Forestry Commission
Designing Forest Edges
to Improve Wind
Stability
Barry Gardiner and Giles Stacey
Forestry Commission
ARCHIVE
I
FORESTRY COMMISSION TECHNICAL PAPER 16
Designing Forest Edges to Improve
Wind Stability
Barry A. Gardiner1 and Giles R. Stacey2,
fo re s tr y Commission, Northern Research Station, Roslin, Midlothian, EH25 9SY
2Department o f Engineering Science, Oxford University.
Present address: Englishworks, P. Paaltjensstraat 20, 7552 VM Hengelo (Ov), The Netherlands.
FORESTRY COMMISSION, EDINBURGH
© Crown copyright 1996
First published 1996
ISBN 0 85538 339 9
FDC 421:614:(410)
K E Y W O R D S: Design, Edges, Forest m anagem ent, Stability
Please address enquiries about this publication to:
The Research Publications Officer
Forestry C om m ission Research Division
A lice H olt Lodge
W recclesham , Farnham
Surrey GU10 4LH
CONTENTS
Page
Sum m ary
iv
Introd u ction
1
E xperim ental arrangem ent
1
W ind tunnel
1
Edge treatm ents
1
M easurem ents
2
R esu lts
3
U ntreated edges w ith different tree spacings
3
Treated edges
3
D iscu ssio n
6
R ecom m end ations
7
A ckn ow led gem en ts
7
R eferen ces
7
Summary
Forest edges are im portant for the stability, visual im pact and biodiversity of forests.
There is grow ing interest in the treatm ent of edges to im prove their stability and the
diversity of habitats they provide. Wind tunnel m easurem ents suggest that trees at
esta b lish ed fo re st ed g es are in h eren tly m ore stab le th an trees w ith in the fo rest
because their form w ill have adapted to the increased w ind exposure. On the other
hand, recently exposed edge trees will be m uch m ore vulnerable because of their lack
of adaptation. Experim ents were carried out in the w ind tunnel on five different edge
treatm ents and show that tapered edges and those w ith a gradation in tree density
have potential stability benefits for both new edges and trees inside an established
edge. However, a low shrub layer placed ju st in front of the forest edge increased the
w ind load in g on the edge trees and reduced their stability. P ractical m ethods for
creating edges that can im prove forest stability and visual appeal are discussed.
iv
Introduction
Experimental arrangement
The edges of forests and stands are im portant
for a num ber of reasons. They represent:
1.
a tran sition from trees to other vegetation
form s;
2.
a transition in light intensity;
3.
a transition in shelter for anim als;
4.
an a re a p o t e n t ia lly v u ln e r a b le to w in d
dam age; and
5.
the m ost visible aspect of a forest.
Wind tunnel
Tests were carried out in the Oxford University
wind tunnel using 1:75 scale m odel spruce trees
th at had b een p re v io u sly used to assess the
stability im plications of thinning, spacing and
cle a r-fe llin g in co m m ercial fo rests (G ard in er
et a l., in p r e s s ). A fu ll d e s c r ip tio n o f the
exp erim en tal arran g em en t and of the w ay in
which the wind loading on the m odel trees was
m easured can be found in Stacey et al. (1994).
C om parison of the w ind tunnel data w ith full
scale experim ents (Stacey et al., 1994) suggests
that the wind tunnel sim ulates conditions in the
forest very successfully.
Presently there is a need for the forest industry
in G re a t B r ita in to ta k e a m o re im a g in a tiv e
approach to edge m anagem ent, particularly as a
m e th o d o f m a k in g f o r e s ts m o re v is u a lly
appealing (Forestry C om m ission, 1994). M any
forests are being restructured to create a greater
spread in age classes w ith a resultant increase in
the num ber of stand edges. M anagem ent actions
of this type are certain to affect forest stability
against wind.
Edge treatments
The m odel forest w as designed to represent a
15 m m ean h eigh t (h) Sitka spruce forest at a
sp acin g o f 1.7 m. The flow in the tunnel w as
representative of open farm land upwind of the
forest edge and a m ean wind speed of 30 m s_1
(15 k n o ts ) at a h e ig h t o f 30 m. F iv e e d g e
treatm ents were tested in the w ind tunnel and
c o m p a re d w ith an u n tr e a te d e d g e ( U l)
r e p r e s e n tin g a sh a rp t r a n s itio n fro m o p e n
ground to forest. The patterns are illustrated in
Figure 1. Treatm ents T'A, T1 and S w ere designed
to taper the forest edge and treatm ents G1 and
This Paper describes experim ents carried out in a
wind tunnel to assess the effect of different forms
of edge treatm ent on forest stability and on the
airflow and w ind loading across the untreated
edges of forests of different planting densities.
