Skógræktarritið - 15.05.2001, Page 109

Table 2. Comparison of Horsfield & Thompson categories (1997) witli NVC (Rodwell, 1991)
Scrub category NVC types included
Alpine Willow Scrub W20 Salix lapponum-Luzula sylvatica scrub CG14 Diyas octopetala-Silene acaulis ledge community U15 Saxifraga aizoides-Alchemilla glabra grassland U16 Luzula sylvatica-Vaccinium myrtillus tall herb community U17 Luzula sylvatica-Geum rivale tall herb community M11 Carex demissa-Saxifraga aizoides mire
Alpine Juniper Scrub W19 Juniperus communis spp communis-Oxalis acetosella scrub H15 Calluna vulgaris-Juniperus communis spp alpina heath
Dwarf Birch Scrub M19b Calluna vulgaris-Eriophorum vaginatum, mire Empetrum nigrum sub community M19ciii C vulgaris-E vaginatum mire Vaccinium vitis-idaea-Hylocomium splendens sub community Betula nana variant M17 Scirpus cespitosa-Eriophorum vaginatum blanket mire M15 Scirpus cespitosa-Erica tetralix wet heath
grassland vegetation communi-
ties (MacKenzie, 2000).
The emphasis of this vegeta-
tion classification system on the
current dístribution of plants in
the presence of heavy grazing
pressure down-plays the poten-
tial importance of structural
diversity in a more natural vege-
tation community. It has also
contributed to the neglect of the
tall shrubs in vegetation surveys
based on NVC, because they
effectively remain invisible in the
habitat descriptions.
More recently, Horsfield and
Thompson (1997) suggested an
unsystematic but useful scrub
categorisation (Table 2.) based
on McVean and Ratcliffe (1962)
which at least allows meaningful
discussion of the main types.
There are three typical situa-
tions in which montane scrub
communities now survive:
• as remnants confined to high
valley walls and cliffs (alpine
willow scrub), out of reach of
mammal herbivores,
• as a component of a Calluna
vulgaris L. sward (alpine
juniper scrub and dwarf birch
scrub);
• and, very rarely, as a fringe to
the surviving forest (tree
species, alpine juniper and
some willows), as at Creag
Fhiaclach, in the Cairngorms.
Values of scrub
Most of the tall shrubs already
mentioned are nationally scarce
(occurring in less than 100 lOkm
squares). Saíix lanata, the least
common, is listed as vulnerable
in the Red Data Book for threat-
ened plants and it now has a
Species Action Plan (SAP) under
the UK BAP (Anon, 1994). luniper
also has a SAP. The Betula nana
variant of the blanket bog, NVC
community M19ciii, forms part of
the priority active blanket bog
habitat in Annex 1 of the
Habitats Directive (The Council
of European Communities,
1992).
A healthy forest spreading
from valley to high mountain has
an intrinsic appeal and would
signify the realisation of an aes-
thetic ideal of ecological poten-
tial. This should be reason
enough but there are many oth-
ers for the restoration of mon-
tane scrub and natural treelines.
It is likely that the nature of the
scrub would be variable, but nor-
mally broken and mosaic in
structure. This structure fits
exactly with the requirements of
the priority Biodiversity Action
Plan species, Tetrao tetrix L. (Black
Grouse), which is currently in
serious decline as a result of
habitat loss, and with Saxicola
rubetra L. (Whinchat), which is
currently causing conservation
concern (Mortimereí al, 2000).
There may be enough attraction
for occasional visiting birds, such
as the Luscinia svecica L. (Blue-
throat), to establish breeding
populations, while Turdus iliacus
L. (Redwing), T. pilaris L. (Field-
fare) and Fringilla montifringilla L.
(Bramblings) may develop more
stable breeding populations
(Scott, 2000). Raptors should not
suffer from the patchy distribu-
tion of scrub and might benefit
from the increase in prey.
Bland, Entwhistle and Hors-
field (1997) concluded that
despite incomplete information
on the invertebrate fauna, cur-
rent knowledge indicates the
conservation importance of mon-
tane scrub for a number of
groups. They advised that action
was urgently required to halt the
fragmentation of the remaining
scrub in order to avoid impover-
ishment of the associated fauna.
The shelter and nutrient recy-
cling of scrub plants plays an
important role for other plants,
mainly tall herbs, some of which,
such as the very rare Cicerbita
glpina (L.) Wallr. (Alpine Blue
sow-thistle), are currently endan-
gered due to the continuing lev-
els of grazing and loss of suitable
habitat
Visually, the restoration of nat-
ural treelines and montane scrub
would add diversity to the hill
landscape. Having succeeded in
returning forests to the valleys,
there is now an opportunity to
soften the normally abrupt upper
margin, providing shelter for the
growing high forests below. This
more natural appearance will
provide a more diverse experi-
ence for walkers making their way
to the hills. In a landscape sub-
stantially bare of vegetation
above half a metre in height, a
broken canopy between one and
SKÓGRÆKTARRITIÐ 2001 l.tbl.
107