Reconstruction of recent forest dynamics based on pollen analysis and micromorphological studies of young acid forest soils under Scots pine plantations

Reconstructions of vegetation development of forest ecosystems have traditionally drawn on pollen samples of thick mor-humus profiles. In The Netherlands, however, well developed acid forest soils are scarce, especially under Scots pine (Pinus sylvestris). Scots pines have been planted from ad 1800 onwards, since when an acid soil profile has developed. This paper aims to show that pollen analysis of young acid forest soils not only can be used for the reconstruction of vegetation development in forests but also, combined with micromorphological observations, reveals information about forest dynamics in terms of litter production, decomposition processes and soil development. For that purpose four sites were selected in Scots pine stands, planted between ad 1900 and ad 1940 on drift sand deposits. At each site samples for pollen analysis were obtained from the entire organic layer and the top of the mineral soil. The pollen records of young acid forest soils show a shift in pollen assemblages, caused by a change from an open heath landscape towards a closed canopy after forest plantation. Micromorphological observations by thin sections of the undisturbed acid soil profile enhanced the interpretations of the pollen records. Micromorphological studies of these forest soils revealed the presence of non-burrowing soil animals and the preservation of pollen grains in the excrements of these soil animals. The absence of soil mixing animals and the pollen preservation in soils results in a pollen stratification, representing the recent local vegetation development. Furthermore, the pollen concentration curves show the stabilization periods of drift sand. The incidental increase of the pollen concentrations in the mineral soil indicates alternations of active sand drifting and stabilization periods, while the continuous increase of pollen concentrations towards the top of the mineral soil points to the final stabilization of the drift sand by Scots pine and the development of an AE-horizon.