The experim ents repeat and extend the earlier
wind tunnel m easurem ents of Fraser (1964).
C o d e : Treatm e nt
U1 : U n t r e a t e d ( 1 . 7 m s p a c i n g )
U2 : U n t r e a te d (3 .5m sp acin g )
U3 : U n t r e a te d (5 .2m sp a c in g )
T 2 : T a p e r e d for h a l l a t r e e h e ig h t
•’h*’
nj2
rrrrr
T V rrrr
T1 : T a p e r e d lo r a t r e e h e i g h t
S : S h r u b s f o r a t r e e h e ig h t
♦ —h
G1 : 5 . 2 m s p a c i n g f o r a t r e e h e ig h t
G2 : 5 .2 m s p a c in g fo r a tre e height
f o l l o w e d by 3 . 4 m s p a c i n g
fo r a t r e e h e i g h t
Figure 1 D esigns of forest edges tested in the wind tunnel, w here h represents mean tree height.
1
'A h in front of the treatm ent, above the edge of
the norm al forest and at 5 h back from the edge.
The applied basal bending m om ents due to the
w ind were m easured at the forest edge and at
5 h back from the edge using a m om ent balance
d ev elo p ed by O xfo rd U n iv ersity. B oth m ean
m om ents and extrem e bending m om ents w ere
record ed .
For
th e
u n tr e a te d
ed g es,
m e a su re m e n ts of w in d p ro file and b e n d in g
m o m en t w ere m ad e at m u ch m ore fre q u e n t
intervals back from the forest edge.
G2 were designed to m ake a gradual transition
from o p en g ro u n d to fo re s t by a lte r in g the
s p a tia l a r r a n g e m e n t o f tre e s . T a p e rin g in
tr e a tm e n ts 1'A an d T1 w a s a c h ie v e d b y
sh o rten in g the stan d ard 20 cm length m od el
trees, which were then deployed in two bands,
one w ith a w idth equ ivalen t to h alf the forest
height (A h) and one with a w idth equivalent to
a fu ll f o r e s t h e ig h t (1 h ). T h e ta p e r in g in
tre a tm e n t S, to re p re se n t d en se sh ru b s, w as
ach iev ed by p lacin g a 1 h w ide and Y h high
layer of horsehair in front of the m odel forest.
T h e fir s t g ra d u a te d d e n s ity e d g e ( G l ) w as
co n stru cted by p la cin g a 1 h w ide m argin of
trees at a planting density of 1 in 9 (com pared
w ith a norm al forest) ahead of the m ain forest
b lock , w h ereas the second g rad u ated d en sity
ed ge (G 2) used a 1 h w id e strip o f trees at a
density of 1 in 9 follow ed by a 1 h wide strip of
tre e s a t a p la n tin g d e n s ity o f 1 in 4. A t a
stan d ard sp acin g of 1.7 m b etw een trees this
rep resen ts a tree sp a cin g of 5.2 m and 3.5 m
respectively. A d d itional tests w ere carried out
on m odel forests w ith untreated edges but with
spacings equivalent to 3.5 m (U2) and 5.2 m (U3)
for com parison w ith the graduated density edge
treatments.
T h e ap p lied b en d in g m o m en t rep resen ts the
torque (force x distance) at the base of the tree
created by w ind pressu re on the canopy. The
m ean applied bending m om ent is a m easure of
the average w ind load in g to w hich the tree is
su bjected . T he tree ad apts to this m ean w ind
loading by m odifying its grow th behaviour and
stem form (T elew sk i an d Ja ffe , 1986) so th at
m ore exposed trees are shorter and have m ore
ta p e r e d a n d s tr o n g e r s te m s . T h e e x tre m e
applied b en d in g m om en t is the w ind loadin g
that the tree has to resist in order not to overturn
or b re a k . If th e ro o ts an d so il are u n a b le to
m atch the extrem e applied bending m om ent the
tree w ill be uprooted and, if the stress created in
the outer fibres of the stem is greater than the
m odulus of rupture for the w ood, the stem will
break (Gardiner and Q uine, 1994).
