Long-term forest-savannah dynamics in the Bolivian Amazon: implications for conservation

Abstract

The aim of this paper is to evaluate the respective roles of past changes in climate, geomorphology and human activities in shaping the present-day forest-savannah mosaic of the Bolivian Amazon, and consider how this palaeoecological perspective may help inform conservation strategies for the future. To this end, we review a suite of palaeoecological and archaeological data from two distinct forest-savannah environments in lowland Bolivia: Noel Kempff Mercado National Park (NKMNP) on the Precambrian Shield and the 'Llanos de Moxos' in the Beni basin. We show that they contain markedly contrasting legacies of past climatic, geomorphic and anthropogenic influences between the last glacial period and the Spanish Conquest. In NKMNP, increasing precipitation caused evergreen rainforest expansion, at the expense of semi-deciduous dry forest and savannahs, over the last three millennia. In contrast, pre-Hispanic indigenous cultures were instrumental in facilitating recent forest expansion in the Llanos de Moxos by building a vast network of earthworks. Insights from Mid-Holocene palaeodata, together with ecological observations and modelling studies, suggest that there will be progressive replacement of rainforest by dry forest and savannah in NKMNP over the twenty-first century in response to the increased drought predicted by general circulation models. Protection of the latitudinal landscape corridors may be needed to facilitate these future species reassortments. However, devising appropriate conservation strategies for the Llanos de Moxos will be more difficult due to its complex legacy of Palaeo-Indian impact. Without fully understanding the degree to which its current biota has been influenced by past native cultures, the type and intensity of human land use appropriate for this landscape in the future will be difficult to ascertain.

Figure 1

MODIS image of the Bolivian Amazon and adjacent areas of Peru and Brazil, 28 July 2000, showing Noel Kempff Mercado National Park (NKMNP) and the Llanos de Moxos. Light areas with herringbone pattern to the north of NKMNP are zones deforested since the 1970s for agriculture in Rondônia, Brazil. Adapted from image processed by Jacques Descloitres, MODIS Land Rapid Response Team, NASA/Goddard Space Flight Center.

Figure 2

Vegetation classification of Noel Kempff Mercado National Park (derived from Landsat TM data) (Modified from Killeen & Schulenberg 1998). Laguna Chaplin and Laguna Bella Vista are marked with circles. Translations of local Bolivian/Brazilian terms are as follows: ^*, open savannah; **, shrubby savannah; ^***, open savannah woodland; ^****, closed savannah woodland; ^∧, seasonally inundated open savannah; ^∧∧, seasonally inundated shrub savannah/termite savannah. (Modified from Gosling et al. 2005.)

Figure 3

Laguna Chaplin summary pollen percentage diagram, showing the most common taxa from the full complement of 290 pollen types. Dots on the curves denote less than 0.5%. Curves showing ×10 exaggeration are depicted for selected taxa which have low percentages. ‘Total land pollen’ (TLP) sums are greater than 300 grains per sample, except for the 4 pollen spectra in zone LCH-1 which had lower TLP sums of 100–160, due to low pollen concentrations. (After Burbridge et al. 2004.)

Figure 4

Microscopic and macroscopic charcoal concentrations for Laguna Chaplin. Pollen assemblage zones are the same as in figure 3. (After Burbridge et al. 2004.)

Figure 5

The δ¹³C values of soil profiles of 15 soil pits dug along an ecotonal transect between open savannah (grassland) and tall forest in the central part of the Huanchaca plateau, NKMNP. (Modified from Killeen et al. 2003.)

Figure 6

Climate predictions of five leading global climate models (GCMs) for NKMNP during the twenty-first century, compared with the twentieth century average data calculated from the Climatic Research Unit (CRU) global meteorology data set (New et al. 1999).

Figure 7

Earthmounds, vegetation and lakes of the Llanos de Moxos. (a) Remote-sensing image showing the forest–savannah mosaic of the Llanos de Moxos, palaeofluvial features and gallery forests (red) trending SW–NE, with intervening open savannahs (light blue). (b) Forest island formation upon abandoned pre-Hispanic raised fields. (c) Forest island upon relict natural levee surface. (d) Aerial photo showing rectangular, parallel raised fields in the Llanos de Moxos. (e) Oblique aerial photograph of a linear zigzag feature (running bottom left to top right) in the savannahs of Baures region, Llanos de Moxos, interpreted by Erickson (2000) as a fish weir. Circular features surrounded by palms (20 m diameter) are interpreted by Erickson (2000) as artificial ponds. N.B. The diagonal feature (running top left to bottom right) is a contemporary path. (Photo courtesy of Clark Erickson, University of Pennsylvania Museum of Archaeology and Anthropology). (f) Remote-sensing image showing rectangular lakes of the Llanos de Moxos oriented SW–NE.