DWARF MISTLETOE CONTROLS I N BRITISH COLUMBIA-I 1
G.A. Van S i c k l e and R.B. Smith-2 1
A b s t r a c t : The d i s t r i b u t i o n and impact a r e b r i e f l y
reviewed f o r t h e f o u r s p e c i e s of dwarf m i s t l e t o e i n B r i t i s h
Columbia, which mainly a f f e c t w e s t e r n hemlock, l o d g e p o l e p i n e ,
D o u g l a s - f i r and w e s t e r n l a r c h . C o n t r o l measures employed o r
t e s t e d by f o r e s t e r s i n r e c e n t y e a r s , i n c l u d i n g a e r i a l and
ground s u r v e y s , s t a n d t h i n n i n g , r e s i d u a l removals, t r e a t m e n t
of advance r e g e n e r a t i o n , f r i n g e p l a n t i n g , s c a r i f i c a t i o n and
s e l e c t i o n c u t t i n g a r e d e s c r i b e d and d i s c u s s e d .
INTRODUCTION
B r i t i s h Columbia's f o r e s t a r e a o f 52.7
m i l l i o n h e c t a r e s is 1%t i m e s t h e s i z e of t h e
s t a t e of C a l i f o r n i a . Although managed under
v a r i o u s l a n d t e n u r e s , 95 p e r c e n t of t h i s
f o r e s t i s owned by t h e P r o v i n c e and f o r e s t r y
is t h e foremost i n d u s t r y , c o n t r i b u t i n g 50 c e n t s
o f e v e r y d o l l a r of economic a c t i v i t y i n t h e
P r o v i n c e . The f o u r s p e c i e s of dwarf m i s t l e t o e
i n B r i t i s h Columbia a r e mainly on w e s t e r n heml o c k , l o d g e p o l e p i n e , D o u g l a s - f i r and w e s t e r n
l a r c h (Baranyay and Smith 1972). These t r e e
s p e c i e s rank second, t h i r d and f o u r t h i n
a n n u a l volumes h a r v e s t e d , and although l a r c h
i s a minor s p e c i e s p r o v i n c i a l l y , i t i s s i g n i f i c a n t regionally, particularly i n the
southeastern c o m e r of t h e Province.
I n B . C . , dwarf m i s t l e t o e s o c c u r o v e r a
g r e a t v a r i e t y of v e g e t a t i o n a l zones which
a r e i n f l u e n c e d by a range i n annual p r e c i p i t a t i o n from a s l i t t l e a s 30 cm up t o 665 cm,
by e l e v a t i o n s from s e a l e v e l t o 1600 m , and
by f o r e s t management systems r a n g i n g from a
s e l e c t i v e b a s i s t o c l e a r c u t t i n g . Some
comments on t h e d i s t r i b u t i o n , major h o s t s ,
impact, s u r v e y s and c o n t r o l e f f o r t s f o r
dwarf m i s t l e t o e s i n B.C. f o l l o w .
I'
Paper p r e s e n t e d a t "A Symposium: Dwarf
M i s t l e t o e C o n t r o l Through F o r e s t Management",
B e r k e l e y , C a l i f o r n i a , A p r i l 11-13, 1978.
'
Research S c i e n t i s t s , Canadian F o r e s t r y
S e r v i c e , P a c i f i c F o r e s t Research C e n t r e , 506
W e s t B u r n s i d e Road, V i c t o r i a , B r i t i s h Columbia.
V8Z 1M5. The w i l l i n g c o o p e r a t i o n of numerous
i n d u s t r i a l and B.C. F o r e s t S e r v i c e p e r s o n n e l
i n providing d e t a i l s of s p e c i f i c f i e l d t r i a l s
was a p p r e c i a t e d .
DISTRIBUTION, HOSTS AND IMPACT
Arceuthob*
t s u g e n s e (Rosendahl) G.N.
Jones
Two r a c e s of t h i s s p e c i e s o c c u r i n B r i t i s h
Columbia, one p r i m a r i l y on w e s t e r n hemlock
(Tsuga h e t e r o p h y l l a (Raf.) S a r g . ) , t h e o t h e r
p r i m a r i l y on s h o r e p i n e ( P i n u s c o n t o r t a Dougl.
e x Loud.). Both r a c e s a r e r e s t r i c t e d t o t h e
f o r e s t s west of t h e Coast Mountains.
Hemlock dwarf m i s t l e t o e o c c u r s throughout
c o a s t a l w e s t e r n hemlock f o r e s t s from s e a l e v e l
t o 1460 m. The most e a s t e r n e x t e n s i o n s o c c u r
i n major r i v e r v a l l e y s up t o 180 tan from s a l t w a t e r . The p r i n c i p a l h o s t , w e s t e r n hemlock,
i s a climax t r e e s p e c i e s and one of t h e major
s p e c i e s i n t h e C o a s t a l Western Hemlock Biog e o c l i m a t i c Zone ( K r a j i n a 1969). S t a n d s w i t h
w e s t e r n hemlock dominating cover about 4
m i l l i o n h a , of which 15% a r e e s t i m a t e d t o b e
i n f e c t e d w i t h dwarf m i s t l e t o e . C u r r e n t l o s s e s
i n s t a n d v o l me growth i n a 110-year-old s t a n d
were 4 - 5 m / h a / y r (Smith 1969). Extending
t h e s e f i g u r e s , annual growth l o s s e s i n B r i t i s h
Columbia a r e about 1.7 m i l l i o n m3. Other
damage i n c l u d e s b o l e s w e l l i n g s 112 p e r c e n t of
t h e merchantable volume of s e v e r e l y i n f e c t e d
t r e e s i n one 110-year-old s t a n d (Hunt 1971)],
up t o 30 p e r c e n t l a r g e r knot s i z e and i n c r e a s e d
b o l e t a p e r (Smith 1969).
5
Within t h e C o a s t a l Western Hemlock Zone,
w e s t e r n hemlock i s b o t h a climax s p e c i e s and
an i m p o r t a n t c o n s t i t u e n t of r e g e n e r a t i o n a f t e r
l o g g i n g and o t h e r d i s t u r b a n c e s . It a l s o s u r v i v e s w e l l a s a n u n d e r s t o r y t r e e , and s m a l l
r e s i d u a l s and advanced r e g e n e r a t i o n of t e n
remain a f t e r l o g g i n g .
