Quelques implications paléoclimatiques de l'observation de bois fossiles du Wealdien du bassin de Mons (Belgique) - Résultats préliminaires.

peer reviewe

PALÉOENVIRONNEMENTS ET PALÉOCLIMATS DURANT LE PLÉISTOCENE SUPERIEUR ET L’HOLOCENE SUR LA DORSALE OCCIDENTALE DU KIVU EN RÉPUBLIQUE DÉMOCRATIQUE DU CONGO

Palynological studies of sedimentary sequences issued from swamps located in the highlands of the KBNP (Kahuzi-Biega National Park) on the western divide of Kivu in Eastern D.R. Congo, revealed important environmental events that occurred during Upper Quaternary. The Cishaka sequence covers the last 35000 years. In the Upper Pleistocene, during the “Kalambo Interstadial” period (32000- 26000 years BP), a mixed forest spread out under a moderately warm-wet climate. In the course of the “Mount Kenya Hypothermal” regressive phase (25000- 15000 years BP), in the “Last Glacial Maximum” (20000-18000 years BP) takes place an exceptional expansion of open grasslands that evidenced an important drought. After that, the revival of an afro-montane forest growing under cold-wet climatic conditions is recorded, but that one is temporarily interrupted by theYoung Dryas dry pulse. At the Humid Holocene Period (10000-7000 years BP), with the increase of rainfall, the Kivu Lake level is raising when the swamps in the highlands are transformed in lakes. Around 6500 yrs BP, the afro-montane rainforest invaded by afro-subalpine taxa turns into a secondary mixed forest as the result of a climatic deterioration. At 4000 yrs BP, an important spreading of grasslands in the highlands and of savannas in the lowlands testifies that an aridity peak occurs at the time. The changes that occurs from 3000 years BP to 2000 years BP in the afromontane forest suggests a climatic instability that moreover speeds up erosion processes. In the course of the first millennium AD, rainforest grows again; that event being shortly interrupted by a drought around 500 years AD. At the beginning of the second millennium AD, the lower belt of the forest is yet deteriorated by anthropic action while middle and upper belts are stable but marked by a fresh climate resulting of the “Mount Kenya Neoglacial” influence. From 17th – 18th centuries, human impact increases progressively in the highlands

PALÉOENVIRONNEMENTS ET PALÉOCLIMATS DURANT LE PLÉISTOCENE SUPERIEUR ET L’HOLOCENE SUR LA DORSALE OCCIDENTALE DU KIVU EN RÉPUBLIQUE DÉMOCRATIQUE DU CONGO

Palynological studies of sedimentary sequences issued from swamps located in the highlands of the KBNP (Kahuzi-Biega National Park) on the western divide of Kivu in Eastern D.R. Congo, revealed important environmental events that occurred during Upper Quaternary. The Cishaka sequence covers the last 35000 years. In the Upper Pleistocene, during the “Kalambo Interstadial” period (32000- 26000 years BP), a mixed forest spread out under a moderately warm-wet climate. In the course of the “Mount Kenya Hypothermal” regressive phase (25000- 15000 years BP), in the “Last Glacial Maximum” (20000-18000 years BP) takes place an exceptional expansion of open grasslands that evidenced an important drought. After that, the revival of an afro-montane forest growing under cold-wet climatic conditions is recorded, but that one is temporarily interrupted by theYoung Dryas dry pulse. At the Humid Holocene Period (10000-7000 years BP), with the increase of rainfall, the Kivu Lake level is raising when the swamps in the highlands are transformed in lakes. Around 6500 yrs BP, the afro-montane rainforest invaded by afro-subalpine taxa turns into a secondary mixed forest as the result of a climatic deterioration. At 4000 yrs BP, an important spreading of grasslands in the highlands and of savannas in the lowlands testifies that an aridity peak occurs at the time. The changes that occurs from 3000 years BP to 2000 years BP in the afromontane forest suggests a climatic instability that moreover speeds up erosion processes. In the course of the first millennium AD, rainforest grows again; that event being shortly interrupted by a drought around 500 years AD. At the beginning of the second millennium AD, the lower belt of the forest is yet deteriorated by anthropic action while middle and upper belts are stable but marked by a fresh climate resulting of the “Mount Kenya Neoglacial” influence. From 17th – 18th centuries, human impact increases progressively in the highlands

A factor analysis approach to modelling the early diversification of terrestrial vegetation

peer reviewedData from a new comprehensive macrofossil-based compilation of early plant genera are analyzed via a Q-mode factor analysis. This compilation ranges from the Silurian to the earliest Carboniferous and illustrates the key vegetation changes that took place during the configuration of early terrestrial ecosystems. Results reveal that four factors can be used to explain more than 90% of the variance in the data. These factors are interpreted as the major phases of the early land plant evolution: a first Eotracheophytic flora (Silurian-Lochkovian) dominated by basal eutracheophytes and rhyniophytoids, an early Eophytic Flora (Early Devonian) dominated by zosterophylls, a transitional late Eophytic Flora (Middle Devonian-earliest Carboniferous) dominated by lycopsids and cladoxylopsids, and finally, the earliest phase of the Palaeophytic Flora (Late Devonian-earliest Carboniferous) dominated by the first seed plants. These floras present different but complementary diversity patterns, which help us to understand the overall trajectory of changes in plant diversity. Results further show how the maximum peaks of diversity appear linked to the rise of each new flora but, interestingly, these diversifications are not associated with any exponential declines of the previously dominant one. This new four-phase diversification model reflects the early steps of Earth's greening