Pollen-based biome reconstructions over the past 18,000 years and atmospheric CO2 impacts on vegetation in equatorial mountains of Africa

• Published in: Quaternary science reviews 2016-11, Vol.152, p.93-103
• Main Authors: Izumi, K., Lézine, A.-M.
• Format: Article
• Language: English
• Subjects: Africa; An inverse-vegetation modeling approach; Biomes; Climatology; Earth Sciences; Holocene; Last glacial-deglacial transition; Pollen; Sciences of the Universe
• ISSN: 0277-3791; 1873-457X
• DOI: 10.1016/j.quascirev.2016.09.023

This paper presents a quantitative vegetation reconstruction, based on a biomization procedure, of two mountain sites in the west (Bambili; 5°56′ N, 10°14′ E, 2273 m) and east (Rusaka; 3°26′ S, 29°37′ E, 2070 m) Congo basin in equatorial Africa during the last 18,000 years. These reconstructions clarify the response of vegetation to changes in climate, atmospheric pressure, and CO2 concentrations. Two major events characterize the biome changes at both sites: the post-glacial development of all forest biomes ca. 14,500 years ago and their rapid collapse during the last millennium. The rates of forest development between the biomes are different; a progressive expansion of lowland biomes and an abrupt expansion of montane biomes. The trends of pollen diagrams and biome affinity scores are not always consistent in some periods such as the Younger Dryas interval and end of the Holocene Humid Period, because the biomization method is not a simple summarization of the pollen data, but also takes biodiversity into consideration. Our sensitivity experiment and inverse-vegetation modeling approach show that changes in atmospheric CO2 concentration unequally influence vegetation in different local environments. The study also suggests that the biome changes prior to the Holocene result from both changes in the atmospheric CO2 concentration and climate. The development of warm-mixed forest from xerophtic vegetation results from increases in atmospheric CO2 concentration and near-surface air temperature. Difference in local dryness results in the different biome distributions, with more forest-type biomes at Bambili and more grass/shrub-type biomes at Rusaka. •Biome reconstructions in equatorial mountains of Africa are provided.•The behavior of lowland and highland forest biomes from 18 ka onward is detailed.•A sensitivity experiment and inverse-vegetation modeling approach are performed.•An atmospheric CO2 effect is a key factor for vegetation distribution.