Annual pollen accumulation rate (PAR) at the boreal and alpine forest-line of north-western Norway, with special emphasis on Pinus sylvestris and Betula pubescens

Abstract

Pollen monitoring at the north-western fringe of the European boreal forest by means of modified Tauber traps, was carried out during the years 1996–2004 along a coast-inland gradient, including two altitudinal transects inland. The relationship between annual pollen deposition and local flora and vegetation was investigated. Pinus sylvestris stands in the open coastal lowland and mixed birch-pine forest inland are reflected by a mean pollen accumulation rate (PAR) of 200–400 grains cm−2 yr−1, and dense pine-dominated forest inland by ≥2000 grains cm−2 yr−1. The deposition of Betula pubescens-type pollen in the coastal birch woodland is 80–350 grains cm−2 yr−1. During the same time interval, the sub-alpine birch forest inland has a PAR of 240–720 grains cm−2 yr−1. This figure increases to c. 2000 when the two high-productive years 1998 and 1999 are included in the mean. The alpine forest-line ecotone is reflected in the pollen deposition by a decrease in Betula pubescens-type, meadow and heath herbs, and an increase in Salix and alpine herbs with altitude. This floristic change starts in the upper part of the sub-alpine belt and continues gradually into the open alpine belts. The presence of phytophagous insects in the pollen traps is found to influence the pollen record by overrepresentation of insect-dispersed herb taxa, but does not obscure the recognition of local vegetation types. PAR and percentages show the same main trends along the geographical gradients.