Measurements
Figure 2 illustrates the m easurem ent positions
used in the experim en ts on the treated edges.
(F orest ed g e alw ays refers to the ed ge o f the
untreated part of the forest, not the edge of the
treatm ent. The treatm ent edge is, therefore, in
fro n t o f the f o r e s t e d g e .) W in d p r o f ile
m easurem ents w ere m ade at three points using
a hot-wire anem om eter. The points w ere located
Location :
a : Open
ground
Measurement:
a : Wind
profiles
b : Treatment
In these exp erim en ts, u nlike a real forest, the
sh ape and h eig h t o f the m od el trees w as not
a fu n c tio n o f th e ir d is ta n c e fro m th e e d g e .
T h is m e a n s th a t th e h e ig h t s o f th e m o d e l
trees clo se to an ed g e w ill b e slig h tly ta lle r
than they should be and the applied ben din g
m om ent w ill be overestim ated. M easurem ents
c : Untreated edge
d : M id -fo re s t
c : Bending moment
d : Bending moment
and wind profiles
and wind profiles
edge
b : No
measurements
Figure 2 Types and positions of m easurem ents in relation to the treated forest edge.
2
of tree heights b ack from a very exposed forest
e d g e in N o r th u m b e r la n d s u g g e s t th a t th e
o v e r e s tim a te w ill in th e w o rs t c a se b e le ss
than 20%.
moment at the edge of treatment U1 in order to
allow easy comparison with the wind loading on
trees at the untreated edge of a norm al spruce
plantation. Figures 3a and 3b show the change in
the mean and extreme bending mom ents over a
distance of five tree heights (5 h) back from the
edges of the three model forests with untreated
edges but different tree spacings (U1,U2 and U3).
T h e v a lu e s o f m ea n an d e x tre m e b e n d in g
m om ents w ere sim ilar at the edge of all three
treatments but back from the edge the reduction
was largest and most rapid in the closely spaced
treatm en t (U l). By a d istan ce o f 1 h from the
Results
U ntreated edges w ith different tree
spacings
All bending m om ents are normalised by dividing
th e m b y th e v a lu e o f th e e x tre m e b e n d in g
D is ta n c e fro m fo re s t e d g e (h )
Figure 3a N orm alised m ean bending m om ents at different distances (in tree heights) back from the
untreated edge of forests w ith different planting densities (U l = 1.7 m spacing, U2 = 3.5 m spacing
and U 3 = 5.2 m spacing). A ll ben din g m om ents are norm alised b y dividing them by the extrem e
b e n d in g m o m en t at th e u n trea ted ed g e of a fo re st w ith sta n d a rd sp a cin g (U l) to allo w easy
com parison betw een treatm ents.
Figure 3b As for Figure 3a but for norm alised extrem e bending m om ents. N ote change in y axis scale.
3
edge, the extreme bending m oments in treatment
U l reached a constant value, whereas this took a
distance of 2 h and 3 h in treatments U2 and U3
respectively.
rap id ly for the clo sest sp acin g to give v alu es
w ell w ithin the forest (8 h) of 8.6, 6.2 and 5.0 for
treatm ents U l, U 2, and U3 respectively. If the
extrem e b en d in g m om en t is g reater than the
m a x im u m r e s is t iv e m o m e n t th e tre e c a n
p ro vid e, the tree w ill be dam aged . H ow ever,
th e m a x im u m r e s is t iv e m o m e n t w ill b e
determ ined by the adaptive grow th of the tree
in re s p o n se to th e m ea n b e n d in g m o m e n t.
Therefore, if the trees are not restricted in their
a b ilit y to a d a p t to t h e ir lo c a l w in d
e n v iro n m e n t, th e r a tio o f e x tre m e to m ean
bending m om ent w ill be a m easure of the trees'
v u ln e ra b ility to d am ag e. T h is su g g e sts th at
trees at the edge are less vulnerable to dam age
th a n th o s e fu r th e r in to th e fo r e s t an d th is
d if fe r e n c e w ill b e m o s t m a r k e d a t h ig h e r
planting densities.
