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| Habitat
changes in British upland landscapes
and their implications for bird populations
by Rob Fuller |
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| 4. Forestry |
The
large expansion of commercial coniferous forestry in the British
uplands during the second half of the 20th century has dramatically
altered the types of habitat available for birds in many regions.
This account focuses on the implications for moorland birds,
though it should be acknowledged that forestry has created
habitats for large populations of songbirds associated with
the developing conifer stands. |
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Short-eared
Owls may make use of very young plantations, but will have
disappeared by canopy closure. |
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| Taken as a whole, conifer plantations support
a high diversity of birds and several species, notably Siskin and
Crossbill, have expanded their national ranges and populations as
they have been able to exploit the new plantations. There are substantial
differences between the bird communities in the first generation forests
and subsequent restocks which are often richer in songbirds such as
warblers and Tree Pipits. The more recent forests also often contain
appreciably larger areas of unplanted land. The forests of the future,
therefore, may support rather different bird communities from those
that were initially established in the uplands. |
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The issue of impacts
on moorland birds has been a contentious one. There has been
no large-scale quantitative appraisal of the effects of afforestation
on moorland birds, though general assessments are given by Avery
and Leslie (1990) and Ratcliffe (1990). Whilst there is no evidence
that afforestation has resulted in the regional extinction of
any moorland birds, it is undeniable that the total area of
nesting habitat and the extent of foraging habitat for several
specialised moorland species has been substantially reduced
in some upland regions. |
| Conifer
plantation in the central Highlands of Scotland. |
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| The general pattern is that soon after
planting there are losses of ground-nesting birds including most waders
and Wheatears. All ground-nesting moorland birds abandon the plantations
by the early thicket stage. However, several upland species colonise
the very young plantations for a limited period, but disappear by
canopy closure; these include Black Grouse, Short-eared Owl, Hen Harrier,
Stonechat and Whinchat. Whilst this is the general sequence of events
at most afforested sites, the exact impacts vary from one region to
another according to both the extent of afforestation and its exact
location. There is much spatial variation in bird densities within
the uplands and afforestation will have far more serious impacts in
some areas than others. Furthermore, relationships between forestry
and bird populations are most unlikely to be of a simple linear form.
Edge effects may exist because ground-nesting birds avoid nesting
close to plantations. Such effects may come about because of higher
predation rates or different types of vegetation close to plantation
edges. The latter may occur if, for example, plantations tend to be
established on drier ground or if moorland close to the trees is not
regularly burnt. There are also likely to be increases in predator
populations (crows and foxes) within plantations that may increase
predation pressure on moorland birds in surrounding areas. There is
much scope for further work on relationships between forestry and
predation. |
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Merlins have started to nest in trees at the
edges of some mature conifer plantations. However, afforestation
has probably reduced availability of hunting habitat for this
species and other moorland raptors in several parts of Britain. |
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| Reduction of foraging habitat as a result
of afforestation can be a problem for some species including Raven,
Merlin and Golden Eagle. However, different studies appear to have
reached somewhat different conclusions, which suggests that the
effects of afforestation on moorland birds are not easy to predict.
A recent study on the effects of forestry on the breeding success
of Golden Eagles on the island of Mull, concluded that most birds
are likely to suffer reduction in productivity when forestry occurs
within their ranges. However, this research indicated that the reduction
in breeding success was not readily predictable from the extent
of forestry within a range; in some instances even small areas of
forest appear to reduce breeding success (Whitfield et al.
2001).
Other examples of papers dealing with various aspects of afforestation
and upland birds include Marquiss et al. (1978), Newton et
al. (1982), Marquiss et al. (1985), Thompson et al.
(1988), Avery et al. (1989), Lavers & Haines-Young (1997),
Madders (2000), Whitfield et al. 2001.
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