Danmarks og Grønlands Geologiske Undersøgelse Rapport ... - Geus

Furthermore, flora lists from present day grazed and ungrazed forest landscapes, and ponds with
and without grazing, are analysed to identify plant species and pollen types which can be considered
indicators of the presence or absence of grazing. More species and types are identified as indicators
of grazing than indicators of absence of grazing. Thus is seems that there are more species that are
favoured by grazing, at least among flowering plants.
A number of the identified grazing indicator species have been found as macrofossils from Atlantic
sediments in Denmark. These include Achillea millefolium, Calluna vulgaris, Eleocharis palustris,
Hippuris vulgaris, Hydrocotyle vulgaris, Lychnis flos-cuculi, Oenanthe aquatica, Polygonum
aviculare, Ranunculus flammula, Ranunculus sclerantus, Rumex acetosa, Rumex crispus, Rumex
maritimus, Schoenoplectus tabernaemontani, Chenopodium rubrum and Apium inundatum. Of the
species which, according to this analysis, indicate absence of grazing Acer platanoides, Alnus
glutinosa, Fraxinus excelsior, Geum urbanum, Rubus idaeus, Stachys sylvatica and Ulmus glabra
have similarly been found as macrofossils.
Indicator values were also calculated for the plant species divided into pollen types. The pollen
types generally have lower indicator values than the plant species, as most types include several
plant species, and can therefore often be found in both grazed and ungrazed habitats. Among the
pollen types indicating grazing, the following have been found in Atlantic pollen samples from
some or all of the 17 sites: Cyperaceae, Chenopodiaceae, Calluna, Artemisia, Plantago lanceolata,
Potentilla, Rumex acetosa, Brassicaceae, Jasione, Solidago type, Succisa, Sedum, Ranunculus,
Campanula, Achillea, Alisma type, Lycopodium clavatum, Juniperus and Botrychium. Some of the
tree pollen types, like Ulmus, Fraxinus, Alnus and Acer are significant indicators of ungrazed
conditions, i.e. they occur significantly more often in the ungrazed modern forests than in the
grazed ones, although they are rather common in both categories. Pollen of Ulmus, Fraxinus and
Alnus are found at all sites and make up quite large proportions of the total pollen. Carpinus and
Acer have also been found. Non arboreal pollen types which can indicate ungrazed conditions, like
Circaea, Lonicera, Oxalis acetosella, Mercurialis perennis and Impatiens noli-tangere have not
been found in the Atlantic sediments from those sites, where data for all taxa were available.
The apparent coexistence of plants indicative of grazing and of absence of grazing indicates that the
landscape contained areas both with and without grazing impact at a given time. The relative spatial
extent of these areas can, however, not be estimated from the indicator species analysis. Jasione,
Botrychium and Sedum are only found as a few pollen grains, but these plants are associated to very
open, dry ground on grassland or heathland, so such habitats much have occurred at least locally
somewhere in the landscape.
For the simulation of pollen sedimentation, a number of hypothetical landscapes were established.
For the landscapes with grazing, the scenarios were based on Kirby (2004), who describes a series
of quantitative models of how a landscape with a vegetation dynamic as that described by Vera may
look. Five different grazing scenarios, with varying grazing pressure and landscape structure, were
used. To represent the closed forest landscape, scenarios were based on the vegetation structure in
Suserup Skov, one of the oldest untouched natural woodlands in Denmark, and also one of the best
investigated. However, the species composition had to be adjusted, as Suserup Skov is dominated
by Fagus sylvatica, which did not occur in Denmark in the Atlantic period. Finally, a scenario was
created based on a simplified version of Draved Skov, which is also an untouched natural
woodland, but on poorer, sandier soils that Suserup Skov. All in all, 17 different combinations of
landscape structure and species composition were created, and 644 pollen assemblages were
simulated and compared to the observed pollen data using the dissimilarity index squared chord
distance (SCD).
The analysis showed, that many of the pollen diagrams from Eastern Denmark were most similar to
the scenarios based on Suserup Skov. Their composition is thus best explained as coming from a
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