Hemlock dwarf m i s t l e t o e a l s o o c c u r s i n
t h e C o a s t a l D o u g l a s - f i r Zone b u t , i n t h i s
d r i e r zone, i t i s r e s t r i c t e d t o t h e e d a p h i c a l l y
w e t t e r s i t e s s u i t e d t o hemlock. C l e a r c u t t i n g
i n t h i s zone w i l l reduce d i s e a s e i n c i d e n c e
b e c a u s e of t h e c o n s i d e r a b l e r e g e n e r a t i o n o f
resistant species.
I n B.C., o n l y one r e c o r d e x i s t s of heml o c k dwarf m i s t l e t o e on mountain hemlock
(Tsupa m e r t e n s i a n a (Bong.) C a r r .) , a s t r o n g
c o n t r a s t t o n o r t h e r n C a l i f o r n i a where mountain
hemlock i s t h e p r i n c i p a l h o s t .
Shore p i n e dwarf m i s t l e t o e s e v e r e l y dama g e s some s h o r e p i n e s t a n d s i n s o u t h c o a s t a l
B .C., p a r t i c u l a r l y i n t h e C o a s t a l D o u g l a s - f i r
Zone up t o 725 m e l e v a t i o n . Shore p i n e is
h i g h l y shade i n t o l e r a n t and forms n e a r l y p u r e
s t a n d s o n l y where w a t e r d e f i c i t s o r e x c e s s e s
l i m i t e s t a b l i s h m e n t of competing t r e e s p e c i e s .
With t h e r e l a t i v e l y low commercial v a l u e
of s h o r e p i n e , growth impact s t u d i e s have n o t
been done. However, t h e i n t e n s i f i c a t i o n of
m i s t l e t o e on s h o r e p i n e is more r a p i d t h a n
on hemlock and e q u a l s t h a t r e p o r t e d f o r lodgep o l e p i n e m i s t l e t o e (Wass 1976).
3
an a v e r a g e e s t i m a t e d growth l o s s of 1 . 4 m / h a / y r
t o t h e infected acreage, the annual l o s s i n
B . C . is about 2.5 m i l l i o n m3.
Arceuthobium l a r i c i s ( P i p e r ) S t . John
The p r i n c i p a l h o s t , w e s t e r n l a r c h ( L a r i x
o c c i d e n t a l i s Mutt.), i s a p a r t i c u l a r l y shade intolerant species restricted t o southeastern
B r i t i s h Columbia. Larch m i s t l e t o e o c c u r s
throughout most of t h e h o s t range a t e l e v a t i o n s
from 300 t o 1460 m.
It i s p r e s e n t mainly i n
t h e I n t e r i o r Western Hemlock Dry Subzone and
t h e I n t e r i o r D o u g l a s - f i r Wet Subzone.
Although t h e a r e a a f f e c t e d i s much l e s s
t h a n t h a t i n f e c t e d by hemlock and l o d g e p o l e
p i n e m i s t l e t o e s , impacts a r e l o c a l l y v e r y
i m p o r t a n t . I n c r e a s e d m o r t a l i t y and d r a s t i c
e f f e c t s on m e r c h a n t a b l e y i e l d s found elsewhere [less t h a n 20 p e r c e n t of p o t e n t i a l (On
and Dooling l969)] could b e e x p e c t e d i n
B r i t i s h Columbia.
Arceuthob ium d o u g l a s i i Engelm.
Arceuthobium americanum N u t t . e x Engelm.
Lodgepole p i n e dwarf m i s t l e t o e i s t h e
w i d e s t r a n g i n g m i s t l e t o e i n B .C., i n f e c t i n g
roughly 1.8 m i l l i o n h a . It is r e s t r i c t e d
l a r g e l y t o a r e a s e a s t of t h e Coast Mountains
and s o u t h of L a t i t u d e 57ON, w i t h a few extens i o n s westward a l o n g major r i v e r v a l l e y s . The
e l e v a t i o n a l r a n g e i s 150 - 1600 m.
The most e x t e n s i v e i n f e s t a t i o n s o c c u r i n
t h e Aspen-Lodgepole pine-Douglas-fir Biogeoc l i m a t i c Zone i n t h e s o u t h - c e n t r a l I n t e r i o r .
Here, l o d g e p o l e p i n e m a i n t a i n s a near-climax
r o l e a s a r e s u l t of t h e c o l d , d r y c l i m a t e and
a h i g h frequency of f i r e .
Lodgepole p i n e dwarf m i s t l e t o e a l s o o c c u r s
i n t h e Sub-boreal Spruce, Engelmann SpruceS u b a l p i n e F i r and I n t e r i o r D o u g l a s - f i r Zones,
where l o d g e p o l e p i n e i s e s s e n t i a l l y a p i o n e e r
s p e c i e s . A l a c k of e x t e n s i v e i n f e s t a t i o n i n
t h e I n t e r i o r Western Hemlock Zone r e f l e c t s
t h e low frequency of f i r e s and a h i g h l y v a r i e d
composition of r e s i s t a n t r e g e n e r a t i o n s p e c i e s .
Growth impact d a t a a r e a v a i l a b l e from
s e v e r a l s t u d i e s . From s i n g l e - t r e e comparisons,
e s t i m a t e d s t a n d volumes i n A l b e r t a were reduced
18 t o 32 p e r c e n t by m i s t l e t o e i n f e c t i o n
(Baranyay and S a f r a n y i k 1970). D a t a of Dobie
and B r i t n e f f (1975) i n d i c a t e a 30 p e r c e n t
lower growth r a t e i n i n f e c t e d t h a n i n h e a l t h y
t r e e s . S i m i l a r growth l o s s e s were found i n
s u r v e y s of t h e Cariboo D i s t r i c t , which w i l l
l a t e r b e d i s c u s s e d i n more d e t a i l . Applying
D o u g l a s - f i r dwarf m i s t l e t o e h a s t h e
s m a l l e s t range of t h e B.C. m i s t l e t o e s .
It is
c o n f i n e d t o t h e extreme s o u t h e r n i n t e r i o r ,
p r i m a r i l y i n t h e Okanagan V a l l e y and a l o n g
t h e s o u t h end of Kootenay Lake. It o c c u r s
almost e x c l u s i v e l y on D o u g l a s - f i r a t e l e v a t i o n s from 300 t o 1350 m i n t h e w e t t e r p o r t i o n
of t h e Ponderosa P i n e Zone and in t h e I n t e r i o r
Douglas-f i r Zone.
