Sensitivity of East African savannah vegetation to historical moisture-balance variation

Fossil pollen records provide key insight into the sensitivity of terrestrial ecosystems to climate change. However, tracing vegetation response to relatively modest historical climate fluctuations is often complicated by the overriding signature of anthropogenic landscape disturbance. Here we use high-resolution pollen data from a similar to 200-year lake-sediment record in open wooded savannah of Queen Elizabeth National Park (southwestern Uganda) to assess the sensitivity of the tropical lowland grassland-forest transition to historical, decade-scale moisture-balance fluctuations. Specifically we trace vegetation response to three episodes of higher average rainfall dated to the 1820s-1830s, ca. 1865-1890 and from 1962 to around 2000. Our pollen data indeed reveal a sequence of three wet periods, separated by two drier periods. During the inferred wetter episodes we find increases in the percent pollen abundance of trees and shrubs from moist semi-deciduous forest (Allophylus, Macaranga, Alchornea, Celtis), riparian forest (Phoenix reclinata) and wooded savannah (Acalypha, Rhus-type vulgaris, Combretaceae/Melastomataceae) as well as taxa common in the local rift-valley grasslands (Acacia, Ficus), together creating strong temporary reductions in Poaceae pollen (to 45-55% of the terrestrial pollen sum). During intervening dry periods, Poaceae pollen attained values of 65-75 %, and dryland herbs such as Commelina, Justicia-type odora and Chenopodiaceae expanded at the expense of Asteraceae, Solanum-type, Swertia usambarensis-type, and (modestly so) Urticaceae. Noting that the overall richness of arboreal taxa remained high but their combined abundance low, we conclude that the landscape surrounding Lake Chibwera has been an open wooded savannah throughout the past 200 years, with historical moisture-balance variation exerting modest effects on local tree cover (mostly the abundance of Acacia and Ficus) and the occurrence of damp soil areas promoting Phoenix reclinata. The strong apparent expansion of true forest trees during wet episodes can be explained partly by enhanced pollen input via a temporarily activated upland stream. Pollen from exotic trees and cultural indicators appears from the 1970s onwards, but their combined influence fails to mask the signature of natural vegetation dynamics in the pollen record

Archeobotanisch onderzoek van enkele laat- en postmiddeleeuwse archeologische contexten uit de onderzoekszone Verrebroekdok (Beveren, prov. Oost-Vlaanderen)

Tijdens het archeobotanisch onderzoek werd geprobeerd om een beeld te krijgen van het laat- en postmiddeleeuwse landschap van de onderzoekszone Verrebroekdok. Er is ook getracht om over de landbouwactiviteiten, voedingspatronen, enz... zoveel mogelijk informatie in te winnen

Paleo-ecologisch onderzoek van een Holocene sequentie uit het Deurganckdok te Doel (Wase Scheldepolders, Noord-België)

De graafwerken van een getijdendok op de linkeroever van de Schelde nabij Doel (België) boden een uitstekende gelegenheid om de stratigrafie en de paleo-ecologie van Holocene afzettingen in de Beneden Scheldepolders te bestuderen. Een complete organische sequentie, gedateerd tussen 6000 en 1400 BP, werd op basis van pollen, sporen en andere microfossielen, macroresten en diatomeeën onderzocht. Naast een volledig goed ontwikkelde representatieve botanische evolutie vanaf het Atlanticum werd ook belangrijke informatie verzameld over twee specifieke gebeurtenissen. Enderzijds kon de uitbreiding en de paleo-ecologische omstandigheden van de late Calais inundatie, tussen 5800 en 5000 BP, worden gereconstrueerd. Anderzijds werd het mogelijk om een beter inzicht te verwerven over de tijdspanne tussen het einde van de veengroei rond de 6de-7de eeuw AD en de grote strategische overstromingen na 1580 AD. Een periode van non-depositie, gevolgd door lokale afzettingen van laatmiddeleeuwse strategische stormvloeden werd namelijk geattesteerd.The excavations of a huge tidal dock on the left bank of the Scheldt river near Doel (Belgium) provided an excellent opportunity for the study of the stratigraphy and palaeoecology of the Holocene deposits in the Lower Scheldt polders. A complete organic sequence from the period between 6000 and 1400 BP was radiocarbon dated and investigated by means of pollen, spores and other microfossils, macroremains and diatoms. Besides a good developed sequence of the botanical evolution since the Atlanticum, interesting information on two specific events was obtained. Firstly the extension and conditions of the late Calais inundation, between 5800 and 5000 BP could be reconstructed. Secondly it became possible to gain more insight in the timespan between the end of the peat growth around the 6th-7th century AD and the large strategic inundation after 1580 AD. A period of non deposition followed by local deposits of late medieval military storm surges could be recognised

Spatio-temporal modeling of soil characteristics for soilscape reconstruction

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