Technical ReportPDF Available

The effects of mammalian herbivores on natural regeneration of upland, native woodland.

I . ":' ;i'*=c* *i i
i,., i_, d :;a ..-..--ri E
i :.-. I s:*\* jr*j.. !
; -- a ..-*>.; I/ il I
February 2000 Number: 115
The effects of mammalian herbivores on natural
regeneration of upland, native woodland
1. lntroduction
1.1 Semi-natural woodland and scrub cover
about 4% of the Scottish landscape. Grazing
and browsing are major factors preventing, or
restricting, the regeneration of woody species
on many of these areas on unenclosed hill
1.2 The two herbivore species that are
considered to have the greatest impact across
Scotland are red deer and sheep, which have
upland populations of about 350,000 and
2,350,000 respectively. Several other
domestic and wild species such as catfle, roe
and sika deer, horses and ponies, goats,
hares, rabbits and voles can also affect rates
of tree regeneration.
1.3 Under natural conditions, herbivore
numbers would have fluctuated with weather
conditions and with predator numbers. Wild
boar would also have scarified the ground,
creating regeneration niches. Conditions
suitable for tree regeneration were therefore
likely to have occurred often enough to
maintain woodland cover across large parts of
Scotland. Winter feeding of sheep and red
deer, land improvement and a lack of
predators have all led to herbivore numbers
being kept continuously at artificially high
2. Requirements for successful tree
regeneration and establishment
2.1 Successful natural tree regeneration
. a source of viable seed or suckers;
r suitable temperatures, and adequate
rainfall and light, to allow seedlings and
saplings to growl;
. the presence of mycorrhizalfungifor some
tree species;
r a suitable seed bed where roots can reach
the mineral soil, nutrient levels and soil
moisture are sufficiently high and there is
not too much competition from other
vegetation; and
o seed predation and browsing levels low
enough to allow sufficient numbers of
saplings to reach a height where they are
no longer susceptible to browsing.
Grazing and browsing directly affect the last
two of these conditions.
2.2 All Scotland's dominant native tree
species require relatively high light conditions
to establish (see 3.3) hence successful
regeneration and establishment happens
either at the woodland edge or in gaps created
by the death of adults, or by felling. ln theory,
the correct combination of conditions for
regeneration and establishment need occur
only once during the lifetime of each adult tree
for it to be replaced and for a woodland to
survive. Normal maximum lifespans for several
native tree species in Scotland are given
below. Little is known about how the
reproductive potential of different tree species
is affected by age and growing conditions. For
this reason, it is hard to predict how frequenfly
successful regeneration and establishment
events must occur to ensure the survival of a
particular woodland.
' There is no consistent distinction in the literature
between a seedling and a sapling. ln this note a
sapling is taken to be a young tree taller than about
25 cm and a seedling is one less than about 25 cm.
Further copies of this note can be obtained from: publications Section, SNH,
@ Scottish Natual Heritage Battleby, Perth PH1 3EW. Tel: 01738 627921
ISSN: 1358 5843
Iree specl'es Lifespan (vears)
Oak About 450 (but has been
recorded uo to 930)
Scots pine 400
Hollv 300
Ash 200-300
Birch (silver
and downv) 180
2.3 lf grazing and browsing are very heavy,
regeneration will be completely suppressed but
if less heavy, the density and species
composition of surviving saplings depends on
r the pre-browsed density and groMh rate of
seedlings and saplings;
o the severity of browsing on seedlings and
saplings; and
. the responses of seedlings and saplings to
being browsed.
An u,nderstanding of the factors affecting each
of these will help in planning appropriate
grazing management for woodland
3. The pre-browsed density and growth
rate of seedlings and saplings
3.1 These are affected by the first four factors
listed in section 2.1.
3.2 Availability of viable seeds depends on
the abundance of seeds produced by local
seed sources, the distance to those sources,
the presence of the agent of dispersal and the
viability of the seed. Abundance and viability
of seed produced by a tree can vary greatly
from year to year depending particularly on
weather conditions. Both production and
viability of seed often decline with altitude. For
wind-dispersed species, such as birch, pine,
willow, alder and ash, most seed falls within a
distance of about twice the height of the parent
tree and there is little regeneration at more
than 1 km, though small numbers of birch
seeds can travel to at least 3 km and those of
pine to at least 7 km. Oak, rowan, juniper,
hazel and holly require an appropriate animal
vector to be dispersed beyond the canopy of
the parent tree. ln Britain, aspen reproduces
largely by suckering. The seeds of most tree
species do not remain viable in the soil for
more than a year but birch seeds can survive
for two to three years and ash seeds survive
for up to six years. Ash and rowan seeds take
at least 18 months to germinate.