Damage i s s e v e r e i n i n d i v i d u a l t r e e s and
s t a n d s . Top k i l l i n g i s common. Reductions
i n merchantable volumes o f 73 p e r c e n t have
been r e p o r t e d f o r w e s t e r n Montana (Haglund
and Dooling 1972) and s i m i l a r l o s s e s might
b e expected i n B.C.
T o t a l growth impact is
s m a l l compared t o hemlock and l o d g e p o l e p i n e
m i s t l e t o e s , b u t f o r e s t management i n t h e s e
zones i s o f t e n on a s e l e c t i v e - c u t b a s i s ,
making c o n t r o l of D o u g l a s - f i r m i s t l e t o e a
g r e a t e r problem.
MISTLETOE SURVEYS
Dwarf m i s t l e t o e s have been c o l l e c t e d i n
B.C. s i n c e 1901, w i t h more t h a n 1500 r e c o r d s
now p r e s e n t i n t h e Canadian F o r e s t r y S e r v i c e ' s
F o r e s t I n s e c t and D i s e a s e Survey Herbarium in
V i c t o r i a . A p r i s m p l o t s u r v e y i n 1969 in 121
a r e a s of known m i s t l e t o e i n d i c a t e d t h e s e v e r i t y
of i n f e c t i o n i n 80- t o 200-year-old s t a n d s
and provided f o r each s p e c i e s a g r a p h i c a l
r e l a t i o n s h i p between t h e p r o p o r t i o n o f h o s t
t r e e s i n f e c t e d and t h e s e v e r i t y o f i n f e c t i o n
( i .e., i n c i d e n c e v s . i n t e n s i t y ) .
The p r e s e n c e of dwarf m i s t l e t o e i s one of
t h e n i n e i n d i c a t o r s used by t h e B.C. F o r e s t
Service Inventory Division t o i n d i c a t e a susp e c t t r e e i n which some c u l l (non-merchantable
p o r t i o n owing t o d e f e c t ) may b e e x p e c t e d . Each
y e a r s e v e r a l thousand i n v e n t o r y p l o t s a r e
e s t a b l i s h e d o r r e v i s i t e d ; however, a s s t a f f i s
l a r g e l y s e a s o n a l , and only s t e m s w e l l i n g s a r e
i n c l u d e d , t h e r e s u l t s a r e of l i m i t e d v a l u e .
A r e s u r v e y of 16 a r e a s by t h e F o r e s t I n s e c t
and D i s e a s e Survey i n d i c a t e d a g r e a t d i v e r s i t y
i n t h e completion of p a t h o l o g i c a l remarks and,
on a v e r a g e , a 70 p e r c e n t u n d e r e s t i m a t e of t h e
i n c i d e n c e o f dwarf m i s t l e t o e . An assessment
of growth l o s s o r m o r t a l i t y owing t o m i s t l e t o e is not y e t included i n t h e inventory
system.
Roadside s u r v e y s f o r dwarf m i s t l e t o e have
been employed i n v a r i o u s s t a t e s . I n 1972 and
1973, t h e l a t e J.A. Baranyay i n i t i a t e d a s i m i l a r s u r v e y of l o d g e p o l e p i n e m i s t l e t o e i n
t h e Cariboo F o r e s t D i s t r i c t , an a r e a w i t h
6.9 m i l l i o n h a of f o r e s t land i n B . C . ' s cent r a l I n t e r i o r . T h i s d i s t r i c t was s e l e c t e d
because l o d g e p o l e p i n e comprises almost h a l f
t h e mature volume i n t h e d i s t r i c t and h a s t h e
g r e a t e s t c o n c e n t r a t i o n of l o d g e p o l e p i n e
m i s t l e t o e . B.C. F o r e s t S e r v i c e 1:15840 s c a l e
f o r e s t - t y p e maps were used t o p r e s e l e c t access i b l e a r e a s i n which l o d g e p o l e p i n e was predominant. Of 1118 km t r a v e l l e d through lodgep o l e p i n e s t a n d s , 28 p e r c e n t were judged
h e a l t h y , and 41 p e r c e n t l i g h t l y , 20 p e r c e n t
moderately and 11 p e r c e n t s e v e r e l y i n f e c t e d .
A d d i t i o n a l ground sampling i n v o l v i n g 473 one
twenty f i f t h - h e c t a r e p l o t s i n 24 s t a n d s i n d i c a t e d t h a t t h e r o a d s i d e s u r v e y s may a d e q u a t e l y
c l a s s i f y t h e l e v e l of i n f e c t i o n i n a broad
f o r e s t d i s t r i c t , b u t t h e y were o n l y a c c u r a t e
about h a l f t h e time f o r s p e c i f i c , i n d i v i d u a l
s t a n d s . On a v e r a g e , moderately and s e v e r e l y
i n f e c t e d t r e e s were 2.7 t o 3.7 m s h o r t e r ,
r e s p e c t i v e l y , t h a n h e a l t h y t r e e s of s i m i l a r
d i a m e t e r s , and volumes p e r a c r e were reduced
25 t o 35 p e r c e n t .
D e t e c t i o n of dwarf m i s t l e t o e on a e r i a l
photographs was demonstrated f o r j a c k p i n e i n
A l b e r t a (Muir and Robins 1973), b u t t h e s m a l l e r
o r l e s s f r e q u e n t brooms and t h e lower m o r t a l i t y
and s u b s e q u e n t s t a n d opening i n l o d g e p o l e p i n e
compared t o j a c k p i n e may r e q u i r e m o d i f i c a t i o n
f o r B.C. c o n d i t i o n s . A s t u d y i n l o d g e p o l e
p i n e by Baranyay ( l 9 6 8 ) , l a r g e l y t h w a r t e d b y
t e c h n i c a l and c o n t r a c t d i f f i c u l t i e s , s u g g e s t e d
t h a t o b l i q u e a e r i a l photos were p r e f e r a b l e t o
v e r t i c a l s ; t h a t a t a 1:7920 s c a l e ' , s t a n d s t r u c t u r e anomalies ( o p e n i n g s , s t o c k i n g o r canopy)
on c o l o r photos may i n d i c a t e h i g h d i s e a s e
i n t e n s i t y ; and a t a 1:2400 s c a l e , i n d i v i d u a l ,
h e a v i l y i n f e c t e d t r e e s p r e s e l e c t e d d u r i n g ground
s u r v e y s were d i s t i n g u i s h a b l e .
