INTERMEDIATE CUTTINGS I N MISTLETOE-INFESTED LODGEPOLE PINE
AND SOUTHWESTERN PONDEROSA PINE STANDS-1/
Frank G. Hawksworth-2 /
A b s t r a c t : I n t e r m e d i a t e c u t s i n m i s t l e t o e - i n f e s t e d lodgep o l e p i n e and ponderosa p i n e s t a n d s i n c l u d e " s a n i t a t i o n c u t t i n g s "
(where a l l v i s i b l y i n f e c t e d t r e e s a r e c u t ) and " s a n i t a t i o n
t h i n n i n g s " (where emphasis i s on s p a c i n g and c u t t i n g t h e t r e e s
t h a t a r e most h e a v i l y i n f e c t e d ) . S a n i t a t i o n c u t t i n g s a r e
recommended o n l y i n s t a n d s where l e s s t h a n a b o u t 40 p e r c e n t of
t h e t r e e s a r e i n f e c t e d . U s u a l l y such s t a n d s a r e l e s s t h a n 30
years old. Sanitation thinnings a r e usually applied t o stands
o v e r 30 y e a r s , b u t a r e n o t recommended i n h e a v i l y i n f e s t e d
s t a n d s b e c a u s e h e a v i l y i n f e c t e d r e s i d u a l t r e e s w i l l show l i t t l e
r e s p o n s e t o t h i n n i n g . P r e s e n t l y , we do n o t s u g g e s t t h i n n i n g i n
s t a n d s w i t h a n a v e r a g e dwarf m i s t l e t o e r a t i n g ( 6 - c l a s s system)
of 3 o r more. Y i e l d s i m u l a t i o n p r o c e d u r e s a r e a v a i l a b l e f o r
m i s t l e t o e - i n f e s t e d l o d g e p o l e p i n e s t a n d s i n t h e c e n t r a l Rockies
and f o r s o u t h w e s t e r n ponderosa p i n e .
INTRODUCTION
Intermediate c u t s include a l l the cutting
t r e a t m e n t s made f o l l o w i n g e s t a b l i s h m e n t of t h e
new s t a n d u n t i l t h e t i m e t o r e p l a c e i t . Cutt i n g s a r e made when needed, n o r m a l l y a t s p e c i f i c
i n t e r v a l s , t o i n c r e a s e t h e q u a n t i t y and q u a l i t y
of t i m b e r produced, and t o s a l v a g e m a t e r i a l
which would o t h e r w i s e b e l o s t . Common i n t e r m e d i a t e c u t s a r e : ( 1 ) t h i n n i n g s , and (2) i m provement c u t t i n g s , i n c l u d i n g s a n i t a t i o n and
s a l v a g e (Myers 1 9 7 4 ) . For p r a c t i c a l p u r p o s e s
h e r e we w i l l c o n s i d e r " s a n i t a t i o n c u t t i n g s "
(where removal of a l l v i s i b l y i n f e c t e d t r e e s
i s a t t e m p t e d ) and " s a n i t a t i o n t h i n n i n g s "
(where t h e emphasis i s on s p a c i n g and u s u a l l y
o n l y t h e most s e v e r e l y d i s e a s e d t r e e s a r e .
removed).
This paper considers lodgepole pine
( P i n u s c o n t o r t a Dougl. e x Loud. subsp.
l a t i f o l i a [ ~ n g e l m . e x Wats ] C r i t c h f . ) s t a n d s
i n t h e c e n t r a l Rocky Mountains a f f e c t e d by
t h e dwarf m i s t l e t o e Arceuthobium americanum
N u t t . e x Engelm. and ponderosa p i n e (P. pond e r o s a Laws. v a r . scopulorum Engelm.) i n t h e
Southwest a f f e c t e d by A. vaginatum (Willd.)
P r e s l . subsp. cryptopodum (Engelm.) Hawks.
& Wiens
.
THINNING I N UNINFESTED STANDS
Before discussing thinning i n mistletoei n f e s t e d s t a n d s , i t would b e h e l p f u l t o sum7
m a r i z e t h i n n i n g recommendations i n n o n i n f e s t e d
s t a n d s , which form t h e b a s i s f o r t h i n n i n g s i n
diseased stands.
