Mercado National Park, in northeastern lowland Bolivia (southwestern Amazon Basin), was predominantly covered by savannas and seasonally dry semideciduous forests. Lowered atmospheric CO2 concentrations, in combination with a longer dry season, caused expansion of dry forests and savannas during the last glacial period, especially at the last glacial maximum. These ecosystems persisted until the mid-Holocene, although they underwent significant species reassortment. Forest communities containing a mixture of evergreen and semideciduous species began to expand between 6000 and 3000 14C yr B.P. Humid evergreen rain forests expanded to cover most of the area within the past 2000 14C yr B.P. coincident with a reduction in fire frequencies. Comparisons between modern pollen spectra and vegetation reveal that the Moraceae-dominated rain forest pollen spectra likely have a regional source area at least 2–3 km beyond the lake shore, whereas the grass- and sedge-dominated savanna pollen spectra likely have a predominantly local source area. The Holocene vegetation changes are consistent with independent paleoprecipitation records from the Bolivian Altiplano and paleovegetation records from other parts of southwestern Amazonia. The progressive expansion in rain forests through the Holocene can be largely attributed to enhanced convective activity over Amazonia, due to greater seasonality of insolation in the Southern Hemisphere tropics driven by the precession cycle according to the Milankovitch Astronomical Theory.

Hydrology and climatology at Laguna La Gaiba, lowland Bolivia: complex responses to climatic forcings over the last 25 000 years

“…Baker et al, 2001), although it may reflect differential sensitivity between tropical forest pollen and diatoms in response to drying. The strengthening of the SASM in the later Holocene has been widely reported as a response to insolation forcing, with southward expansion of the Amazon rainforest (Mayle et al 2000;Burbridge et al, 2004) and SDTF (Taylor et al, 2010) in more southerly locations and wetter conditions recorded by speleothems east and west of Amazonia (Wang et al, 2006;Mosblech et al, 2012). As Mosblech et al suggest this more uniform and predictable monsoon response to insolation may reflect the different boundary conditions of the Holocene compared with the full glacial period.…”

Fire, climate and vegetation linkages in the Bolivian Chiquitano seasonally dry tropical forest

“…These unique and isolated SDTFs of the inter-Andean valleys have experienced an evolutionary history separate to that of lowland SDTFs, having been separated for ca 10 Myr [52]. Andean SDTFs may very probably show a sensitivity to fire that is not demonstrated by the lower-diversity Chiquitano forest biome, which have shown resilience and adaptability in occupying new regions through rapid post-glacial migration [23,53]. Regardless of whether dry forests of inter-Andean valleys would be able to maintain a closed-canopy structure in the event of high fire activity, they contain some of the highest concentrations of endemics in the world [54], and the negative impact of fires on plant richness could have a devastating effect on this biodiversity hotspot.…”

Pollen-vegetation richness and diversity relationships in the tropics

“…The similarity between the diversity of the vegetation likely reflects a low diversity of the moist evergreen forest plot relative to moist evergreen forest found elsewhere in the Neotropics (Gentry 1988). Two factors likely contribute to the low diversity of the vegetation in the Bolivian plots: (1) the young age of the moist evergreen forest (Mayle et al 2000;Burbridge et al 2004), these forests are just a few 1,000 years old and the high diversity levels typically associated with rainforest may not have had time to develop yet; and (2) the close proximity to the southerly extent of moist evergreen rainforest probably means some typical moist evergreen forest taxa are excluded due to drought stress.…”