A t th e fo r e s t e d g e the r a t io b e tw e e n th e
e x tr e m e an d m e a n b e n d in g m o m e n ts (se e
Table 1) was higher for the m ore open spacings
(U 2, U 3). From Figures 3a and 3b we can see
th a t the m ean b e n d in g m o m e n ts w ere v ery
sim ilar betw een the treatm ents but the extrem e
b e n d in g m o m en ts w ere h ig h e r at the w id er
spacings. This illustrates that, even at the forest
edge, trees at the d ensest spacing (U l) derive
s o m e m e a s u r e o f s u p p o r t fro m t h e ir
n e ig h b o u r s . B a c k fro m th e e d g e th e r a tio
b etw een extrem e and m ean b en d in g m om en t
in c r e a s e d fo r a ll s p a c in g s b u t d id so m o st
Table 1 Ratio of extrem e to m ean bending m om ents as a function of distance from the forest edge
Treatment
Oh
lh
2/i
3h
4h
5h
6h
7h
8h
U3
U2
Ul
3.0
2.9
2.2
3.0
3.4
2.3
3.1
4.0
2.6
3.3
4.5
3.1
3.5
4.9
3.8
3.8
5.3
4.7
4.1
5.6
5.8
4.4
5.9
7.1
5.0
6.2
8.6
d ifferen t edge treatm en ts. A ll the treatm en ts
except for the shrub layer (S) reduced both the
extrem e and m ean m om ents at the edge. Wind
profile m easurem ents above the forest showed a
speeding up of the airflow over the edge as the
Treated edges
In F ig u res 4a and 4b the m ea n and ex trem e
bending m om ents for the edge tree and a tree
5 h b ack from the ed g e are d isp layed for the
0 . 5-1
-
0 .4 -
cm
A
0.3-
©
XI
■o
©
O
z
0.2 -
0 . 1-
i
D ista nc e from lo re s l ed ge (h)
Figure 4a N orm alised m ean bending m om ents at the forest edge and 5 tree heights back from the
edge for different edge treatm ents. As in Figures 3a and 3b, all bending m om ents are norm alised by
dividing through by the extrem e bending m om ent at the untreated edge of a forest w ith standard
spacing (U l). See Figure 1 for explanation of symbols.
4
1 .2 - i
Edge treatm ent
1.0
o U1
O T 2
-
a T1
A
0 .8 -
S
• G1
I
O
• G2
0.6
E
£
9
Sw
E
o
0.4
15
0
I
0.2 -
Distance from forest edge (h)
Figure 4b As for Figure 4a but for norm alised extrem e bending m om ents. N ote change in y axis scale.
M e a n h o r iz o n ta l w in d s p e e d (m s - 1 )
D is ta n c e fro m f o r e s t e d g e (h )
Figure 5 Contours of m ean w ind speed across an untreated forest edge (U l). N ote the increase in
w ind speed ju st above the edge trees.
2 h wide. There w as no difference betw een the
redu ctions due to the tw o tapered treatm ents
(TV2 an d T l ) an d th e 1 h w id e g ra d u a te d
treatm en t (G l). By a distan ce of 5 h from the
e d g e th e d iffe r e n c e s in b e n d in g m o m e n t
b e tw e e n th e d if fe r e n t tr e a tm e n ts h a d
d isap p eared , illu stra tin g th at the treatm en ts
air is sq u eez ed b y the p re sen ce o f the fo re st
(Figure 5). This increases the w ind loading on
the edge trees and the effect was enhanced when
a shrub layer w as placed in front of the edge.
T h e la r g e s t r e d u c tio n in b e n d in g m o m e n t
occurred for graduated treatm ent G2 w hich is
5
The graduated density edges (G1 and G2) m ove
the edge aw ay from the u ntreated p art of the
forest and provide a buffer of trees. Any dam age
in this buffer strip will have less im pact on the
rest of the forest than dam age at the edge of a
d en se fo rest w h ere in d iv id u al trees are m ore
depend ent on their neighbours for support. A
graduated density edge of w idely spaced trees
would have to be created early in the life of that
part of the forest so that the trees can grow and
a d a p t to th e ir e x p o se d p o s itio n . C re a tin g a
g ra d u a te d d e n s ity ed g e b y re s p a c in g in an
existing exposed m ature forest, w hich w as close
to or b ey on d critica l h eig h t, w ou ld n o t w ork
because the respaced trees w ould be unadapted
to the increased w ind loading and w ould very
q u ic k ly b lo w d o w n o r b r e a k (Q u in e an d
Gardiner, 1992).
h a v e o n ly a lo c a l e ffe c t. T h e r e s u lts o f th e
different edge treatments are in good agreem ent
w ith the findings of Fraser (1964).