Lodgepole p i n e
The f o l l o w i n g t h i n n i n g recommendations
a r e summarized from Alexander (1974) and Cole
(1975).
a.
I f s t a n d s have fewer t h a n 2,500 stems
per a c r e , thinning can be delayed
u n t i l age 30 ( t o t a l a g e ) .
b.
I f s t a n d s have more t h a n 2,500 stems
p e r a c r e , t h i n n i n g should b e done
b e f o r e a g e 30, i d e a l l y between a g e s
1 0 and 20, and should l e a v e 1 , 2 0 0 t o
1,500 stems p e r a c r e .
c.
I f s t a n d s have 2,500 t o 4,000 stems
p e r a c r e , t h i n n i n g w i l l show some
reponse up u n t i l a b o u t a g e 70, b u t
wider s p a c i n g s s h o u l d b e used t h a n
i n younger s t a n d s .
d.
S t a n d s w i t h more t h a n 2,500 t o 4,000
stems p e r a c r e o r more t h a n a b o u t 70
years old generally w i l l not recover
s u f f i c i e n t l y t o cover c o s t s of t h i n n i n g .
at Symposium o n Dwarf M i s t l e t o e
Ñ'presente
C o n t r o l t h r o u g h F o r e s t Management, Berkeley,
C a l i f . A p r i l 11-13, 1978.
à ‘ ' ~ u ~ e r v i s oF ro r e s t P a t h o l o g i s t , Rocky Mountain
F o r e s t and Range Experiment S t a t i o n , F o r e s t
S e r v i c e , U.S. Department o f A g r i c u l t u r e , F o r t
C o l l i n s , Colo.
L a t e r t h i n n i n g recommendations i n lodgep o l e p i n e a r e based on t h e growing s t o c k l e v e l
(GSL) c o n c e p t (Edminster 1978). The GSL's a r e
numerical i n d i c e s representing r e s i d u a l b a s a l
a r e a s when t h e a v e r a g e t r e e d i a m e t e r r e a c h e s
1 0 i n c h e s o r more. I n s t a n d s where a v e r a g e
t r e e d i a m e t e r is more t h a n 1 0 i n c h e s d.b.h.,
GSL and b a s a l a r e a a r e t h e same.
Ponderosa p i n e
Thinning recommendations f o r ponderosa
p i n e i n t h e Southwest and i n Colorado a r e
a l s o based on GSL (Schubert 1974, Myers 1974).
The GSL recommended depends on t h e management
o b j e c t i v e s f o r t h e p a r t i c u l a r s t a n d . For
example, i f t i m b e r volume p r o d u c t i o n i s t h e
p r i m a r y o b j e c t i v e , a moderately h i g h GSL
(e.g.,100 t o 120) i s s u g g e s t e d . However, i f
o t h e r f o r e s t v a l u e s need t o b e c o n s i d e r e d , such
a s g r a z i n g and r e c r e a t i o n , lower l e v e l s ( e . g . ,
GSL 40 t o 60) a r e f r e q u e n t l y recommended).
Ponderosa p i n e remains p h y s i o l o g i c a l l y
young and r e s p o n d s t o t h i n n i n g up t o a t l e a s t
200 (Pearson 1950). However, from a p r a c t i c a l
s t a n d p o i n t , t h i n n i n g i n o l d e r s t a n d s may n o t
b e economical.
SANITATION CUTTINGS
" S a n i t a t i o n c u t t i n g " a s used h e r e i n v o l v e s
removal o f a l l v i s i b l y i n f e c t e d t r e e s i n a
stand, usually i n conjunction with a thinning
o p e r a t i o n . I n l o d g e p o l e p i n e and ponderosa
p i n e , s t a n d s i n which s a n i t a t i o n i s f e a s i b l e
a r e u s u a l l y l e s s t h a n 30 y e a r s o l d . I n o l d e r
s t a n d s , dwarf m i s t l e t o e i n f e s t a t i o n f r e q u e n t l y
d e v e l o p s t o s u c h a n e x t e n t t h a t removal of
a l l i n f e c t e d t r e e s would c r e a t e t o o l a r g e
openings.
