Long-term impacts of mid-Holocene drier climatic conditions on Bolivian tropical dry forests

Abstract

The Bolivian Chiquitano dry forest is the largest block of intact seasonally dry tropical forest in South America and is a priority ecoregion for conservation due to its high threat status. However, the long-term impacts of drier climatic conditions on tropical dry forests are not well understood, despite climate models predicting increased droughts over Bolivia in the coming century. In this paper, we assess the impacts of drier climatic conditions during the mid-Holocene on the Bolivian Chiquitano tropical dry forest using fossilised pollen, phytoliths, macro-charcoal, and geochemical proxies from a sediment core from a large lake (Laguna Mandioré) on the Bolivia–Brazil border. Our results show that drier climatic conditions during the mid-Holocene caused a local-scale, ecotonal expansion of upland savannah at the expense of dry forest. Interaction between drier climatic conditions and fire regime likely exerted a stronger control over the position of the dry forest–savannah ecotone than edaphic factors. However, the majority of the dry forest within the lake catchment maintained a closed canopy throughout the drier conditions of the mid-Holocene, despite floristic turnover towards more drought-tolerant taxa. These findings imply overall resilience of the Chiquitano dry forest biome to future drought, albeit with floristic changes and upland savannah encroachment at ecotones.

Climate‐driven shifts in the diversity of plants in the Neotropical seasonally dry forest: Evaluating the effectiveness of protected areas

“…Given these nuclei's geographical location (Linares‐Palomino et al., 2022), the impacts of new climates are anticipated to vary from site to site, possibly affecting forests in the lowlands more than in the mountains. In the cores of Chiquitano, Misiones, and Caatinga, the climate alterations mentioned above may lead to floristic turnover (encompassing recurrent expansions and retraction of species ranges) within these forests (Plumpton et al., 2020), just as it happened during the middle and late Pleistocene that shaped the biogeographic history and species composition within these current cores (Prado & Gibbs, 1993). Although some species within the Caatinga dry forest may withstand the novel conditions (temperature increases and extended drought) due to their existing physiological adaptations to semiarid climates (Cavalcante & Praciano Sampaio, 2022; Santos et al., 2014), numerous species are likely at risk due to desertification causing contraction of the distribution ranges (Cavalcante et al., 2020).…”

Differing local‐scale responses of Bolivian Amazon forest ecotones to middle Holocene drought based upon multiproxy soil data

“…Balesdent et al, 2018;McMichael et al, 2015;Pessenda et al, 1998Pessenda et al, , 2001Pessenda et al, , 2004Watling et al, 2017), we can cautiously infer that all our 1 m deep soil profiles likely span the middle Holocene to the present day. Despite Bolivia's Chiquitano dry forest being a global conservation priority, as the largest and most threatened intact block of dry forest remaining in South America (Miles et al, 2006), its palaeoenvironmental history remains poorly understood, based on only two neighbouring fossil pollen records from its eastern ecotone (Whitney et al 2011;Plumpton et al 2020)). The Ottavio and Santa Cruz data presented here are the first soil profile palaeodata from this ecosystem.…”

A Review of Archaeological and Paleoecological Radiocarbon Dating in Bolivia

“…Towards the east, a series of lakes that are part of the headwaters of the Paraguay River and many of which are intersected by the international border with Brazil, have been sampled to reconstruct paleoenvironmental change. Specifically, cores from Laguna La Gaiba (or Lagoa La Gaíva) and Laguna Mandioré on both sides of the border, provide extensive records of vegetational dynamics and formation of the biodiverse Pantanal and associated biomes (McGlue et al, 2012;Metcalfe et al, 2014;Plumpton et al, 2020;Whitney et al, 2011). Particularly significant has been evaluating the response of forests to increasing aridity during the Middle Holocene.…”