IMPACT EVALUATION FOR DWARF
MISTLETOE-INFESTED PONDEROSA PINE IN THE
SOUTHWESTL!
James W. waltersZ7
Abstract: Southwestern dwarf m i s t l e t o e (Arceuthobium
vaginatum subsp. cryptopodum) occurs on more than one-third
of t h e commercial ponderosa pine f o r e s t i n Arizona and New
Mexico. Annual volume l o s s from t h i s d i s e a s e i s estimated
a t 150-200 m i l l i o n board f e e t on National Forests i n t h e
Southwestern Region. The simulated y i e l d program SWYLD2
i s used t o h e l p e v a l u a t e impact of southwestern dwarf
m i s t l e t o e . A survey procedure and d a t a summary program
have been designed t o compile input f o r t h e SWYLD2
program. This program provides resource managers with
simulated y i e l d t a b l e s f o r dwarf m i s t l e t o e - i n f e s t e d
s t a n d s of ponderosa pine. Yield t a b l e s h e l p quantify
timber volume l o s s , and allow resource managers t o
examine various manaeement
a l t e r n a t i v e s and t h e i r e f f e c t s
"
on dwarf m i s t l e t o e l e v e l s .
Southwestern dwarf m i s t l e t o e (Arceuthobium
vaginatum subsp. cryptopodum) i s t h e most
d e s t r u c t i v e d i s e a s e on ponderosa pine i n t h e
Southwest. This d i s e a s e occurs on a l l National
F o r e s t s i n Arizona and New Mexico. Andrews
and Daniels (1960) c a l c u l a t e d southwestern
dwarf m i s t l e t o e t o be p r e s e n t on a t l e a s t 2.5
m i l l i o n a c r e s of commercial ponderosa pine
f o r e s t i n Arizona and New Mexico. Annual volume
l o s s from t h i s d i s e a s e i s estimated t o exceed
h a l f of t h e annual allowable c u t on National
F o r e s t s i n Region 3. P r i n c i p a l h o s t s f o r southwestern dwarf m i s t l e t o e include ponderosa pine,
Pinus oonderosa- v a'r . ,scooulorum. P. uonderosa
-.
v a r . a r l z o n i c a , and Apache pine, P. engelmannii.
The adverse e f f e c t s of southwestern dwarf
m i s t l e t o e have been q u a n t i f i e d i n several ways.
M o r t a l i t y e s t i m a t e s have been made f o r i n f e s t e d
s t a n d s , p o t e n t i a l s a f e t y hazard i n r e c r e a t i o n
a r e a s has been evaluated, and timber volume
l o s s has been q u a n t i f i e d on a stand b a s i s .
-
^presented a t t h e Symposium on Dwarf l l i s t l e t o e
Control Through Forest rianagement, Berkeley,
C a l i f . April 11-13, 1978.
2 ' ~ o r e s t P a t h o l o g i s t , Southwestern Region,
Forest Service, U.S. Department of Agricult u r e , Albuquerque, New Mexico.
The l a t t e r i s perhaps t h e most u s e f u l t o o l f o r
evaluating dwarf m i s t l e t o e e f f e c t s over l a r g e
areas.
Three f a c t o r s c o n t r i b u t e t o timber volume
l o s s : growth reduction, t r e e m o r t a l i t y , and
d e f e c t . Growth reduction i s t h e most important
and most d i f f i c u l t value t o estimate. Heavilyi n f e c t e d t r e e s may s u s t a i n a 30-60 percent
growth reduction, compared t o non-infected t r e e s .
The amount of reduction depends on time and
i n t e n s i t y of i n f e c t i o n , t r e e s i z e and age,
s i t e f a c t o r s , and many o t h e r a s p e c t s of t r e e
environment.