An i m p o r t a n t c o n s i d e r a t i o n i s t h e number
of l a t e n t dwarf m i s t l e t o e p l a n t s ( i . e . , t h o s e
overlooked i n t h e f i r s t o p e r a t i o n o r i n c i p i e n t ) .
As a g u i d e from o u r s t u d i e s i n l o d g e p o l e p i n e ,
s u p p o r t e d somewhat by r e s u l t s i n o t h e r s p e c i e s ,
we developed t h e " h a l f - a g a i n r u l e . " T h i s
s t a t e s t h a t t h e p r o p o r t i o n of t r e e s i n f e c t e d
about 5 years a f t e r an i n i t i a l s a n i t a t i o n w i l l
b e about h a l f t h e amount removed i n t h e f i r s t
o p e r a t i o n . For example, i f 1 2 p e r c e n t of t h e
t r e e s were i n f e c t e d a t t h e time of t h e f i r s t
o p e r a t i o n , a b o u t 6 p e r c e n t more w i l l develop
i n f e c t i o n s . T h i s g u i d e seems t o a p p l y t o
s t a n d s w i t h up t o a b o u t h a l f of t h e t r e e s
infected before the f i r s t sanitation.
I n t e r i m r e s u l t s from s a n i t a t i o n c u t t i n g s
i n young l o d g e p o l e p i n e s t a n d s p r o v i d e some
g u i d e s (Baranyay 1975, Hawksworth e t a l . 1977).
The d e g r e e of i n f e s t a t i o n i n t h e s t a n d , n o t
s t r i c t l y stand age, is t h e best c r i t e r i o n t o
d e c i d e whether s a n i t a t i o n i s p r a c t i c a l . A
g e n e r a l g u i d e i s t h a t s t a n d s w i t h more t h a n
a b o u t 40 p e r c e n t of t h e t r e e s i n f e c t e d a r e
t o o h e a v i l y i n Âe c t e d t o a t t e m p t s t r i c t s a n i t a t i o n c u t t i n g (removal of a l l i n f e c t e d t r e e s ) .
I n such s t a n d s , t h e l a r g e numbers of r e i n f e c t e d
t r e e s would n e c e s s i t a t e removal of s o many t r e e s
t h a t s t o c k i n g would b e s e r i o u s l y reduced.
In
t h e s e s t u d i e s , a l l of t h e 20-year-old, and
most of t h e 30-year-old s t a n d s had fewer t h a n
40 p e r c e n t of t h e t r e e s i n f e c t e d . Most of t h e
40-year-old s t a n d s had more t h a n 40 p e r c e n t of
t h e t r e e s i n f e c t e d , b u t i n t h e one t h a t had
l e s s t h a n 20 p e r c e n t i n f e s t a t i o n , s a n i t a t i o n
a p p e a r s t o have been s u c c e s s f u l .
SANITATION THINNINGS
It w a s n ' t t o o many y e a r s ago t h a t t o
recommend any t h i n n i n g i n m i s t l e t o e - i n f e s t e d
s t a n d s would have been c o n s i d e r e d t o b e t h e
h e i g h t of f o l l y . For y e a r s , I was a s t r o n g
a d v o c a t e of t h e "no-thinning" philosophy.
When I began working on dwarf m i s t l e t o e s i n
t h e Southwest i n t h e e a r l y 1 9 5 0 1 s , I was
shown s e v e r a l i n f e s t e d s t a n d s t h a t had been
t h i n n e d some 15-20 y e a r s p r e v i o u s l y . These
s t a n d s were r e a l " d i s a s t e r a r e a s " and t h e y
made q u i t e a n i m p r e s s i o n on me. The ground
i n t h e s e s t a n d s was jackstrawed w i t h t h e
c a r c a s s e s of m i s t l e t o e - k i l l e d t r e e s and t h e
few s u r v i v i n g t r e e s were s o s e v e r e l y i n f e s t e d
t h a t t h e i r d a y s , t o o , were numbered. The
t h e o r y was t h a t t h e i n c r e a s e d l i g h t i n t h i n n e d
s t a n d s s t i m u l a t e d t h e p a r a s i t e , s o i t was a b l e
t o r a p i d l y i n t e n s i f y and k i l l t h e r e s i d u a l
t r e e s . Obviously t h e o n l y answer was n o t t o
t h i n i n infested stands.