Discussion
An untreated forest edge is extrem ely abrupt
and acts like a solid body w ith the edge trees
subjected to severe w ind loading. The edge also
forces the approaching airflow upwards and at
som e poin t dow nstream w here the air returns
towards the ground there is a zone of increased
ris k w h e re d a m a g e a p p e a rs to b e in itia te d
during catastroph ic storm s (Som erville, 1989).
The trees back from the edge m ay also be more
at risk b eca u se the ra tio o f ex trem e to m ean
bending m om ent is higher inside the forest than
at the edge (Table 1).
Treatments to existing edges have been tested in
th e fie ld b y to p p in g (c f. ta p e r in g ) o r h ig h
pruning (cf. graduated density) trees. M attheson
(1 9 9 2 ) c a r r ie d o u t fie ld tr ia ls at 14 s ite s in
Ju tlan d , D enm ark using m id d le-aged and old
N o rw a y sp ru ce sta n d s (a p p ro x im a te ly 1000
stem s per ha) in w hich the canopy occupied on
average the top 54% of the stem. Three adjacent
treatm ents w ere involved: a control, strips 1 h
w ide in w hich the top 25% of the tree was cut off
and strips 1 h w ide in which the lower half of the
c a n o p y w as re m o v e d . T h e tre a tm e n ts w ere
ap p lied in 1988/ 89 and sev ere sto rm s in the
w in te r s o f 1 9 9 0 / 9 1 a n d 1 9 9 1 / 9 2 c a u s e d a
considerable am ount of damage. A lm ost all the
dam age was due to overturning and the dam age
w as virtually confined to the untreated control
plots. In the control plots 20% of the trees were
blow n down compared w ith less than 3% in the
plots w ith pruned and topped edges. However,
th ere w as a ten d en cy fo r the top p ed trees to
su ffer slig h tly m ore from d e sicca tio n d u rin g
sum m er drought than the other treatments.
Any treatm ent that reduces the abrupt nature of
the forest edge is likely to be beneficial. Tapered
edges cause the airflow to be directed upwards
in a m ore gentle fashion than an untreated edge
so that the w ind lo ad in g on the ed ge trees is
reduced and the im pact of the dow nw ard return
flow is less severe. G ra d u a ted d en sity ed ges
p resen t a m ore grad u al tra n sitio n from open
g ro u n d to fo r e s t. B y a llo w in g a ir to f ilte r
through the edge they reduce the strength of the
w ind sp eed -u p ab ov e the ed ge trees and the
d o w n w a rd r e tu rn flo w fu r th e r b a c k in th e
forest.
N o d ifference w as ob serv ed b etw een the two
tap er treatm en ts (T'A and T l ) , w h ich su ggests
th a t e v e n a n a rro w s tr ip a ro u n d th e fo re s t
ed ge can be effectiv e in red u cin g the risk of
w in d d a m a g e . H o w e v e r , a s n o t a p e r
treatm en ts n a rrow er than trea tm en t T'A w ere
tested in the w ind tu n n el it is recom m end ed
that tapered edges are designed to be at least A
h w ide by the tim e the fo rest reach es critical
h e ig h t (M iller, 1985). T h e ta p e rin g co u ld be
a ch iev ed b y e ith e r p la n tin g slo w er g ro w in g
s p e c ie s at th e tim e o f th e m a in p la n tin g or
p la n tin g in d iv id u al row s of the sam e sp ecies
in su b seq u e n t y ears. C are n eed s to b e taken
that the effect is n ot to p rod uce a step change
in h eig h t sim ilar to the shrub layer treatm ent
(S), w h ich w ill in crease the w ind lo ad in g on
the ed ge trees. H ow ever, shrubs and trees used
in c o m b in a tio n to p r o d u c e a ta p e re d e d g e
w o u ld b e b e n e f ic ia l fo r b o th s t a b ilit y an d
w ildlife.