Tree m o r t a l i t y i s t h e second most important
volume l o s s f a c t o r . Mistletoe-caused m o r t a l i t y
can be d i f f i c u l t t o q u a n t i f y due t o invasion
of i n f e c t e d t r e e s by i n s e c t s . Assigning t h e
primary m o r t a l i t y f a c t o r o f t e n becomes impract i c a l . Andrews and Daniels (1960) estimated
annual m o r t a l i t y l o s s e s i n m i s t l e t o e - i n f e s t e d
ponderosa pine a t 55-75 m i l l i o n board f e e t i n
t h e Southwest.
Defect caused by dwarf m i s t l e t o e i s r e l a t e d
t o g r a i n d i s t o r t i o n and r e s i n impregnation a t
i n f e c t i o n s i t e s . This aspect of volume l o s s
i s seldom measured, and i t s o v e r a l l importance
i s not well-defined f o r Southwestern f o r e s t s .
Commonly used e v a l u a t i o n techniques, such
a s measurement of volume l o s s , f r e q u e n t l y
e s t i m a t e only one of t h e many e f f e c t s r e s u l t i n g
from a dwarf m i s t l e t o e i n f e s t a t i o n . For examp l e , e x p r e s s i n g adverse e f f e c t s of dwarf m i s t l e t o e i n terms of cubic f o o t l o s s p e r a c r e emphas i z e s t h e timber production a s p e c t . I t becomes
more d i f f i c u l t t o apply cubic f o o t l o s s t o
d e t e r i o r a t i o n of w i l d l i f e h a b i t a t , r e c r e a t i o n a l
o p p o r t u n i t y , o r watershed p r o d u c t i v i t y . In
f a c t , what i s an adverse e f f e c t on one resource
may be b e n e f i c i a l t o o t h e r r e s o u r c e s . When a
d i s e a s e such a s dwarf m i s t l e t o e a l t e r s t h e
f o r e s t environment, q u e s t i o n s must be answered
t o determine t h e t o t a l e f f e c t s on a l l resources
and r e s o u r c e u s e r s . These e f f e c t s , when i d e n t i f i e d and q u a n t i f i e d , c o n s t i t u t e t h e impact of
a f o r e s t d i s e a s e . Can we measure t h i s complex
of e f f e c t s ? Do we have t h e e x p e r t i s e t o evalu a t e such a v a s t a r r a y of f a c t o r s ? What terminology do we use t o express p o s i t i v e and negat i v e e f f e c t s ? These q u e s t i o n s must be answered
b e f o r e impact e v a l u a t i o n can be r e a l i z e d .
There may be some confusion about who has
r e s p o n s i b i l i t y f o r impact e v a l u a t i o n of dwarf
m i s t l e t o e . In t h e U. S. Forest Service,
personnel i n F o r e s t I n s e c t and Disease Management cooperate with designated National Forest
System personnel t o develop impact d a t a on
dwarf m i s t l e t o e . In t h e Southwest, a f o r e s t
d i s e a s e s p e c i a l i s t provides an assessment of
t h e e f f e c t s dwarf m i s t l e t o e i s and w i l l be
having on i n f e s t e d s t a n d s ( b i o l o g i c a l evalua t i o n ) . This information i s provided t o t h e
resource manager, so t h a t , j o i n t l y , an impact
e v a l u a t i o n can be prepared. Resource managers
c a l l on o t h e r s p e c i a l i s t s t o h e l p e v a l u a t e
impact of dwarf m i s t l e t o e on o t h e r resources.
In essence, a team of s p e c i a l i s t s provides i n p u t
t o t h e r e s o u r c e manager r e l a t i v e t o m i s t l e t o e
e f f e c t s and t h e i r a r e a of s p e c i a l i z a t i o n . The
r e s o u r c e manager then combines t h i s information
and completes t h e impact e v a l u a t i o n . An import a n t f a c t o r t o n o t e i s t h a t we, i n Forest I n s e c t
and Disease Management, r e a l l y do not e v a l u a t e
impact of a f o r e s t d i s e a s e p e r s e . We e v a l u a t e
t h e c u r r e n t s t a t u s of a d i s e a s e , q u a n t i f y c e r t a i n e f f e c t s of t h a t d i s e a s e , p r o j e c t t h e
d i s e a s e s i t u a t i o n i n t o t h e f u t u r e , whenever
p o s s i b l e , and a s s e s s o r recommend p o t e n t i a l
c o n t r o l measures.