I n 1975, t h e
B.C. F o r e s t S e r v i c e endeavored t o d e t e r m i n e t h e
d i s t r i b u t i o n and s e v e r i t y of l o d g e p o l e p i n e
dwarf m i s t l e t o e i n a management u n i t , u s i n g
a i r c a l l s , low l e v e l p h o t o g r a ~ h y and ground
s u r v e y s (Hanson 1975). Ground p l o t s employing
t h e s i x - c l a s s m i s t l e t o e r a t i n g s y s t e m were
almost immediately d i s c o u n t e d a s t o o timeconsuming f o r t h e i n f o r m a t i o n o b t a i n e d and
because a c c e s s was o f t e n r e s t r i c t e d .
Subjective
o b s e r v a t i o n a l r e c o r d s i n s t a n d s and a l o n g roads i d e s were a c c e p t e d a s a f i r s t o r d e r e s t i m a t e
of t h e abundance of d i s e a s e . The most promising survey method comes w i t h t h e o b s e r v a t i o n
t h a t an experienced c l a s s i f i e r i n a h e l i c o p t e r ,
and v e r y f a m i l i a r w i t h c o n d i t i o n s on t h e ground,
c o u l d u s u a l l y r e c o g n i z e and c l a s s i f y t h e m i s t l e t o e i n f e c t i o n l e v e l of v a r i o u s t y p e i s l a n d s .
An o b l i q u e view of l a r g e m i s t l e t o e brooms i n
t h e lower crown o r i n t r e e s n e a r s t a n d openi n g s was t h e b a s i s f o r i d e n t i f i c a t i o n and t h e
i n f o r m a t i o n was recorded d i r e c t l y o n t o a e r i a l
photographs, t h e n t r a n s f e r r e d t o f o r e s t - t y p e
maps. Brooming was n o t d i s t i n g u i s h a b l e i n
low l e v e l , v e r t i c a l photography. Typing of
1:15840 s c a l e photography d i r e c t l y f o r m i s t l e t o e i n f e c t i o n was n o t p o s s i b l e , b u t t h e t y p i c a l open, overmature p i n e s t a n d s produced by
numerous l i g h t ground f i r e s a r e v i s i b l e and
h i g h l y s u s p e c t f o r such s t a n d s i n t h e c e n t r a l
I n t e r i o r a r e frequently infected with mistletoe.
SILVICULTURAL TREATMENTS I N YOUNG STANDS
J u v e n i l e s p a c i n g h a s n o t been widely
p r a c t i s e d i n B.C., t o t a l l i n g o n l y s l i g h t l y
more t h a n 1200 h a on crown P u b l i c S u s t a i n e d
Yield U n i t s i n 1976. However, s e v e r a l comp a n i e s on t h e c o a s t a r e now t r e a t i n g up t o
1000 h a p e r y e a r . The P r o v i n c i a l F o r e s t
Service contracts out the majority o f its
spacing, but incorporates s p e c i f i c requirements i f m i s t l e t o e i s recognized a s a problem.
According t o t h e s p e c i e s o f m i s t l e t o e p r e s e n t ,
s u s c e p t i b l e s p e c i e s a r e i d e n t i f i e d and s e l e c t e d
a g a i n s t , a l l medium t o h e a v i l y i n f e c t e d t r e e s
must b e c u t and t h e s p a c i n g requirement i s
waived t o accommodate t h i s r e g u l a t i o n , and i n
some a r e a s a c o r r i d o r around t h e i n f e c t i o n i s
c u t of a l l s u s c e p t i b e t r e e s , r e g a r d l e s s o f
s i z e and c o n d i t i o n . - 3}
To d a t e , s p a c i n g by f o r e s t companies h a s
f o r t u n a t e l y been mainly i n n o n - s u s c e p t i b l e o r
-'
B.C.F.S. R e f o r e s t a t i o n Div. 1976. C o n t r a c t
specifications f o r juvenile spacings.
u n i n f e c t e d s t a n d s ; however, a r e c e n t t r i a l i n
a 9 ha s e v e r e l y i n f e c t e d young s t a n d provided
some i n d i c a t i o n of p o s s i b l e problems i n c o a s t a l
w e s t e r n hemlock s t a n d s . Spacing i n 1976 reduced
t h e s t o c k i n g of t h i s s t a n d from 8350 t o 950
stems p e r h a b u t , changed t h e m i s t l e t o e s i t u a t i o n v e r y l i t t l e . Of t h e s e l e c t e d c r o p t r e e s ,
98 p e r c e n t were i n f e c t e d , w i t h a n a v e r a g e
i n f e c t i o n r a t i n g of 2.1 compared t o 83 p e r c e n t
and 2.5 f o r t h e c u t t r e e s . Based o n a stump
e x a m i n a t i o n , 62 p e r c e n t o f t h e t r e e s were
r e s i d u a l from t h e logged s t a n d , a v e r a g i n g 37
y e a r s compared t o 20 y e a r s f o r t h e r e g e n e r a t i o n .
At t h e t i m e of l o g g i n g , t h e s e advanced regene r a t i o n averaged 2.2 m i n h e i g h t . With a s i g n i f i c a n t d e c r e a s e i n t h e a c r e a g e s now b e i n g
s l a s h burned, m i s t l e t o e w i l l be a n increasingly
i m p o r t a n t problem, n e c e s s i t a t i n g g r e a t e r
emphasis on "clean" l o g g i n g w i t h a minimum of
r e s i d u a l s l e f t , and e a r l i e r s p a c i n g o f i n f e c t e d
stands before a high proportion of the t r e e s
are infected.
Only w i t h t i m e w i l l we know i f s p a c i n g of
t h e above s t a n d w i l l g r e a t l y s t i m u l a t e m i s t l e t o e i n t e n s i f i c a t i o n b e c a u s e o f i n c r e a s e d seed
p r o d u c t i o n and d i s p e r s a l e f f i c i e n c y , o r i f h o s t
h e i g h t growth w i l l s u f f i c i e n t l y exceed t h e
upward s p r e a d o f t h e d i s e a s e t o c o n f i n e t h e
m i s t l e t o e t o t h e lower crown l e v e l . I n 1976,
on a v e r a g e , i n f e c t i o n s were c o n t a i n e d w i t h i n
t h e lower 42 p e r c e n t o f t h e l i v e crown l e n g t h
b u t , 1 y e a r a f t e r t r e a t m e n t , 80 p e r c e n t o f
t h e t a g g e d , o l d e r and a p p a r e n t l y dormant swell i n g s had produced a n a v e r a g e o f 7 . 3 a e r i a l
s h o o t s , and t h e number o f s h o o t s on a c t i v e
s w e l l i n g s had doubled.