3.3 Seedling germination and survival may be
affected by lack of light, not only under an
existing tree canopy but also where there is
dense heather, bracken or bramble cover.
Pine, birch, alder and willow seedlings are all
light demanding. Oak seedlings can survive
beneath a canopy for up to four years and ash
will also tolerate shade for the first few years
but then becomes light demanding. Rowan is
tolerant of limited shade and can regenerate
under a birch canopy whereas birch itself
cannot. Holly seedlings are shade-tolerant and
holly can reach 5-10 m in height underneath a
woodland canopy. The high palatability of
rowan and holly probably accounts for the
rarity of woodlands dominated by these
3.4 Competition for nutrients and light from
ground layer vegetation e.g. a dense carpet of
dog's mercury or wavy hair grass, will limit
seedling survival. Grazing helps to reduce the
cover of ground layer vegetation.
3.5 Mycorrhizalfungi are found associated
with almost all trees in long standing
woodlands. Mycorrhizae seem to improve the
ability of trees to absorb nutrients, especially
phosphate, make them more resistant to
infection and may also improve water
economy. They thus allow seedlings to grow
more quickly and seem to be essential where
site conditions are particularly demanding e.g.
at the tree line. Mycorrhizal fungi may be
absent from sites that have been without tree
cover for many years but they should quickly
colonize any soil other than peats or podzols.
3.6 A deep raw humus layer, or dense ground
layer vegetation, can increase the chances of
seedlings drying out by preventing their roots
gaining access to the mineral soil.
3.7 Where conditions are good, and growth
rates high, there is a greater chance that
saplings will get their leading shoot out of
reach of large herbivores before they are
browsed. However, where soil and tree nutrient
levels are high, it is possible that there will be
an increased chance of browsing (see 4.2.3).
4. The severity of browsing on seedlings
and saplings
4.1 This depends on
r the species and condition of seedlings and
saplings present;
r the nature of the ground layer vegetation
. the density and height of seedlings and
o the herbivore species; and
. the seasonality, intensity and spatial
distribution of grazing and browsing.
4.2 Species and condition of seedlings and
sap/rngs present
4.2.1 Herbivores are selective feeders, their
preferences being influenced by several
attributes of the foliage of different tree and
shrub species. These are thought to include
digestibility, shoot biomass, fibre content,
nutrient concentrations, level of toxic
secondary compounds and spininess.
4.2.2 ln general, the relative preferences of
red deer and sheep for the foliage of different
native tree species are given below.
ranking (1 is most
hiohlv oreferredl
Iree species
1ash, aspen, willow,
hazel. hollv. rowan
3birch, pine
4alder. iunioer
4.2.3 All the attributes of a tree's foliage that
determine its preference ranking can vary
throughout the year, with the age of the foliage
and with growing conditions. Digestibility tends
to be higher, and fibre content lower, in new,
spring growth. Birch is seldom eaten by red
deer when it is not in leaf unless little other
food is available. lt is often heavily browsed at
bud burst. Nutrient concentrations in foliage
can be higher if the tree is growing on more
fertile soils and there is evidence that deer and
sheep selectively browse trees growing on
more nutrient-rich soils.
4.3 The nature of the ground layer vegetation
4.3.1 The preference shown by a herbivore
for a particular tree species is crucially
dependent on what else is on offer. Pine and
juniper are not favoured in summer when other
food is usually abundant because the leaves
contain terpenes, which are distasteful. Deer
will, however, browse pine shoots around the
time of bud burst. Pine and juniper are eaten
in winter when deciduous trees and shrubs are
bare of foliage and when other vegetation is of
low digestibility or is relatively inaccessible
under snow. Leafless shoots and twigs are
normally not eaten unless there is a scarcity of
other vegetation.
4.3.2 When seedlings are about the same
height as the surrounding ground vegetation,
they will often be eaten along with it.