Ifore f i n i t e l y , i n r e l a t i o n t o southwestern
dwarf m i s t l e t o e , we most f r e q u e n t l y e s t i m a t e
only timber volume l o s s i n an i n f e s t e d s t a n d .
This q u a n t i t y then, c o n s t i t u t e s our major input
i n t h e impact e v a l u a t i o n process.
Dwarf m i s t l e t o e e v a l u a t i o n e f f o r t s i n t h e
Southwest have been concentrated i n high p r i o r i t y r e s o u r c e a r e a s . Such a r e a s a r e c h a r a c t e r i z e d by high-timber production p o t e n t i a l ( i . e . ,
s i t e index and a c c e s s i b i l i t y ) high-value
r e c r e a t i o n a l opportunity, o r a r e a s of s p e c i a l
i n t e r e s t t o resource managers ( i . e . , d i f f i c u l t
Economics d e f i n e t h e s e
regeneration areas)
t y p e s of a r e a s a s l o c a t i o n s where adverse
e f f e c t s of dwarf m i s t l e t o e can be e f f i c i e n t l y
reduced. I f a resource manager does not have
s u f f i c i e n t funds t o c o n t r o l dwarf m i s t l e t o e ,
there i s l i t t l e benefit i n quantifying those
e f f e c t s . Exceptions occur i n a r e a s where
q u a n t i f y i n g d i s e a s e e f f e c t s can a l t e r p r i o r i t i e s
( i . e . , d o l l a r s and p e r s o n n e l ) . Eventually, we
hope t o p a r t i c i p a t e i n e v a l u a t i n g impact f o r
a l l dwarf m i s t l e t o e - i n f e s t e d s t a n d s , but a
system of p r i o r i t i e s must be followed t o o b t a i n
maximum b e n e f i t from our e f f o r t s .
.
Current Region 3 e v a l u a t i o n s of southwestern dwarf m i s t l e t o e use t h e simulated y i e l d
program SWYLD2 (Myers e t a l . 1976, Edminster
and Hawksworth 1976). This program provides
resource managers with simulated y i e l d t a b l e s
f o r dwarf m i s t l e t o e - i n f e s t e d s t a n d s of ponderosa
p i n e . Yield t a b l e s h e l p q u a n t i f y timber volume
l o s s caused by dwarf m i s t l e t o e . Resource
managers can examine v a r i o u s management a l t e r n a t i v e s and t h e i r e f f e c t s on dwarf m i s t l e t o e
l e v e l s . In a d d i t i o n , they can b e t t e r e v a l u a t e
t h e b e n e f i t s and consequences of c o n t r o l l i n g
dwarf m i s t l e t o e .
Application of t h e SWYLD2 program i s
r e s t r i c t e d t o even-aged o r two-storied s t a n d s
t h a t a r e a t l e a s t 90 p e r c e n t ponderosa p i n e .
Stands not meeting t h e s e requirements a r e not
n e c e s s a r i l y precluded from t h e m i s t l e t o e evalua t i o n process, but our assessment l a c k s t h e
predictive aspect.
Basic input i n t h e SWYLD2 program i s
r e l a t i v e l y uncomplicated. Stand c o n d i t i o n
v a r i a b l e s needed f o r SWYLD2 input include:
s i t e index, average age, height and d.b.h.,
number of t r e e s p e r a c r e , and s t a n d DMR o r
percent t r e e s i n f e c t e d with dwarf m i s t l e t o e .