E r a d i c a t i o n and Thinning T r i a l s i n Lodgepole
P i n e a s a Dwarf M i s t l e t o e C o n t r o l
In the c e n t r a l i n t e r i o r o f B.C., v a s t b u t
u n q u a n t i f i e d a c r e a g e s of young, i n f e c t e d
lodgepole pine e x i s t . S i l v i c u l t u r a l treatments
h a v e been c o n s i d e r e d a s a means of p r e v e n t i n g
o r r e d u c i n g t h e l o s s i n s t a n d v a l u e s from t h e
p r o g r e s s i v e i n t e n s i f i c a t i o n of dwarf m i s t l e t o e , b u t p r e c i s e information on the e f f e c t i v e n e s s of such s a n i t a t i o n p r o c e d u r e s was l a c k i n g .
I n t h e e v e n t t h a t management o f such s t a n d s
would some day b e economic and more w i d e l y
a p p l i e d , t h e l a t e J.A. Baranyay, i n 1967,
i n i t i a t e d a Canadian s t u d y t o d e t e r m i n e t h e
e f f e c t i v e n e s s o f two t h i n n i n g methods t o cont r o l dwarf m i s t l e t o e . The 23 f i f t h - h e c t a r e
p l o t s were re-examined i n 1976-77 and t h e
d a t a a r e b e i n g summarized.
I n t h e 9 y e a r s of t h e s t u d y , t h e a v e r a g e
p e r c e n t a g e of t r e e s i n f e c t e d g r a d u a l l y
i n c r e a s e d from 45 t o 68 p e r c e n t (+ 23 p e r c e n t )
on t h e infected untreated p l o t s , while decreas-
i n g from 42 t o 37 p e r c e n t (- 5 p e r c e n t ) w i t h
t h i n n i n g and pruning t r e a t m e n t s and from 52
t o 18 p e r c e n t (- 34 p e r c e n t ) when complete
e r a d i c a t i o n was a t t e m p t e d . Comparable changes
i n a v e r a g e s t a n d i n f e c t i o n r a t i n g s were + 0.62,
0.08 and - 0.64, r e s p e c t i v e l y . However, desp i t e t h e t h r e e t r e a t m e n t s each p l o t r e c e i v e d
a t 3-year i n t e r v a l s , m i s t l e t o e was n o t e r a d i c a t e d from any s t a n d . Assuming a n a v e r a g e
increase i n stand infection index, the eradic a t i o n p l o t s would r e a c h t h e 3.0 l e v e l a t which
growth l o s s e s a r e f e l t t o b e s i g n i f i c a n t i n
a b o u t 40 y e a r s , a 20 y e a r g a i n o v e r comparable
u n t r e a t e d p l o t s . N o n e t h e l e s s , such t r a i n e d l a b o r i n t e n s i v e t r e a t m e n t s i n immature lodgep o l e p i n e a r e u n l i k e l y t o b e common soon, and
b e t t e r r e t u r n s would r e s u l t from c o n t r o l meas u r e s done i n c o n j u n c t i o n w i t h t h e h a r v e s t i n g
of infected stands t o e s t a b l i s h vigorous,
healthy regeneration.
-
P o s t H a r v e s t Removal of R e s i d u a l s t o C o n t r o l
Dwarf M i s t l e t o e
S e v e r a l companies have u n d e r t a k e n r e s i d u a l
removals i n c o a s t a l w e s t e r n hemlock, u s u a l l y a s
o f f s e a s o n work f o r a s m a l l , permanent crew
whose primary t a s k i s t r e e p l a n t i n g . T r e e s
a r e usually f e l l e d o r girdled to guarantee
r e s u l t s and t o avoid p o s s i b l e environmental o r
worker s a f e t y c o n c e r n s from t h e u s e of h e r b i c i d e s . At l e a s t one company h a s a t t e m p t e d t o
"hack and s q u i r t " t h e few s e v e r e l y i n f e c t e d
r e s i d u a l s o n more t h a n 16 h a . Tordon 101 and
Glowon (MSMA) were i n j e c t e d , b u t b o t h t r i a l s
were judged f a i l u r e s , w i t h 5 p e r c e n t of t h e
t r e e s k i l l e d , o r o n l y a few b r a n c h e s k i l l e d ,
r e s p e c t i v e l y . N e i t h e r t r e a t m e n t had any
a p p a r e n t e f f e c t on t h e a e r i a l s h o o t s of t h e
m i s t l e t o e u n t i l t h e h o s t branch o r t r e e d i e d .
Axe o r saw g i r d l i n g was v e r y e f f e c t i v e i f done
below t h e l o w e s t l i v e b r a n c h , b u t t r e e s t r e a t e d
i n J u l y 1975 r e t a i n e d s u f f i c i e n t v i g o r t h a t
m i s t l e t o e s e e d s were d i s c h a r g e d n o r m a l l y i n
September. To p r e v e n t seed d i s p e r s a l , t r e e s
had t o b e g i r d l e d e a r l y i n A p r i l b e f o r e f l u s h .
TREATMENTS BEFORE, DURING AND
AFTER STAND HARVEST
Residual f a l l i n g
With t h e c u r r e n t l e v e l of f o r e s t management i n B.C. and c o n s i d e r i n g dwarf m i s t l e t o e s '
symptoms, h o s t s p e c i f i c i t y , and i t s n a t u r e and
slow r a t e of s p r e a d , t h i s d i s e a s e c a n b e s t and
most economically b e c o n t r o l l e d d u r i n g t h e
l o g g i n g and s t a n d r e - e s t a b l i s h m e n t s t a g e . Spec i f i c a l l y , t h i s involves c u t block layout,
a d h e r e n c e t o a r e s i d u a l f a l l i n g r u l e , and
e l i m i n a t i o n of i n f e c t e d advance r e g e n e r a t i o n ,
p a r t i c u l a r l y i n t h e c o a s t a l hemlock and i n t e r i o r l o d g e p o l e p i n e zones. Old-growth h a r v e s t i n g
s t i l l dominates B.C. f o r e s t r y b u t , i n some
cases, special early harvesting of severely
i n f e c t e d c o a s t a l hemlock s t a n d s b e f o r e r o t a t i o n a g e h a s been allowed w i t h t h e o b j e c t i v e
of q u i c k l y r e t u r n i n g h i g h s i t e land t o i t s
f u l l p r o d u c t i v e p o t e n t i a l . There i s , however,
no f i r m P r o v i n c i a l p o l i c y f o r a s s e s s i n g s t a n d
p r o d u c t i v i t y o r s i l v i c u l t u r a l programs, and
much depends on t h e p e r s o n a l c o n v i c t i o n s ,
i n f l u e n c e and i n i t i a t i v e o f l o c a l f o r e s t r y
o f f i c e r s and i n d u s t r i a l p e r s o n n e l .
