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References
Alexander K, Allen M, Butler J, Green T, Woods R. 2018.
Britain’s natural landscapes – promoting improved
understanding of the nature of post-glacial vegetation of
lowland Britain. British Wildlife 25:5, 330-338.
Birks HJB, Birks HH. 2004. The rise and fall of forests.
Science 305:5683, 484-5.
Fenton JHC. 2008. A postulated natural origin for the
open landscape of upland Scotland. Plant Ecology &
Diversity 1:1, 115-127.
Klinger LF. 1996. Coupling of soils and vegetation in
peatland succession. Arctic and Alpine Research 28, 380-
387
Ratcliffe DA. 1977. A Nature Conservation Review Vol.1.
Cambridge: Cambridge University Press.
Veldman JW, Overbeck GE, Negreiros D, Mahy G, Le
Stradic S, Fernandes GW, Durigan G, Buisson E, Putz FE,
Bond WJ. 2015. Tyranny of trees in grassy biomes.
Science 347:6221, 484-485.
Vera FWM. 2000. Grazing Ecology and Forest History.
Wallingford: CABI Publishing.
WOODLAND OR OPEN GROUND? Scenarios for the persistence of woodland in the presence of grazing
Figure 13. New native woodlands in the name of ecological restoration
are being planted all over the Highlands, here a new Pinus sylvestris
wood near Gairloch in Wester Ross planted on unwooded moorland.
Recent conservation effort in the Highlands
A point which is often missed is that, come 1750, 95% of the
Highland landscape would have been open moorland, so that,
taking a wide strategic overview, any woodland loss subsequent to
this becomes largely irrelevant. In practice, though, because
woodland is rare in the landscape, and because rarity is a criterium
indicating nature conservation importance (Ratcliffe 1977), a
significant amount of conservation effort has been focussed on the
woodland habitat: whether encouraging tree regeneration or on
creating new woodland of indigenous species on open moorland.
(Figure 13). This strong focus on one rare and declining habitat
type has tended to skew the nature conservation effort: no value is
ascribed to the common open ground habitats – with the
exception of peatland.
However, if you stand back and view the Highlands from an
international perspective, then that which is locally common
(temperate moorland) is seen to be globally rare, and that which is
locally rare (temperate woodland) is globally common. Indeed,
many of the open moorland habitats are recognised as being of
international importance under the EU Habitats Directive.
It should also be noted that reintroducing the wolves, although
introducing more balance to the ecosystems (Figure 2a), is unlikely
to cause a significant increase in woodland cover: postglacial
woodland expansion and decline occurred during the 10,000 year
period when wolves were present in the landscape.
Conclusions
The Highlands are different from most of Europe in that the
human population over most of history has been low, with some
areas, particularly away from the coast and the main valleys,
uninhabited; and that indigenous large mammalian herbivores (the
red deer) have been present throughout the postglacial period.
This makes the Scottish Highlands unique in that the continuing
processes of postglacial plant succession can be observed in a
location of minimal human impact, particularly away from the
coasts where population has tended to be more sparse.
The analysis here shows how the open nature of the landscape can
be explained through natural processes, and demonstrates the
successional process of natural regression of forests in this, the
oligocratic phase of an interglacial, from a postglacial maximum as
described by Birks and Birks (2004). Related to this is the fact that
much of the level and gently sloping ground of the Highlands is
peat covered, which supports the view of Klinger (1996) that peat
bogs can be the end point of succession in many parts of the
world.
Hence the mainstream view that the Highlands are a once-forested
landscape, the forest destroyed by anthropogenic activity, needs
revision, as it does for other naturally open landscapes in the
world. Veldman et al. (2015) state:
“The WRI [World Resources’ Institute] erroneously assumes that
nonforest areas where climate could theoretically permit forest
development are ‘deforested’, an assumption rooted in outdated
ideas about potential vegetation and the roles of fire and herbivores
in natural systems.”
The open landscape of the Highlands is caused by the discrepancy
between the herbivore carrying capacity and the lower density
required to ensure woodland survival, combined with a lack any
natural mechanism to prevent young trees from browsing which is
found in other areas of Europe, such as the presence of thorny
shrubs or persistent winter snow cover. The dominance of acidic,
waterlogged soils, resulting in sub-optimal soils for tree
regeneration, is also a major contributing factor, resulting in both a
lower probability of seeding establishment and a higher probability
of seedlings and saplings being eaten.
It should be noted, though, that across the Highland landscape as
a whole all three models of woodland dynamics (Fenton 2008) can
be observed: ‘woodland as climax’ in the few locations with better
soils naturally protected from grazing by topography; ‘the cyclical
model‘ as proposed be Vera (2000) on the better soils and more
favourable climate of coastal Argyll in the southwest Highlands;
and ‘natural decline’, the dominant model over most of the
landscape.
The trophic level model as applied here, combined with an
understanding of the ecological mechanisms which deter
browsing, can provide a sufficient prediction of whether a given
natural landscape will be wooded or not; although where the
availability of palatable biomass is highly seasonal, the trophic level
model is likely to over-estimate the expected herbivore population.
It should be noted that the ecology would be expected to be
different in ecosystems which have never had indigenous
mammalian herbivores, such as Iceland: in these situations the
probability of native wood and/or scrub being a natural
component is increased (although in Iceland introduced livestock
have since destroyed most of the woodland).
The hypothesis presented here is that, in temperate ecosystems
able to support trees, high forest is not always the pre-determined
climax vegetation. An alternative model of an ever-changing
mosaic of vegetation instead of a stable Clementsian climax, as
proposed by Vera (2000) is supported by recent evidence for
lowland Britain (Alexander et al. 2018), but will not apply to most of
the Scottish Highlands where the end result of succession appears
to be various types of resilient moorland plant communities. The
current conservation practice of converting these areas to
woodlands composed of indigenous trees therefore reduces the
naturalness and biodiversity value of the Highlands.
The current natural vegetation of the Highlands (Figure 14),
comprising a range of open moorland plant communities, appears
to have become dominant owing to its greater resilience than
woodland over time. This suggests that with continuing climate
change it will remain dominant. With climate change causing a
reduction in consistent winter snow cover in parts of Europe, this
could increase the potential for over-wintering herbivores and
hence lead to woodland loss. However, it could also encourage the
spread of temperate thorny shrubs, allowing woodland expansion .
Hence there is possibility of both woodland loss and woodland
expansion in different regions if natural processes are allowed to
determine the direction of ecological change.
This paper, which has gone back to first principles, will hopefully
result in a wider recognition of the role of herbivores in the
landscape – and of the fact that open landscapes can occur
naturally in locations climatically suitable for trees.
All photographs James Fenton
Figure 14. The Scottish Highlands: perhaps one of the most natural
vegetation patterns remaining in Europe?