Stand DMR i s t h e average dwarf m i s t l e t o e r a t i n g ,
based on t h e s i x c l a s s system, f o r a l l t r e e s
i n a stand. These values must be provided f o r
both s t o r i e s i n a two-storied s t a n d . We have
designed a survey procedure f o r g a t h e r i n g t h i s
information i n even-aged o r two-storied ponderosa p i n e s t a n d s .
Sample p o i n t s a r e l o c a t e d on a g r i d
throughout t h e survey a r e a . Grid i n t e r v a l
v a r i e s with s t a n d s i z e . A 4- by 4-chain g r i d
may be used i n a 200-acre stand, while a 10by 10-chain g r i d may be s e l e c t e d f o r use i n a
1,000-acre a r e a . Fixed and v a r i a b l e r a d i u s
p l o t s (B.A.F.) a r e e s t a b l i s h e d a t each sample
p o i n t . The sample c o n s i s t s of a l l l i v e t r e e s
4.5 f e e t t a l l t o 5 . 9 inches d.b.h. on t h e fixed
p l o t , and l i v e t a l l y t r e e s 6.0 inches d.b.h.
and l a r g e r on t h e B.A.F. p l o t . Presence/absence
of dwarf m i s t l e t o e o r dwarf m i s t l e t o e r a t i n g
(DMR) and d.b.h. a r e recorded f o r a l l sample
t r e e s . A s k e t c h map of p l o t l o c a t i o n s i s made
during t h e survey f o r l a t e r u s e i n showing
dwarf m i s t l e t o e d i s t r i b u t i o n . A s p e c i f i e d
number of age and h e i g h t measurements a r e
taken t o e s t i m a t e s i t e index. Age and h e i g h t
measurements a r e a l s o taken from a s p e c i f i e d
number of codominant o r dominant t r e e s i n each
s t o r y of t h e stand. Data a r e recorded on forms
s p e c i f i c a l l y designed f o r r a p i d t r a n s f e r of
information i n t o a computer summary program.
F i e l d d a t a a r e then processed through t h e
SWSUIMARY computer program. This program was
designed t o accommodate d a t a from t h e p r e v i o u s l y
o u t l i n e d survey. SWSWRY prepares s t a n d
summary t a b l e s and c a l c u l a t e s SWYLD2 s t a n d
c o n d i t i o n v a r i a b l e s from survey d a t a . The
program a l s o summarizes age and h e i g h t i n f o r mation f o r t h r e e s e t s o f s e l e c t e d t r e e s . These
s e l e c t e d t r e e s r e p r e s e n t ( I ) maximum s i t e
p o t e n t i a l of t h e s t a n d , (2) average age and
h e i g h t of o v e r s t o r y dominant and codominant
t r e e s , and (3) average age and h e i g h t of unders t o r y "dominant" and "codominant" t r e e s . The
summary t a b l e s provide a s t a n d inventory and
a r e u s e f u l i n determining SWYLD2 management
options.
Resource managers develop v a r i o u s management o p t i o n s and combine them with s t a n d condit i o n v a r i a b l e s t o produce simulated y i e l d
t a b l e s . Comparison of v a r i o u s management a l t e r n a t i v e s h e l p s t h e r e s o u r c e manager q u a n t i f y
e f f e c t s of dwarf m i s t l e t o e i n an i n f e s t e d s t a n d .
A c o s t a n a l y s i s was made f o r e i g h t survey
a r e a s completed i n 1977. A 10- by 10-chain
g r i d was used f o r a l l surveys. Cost e s t i m a t e s
a r e based on f i e l d crew of two f o r e s t r y t e c h n i c i a n s ( i - e . , $ 4 / h r . / t e c h n i c i a n ) working 40
hours p e r week. Average c o s t , i n c l u d i n g t r a v e l
time from Ranger D i s t r i c t o f f i c e t o survey a r e a ,
was 30$ p e r a c r e . Pure survey c o s t , excluding
t r a v e l t o t h e survey a r e a , averaged 23$ p e r
a c r e . Reducing t h e g r i d i n t e r v a l from 10- by
10-chains t o a c l o s e r spacing w i l l i n c r e a s e
survey c o s t . However, we e s t i m a t e t h a t even a t
a 4-chain i n t e r v a l , survey c o s t w i l l not exceed
754 p e r a c r e . The range i n survey c o s t from
23$ t o 75$ p e r a c r e appears reasonable f o r use
of an i n t e n s i v e f o r e s t management t o o l .