A c o n d i t i o n of h a r v e s t , a p p l i e d and somet i m e s enforced by t h e B.C. F o r e s t S e r v i c e , may
require the operator i n a clear-cut area to
remove o r d e s t r o y a l l t r e e s over 3 m i n h e i g h t .
The purpose may b e e i t h e r a e s t h e t i c , f u e l
hazard a b a t e m e n t , o r f o r s i l v i c u l t u r a l purposes p r i m a r i l y t o c o n t r o l t h e s p r e a d o f dwarf
m i s t l e t o e . S l a s h d i s p o s a l t o reduce f i r e haza r d c a n a l s o e f f e c t i v e l y reduce t h e p o t e n t i a l
m i s t l e t o e problem; however, b u r n i n g i s n o t
always e n v i r o n m e n t a l l y and l o c a l l y a c c e p t e d
and a c r e a g e s t r e a t e d have d e c l i n e d i n r e c e n t
y e a r s . A l s o , s p o t and l a n d i n g b u r n s have been
favored more t h a n b r o a d c a s t b u r n i n g , l e a v i n g ,
i n some c a s e s , l i v i n g i n f e c t e d r e s i d u a l s which
s h o u l d b e c u t . I n t h e absence of c r i t i c a l
c o s t - b e n e f i t a n a l y s i s c o v e r i n g t h e wide range
o f s i t e and d i s e a s e l e v e l s encountered, some
f o r e s t companies, p a r t i c u l a r l y on t h e C o a s t ,
a r e questioning the universal application
of t h e r e s i d u a l f a l l i n g c l a u s e . I n such
c a s e s , a n e v a l u a t i o n of t h e m i s t l e t o e i n t h e
stand before logging is an important, but
o f t e n ignored c o n s i d e r a t i o n which may a l l o w
g u i d e l i n e s t o b e more s i t e s p e c i f i c , w i t h t h e
g r e a t e s t e f f o r t s d i r e c t e d toward t h e r e l a t i v e l y
pure hemlock s t a n d s . A l t e r n a t i v e l y , some
companies a t t e m p t t o a l t e r t h e f o r e s t s t a n d
composition by p l a n t i n g n o n - s u s c e p t i b l e s p e c i e s ,
u s u a l l y D o u g l a s - f i r , provided t h e s i t e i s
acceptable.
C o n t r o l E f f o r t s i n Lodgepole P i n e
I n 1976, 8 5 p e r c e n t of t h e s t a n d improvement work f o r m i s t l e t o e c o n t r o l i n t h e P r o v i n c e
was i n t h e I n t e r i o r l o d g e p o l e p i n e r e g i o n o f
t h e Cariboo F o r e s t D i s t r i c t . C o n t r o l e f f o r t s
were s c a t t e r e d and token u n t i l 1974, b u t s i n c e
t h e n t h e a r e a t r e a t e d each y e a r h a s g r a d u a l l y
increased, the l i c e n s e e undertaking a g r e a t e r
p r o p o r t i o n o f t h e work each y e a r . I n 1977,
of t h e 2270 h a t r e a t e d f o r m i s t l e t o e , 230 ha
were d r a g s c a r i f i e d , r e s i d u a l f a l l i n g was conducted on 40 h a , and advanced r e g e n e r a t i o n
was e r a d i c a t e d by hand on 2000 h a ; 77% by t h e
l i c e n s e e , 23% by t h e P r o v i n c i a l F o r e s t S e r v i c e .
Even s o , w i t h 6800 ha of i n f e c t e d l o d g e p o l e
p i n e h a r v e s t e d i n t h i s D i s t r i c t each y e a r , cont r o l e f f o r t s a r e s t i l l minimal and ad hoc.
No method of p r i o r i z i n g s t a n d s f o r t r e a t m e n t i s
a p p l i e d , nor i s t h e p r e s e n c e of m i s t l e t o e syst e m a t i c a l l y c l a s s i f i e d and recorded.
C o n t r o l measures employed and t e s t e d i n
r e c e n t y e a r s a r e mainly b e f o r e , d u r i n g and
a f t e r h a r v e s t of i n f e c t e d mature s t a n d s . When
a c u t a p p l i c a t i o n i s r e c e i v e d and m i s t l e t o e is
recognized a s a problem, f u t u r e c o n t r o l c o s t s
c a n b e minimized by c a r e f u l p l a n n i n g of t h e
c u t b l o c k boundaries. Non-susceptible o r
u n i n f e s t e d s t a n d s , w a t e r , rights-of-way, e t c ,
a r e used t o minimize t h e l e n g t h of i n f e c t e d
margin c r e a t e d , and c u t b l o c k s i z e i s u s u a l l y
r e g u l a r and maximized around 80 ha
t o provide t h e g r e a t e s t area with the l e a s t
p e r i m e t e r . Where unacceptably l a r g e c l e a r c u t s would r e s u l t from expanding c u t t i n g
boundaries t o t h e i n f e c t i o n l i m i t s , a h i g h
p r i o r i t y i s placed on t h e a d j a c e n t f r i n g e s f o r
c u t t i n g a t a l a t e r d a t e , u s u a l l y once t h e
r e g e n e r a t e d s t a n d p r o v i d e s adequate game c o v e r .
With c u r r e n t l o g g i n g by tractor-mounted s h e a r s
o r f e l l e r - b u n c h e r s t o a 15 cm diameter stumph e i g h t l i m i t , only skinny p o l e s and advance
r e g e n e r a t i o n remain. With some i n s t r u c t i o n
and guidance, machine o p e r a t o r s c a n make
s e v e r a l p a s s e s through s u s c e p t i b l e p a t c h e s
w h i l e l e a v i n g any e x i s t i n g non-host s p e c i e s
undamaged.
.