Seedlings therefore have a greater chance of
survival if they are growing amongst a non-
preferred vegetation type. Thus seedlings
growing amongst tall heather are less likely to
be browsed than those growing amongst short,
grassy vegetation.
4.3.3 Most preferences are over-ridden by
hunger. Red deer will browse pine in summer
or birch in winter if there is no alternative and,
when pressed, all herbivores may eat foliage
or twigs or strip bark from species of trees
which they would otherwise avoid.
4.3.4 Heavy grazing on ground layer
vegetation can reduce the availability of good
quality forage and lead to an increase in
browsing rates on trees. When grazing
pressures are low, ground cover may be high
and seedlings will be less easily detected by
herbivores until they emerge above the level of
the surrounding vegetation. Even then, if there
is an abundant source of alternative food,
saplings will only be readily browsed by
herbivores which have a high preference for
browse (goats, roe deer and, to some extent,
red deer).
4.3.5 When ground layer vegetation is tall and
abundant, field vole numbers are likely to
increase and they can also damage seedlings
and saplings (see 5.1.5).
4.4 The density and height of seedlings and
4.4.1 For a given herbivore density, the
chances of achieving successful rates of
sapling establishment are likely to increase as
the initial, pre-browsed, density of saplings
increases. However the density of established
saplings may not increase in direct proportion
to any increase in the initial density of saplings.
Little work has been carried out on the form of
this relationship so it is currently not possible to
predict the likely effect of changing the initial
abundance of saplings on final sapling density.
4.4.2 Seedlings and saplings which project
above the level of the surrounding vegetation
are more likely to be browsed until they grow
taller than the mouth height of any herbivores
present. At Beinn Eighe, browsing by red deer
was found to be most severe on trees ol 1-2 m
in height. Browsing by sheep is likely to be
most severe on shorter saplings. Maximum
5. Herbivore
soecies Maximum browse
heiqht h)
Cattle 2
Red deer 1.8
Sika deer 1.8
Sheep 1.5
Goats 1.5
Roe deer 1.1
Rabbits 0.54
Hares o.7
browse heights for different herbivore species
are given below.
5.1 The herbivore species
5.1.'1 The main impact of browsing by sheep
and red deer is at the seedling and small
sapling stage, when they clip leading, and
lateral, shoots. Sheep of most breeds, and
cattle, show less of a tendency to browse than
do red deer. However, the more primitive
breeds, such as Hebrideans, browse more
readily and are used for scrub control on some
grassland and heathland nature reserves.
Sheep are also reputed to displace red deer
from favoured areas hence a reduction in
sheep numbers may lead to an increase in
deer browsing on tree seedlings and saplings
in these areas. Red and sika deer can strip
bark from saplings and roe deer fray them with
their antlers. Bark stripping is more likely than
fraying to remove bark in a ring around the tree
and therefore to kill it. Otherwise, within
woodland, roe and sika deer can have similar
impacts to those of red deer.
5.1.2 Cattle and ponies can cause damage
by eating seedlings and by trampling. Ponies
have a greater tendency to browse than do
cattle. They also strip bark from trees of all
5.1.3 Feral goat populations are restricted to
a small number of sites in Scotland but, where
they occur, they can have a major effect on
tree regeneration because of their high
propensity to browse. They tend to browse
taller saplings than do sheep and can affect
regeneration on cliff ledges or boulder fields
that are inaccessible to other herbivore
5.1.4 Mountain hares browse and bark strip
saplings, as do rabbits, and both can be
particularly harmful when herbs and grasses
are under snow cover. Rabbit damage can
occur throughout the year but tends to
increase in winter and early spring. Bark
stripping is commonest in hard winters and late
springs when snow persists.
5.1.5 Field Voles can be significant browsers
of tree seedlings and, where they occur in high
numbers, will often ring-bark saplings. One
study found that voles killed 73% of seedlings
regenerating on open moor by eating the main
shoots. Wood mice and squirrels eat tree
seeds and bank voles may eat smalltree
5.2 The seasonality, spatialdistribution and
intensity of grazing and browsing
5.2.1 Because of the seasonal changes in the
attractiveness of different species of seedling
and sapling and in the abundance and
digestibillty of the ground layer vegetation, the
same density of herbivores can have a very
different effect on regeneration at different
times of year. ln summer, when ground layer
vegetation is usually more abundant, saplings
are less likely to be browsed than in winter,
when food is often in short supply. On the
other hand, deciduous saplings are more
attractive in summer, when they have leaves.