But, a s I began t o examine o t h e r t h i n n i n g s
i n i n f e s t e d s t a n d s , b o t h i n ponderosa p i n e i n
t h e Southwest and i n l o d g e p o l e p i n e i n t h e
c e n t r a l Rockies, I n o t i c e d t h e r e were some
s t a n d s t h a t d i d n o t b r e a k up a f t e r t h i n n i n g ,
b u t r a t h e r , seemed t o b e growing more volume
than before.
We s t i l l d o n ' t know why t h i n n i n g s a r e
s u c c e s s f u l i n some s t a n d s and n o t i n o t h e r s ,
b u t we t h i n k t h a t a t l e a s t two i m p o r t a n t f a c t o r s
a r e i n v o l v e d : ( 1 ) t h e d e g r e e of i n f e s t a t i o n
i n t h e s t a n d , and ( 2) s i t e q u a l i t y .
The p r e s e n t e v i d e n c e s u g g e s t s t h a t t h i n n i n g s i n i n f e s t e d s t a n d s can i n c r e a s e volume
i n c r e m e n t , provided i n f e c t i o n i s n o t t o o heavy.
I t i s n o t known where t h i s c u t o f f l i n e i s , and
how i t v a r i e s w i t h t y p e of s t a n d , a g e c l a s s ,
o r s i t e q u a l i t y . For example, we t h i n k t h a t
e f f e c t s o f dwarf m i s t l e t o e a r e s i t e - r e l a t e d ;
t h a t i s , a g i v e n d e g r e e of i n f e c t i o n w i l l have
r e l a t i v e l y l e s s e f f e c t on growth on a good
s i t e t h a n on a poor one. However, m i s t l e t o e
incidence frequently is not site-related.
For
example, t h e dwarf m i s t l e t o e s o c c u r on t h e b e s t
l o d g e p o l e p i n e s i t e s t h a t we have s e e n i n t h e
C e n t r a l Rockies and on t h e b e s t ponderosa p i n e
s i t e s i n t h e Southwest, b u t t h e i r e f f e c t s on
t h e s e good s i t e s a r e r e l a t i v e l y i n s i g n i f i c a n t .
A t p r e s e n t , we do n o t recommend t h i n n i n g
i n s t a n d G h a t have a n a v e r a g e dwarf m i s t l e t o e
r a t i n g (DMR) of 3 . 0 o r more ( 6 - c l a s s system,
Hawksworth 1977). T h i s may seem r a t h e r low,
but a s shown i n f i g u r e 1, about 90 p e r c e n t
of t h e t r e e s i n s u c h s t a n d s a r e i n f e c t e d ,
l e a v i n g r e l a t i v e l y few u n i n f e c t e d o r l i g h t l y
i n f e c t e d t r e e s t o work w i t h . We recommend
removal of a s many i n f e c t e d t r e e s a s p o s s i b l e
w i t h o u t c r e a t i n g l a r g e openings. U s u a l l y ,
t r e e s w i t h a DMR of 4 o r h i g h e r should n o t b e
r e t a i n e d . I t i s b e t t e r t o s a c r i f i c e some
s p a c i n g t o remove such h e a v i l y i n f e c t e d t r e e s ,
s i n c e t h e y w i l l u s u a l l y show l i t t l e growth
response a f t e r thinning.
b e analyzed c o n s i d e r i n g t h e :
(1) p r o t e c t e d
y i e l d s , (2) market c o n d i t i o n s , and (3) economics.
Research c a n now p r o v i d e i n f o r m a t i o n o n l y on
t h e f i r s t , using simulated y i e l d projections.