The results of the w ind tunnel and field trials
are e n c o u r a g in g b e c a u s e th e y s u g g e s t th a t
fo r e s t s c a n h a v e t h e ir lik e lih o o d o f w in d
d a m a g e re d u c e d th r o u g h s ilv ic u lt u r a l
in t e r v e n t io n . In m a tu re fo r e s ts n ew e d g e s
c r e a te d b y n e a r b y c le a r f e llin g o r ro a d
construction can be im proved by high pruning
or top p in g. T h is cou ld b e v alu ab le for sh o rt­
term p ro tectio n in forest restru ctu rin g . W hen
establishing or restructuring forests, long-term
p r o te c t io n o f e d g e s m a y b e a c h ie v e d b y
planning tapered or graduated density edges.
6
Recommendations
10. A n y a ctio n th at c re a te s e d g e s sh o u ld be
designed to take place as early in the life of
the crop as p ossib le and the w idth of any
gaps created should be kept to a minimum.
Any abrupt edge to a forest is not only visually
u n a p p e a lin g b u t is o f le ss v a lu e to w ild life
(Ferris-Kaan, 1991) and enhances the possibility
of w ind d am age. M an ag em en t p ractices that
m od erate the tran sitio n from open ground to
forest and vice versa w ill have visual, w ildlife,
and stability benefits.
1.
2.
T ra n s itio n s c a n b e m o d e ra te d b y e ith e r
tapering or graduating the planting density
at the edge.
12. S e v e r a n c e c u ts c a n b e c o m b in e d w ith
respacing to create a graduated density edge.
Tapering can be achieved by planting slower
grow ing species around the forest edge or
by p la n tin g the sam e sp e cies arou n d the
edge of a new plantation at a later stage.
3.
The tapered edge should be designed to be
at le a st h a lf a tree h eig h t w id e w h en the
m ain crop reaches critical height. Care m ust
b e ta k en to crea te a sm o o th tra n sitio n in
height rather than a step change.
4.
Tapered edges can be created late in the life
of the crop by topping edge trees b u t this
w ill b e c o s tly a n d , a t b e s t, a sh o rt-te rm
m easure due to the subsequent m ortality of
the topped trees.
5.
11. Severance cuts can be used to create a windfirm e d g e b y e x p o s in g y o u n g tre e s to
increased w ind loading so that they adapt
th e ir g r o w th in s u b s e q u e n t y e a r s . T h e
s e v e r a n c e c u t sh o u ld b e as w id e as the
h e ig h t th e tr e e s w ill b e w h e n th e y are
expected to form a new edge.
Forest edges should be regarded as an integral
part of the forest design from inception rather
than as a m odification late in the crop rotation.
New edges or edges being considered for long­
te rm r e te n tio n s h o u ld h a v e a n y p o te n tia l
treatm ents set alongside other factors affecting
s t a b ility su c h as e d g e s h a p e , s o il ty p e ,
c u lt iv a tio n tr e a tm e n t, s lo p e a s p e c t, lo c a l
topography, and d irection of p rev ailin g w ind
(Q u in e an d M ille r, 1 9 9 0 ). F u r th e r id e a s on
incorporating forest stability into the long-term
d e s ig n o f fo r e s ts a re g iv e n in Q u in e an d
Gardiner (1992) and Q uine et al. (1995).
Acknowledgements
Graduated density edges can be achieved by
planting or respacing the edge trees to wider
spacings. Respacing needs to be done early
in th e life o f the crop b e c a u s e re sp a cin g
m a tu re trees is a lm o st c e rta in to le ad to
damage.
T h a n k s a re d u e to th e W in d E n g in e e r in g
Research Group at Oxford U niversity where the
w ind tunnel m easurem ents were made.
References
6.
A graduated density edge of one tree height
in w idth is su fficie n t.
FER R IS-K A A N , R. (1991). Edge m anagem ent in
w oo d lan d s. O cca sio n a l P ap er 28. F o restry
C om m ission, Edinburgh.
7.
H igh pruning of m ature edge trees can have
a s im ila r e f f e c t to g r a d u a te d e d g e s b y
im p ro v in g th e p o r o s ity o f th e e d g e and
producing a m ore gradual transition.
F O R E S T R Y C O M M IS S IO N
(1 9 9 4 ). F o r e s t
la n d s c a p e d esig n g u id e lin e s . 2n d e d itio n .