5.2.2 Herbivores do not normally distribute
themselves evenly across a landscape and
young trees will suffer a heavier browsing
pressure when they grow within, or adjacent to,
heavily used areas. Forage quality and
abundance and, in poor weather conditions,
shelter, are the major factors affecting the
distribution of large herbivores (See SNH l&A
Note 47, The grazing behaviour of large
herbivores in the uplands). Thus, areas of
nutritious grassland on good soil will always be
preferred and red deer tend to spend more
time in at lower altitudes in winter than in
summer. The latter can lead to lower browsing
pressures, and more successful regeneration
of young trees, at higher altitudes. For rabbits,
hares and voles, cover, such as long grass or
scrub, which gives protection from predators,
is also a major factor affecting their distribution
in the landscape.
5.2.3 Grazing and browsing pressure
obviously have a large effect on regeneration
success but numbers of successfully
regenerating trees do not necessarily keep
increasing as herbivore numbers decline to low
levels. This is because, at low grazing
pressures, the ground layer vegetation builds
up resulting in both fewer regeneration niches
and increased competition for soil nutrients
and Iight.
6. The responses of saplings to being
6.1 The ability of saplings to survive and
resprout after browsing varies with
. the age and species of tree or shrub;
. the proportion of the plant removed;
o the type of damage;
o the plant's growing environment ; and
. the season in which the browsing occurs.
6.2 Mature trees are relatively resistant even
if their lower branches are completely removed
up to the grazing height of the herbivores.
Young trees are more at risk as a greater
proportion of total foliage area may be
removed. Trees up to 2 m tall are vulnerable
and saplings of less than 50 cm are often
6.3 Even so, birch, rowan and pine can all
tolerate removal of up to half of the current
year's growth. The effect of removal of more
than this differs with species. pine seems
least tolerant of damage. Two year old pine
usually dies if eaten back into the previous
season's wood whereas most birch and all
rowan are likely to survive. Other broadleaves
are probably similarly resistant.
6.4 Trees which are tolerant of browsing may
be kept small above ground but developln
extensive root system, enabling them to
respond rapidly if browsing pressure is
reduced or removed. ln general, recovery is
likely to be better on sites with favourabls
growing conditions including good soil nutrient
levels and climatic conditions although, under
these conditions, saplings may have to
compete with a vigorous growth of ground
layer vegetation.
6.5 Browsing on seedlings and saplings in
early summer, when nutrient concentrations in
the shoots and leaves are high, is likely to be
more detrimental than browsing in late
summer or winter, when most of the nutrients
have been re-allocated to stems and roots.
This applies to birch and may also apply to
other broadleaved species. Coniferous ipecies
store nutrients in their leaves as well.
7. What herbivore densities will attow tree
7.1 Given the range of factors involved, and
that large herbivores do not usually distribute
themselves evenly across the range available
to them, it is not surprising that there are no
clear thresholds for the numbers of deer or
sheep at which adequate regeneration may
occur. The few studies which have been
carried out in this area can, however, give us
an idea of the range of herbivore densities that
might be appropriate. lt should be borne in
mind that, even at low overall densities,
grazing pressures in preferred areas can be
very high.
7.2 Hester, Mitchell and Kirby (1996) studied
the effects of sheep grazing and browsing on
regeneration in an upland wood in Cumbria at
three stocking densities and in either summer
or winter. The study looked at germination and
survival rates of seedlings and saplings of
downy birch, rowan and ash.
7.3 Although germination rates were higher
under heavier grazing pressures (2.1-3.8
sheep ha''), probably because of the higher
number of regeneration niches, there were still
large numbers of seedlings appearing even in
the,most lightly grazed ptots (0.6-1.2 sheep
7.4 Seedling survivalwas higher at lower
grazing intensities, and in summer-grazed
plots. The latter was probably because
summer grazing prevented the build-up of
ground vegetation that would compete with
7.5 At high levels of summer grazing (2.1-3.4
sheep ha-'), almost all the saplings were
browsed whereas at low levels (0.6-0.g sheep
ha-l), only 25o/o of the saplings were browsed.
ln winter, browsing rates on saplings were
generally lower, with 40% of saplings
remaining undamaged even at 3.8 sheep ha-1.