Yield p r o j e c t i o n s f o r mistletoe-infested
s t a n d s have been p u b l i s h e d f o r even-aged lodgep o l e p i n e i n t h e c e n t r a l Rocky Mountains (Myers
e t a l . 1971) and f o r even-aged and two-storied
ponderosa p i n e i n t h e Southwest (Myers e t a l .
1976, Edminster and Hawksworth 1976). These
a r e b e i n g a d a p t e d and t e s t e d on o t h e r a r e a s
and f o r o t h e r h o s t - p a r a s i t e combinations.
Using t h e s e programs on a s t a n d b a s i s ,
t h e f o r e s t manager c a n examine many o p t i o n s
f o r a v e r y low c o s t and t h e n d e c i d e on t h e
t r e a t m e n t t h a t w i l l g i v e maximum y i e l d s commensurate w i t h management o b j e c t i v e s f o r t h e
a r e a . For example, he can compare c u b i c
f e e t v s . board f e e t y i e l d s . He c a n examine
such o p t i o n s a s :
(1) do n o t h i n g , (2) t h i n t o
v a r i o u s growing s t o c k l e v e l s , (3) t h i n a t
v a r i o u s i n t e r v a l s , and ( 4 ) d e l a y e d t h i n n i n g s .
Also, he c a n compare y i e l d s i n i n f e s t e d s t a n d s
with uninfested stands t o determine p o t e n t i a l
y i e l d s on t h e s i t e .
Examples from t h e l o d g e p o l e p i n e program
a r e g i v e n from two s t a n d s i n t h e R o u t t N a t i o n a l
F o r e s t i n n o r t h e r n Colorado ( t a b l e s 1-3).
0
8
I
,
,
I
I
2
3
4
5
Average stand dwarf mistletoe rating
.
6
(m~)
F i g u r e 1 - - R e l a t i o n s h i p between p e r c e n t of
t r e e s i n f e s t e d a n d x e r a g e s t a n d dwarf
m i s t l e t o e r a t i n g (DMR) f o r l o d g e p o l e p i n e
stands.
Dwarf m i s t l e t o e l e v e l s i n r e s i d u a l t r e e s
should b e low i n young s t a n d s because i t w i l l
b e many y e a r s b e f o r e t h e y a r e of m e r c h a n t a b l e
s i z e . Conversely, h i g h e r l e v e l s can be l e f t
i n o l d e r s t a n d s , s i n c e t h e y w i l l be h a r v e s t e d
b e f o r e t h e m i s t l e t o e l e v e l s i n c r e a s e t o damaging proportions.
At p r e s e n t , t h e r e a r e no "hard and f a s t "
r u l e s t o d e t e r m i n e whether s a n i t a t i o n t h i n n i n g
w i l l h e l p a p a r t i c u l a r s t a n d . Each s t a n d must
T a b l e 1 shows t h e ~ r o j e c t e d~ i e l d si n r e l a t i o n t o GSL. I n t h i s c a s e , i f t h e s t a n d s a r e
n o t t r e a t e d , a f t e r 1 0 0 y e a r s , we c a n e x p e c t
no board f e e t volume, s i n c e t h e t r e e s w i l l n o t
r e a c h t h e 6.5 i n c h e s minimum s t a n d d i a m e t e r .
A f t e r 100 y e a r s , t h i n n i n g t o GSL 70 w i l l y i e l d
a b o u t 1 5 , 2 0 0 board f e e t p e r a c r e and t o GSL 90
about 16,600 f e e t . I n g e n e r a l , h i g h e r GSL1s
y i e l d more volume i n u n i n f e s t e d s t a n d s ; t h e
converse is t r u e f o r moderately t o heavily
i n f e s t e d s t a n d s . I n t h i s c a s e , h i g h e r GSL
r e s u l t s i n h i g h e r p r o j e c t y i e l d s , presumably
because m i s t l e t o e was r e l a t i v e l y l i g h t ( o n l y
27 p e r c e n t of t h e t r e e s i n f e c t e d ) . Table 2
shows a n a n a l y s i s of c u t t i n g c y c l e s i n t h e same
s t a n d . Examining j u s t t h r e e a l t e r n a t i v e s shows
t h a t c u t t i n g c y c l e s a t 30-year i n t e r v a l s w i l l
i n c r e a s e b o t h m e r c h a n t a b l e and board f e e t y i e l d s .
