Christin Jensen

Some comments on spatial variation in arboreal pollen deposition: first records from the Pollen Monitoring Programme (PMP)

Some comments on spatial variations in arboreal pollen deposition: first records from the Pollen Monitoring Programme (PMP).

Pollen deposition rates in peat and lake sediments from the Pinus sylvestris L. forest-line ecotone of northern Norway

A comparative investigation of pollen deposition in peat and limnic sediments from the Pinus sylvestris-Alnus incana forest line in Dividalen, central Troms, northern Norway was performed by pollen analyses of sub-modern sediments. The possibilities of using 210Pb and 137Cs-datings in calculations of pollen influx in peat and limnic sediments are discussed. Correlation between the lead–cesium peat chronology and a marker-based limnic chronology is achieved at AD 1945–1946 by comparing the percentual pollen-curves. The upper 14 cm of the peat and 12 cm of the limnic sequence are hence supposed to represent the period ca. 1945–ca. 1996. The mean percentual representation of Pinus pollen is nearly twice as high in the peat sediments as in the limnic sediments, probably due to a slight over-representation from pine trees at the edge of the mire. The mean percentual pollen values for Alnus and Betula pubescens-type is fairly equal in peat and lake sediments, while the pollen influx rates are higher for all tree taxa in the lake sediments. This may be caused by the lake being exposed to a larger regional component than the smaller and topographically more sheltered mire. To achieve reliable pollen influx data at a near annual resolution, one needs a good control of the sedimentation processes, close intervals of isotope measurements and additional chronostratigraphically fixed marker horizons.

The use of quantitative models to assess long-term climate–vegetation dynamics – A case study from the northern Scandinavian Mountains

Quantitative vegetation models combined with fossil pollen records have large potentials for assessing long-term vegetation dynamics. In this study, vegetation cover as a function of July temperatures was modelled for the Dividalen valley area situated in the northern Scandinavian Mountains. Site-specific pollen deposition values of the two dominating tree species pine and birch were simulated and compared with empirical fossil pollen values. The applied vegetation model could not explain the forest dynamics prior to 7400 cal. BP, although after this date, the forest seemed to have received a modern structure, and summer temperatures could potentially explain the long-term variations in forest cover. The most extensive forest cover occurred c. 7400–3800 cal. BP, corresponding to July temperatures of 0.5–1°C above the present. The approach proved sensitive to both site location and data quality. Careful site-selection is of importance for the application, and pollen accumulation rates are to be preferred as pollen percentage values proved problematic.

A Synthesis of Pollen Composition in Prehistoric Cultivation Layers in Southwestern Norway

Pollen records and radiocarbon dates from cultivation layers were compiled to explore agricultural changes in southwestern Norway, with a focus on cereals and associated herbs. Variations in the po...