The higher browsing rates in summer are likely
to be because the saplings had leaves at this
7.6 A parallel study of browsing of planted
saplings also found a decreasing impact as
sheep densities decreased, apparenfly
because the sheep browsed saplings less
frequently when more ground-layer vegetation
was available. However, planted saplings were
more heavily browsed on average than
naturally regenerated saplings, which is
commonly the case.
7.7 The winter browsing of naturally
regenerated, leafless birch saplings at Glen
Feshie has been found to be linearly related to
local densities of red deer (Miller & Cummins
1998) with the browsing rate ranging from
about 5% of birch saplings being browsed per
week at about 200 red deer *m'z 12 ha-1) to <
1% of saplings browsed per week at less than
about 25 red deer km-' (0.25 ha-'). Deer
numbers on low ground are often over 150
km-z in winter.
7.8 Several attempts have been made to
estimate the density of red deer that might
allow successful woodland regeneration.
Fraser Darling (1947) guessed at 6 km-',
Holloway (1967) found partial regeneration at 4
km-' and unimpeded regeneration at 2 km-'
and Mitchell, Staines & Welch (1977) found
regeneration occurring at about 10 km-'. The
latter was at a site with a relatively high density
of saplings of around 4,000 saplings ha-'.
Ratcliffe (1988) found that in forests there was
a heavy impact on most broadleaved trees at
red deer densities of about 7 deer km'2.
7.9 At Creag Meagaidh, following culling of
red deer, regeneration of birch from previously
suppressed saplings appears to be taking
place at densities of 8 red deer km-2. At
Abernethy Forest densities of up to 12 km-z in
1988/9 were reduced by culling to about 5 km2
by 1993. Roe were also culled but the
proportion of the population this represented is
not known. A20o/o increase in the number of
established seedlings and saplings was
recorded over this time, with rowan accounting
for 68% of new saplings. Most of the rest were
pine (the first species to respond), with some
birch and willow.
7.10 Densities of herbivores low enough to
permit regeneration may still be high enough to
affect the composition of ground layer
vegetation. At about 5 red deer km-2, Ratcliffe
(1988) suggested that plant diversity in forests
would be reduced.
8. Planning regeneration
8.1 Thus, some general conclusions on the
impact of grazing on tree regeneration in the
uplands are as follows.
. There will normally be insufficient seeds of
wind-dispersed species to initiate much
regeneration at distances of more than
about 1 km from existing woods. Seed
densities fall off rapidly with distance from
the parent tree.
. Ground conditions may be unsuitable for
regeneration, especially if there is a deep
raw litter layer or dense vegetation.
. Grazing and trampling may assist initial
establishment of seedlings by suppressing
competing vegetation, creating
regeneration niches and limiting field vole
. Grazing and browsing impact on
regenerating trees is likely to be
concentrated in the most heavily used
areas such as those providing high quality
grassland or winter shelter.
o Seedlings are less likely to be browsed
where the surrounding vegetation partly
conceals them but if the vegetation is
dense there will be more competition with
the seedlings for resources.
. The greatest grazing and browsing
pressure will fall on the most preferred
species present.
. There may be less browsing impact on
saplings where sufficient, preferred foods
are available elsewhere.
e Stopping grazing (e.9. by fencing) may lead
to increases in grass groMh, field vole
numbers and seedling destruction by voles.
o Some trees are relatively tolerant and will
recover if pressure reduces or ceases.
. Tolerance and recovery will be better on
sites where the growing conditions are
more favourable but herbivores may
selectively browse those on more nutrient-
rich sites.
. Deer are more likely to browse saplings
than are sheep or cattle.
8.2 This suggests that total exclusion of
grazing may be a mistake where there is a lack
of germination and /or low densities of
seedlings. Where adequate numbers of
seedlings or saplings already exist, very low
grazing pressures may be the best means of
allowing these young trees to establish.
Herbivores are an important component of
natural ecosystems, so the preferred policy is
to achieve regeneration without the need for
their total removal.