T a b l e I - - E f f e c t s of growing s t o c k l e v e l (GSL)
on s i m u l a t e d y i e l d s i n a 30-year o l d lodgep o l e p i n e s t a n d , P o r c u p i n e Creek, Routt
N a t i o n a l F o r e s t , Colorado. P r e s e n t s t a n d
c o n d i t i o n s : avg. d . b . h . - 2 i n c h e s , S i t e
Index - 60, t r e e s p e r a c r e - 2,680, and
p e r c e n t of t r e e s i n f e s t e d - 27.
100-year
yield/acre
Merchantable
Board
cubic f e e t
feet
Treatment
None
2,460
0
Thin GSL 70
(30-year i n t e r v a l s )
3,290
15,200
Thin GSL 90
(30-year i n t e r v a l s )
3,810
16,600
T a b l e 2--Effects of l e n g t h of c u t t i n g c y c l e
( a t GSL 90) on s i m u l a t e d y i e l d s i n a 30-year
o l d l o d g e p o l e p i n e s t a n d , Porcupine Creek,
R o u t t N a t i o n a l F o r e s t , Colorado. P r e s e n t
s t a n d c o n d i t i o n s : avg. d . b . h . - 2 i n c h e s ,
S i t e I n d e x - 60, t r e e s p e r a c r e - 2,680,
and p e r c e n t of t r e e s i n f e s t e d - 27.
100-year
yield/acre
Merchantable
Board
cubic f e e t
feet
None
2,460
0
Thin 30-year
intervals
3,810
16,600
Thin 50-year
intervals
3,510
14,700
T a b l e 3 shows a n o l d e r s t a n d (age 70
y e a r s which i s g e n e r a l l y c o n s i d e r e d t o b e
n e a r t h e upper l i m i t of t h i n n i n g f e a s i b i l i t y .
However, even i n t h i s c a s e , we c a n s e e a
market improvement by t h i n n i n g . The s t a n d ,
i f l e f t alone, w i l l not y i e l d merchantable
o r board f e e t volume b e c a u s e t h e t r e e s w i l l
n o t r e a c h t h e a v e r a g e 6.0 and 6 . 5 i n c h e s ,
r e s p e c t i v e l y , f o r c a l c u l a t i o n of t h e s e volumes
Thinning can y i e l d 9,000-10,000 board f e e t
p e r a c r e a f t e r 60 y e a r s .
T a b l e 3. E f f e c t s of one v s . two t h i n n i n g s
( a t GSL 90) on s i m u l a t e d y i e l d s i n a 70-year
o l d l o d g e p o l e p i n e s t a n d , Snyder Creek, R o u t t
N a t i o n a l F o r e s t , Colorado. P r e s e n t s t a n d
c o n d i t i o n s : avg. d.b.h. - 3 i n c h e s , S i t e
Index - 55, t r e e s p e r a c r e - 4,330, and
p e r c e n t of t r e e s i n f e s t e d - 34.
60-year
fieldlacre
Merchantable
Board
cubic f e e t
feet
Treatment
None
0
0
Thin a g e 70 and 100;
h a r v e s t a g e 130
2,350
9,000
Thin a g e 70; h a r v e s t
a g e 130
2,930
9,900
To e s t i m a t e t h e r e l a t i v e e f f e c t s of dwarf
m i s t l e t o e i n ponderosa p i n e and l o d g e p o l e p i n e ,
y i e l d s i m u l a t i o n s were made f o r t h e same hypot h e t i c a l stand conditions: present stand age
- 30; a v e r a g e d . b . h . - 3 i n c h e s ; d e n s i t y 1 , 0 0 0 stems p e r a c r e ; S i t e Index - 40, 60, and
8 0 ; and m i s t l e t o e i n f e c t i o n - none, o r 50 p e r c e n t of t r e e s i n f e c t e d . P r o j e c t i o n s were made
f o r 90 y e a r s ( u n t i l s t a n d a g e 120) assuming
(1) no t h i n n i n g , and ( 2 ) t h i n n i n g t o growing
s t o c k l e v e l s 60, 8 0 , and 100 a t a g e s 30, 60
and 90.