H M SO , London.
8.
Edges could com bine graduated density and
ta p e r in g so th a t tre e s iz e a n d p la n tin g
density increase into the forest. This would
m ore clo sely sim u late som e n atu ral forest
edges.
9.
FR A SE R , A. I. (1964). W ind tu n n el and oth er
related studies on coniferous trees and tree
crops. Scottish Forestry, 18, 84-92.
G A R D IN ER, B. A., STACEY, G. R., BELCH ER,
R. E. and W O OD, C. J. (in press). Field and
wind tunnel assessm ents of the im plications
of respacing and thinning for tree stability.
Forestry.
N ew e d g e s c r e a te d b y th in n in g , c le a r
cutting or road building are m ore vulnerable
than any other part of a forest.
7
design plans. Research Inform ation N ote 220.
Forestry Com m ission, Edinburgh.
G A R D IN E R , B. A. an d Q U IN E , C. P. (1994).
W ind d am age to forests. B iom im etics, 2(2),
139-147.
Q U IN E, C. P., C O U TTS, M. P., G A R D IN ER, B.
A. and PYATT, D. G. (1995). Forests and wind:
m a n a g em en t to m in im ise d am ag e. F o re stry
C om m ission Bulletin 114. H M SO , London.
M A TTH ESO N , P. (1992). S tabilisin g effect from
p ru n in g an d toppin g in n ew ly exposed edges
of
o ld
and
m id d le - a g e d
N o rw a y
s p r u c e . V id e n b la d e S k o v b r u g 5 .5 -1 .
F o rs k n in g sc e n tre t fo r Sk ov & L a n d sk a b ,
Skovbrynet 16, D K 2800 Lyngby, D enm ark
(in Danish).
S O M E R V IL L E , A. (1989). Tree w ind sta b ility
an d fo re st m a n a g e m e n t p ra c tic e s . In: A.
S O M E R V IL L E ,
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W A K E L IN
an d
L. W H IT E H O U SE , eds. W orkshop on w ind
d am ag e in N ew Z ea lan d ex o tic fo r e s ts . FRI
B u lle tin 1 4 6 . F o r e s t R e s e a r c h I n s tit u t e ,
Rotorua, N ew Zealand, pp. 38-58.
M IL L E R , K . F. (1 9 8 5 ). W in d th ro w h a z a r d
classification . Forestry C om m ission L eaflet
85. H M SO , London.
STACEY, G. R., BELCH ER, R. E., W O O D , C. J.
and G A R D IN E R , B. A. (1 9 9 4 ). W ind and
w in d fo r c e s in a m o d e l s p r u c e fo r e s t.
Boundary-Layer M eteorology, 69, 311-334.
Q U IN E , C . P. an d M IL L E R , K . F. (1 9 9 0 ).
W indthrow - a factor influencing the choice
of silvicultural system . In: P. G O RD O N , ed.
Silvicu ltu ral system s. Institu te of C hartered
Foresters, Edinburgh, pp. 71-80.
T E L E W S K I, F. W. an d JA F F E , M . J. (1 9 8 6 ).
Thigm om orphogenesis: field and laboratory
studies of Abies fraseri in response to w ind or
m e c h a n ic a l p e r tu r b a t io n . P h y s io lo g ia
Plantarum, 66,211-218.
Q U IN E , C. P. and G A R D IN E R , B. A. (1992).
Incorporating the threat o f w indthrow into forest
8
Other windthrow titles available
from the Forestry Commission
Bulletin 114
Forests and wind: m anagem ent to minimise
damage.
HMSO, 1995, £7.
Occasional Paper 24
M echanical characteristics of Sitka spruce.
Forestry Commission, 1989, £1.50.
Occasional Paper 25
A new series of windthrow monitoring areas
in upland Britain.
Forestry Commission, 1990, £1.50.
Besearch Information Notes (free)
169 Planting at stump - preliminary evidence of its effect on root
architecture and tree stability.
220 Incorporating the threat of windthrow into forest design plans.
250 Revised windiness scores for the windthrow hazard classification;
the revised scoring method.
231 The effects of revised windiness scores on the calculation and
distribution of windthrow hazard classes.
257 An improved understanding of windthrow - moving from hazard
towards risk.
£5
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