8.3 Options include:
. Where there are sufficient numbers of
suppressed seedlings or saplings already
present, the elimination, or drastic
reduction, of grazing and browsing pressure
will allow the young trees to 'get away'. This
regime should be continued untilthe
saplings are tall enough to withstand
. Where there are insufficient numbers of
seedlings or saplings present, the
instigation of a low and/or periodic grazing
regime may be appropriate. This could be
brought about by a reduction in overall
stock, or wild herbivore, densities or by
periodic, or seasonal, exclusion of stock by
fencing. Animal numbers might have to be
progressively reduced until the optimum
balance between the positive and negative
effects of herbivores is reached. The
regime should be continued until the
required density of saplings becomes tall
enough to withstand browsing. This is likely
to be about the lifetime of a conventional
fence. lt should, however, be borne in mind
that, if fences are used, they can have a
number of important side effects (see the
SNH I & A Note 59 Fences and upland
conservation management).
. Replacement of red deer with sheep may
lead to lower browsing rates on saplings.
. lf ground layer vegetatlon is dense,
mechanical scarification may be needed to
increase the number of regeneration
niches. Pigs and cattle can also be used
for this purpose.
. Felling, or coppicing, of selected trees will
increase the amount of light available and
may increase the density of seedlings
and/or suckers of lighldemanding species.
r lf the supply of seed is limiting, it may be
necessary to increase the density of trees
nearby either by encouraging the spread of
woodland from existing sites or by planting
trees to provide a seed source. This is a
long term strategy and, if regeneration is
wanted in the short term, direct planting will
be necessary.
9. Further reading
1. Beaumont, D., Dugan, D., Evans, G. &
Taylor, S. (1995) Deer management and tree
regeneration in the RSPB reserve at
Abernethy Foresf. ln: Aldhous, J.R. (Ed). Our
Pinewood Heritage. Forestry Commission,
2. Fraser Darling, F.F. (1947) Natural history in
the Highlands and lslands. Collins, London.
3. Harmer, R. (1995) Naturalregeneration of
broadleaved trees in Britain: ilt. Germination
and establishment. Forestry, 68, 1-9.
4. Hester, A.J. & Mitter, G.R. (i99S) Scrub and
Woodland Regeneration: Prospects for the
Future. ln: Thompson, D.B.A., Hester, A.J. &
Usher M.B. (Eds). Heaths and Moorland:
Cultural Landscapes. HMSO, Edinburgh.
5. Hester, A.J., Mitchell, F.J.G. & Kirby, K.J.
(1996) Effects of season and intensity of sheep
grazing on tree regeneration in a British uptand
woodland. Forest Ecology and Management,
6. Hodge, S. & Pepper, H. (1998) Ihe
prevention of mammal damage to trees in
woodland. Forestry Commission Practice Note
No. 3.
7. Holloway, C.W. (1967) The effects of red
deer and other animals on the natural
regeneration of Scofs prne. Ph.D. thesis.
University of Aberdeen.
8. Kinnaird, J.W. (1974) Effect of site
conditions on the regeneration of birch (Betula
pendula Roth and B. pubescens Ehrh.).
Journal of Ecology, 62,467-472.
9. Miller, G.R. & Cummins, R.P. (1998)
Browsing by red deer on naturally regenerated
birch and juniper saplings on wintering ground
at Glen Feshie. Scottish Forestry, 52,138-145.
10. Miller, G.R., Cummins, R.P. & Hester, A.J.
(1998) Red deer and woodland regeneration in
the Cairngorms. Scottish Forestry, 52,14-20.
11. Miller, G.R., Kinnaird, J.W. & Cummins,
R.P (1982) Liability of saplings to browsing on
a red deer range in the Scoffish Highlands.
Journal of Applied Ecology, 19, 941-951 .
12. Mitchell, 8., Staines, B.W. & Welch, D.
(1977) Ecology of red deer. lnstitute of
Terrestrial Ecology, Cambridge.
13. Pepper, H. (1998) The prevention of rabbit
damage fo frees in woodland. Forestry
Commission Practice Note No. 2.
14. Ratcliffe, P.R. (1988) The management of
red deer populations resident in upland foresfs.
In: D.C. Jardine (Ed). Wildlife Management in
Forests. Proceedings of a symposium held by
the lnstitute of Foresters.
15. Staines, B.W., Balharry, R.& Wetch, D.
(1995) Moorland management and impacts of
red deer. ln: Thompson, D.B.A., Hester, A.J.
and Usher M.B. (Eds). Heaths and Moorland:
Cultural Landscapes. HMSO, Edinburgh.