P o s t l o g g i n g m i s t l e t o e c o n t r o l h a s mainly
involved e r a d i c a t i o n of advance r e g e n e r a t i o n ,
u s i n g hand s h e a r s . Since 1974, more t h a n 4850
ha have been t r e a t e d a t an average c o s t of
$20 p e r h e c t a r e . Drag s c a r i f i c a t i o n w i t h
c h a i n s o r s h a r k f i n n e d b a r r e l s and c h a i n s h a s
been used on more t h a n 250 ha t o e r a d i c a t e
dense s t o c k i n g of advance r e g e n e r a t i o n .
Although i n i t i a l l y many wounded s a p l i n g s sprung
back up behind t h e d r a g , v e r y few r e s i d u a l
stems remained 2 y e a r s a f t e r t r e a t m e n t . However, t h e s e s i t e s were h i g h l y exposed and r e c e n t
summers have been h o t and d r y ; hence, t h e r e
remains a concern t h a t dragging may n o t k i l l
saplings as effectively i n wetter s i t e s o r
years.
Some combinations o f p a r t i a l s c a r i f ic a t i o n and hand e r a d i c a t i o n have been used i n
a t t e m p t s t o a l s o c o n t r o l s t o c k i n g . Average
t r e a t m e n t c o s t s were $54/ha, comparable t o
$62/ha i n t h e P r i n c e George D i s t r i c t f u r t h e r
north.
F r i n g e p l a n t i n g a 36-m wide s t r i p a d j a cent t o infected borders with r e s i s t a n t
s p e c i e s such a s Douglas-fir o r s p r u c e t o t a l s
about 47 km, e q u i v a l e n t t o 170 h a . The t r e a t ment may reduce t h e s p r e a d of m i s t l e t o e b u t
d o e s n o t p r e v e n t i t , owing t o t h e r a p i d n a t u r a l
r e g e n e r a t i o n and c o m p e t i t i o n by l o d g e p o l e p i n e .
S i n c e p e r i o d i c e r a d i c a t i o n of t h e p i n e would
be a d d i t i o n a l l y e x p e n s i v e , t h e p l a n t e d s t o c k
a r e o f t e n o f f - s i t e w i t h poor s u r v i v a l , and
i n i t i a l p l a n t i n g c o s t s a r e h i g h ($270/ha),
f r i n g e p l a n t i n g i s n o t l i k e l y t o b e more w i d e l y
applied.
s c a r i f i c a t i o n , p i l i n g and b u r n i n g of s l a s h ,
l e a v i n g non-hos t seed t r e e s , t r i a l p l a n t i n g s
t o change t h e s p e c i e s composition, and two o r
t h r e e p a s s s t r i p l o g g i n g . Areas of noncommercial volume, s t i l l u n i d e n t i f i e d and
unmeasured, w i l l r e q u i r e a s p e c i a l program o f
r e h a b i l i t a t i o n before they again support a
productive f o r e s t .
I n 1976, i n c o n j u n c t i o n w i t h a mechanical
t h i n n i n g t r i a l , 8 ha of i n f e c t e d immature
edge were removed, p a r t l y by hydro axe and
p a r t l y by windrowing w i t h a s m a l l d o z e r and
t h e n b u r n i n g . An a v e r a g e c o s t f o r t h e t r i a l
was $370/ha. Such t r e a t m e n t s may b e more
economical a n d w i d e l y p r a c t i s e d when a d j a c e n t
s t a n d s a r e logged a s a means of removing t h e ,
by t h e n , young i n f e c t e d s t a n d s a d j a c e n t t o
h e a v i l y i n f e c t e d mature b o r d e r s .
DWARF MISTLETOE MANAGEMENT AIDS
REQUIRED OR UNDER DEVELOPMENT
An e s t i m a t e i s n o t a v a i l a b l e of t h e a c r e age of young second-growth p i n e on which dwarf
m i s t l e t o e i s a problem b u t , w i t h a b o u t 6800
ha l o g g e d e a c h y e a r , t h e backlog is s u b s t a n t i a l .
I n a r e a s f e l l e d by hand o r w i t h o u t enforcement
of r e s i d u a l f a l l i n g , i n d i v i d u a l t r e e s and
p a t c h e s of i n f e c t e d r e s i d u a l s o f t e n remain.
F a l l i n g of t h e r e s i d u a l s i s being done a s time
and money p e r m i t s . To d a t e , 170 h a have been
t r e a t e d , b u t c o s t s a r e h i g h l y v a r i a b l e ($373 0 0 / h a ) , depending on t h e d e n s i t y , d i s t r i b u t i o n and s i z e of t h e r e s i d u a l t r e e s .
S e l e c t i o n C u t t i n g of I n f e c t e d Douglas-fir
t h e Okanagan V a l l e y
C u r r e n t e f f o r t s i n dwarf m i s t l e t o e r e s e a r c h
a t t h e P a c i f i c F o r e s t Research C e n t r e a r e
mostly d i r e c t e d t o t h e development of a mathem a t i c a l model of hemlock m i s t l e t o e s p r e a d ,
based on t h e d a t a c o l l e c t e d s i n c e 1964 on seed
d i s p e r s a l , i n t e r c e p t i o n , i n Âe c t i o n and r a t e s o f
intensification.
The model w i l l g e n e r a t e v a l u e s
of t h e i n f e c t i o n l e v e l and p a t t e r n i n r e g e n e r a t i o n a t v a r y i n g d e n s i t i e s and d i s t a n c e s from
i n f e c t e d r e s i d u a l s t o a s s i s t f o r e s t managers
i n d e t e r m i n i n g t h e t i m i n g , d e g r e e and c o s t of
s a n i t a t i o n s p a c i n g t r e a t m e n t s . Surveys and
a d v i c e w i l l c o n t i n u e t o b e provided t o f o s t e r
a n awareness and p r a c t i c e of a l l r e a s o n a b l e
management a l t e r n a t i v e s aimed a t r e d u c i n g
c u r r e n t and f u t u r e l o s s e s from dwarf m i s t l e t o e .
