It is not that the Scottish Highlands are ecologically unsuited to all
trees, just to the tree species that naturally colonised Scotland in
the postglacial period. If soils are modified to reflect the early
postglacial conditions by draining, ploughing and addition of
fertiliser (particularly phosphate) then the indigenous trees grow
well in locations not exposed to the strong winds characteristic of
the area, as indicated by the numerous successful plantations of
native trees.
E) Anthropogenic grazing reduction
Where humans have either eliminated grazing, or reduced it
significantly from the expected natural level, then this can result in
an increase in woodland cover, or allow woodland to persist where
it otherwise might have declined or moved around the landscape
(Figure 9). This has been a common situation within Europe in
historical times where enclosed woodland blocks have been
managed to provide a permanent supply of wood and timber; and
perhaps also in large scale landscapes such as western Norway
where in the past humans have made large herbivores functionally
extinct.
Woodland localised in the landscape
F) Geomorphological features
In many landscapes there are locations where the
geomorphological features provide a natural barrier to large
herbivores, resulting in no or reduced grazing (Figure 10). These
are generally steep slopes or areas of rough topography. However
it should be noted that in wet climates steep slopes may also hold
trees because the better drainage and mineral flushing results in
soil conditions more suitable for trees.
Hence the presence of trees in such places might be a result of a
combination of both reduced grazing and better soil conditions.
There are also instances where dense vegetation such as tall
Calluna vulgaris saplings can provide some protection from grazing,
allowing occasional trees to survive.
G) Episodic events
It is possible to envisage situations where episodic events provide a
temporary reduction in grazing allowing some woodland
regeneration. Examples could include an outbreak of disease or, as
in tundra ecosystems harsh winters causing heavy herbivore
mortality (Ims and Fueglei 2009).
H) Predation hotspots
The trophic level model discussed above indicates that there has to
be a significant herbivore population in order to support the
presence of large carnivores, and that a population sufficient to
allow tree regeneration would not be large enough to allow for a
significant wolf population at the local level. Indeed, Warren (2002)
concludes:
“The evidence from Norway and America is that low numbers of
large predators have little effect on deer numbers ... To have a
significant impact on deer populations, a very large number of
wolves would be needed, and there is unlikely to be enough space in
Scotland (either ecologically, or socio-politically) for such large wolf
populations.”
Large carnivores have become extinct over much of Europe so that
it is hard to know what their impact in practice would be on both
the population levels and distribution of large herbivores. In the
Highlands stalking (shooting) of red deer by humans causes the
deer to move up to the higher slopes of the hills. This suggests that
predation by wolves might also cause the deer to move up the hill,
thus increasing the grazing level on the higher slopes and also
preventing the growth of montane scrub.
Although both the climate and ecology are different, there has
been much debate about the impact of the reintroduction of the
wolf (Canis lupus) on the elk (Cervus elaphus Canadensis, a sub-
species of red deer) population of Yellowstone Park in the USA.
However MacNulty et al. (2016) conclude:
“Scientific consensus about the role of wolves in driving the
dynamics of the northern herd has yet to emerge, despite 20
years of research by numerous federal, state, and academic
investigators.”
A key point is that the wolf became extinct in Scotland in the
eighteenth century, which is relatively recently in ecological terms,
and that the woodland declined naturally over the previous
millennia when wolves were present. This, together with the
trophic level model, suggests that their reintroduction is unlikely to
result in large scale recolonisation of the Highlands by trees. It is
possible the presence of wolves might cause a reduction in grazing
pressure in locations favoured by them and so promote localised
woodland regeneration; but the only way to be sure of this is
reintroduce the wolf and observe the result.
Application of the above scenarios to different areas of Europe
The above analysis indicates that in northwest Europe different
geographical regions might be expected to possess different
percentages of woodland cover. As an example, Table 1
summarises the above scenarios and applies them to three
different areas of Europe.
Discussion in relation to the Highlands of Scotland
There has been a lot of work carried out on pollen analysis in the
Highlands, and the results are generally in keeping with the
interglacial succession process as discussed above and supporting
the original views of Geikie (1867) who stated ‘It can be shown that
the destruction of our ancient forests has not been primarily due
to man.’; i.e. a natural regression of woodland from a postglacial
maximum. Paterson (2011) gives a good summary of this research
in relation to indigenous pinewood:
“In core areas, woodland is subject to fragmentation from as early as
c. 7500 cal BP; fragmentation is diachronous and is believed to have
been earliest in the west. Human activity is sometimes implicated in
woodland fragmentation but is more often cited as reinforcing the
effects of a maritime climate preferentially affecting Pinus
dominated woodlands … Only in Speyside is human activity thought
to initiate disintegration.”
Fyfe (2018) has recently reviewed the evidence from pollen analysis
on the openness or otherwise of the British vegetation and
concluded:
“At the continental scale, western Atlantic Europe has for long been
more open than other parts of the mainland. Britain and Ireland
(especially western and northern regions) are particularly notable in
this context, and are different from much of inland continental
Europe. This conclusion is replicated irrespective of which analytical
method is applied to the pollen data.”
Page 5
References
Fyfe R. 2018. ‘Natural’ vegetation in Britain: the pollen-
eye view. British Wildlife 25:5, 339-349.
Geikie J. 1867. On the buried forests and peat mosses of
Scotland, and the changes of climate which they indicate.
Transactions of the Royal Society, Edinburgh XXIV: Part II,
363-384.
Ims RA, Fuglei E. 2009. Trophic interaction cycles in
tundra ecosystems and the impact of climate change.
BioScience 55, 311-322.
MacNulty DR, Stahler DR, Wyman CT, Ruprecht J, Smith
DW. 2016. The challenge of understanding Northern
Yellowstone elk dynamics after wolf reintroduction.
Yellowstone Science 24:1, 25-33.
Paterson D. 2011. The Holocene history of Pinus
sylvestris woodland in the Mar Lodge Estate,
Cairngorms, Eastern Scotland. PhD dissertation.
University of Stirling.
Warren CR. 2002. Managing Scotland’s Environment.
Edinburgh: Edinburgh University Press.
WOODLAND OR OPEN GROUND? Scenarios for the persistence of woodland in the presence of grazing
Figure 9. Scenario E: An example of an ancient broadleaved
woodland in England (Dorset) where enclosure, grazing exclusion
and management has allowed it to persist in situ.
Figure 10. Scenario F: Glen Coe in the Highlands showing
persistence of woodland on steep slopes, cliffs and gorges where
grazing is naturally reduced or absent.
Table 1. Theoretical probability of woodland in the landscape in
three different areas of Europe.