10. Authors
John Andrews
Andrews Ward Associates
17 West Perry
Gordon Miller
School Hill
AB31 5TQ
Helen Armstrong
Woodland Ecology Branch
Forest Research
Northern Research Station
EH25 gSY
11. Acknowledgements
Comments were kindly provided by Alison
Hester (Macaulay Land Use Research
lnstitute), Richard Thompson, Brenda Mayle,
Jonathan Humphrey and Robin Gill (Forest
Research), Kate Holl and Roland Stiven
(SNH), Steve Palmer (lnstitute of Terrestrial
Ecology), Lars Edenius (Swedish University of
Agricultural Sciences), Pete Reynolds
(Capreolus consultants), Fiona Stewart and
Dick Balharry.
12. Contacts for advice and information
Kate Holl
Land Use Group
Scottish Natural Heritage
2, Anderson Place
Tel: 0131 447 4784
Duncan Stone
Land Use Group
Scottish Natural Heritage
27 Ardconnel Terrace
Tel: 01463 712221
Full-text available
Persistent browsing by red deer checked the development of young trees and shrubs on wintering ground at Glen Feshie and so maintained a stock of stunted saplings. This 'sapling bank' was composed predominantly of birch, with rowan, alder and juniper as the main subsidiary species. Saplings of Scot's pine, the dominant tree in the relict woodlands, were rare. Damage to birch during winter was broadly correlated with local densities of red deer, one deer per ha being roughly equivalent to 2% of saplings browsed per week. However relatively few birches were taken during winter and almost none at all in April. They were mostly eaten during summer following a peak of browsing at bud-break in May-June. Annual birch mortality was 15%. Junipers, on the other hand, were browsed mainly in mid-late winter when preferred forage had become scarce. They were then more severely browsed than were birches but their annual mortality was only 6%. Neither species grew in height during 32 months of observation. The findings are discussed in relation to the problem of regenerating woodland in deer wintering areas. It is concluded that the sapling banks at Glen Feshie and elsewhere confer a potential for rapid woodland development if red deer numbers were to be reduced. However the initial tree species composition is likely to differ from that of existing relict woodland.
Full-text available
Many of the few remaining patches of natural woodland in the Cairngorms are failing to regenerate because tree and shrub saplings ore repeatedly checked or killed by browsing red deer. Liability to browsing is governed by a complex of interacting factors including a sapling's physical and chemical properties, season of year, availability of alternative foods, soil conditions, nature of surrounding vegetation and local red deer density. Amongst common native tree and shrub species in the Cairngorms, deer prefer to eat rowan but generally take juniper only when alternative foods are scarce. Young Scots pine saplings are the most easily killed by browsing whereas birch and rowan can survive repeated damage. Many saplings, including pines, are maintained in a suppressed state by repeated browsing. These plants constitute an often long-lived 'sapling bank' from which rapid growth can occur once browsing pressure has been relieved. On unburnt ground in the Cairngorms, conditions for tree regeneration are currently most favourable at altitudes greater thon 550 m because here there are (a) fewer deer and (b) more gaps for seedling establishment than is the case on lower ground. Reducing red deer density to fewer thon about 5 animals per km2 increases the possibility of woodland regeneration everywhere. However, this in itself may be insufficient to produce good seedling establishment in dense ericoid or graminoid vegetation with its associated deep mor humus layer. Ground preparation by fire or by mechanical disturbance may be necessary in such circumstances if rapid and extensive regeneration is required.