Numerous p e o p l e , companies and f o r e s t
s e r v i c e groups s c a t t e r e d throughout B.C. a r e
expending c o n s i d e r a b l e e f f o r t toward t h e
c o n t r o l of dwarf m i s t l e t o e s through f o r e s t
management. Much, however, i s ad h o e , r e l y i n g
l a r g e l y on an i n d i v i d u a l ' s c o n v i c t i o n , pers u a s i v e n e s s and perhaps s t u b b o r n n e s s t o i n i t i a t e and complete any t r e a t m e n t s . Major
r e q u i r e m e n t s f o r improved management i n c l u d e
several inter-related factors :
in
Douglas-fir m i s t l e t o e is s c a t t e r e d but
common i n t h e Okanagan and Kootenay v a l l e y s
and, a s i n d i c a t e d by one 1975 T r e e Farm Licence
i n v e n t o r y , a b o u t 25% o f t h e timber may b e
i n f e c t e d . As e a r l y a s 1965, t h e F o r e s t S e r v i c e
s a n i t i z e d a 4.7 ha p r e v i o u s l y logged area a s a
p i l o t control project
V i s i b l y i n Âe c t e d t r e e s
were p i l e d and burned, s m a l l t r e e s w i t h s i n g l e
b r a n c h e s i n f e c t e d were pruned, and a road and
15 m i s o l a t i o n s t r i p surrounded t h e p l o t .
A d d i t i o n a l i n f e c t i o n s throughout t h e p l o t were
removed i n 1971, b u t i t became a p p a r e n t t h a t
complete e r a d i c a t i o n was n o t f e a s i b l e and a
reduction of the mistletoe t o a reasonable
l e v e l is a l l t h a t can b e e x p e c t e d .
.
i.
S i n c e 1969, one f o r e s t company h a s logged
o r r e l o g g e d 727 h a and removed i n f e c t e d r e s i d u a l s on a n a d d i t i o n a l 1000 h a i n a n a t t e m p t
t o c o n t r o l dwarf m i s t l e t o e . E f f o r t s have been
complex b e c a u s e D o u g l a s - f i r , l o d g e p o l e p i n e
and l a r c h m i s t l e t o e s a l l o c c u r i n v a r y i n g
p r o p o r t i o n s i n p a r t s of t h e a r e a (ponderosa
p i n e i s t h e only common r e s i s t a n t comm e r c i a l s p e c i e s ) and y e t o v e r s t o r y shade i s
c r i t i c a l f o r successful regeneration i n these
v e r y d r y s i t e s . Treatments i n merchantable
s t a n d s have i n c l u d e d d i a m e t e r l i m i t c u t t i n g
w i t h f e l l i n g of i n f e c t e d r e s i d u a l s , some
Ill
a P r o v i n c i a l p o l i c y and funding f o r
s i l v i c u l t u r a l programs aimed a t p e s t
management.
ii.
q u a n t i f i e d , long-term f o r e s t r y d a t a t o
i d e n t i f y and a s s e s s l o s s e s and p r o v i d e
t h e b a s i s of a s s i g n i n g s p e c i f i c c o n t r o l
a c t i o n s a c c o r d i n g t o economic o r f o r e s t
s i t e values.
iii.
m o n i t o r i n g of c u r r e n t c o n t r o l p r o j e c t s
t o o b t a i n a b i o l o g i c a l and economic
assessment of p r e s e n t c o n t r o l p r a c t i c e s .
C u r r e n t l y most e f f o r t i s expended s o l e l y
i n t h e hope of having m i s t l e t o e - f r e e o r
a c c e p t a b l e second-growth s t a n d s .
LITERATURE CITED
Baranyay, J.A.
1968. Experiment w i t h a e r i a l c o l o u r photography f o r d e t e c t i n g dwarf m i s t l e t o e
i n f e c t e d lodgepole pine stands i n the
A l b e r t a - T e r r i t o r i e s r e g i o n . Can. Dep. For.
I n t e r n a l Rep. A-12.
Calgary, Alberta.
35 p.
Baranyay, J.A. and L. S a f r a n y i k
1970. E f f e c t of dwarf m i s t l e t o e on growth
and m o r t a l i t y of l o d g e p o l e p i n e i n A l b e r t a .
Can. Dep. F i s h . and F o r . , For. Serv. P u b l .
1285.
Baranyay , J . A . and R.B. Smith
1972. Dwarf m i s t l e t o e s i n B r i t i s h Columbia
and recommendations f o r t h e i r c o n t r o l .
Can. For. Serv. BC-X-72, p. 18. V i c t o r i a ,
B.C.
Dobie, J. and A.A. B r i t n e f f
1975. Lumber g r a d e s and volumes from
l o d g e p o l e p i n e i n f e c t e d w i t h dwarf m i s t l e t o e . Wood and F i b e r 7(2) : 104-109.
Haglund, S.A. and O . J . Dooling
1972. O b s e r v a t i o n s on t h e impact of dwarf
m i s t l e t o e on D o u g l a s - f i r i n w e s t e r n
Montana. USDA, For. S e r v . , Northern
Region, Rep. D-72-1.
Hanson, G.F.
1975. Lodgepole p i n e dwarf m i s t l e t o e s u r v e y
-- Westlake p u b l i c s u s t a i n e d y i e l d u n i t .
BCFS, s p e c i a l p r o j e c t .
V i c t o r i a , B.C.
Mimeo. r e p o r t .
Hunt, K.
1971. A comparison o f k r a f t p u l p i n g o f
sound and dwarf m i s t l e t o e - i n f e c t e d w e s t e r n
hemlock wood. Can. Dep. F i s h . and Tor.,
For. S e r v . , Inform. Rep. VP-X-78.
Vancouver, B.C
.
Krajina, V.J.
1969. Ecology of f o r e s t t r e e s i n B r i t i s h
Columbia. Ecology of West. North Amer.
2 ( 1 ) : 1-147.
Muir, J.A. and J.K. Robins
1973. D e t e c t i o n of dwarf m i s t l e t o e of j a c k
p i n e on a e r i a l photographs. P l a n t D i s .
R e p t r . 57: 951-954.
On, D. and 0. Dooling
1969. A s t u d y of t h e e f f e c t of dwarf
m i s t l e t o e i n f e c t i o n on t h e growth of
w e s t e r n l a r c h . USDA, For. S e r v . , Div.
S t a t e and P r i v a t e F o r . , Missoula, Mont.
Misc. Rep.
Smith, R.B.
1969. A s s e s s i n g dwarf m i s t l e t o e on w e s t e r n
hemlock. For. S c i . l 5 ( 3 ) : 277-285.
Wass, E.F.
1976. Ecology of s h o r e p i n e s t a n d s i n f e s t e d
w i t h dwarf m i s t l e t o e on s o u t h e a s t e r n
Vancouver I s l a n d . Can. For. S e r v . , Rep.
BC-X-142.