Some of t h e r e s u l t s a r e g i v e n i n T a b l e 4
f o r l o d g e p o l e p i n e and i n T a b l e 5 f o r ponderosa
p i n e . Thinning t o GSL 100 i s shown f o r t h e s e
examples o n l y . Some of t h e r e s u l t s o'f t h e s e
analyses a r e :
1.
For n o n i n f e s t e d s t a n d s , i n c r e a s e d
y i e l d s p e r a c r e due t o t h i n n i n g a r e
a b o u t t h e same r e g a r d l e s s of S i t e
Index, b u t t h e p r o p o r t i o n of t h e
i n c r e a s e i s much h i g h e r on p o o r e r
sites.
2.
For a g i v e n amount of i n f e c t i o n ,
assuming t h e same s t a n d t r e a t m e n t s ,
dwarf m i s t l e t o e l o s s e s a r e s i g n i f i c a n t l y g r e a t e r i n ponderosa p i n e
than i n lodgevole pine.
3.
I f infested stands a r e not thinned,
t h e cubic f o o t l o s s e s a r e g r e a t e r
on s i t e 8 0 t h a n on s i t e 40, b u t t h e
p r o p o r t i o n a l l o s s i s g r e a t e r on t h e
lower s i t e s . For example, i n t h e
case c i t e d f o r lodgepole pine i n
T a b l e 4 , t h e volume i n t h e i n f e s t e d
s t a n d was 64 p e r c e n t of t h a t of t h e
u n i n f e s t e d s t a n d i n s i t e 40, b u t t h e
T a b l e 4 ~ S i m u l a t e d90-year y i e l d s i n l o d g e p o l e p i n e s t a n d s now 30 y e a r s o l d . Average d.b.h.
30 i n c h e s , 1,000 t r e e s p e r a c r e . Treatment s t a n d s thinned a t a g e 30, 60, and 90.
=
Merchantable c u b i c f o o t volume a c r e
s i t e index
Stand
Condition
Treatment
No m i s t l e t o e
None
40
60
80
1,490
5,220
8,610
180
106
112
259
141
129
93
98
97
t h i n GSL 100
Difference
cubic f e e t
percent increase
50% t r e e s
infected
(DMR = .07)
None
t h i n GSL 100
Difference
cubic f e e t
percent increase
Uninfected v s .
50% t r e e s
i n Âe c t e d
None
Difference
cubic f e e t
percent decrease
Uninfected v s .
50% t r e e s
i n Âe c t e d
Thin GSL-100
Difference
cubic f e e t
percent decrease
comparable f i g u r e on s i t e 8 0 was
84 p e r c e n t .
4.
For a g i v e n s i t e i n d e x , t h e r e l a t i v e
g a i n s due t o t h i n n i n g ( e . g . , y i e l d s
i n t h i n n e d s t a n d s l y i e l d s i n unthinned
s t a n d s ) i n c r e a s e a s dwarf m i s t l e t o e
i n t e n s i t y i n c r e a s e s . For example,
i n l o d g e p o l e p i n e , on s i t e 60, i n c r e a s e
i n y i e l d s due t o t h i n n i n g i n s t a n d s
w i t h o n l y 1 0 p e r c e n t of t h e t r e e s
infected is only about 6 percent
( e s s e n t i a l l y t h e same a s f o r noninf e s t e d stands), but i n stands with
50 p e r c e n t of t h e t r e e s i n f e c t e d ,
y i e l d s a r e i n c r e a s e d by 40 p e r c e n t .
T a b l e 5--Simulated 90-year y i e l d s i n ponderosa p i n e s t a n d s now 30 y e a r s o l d . Average d . b . h .
i n c h e s , 1 , 0 0 0 t r e e s p e r a c r e . T r e a t e d s t a n d s t h i n n e d a t a g e 30, 60, and 90.