RSPB's Abernethy Forest Reserve in Strathspey contains the largest single area of native pine in the UK, 1889 ha, amounting to 15.7% of the native Scots pine Pinus sylvestris forest. Management is centred on the conservation and extension of the native pinewood ecosystem by allowing regeneration and development of self-sustaining forest over the potential woodland area. Densities of red deer Cervus elaphus were up to 12 per km² in 1988/1989, too high for such development. A fully monitored cull has reduced red deer densities to 5 per km². Vegetation monitoring was initiated in 1989. By 1992 the percentage of seedlings with evidence of browsing had fallen from 72% to 43% with a concomitant increase of 20% in the total number of established seedlings and saplings over the survey area. Recent regeneration is occurring in all major vegetation types where woodland recovery is most desired, though seedlings remain rare in many open heathland areas. -from Authors
The distribution and abundance of birch seedlings and saplings was studied in relation to habitat conditions at twenty sites in the north-west, central and eastern Highlands of Scotland. Young birches occurred at all sites and the age structure of the populations was similar: first-year plants were numerous and older plants relatively scarce. Few plants survived to the second year and the number of survivors decreased progressively with advancing age. Bare soils and dense cushions of Sphagnum bore the highest densities of seedlings but were sparsely and irregularly distributed. Litter and mosses supported few seedlings, and other surface types rarely had any. Grazing, shading and the slope of the ground had little effect on seedling establishment. Some of the variation between sites in the mean densities of seedlings was related to differences in the proportion of different surface types. It is suggested that much of the remaining variation is due to moisture differences between the habitats. There were fewer saplings wherever there was heavy grazing or a dense cover of trees or ferns. They appeared to survive and develop best in gaps in woodland and on open ground, particularly among heather.
(l) The amount and seasonality of browsing on experimentally planted saplings (<30 cm tall) of Scots pine (Pinus syluestris L.), silver birch (Betuta pendula Roth), rowan (Sorbzs aucuparia L.) and juniper (Juniperus communis L.) were observed on rangeland where red deer (Ceruus elaphus L) was the main herbivore. The effects of clipping on the survival of saplings grown outdoors in pots was also studied. (2) The extent to which saptings were browsed varied according to their location and species. In general, deer spent most time on the lower slopes olhills and so there was an inverse correlation between altitude and the frequency ofbrowsing on saplings. (3) Tall, conspicuous saplings were more liable to browsing than small, partially obscured plants. (4) Overall, pine was the species most liable to browsing. Juniper and birch were browsed least. Deciduous species were browsed most often in summer, when they were leafy. There was much less seasonal variation in the browsing of pine and juniper. (5) Pine was easily killed by clipping. Rowan was most tolerant of damage. (6) Pine seems least able to regenerate where deer stocks are large because of its high liability to browsing and consequent heavy mortality. In general, the regeneration oftall woody species could be increased, especially at 600-700 m above sea level, if deer numbers were to be reduced substantially.
The viability and germination of broadleaved tree seed are discussed within the context of natural regeneration. A survey of the literature showed that viability of seedlots is variable. Ash is dormant until the second spring after seed fall and can remain in the soil seedbank for several years but other species germinate in spring of the year following their production. Field studies have shown that germination depends on the position of the seed and that preparation of a seedbed is advantageous for some species. The effects of browsing, competition and shade on the establishment of seedlings are briefly described. A wide variety of browsing animals can adversely affect the success of natural regeneration by reducing tree growth and influencing the proportion of species regenerating. Although competition will reduce growth, the severity of this effect depends on many factors including soil type and species of competing weeds. Overstorey trees suppress growth by casting shade and providing root competition. Possible areas for future research are discussed.
This paper reports some effects of experimental alteration of season (summer, winter) and intensity of sheep grazing on tree regeneration, growth and browsing damage in an upland broadleaved woodland in Cumbria, UK. During the first 3 years of grazing treatments, seedling recruitment was primarily Betula pubescens, Sorbus aucuparia and Fraxinus excelsior. After 7 years of grazing treatments, seedlings and saplings of many species were numerous, with fewer seedlings in winter-grazed plots but a higher proportion of these were browsed. More seedlings had reached sapling stage in winter-grazed plots. Sapling numbers increased with decreasing grazing intensity, with lower proportions browsed at low grazing intensities.
Our Pinewood Heritage
  • Abernethy Foresf
  • Ln
Abernethy Foresf. ln: Aldhous, J.R. (Ed). Our Pinewood Heritage. Forestry Commission, RSPB, SNH.
Natural history in the Highlands and lslands
  • Fraser Darling
Fraser Darling, F.F. (1947) Natural history in the Highlands and lslands. Collins, London.
(i99S) Scrub and Woodland Regeneration: Prospects for the Future
  • A J Hester
  • G R Mitter
Hester, A.J. & Mitter, G.R. (i99S) Scrub and Woodland Regeneration: Prospects for the Future. ln: Thompson, D.B.A., Hester, A.J. & Usher M.B. (Eds). Heaths and Moorland: Cultural Landscapes. HMSO, Edinburgh.