Tracing long-term tropical montane ecosystem change in the Eastern Arc Mountains of Tanzania

Pollen, charcoal, stable carbon and nitrogen isotope, and radiocarbon analyses are used to reconstruct a palaeoenvironmental record from the Eastern Arc Mountains (EAM), Tanzania, dating back >45 000 years. A sedimentary hiatus covering the last glacial-interglacial transition (LGIT) and early to mid Holocene follows the lead up to the Last Glacial Maximum (LGM) period. A late Holocene portion of the record is included as a modern analogue. Before 45 000 cal a BP, very low regional pollen counts imply open vegetation surrounding the site. Subsequently, the development of extensive montane forest characterizes a relatively mesic pre-LGM. The transition into the LGM witnessed a marked shift from C3- to C4-dominated biomass, representing an expansion of open forest dominated by grasses. These changes may be attributed to a combination of enhanced moisture stress and CO2 limitation, factors that may have been exacerbated by an intensive fire regime, as evident from the charcoal record. This is supported by a decrease in montane forest taxa, coupled with an associated expansion of C4 graminoids and ericaceous heathland to form a montane grassland mosaic similar to that previously recorded on other East African mountains around the time of the LGM but not, to date, having been shown in the Eastern Arc Mountains.