= 3.0
Merchantable c u b i c f o o t volume a c r e
s i t e index
Stand
Condition
Treatment
No m i s t l e t o e
None
40
60
80
1,840
4,180
6,480
143
Ill
112
170
740
2,670
680
+1,890
+3,570
500
355
234
33
57
86
t h i n GSL 100
Difference
cubic f e e t
percent increase
50% t r e e s
infected
(DMR = 0.8)
None
t h i n GSL 1 0 0
Difference
cubic f e e t
percent increase
.
Uninf ec t e d v s
50% t r e e s i n f e c t e d
+
None
Difference
cubic f e e t
percent decrease
Uninfected vs.
50% t r e e s i n f e c t e d
Thin GSL-100
Difference
cubic f e e t
percent decrease
CONCLUSIONS
Many s t u d i e s have shown t h a t dwarf m i s t l e t o e s a r e s t i m u l a t e d by opening up s t a n d s by
t h i n n i n g . However, i t h a s n o t been determined
whether t h i s i s due t o i n c r e a s e d l i g h t o r t o
improved t r e e v i g o r of t h e r e s i d u a l t r e e s , o r ,
a s I s u s p e c t , t o a combination of b o t h f a c t o r s .
We a l s o know t h a t t h e e f f e c t s of dwarf m i s t l e t o e a r e l e s s pronounced i n more v i g o r o u s t r e e s ,
s o t h e b e n e f i c i a l e f f e c t s of t h i n n i n g w i l l be
e v i d e n t i n i n c r e a s e d growth r a t e s , d e s p i t e t h e
f a c t t h a t m i s t l e t o e might a l s o i n c r e a s e . Howe v e r , t h i n n i n g c a n n o t b e recommended i n h e a v i l y
i n f e s t e d s t a n d s . We do n o t know e x a c t l y when
a given s t a n d i s t o o h e a v i l y i n f e s t e d t o t h i n ,
b u t we t e n t a t i v e l y s u g g e s t z a t t h i n n i n g b e
c o n f i n e d t o s t a n d s w i t h a DMR of 3 o r l e s s .
Although t h e s e a r e some g u i d e s t o h e l p
d e t e r m i n e whether a g i v e n i n f e s t e d s t a n d
should be t h i n n e d o r n o t , each s t a n d must b e
e v a l u a t e d on a n i n d i v i d u a l b a s i s .
We d o n ' t know how c l o s e o u r p r o j e c t i o n s
a r e t o a c t u a l y i e l d s , except t h a t our d a t a
a r e based on a c t u a l s t a n d s and should b e
reliable.
Some p a t h o l o g i s t s and f o r e s t e r s
t h i n k t h a t we a r e o v e r e s t i m a t i n g l o s s e s ,
o t h e r s t h i n k we a r e u n d e r e s t i m a t i n g them, s o
p e r h a p s we a r e on t h e r i g h t t r a c k . To monitor
t h e e f f e c t s of t h i n n i n g i n dwarf m i s t l e t o e
i n f e s t e d s t a n d s , we a r e e s t a b l i s h i n g a s e r i e s
of p l o t s i n i n f e s t e d l o d g e p o l e p i n e s t a n d s i n
Colorado and i n ponderosa p i n e i n Colorado and
Arizona.
S t a n d s w i t h v a r i o u s i n t e n s i t i e s of
dwarf m i s t l e t o e ( i n c l u d i n g m i s t l e t o e - f r e e
s t a n d s ) a r e b e i n g t h i n n e d t o s e v e r a l GSLs.
P e r i o d i c examination of t h e p l o t s w i l l show
how c l o s e o u r p r o j e c t i o n s a r e t o t h e a c t u a l
y i e l d s and w i l l p r o v i d e d a t a f o r a d j u s t i n g
growth and m i s t l e t o e - e f f e c t s e q u a t i o n s a s
needed.
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Hawksworth, Frank G.
1977. The 6 - c l a s s dwarf m i s t l e t o e r a t i n g
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