The representation of taxa in surface pollen spectra on alpine and sub-alpine glacier forelands in southern Norway

Abstract

The relationship between vegetation and surface pollen deposition is examined in a range of alpine and sub-alpine plant communities on 26 glacier forelands in southern Norway. Plant–pollen relationships of individual taxa are emphasised, particularly herb taxa which have rarely been considered quantitatively. Three categories of pollen taxa can be recognised: (1) Mostly insect-pollinated taxa showing relatively strong plant–pollen correlations (e.g. Empetrum, Oxyria and Salix); (2) Wind-pollinated taxa, such as Betula, Pinus and Gramineae, that show a very poor correlation; and (3) Herb taxa that produce relatively little pollen and rarely register in the pollen spectrum.For example, total Ericales has a plant–pollen correlation coefficient as high as 0.74 and it’s pollen frequencies are ten-fold higher where the plant is present than where it is absent. This contrasts with wind-pollinated taxa such as Gramineae that has a correlation coefficient of 0.37 and has no statistical difference in pollen frequencies between sites where the plant occurs and sites where it is absent. Regional scale plant–pollen relationships, for most taxa, are similar to relationships at the scale of the single glacier foreland.An additional study was made of the impact of local woodland on the composition of surface pollen spectra. The relationship was examined between local woodland characteristics, tree height and girth, woodland density and canopy cover and tree pollen at nine sub-alpine glacier forelands (312 trees measured at 36 sampling sites). A clear negative correlation was found between both Betula and total arboreal pollen frequency with tree height and tree girth, suggesting that woodland filters out regional tree pollen and that the local pollen contribution is relatively unimportant.This study provides potentially valuable analogues for early Holocene successional stages from elsewhere in Europe. The proportion of pollen with a regional source may have been underestimated in some previous studies. It is suggested that relatively rare herb pollen taxa should be given greater consideration, since they provide valuable indications of the composition of the local plant community, past and present.