Once t h e resource manager has a s e t of
y i e l d t a b l e s d i s p l a y i n g volume l o s s caused by
dwarf m i s t l e t o e over a r o t a t i o n , v a r i o u s degrees
of
can be
Management a l t e r n a t i v e s which b e s t meet t h e r e s o u r c e manager's
needs can t h e n be s e l e c t e d f o r implementation.
SWYLD2 output i s expressed i n t o t a l cubic f o o t
volume, merchantable c u b i c f o o t volume, and
board f o o t volume on a per-acre b a s i s . These
v a l u e s can be converted i n t o d o l l a r e s t i m a t e s
by each i n d i v i d u a l resource manager. I n d i v i d u a l
conversion t o d o l l a r v a l u e s i s e s s e n t i a l a s
market v a l u e s vary with a c c e s s i b i l i t y t o production f a c i l i t i e s , access t o a l a b o r f o r c e ,
e t c . Once l o s s e s t i m a t e s a r e converted from
cubic o r board f o o t volume t o d o l l a r v a l u e ,
resource managers can determine t h e c o s t of
dwarf m i s t l e t o e c o n t r o l ; then, a c o s t / b e n e f i t
r a t i o can be determined. Often, impact on
o t h e r resource v a l u e s can be q u a n t i f i e d and
compared with m i s t l e t o e c o n t r o l c o s t s a t v a r i o u s
management i n t e n s i t i e s .
The f i n a l s t e p i n t h e e v a l u a t i o n p r o c e s s
d e a l s with follow-up on m i s t l e t o e e v a l u a t i o n s .
When a resource manager implements a s i l v i c u l t u r a l treatment, a s p r o j e c t e d by t h e SWYLD2
program, Forest I n s e c t and Disease Management
personnel may resurvey t h e s t a n d . Follow-up
survey d a t a provide an assessment of how well
simulated s t a n d c o n d i t i o n s match on-the-ground
c o n d i t i o n s . When a c t u a l c o n d i t i o n s do not match
t h o s e p r o j e c t e d , an attempt i s made t o determine
where t h e discrepancy occurred. In a d d i t i o n ,
simulations a r e made f o r t h e r e s i d u a l s t a n d
a f t e r t r e a t m e n t . Thus, t h e resource manager
has an opportunity t o c o r r e c t inadequate t r e a t ments and t o r e a s s e s s t h e dwarf m i s t l e t o e s i t u a t i o n f o r f u t u r e y e a r s . This, i n t u r n , provides
more f i n i t e information f o r f u t u r e timber
management planning.
Through t h i s follow-up procedure, f o r
i n s t a n c e , we have found t h a t maximum diameter
l i m i t s and/or spacing r e s t r i c t i o n s i n precommercial thinnings result in poor mistletoe
c o n t r o l . These f a c t o r s a l s o can make simulat i o n of such t r e a t m e n t s l e s s r e l i a b l e . Such
information i s valuable t o t h e r e s o u r c e manager
who has based an impact e v a l u a t i o n on SWYLD2
projections~
A s f o r e s t management continues t o i n t e n sify, use of simulated yield programs will inc r e a s e . Yield s i m u l a t i o n s , such a s t h o s e provided by t h e SWYLD2 program, w i l l continue t o
h e l p t h e resource manager e v a l u a t e t h e impact
of a f o r e s t d i s e a s e such a s southwestern dwarf
mistletoe.
Dwarf m i s t l e t o e poses an unquestionable
t h r e a t t o t h e p o t e n t i a l of f o r e s t resource
production i n t h e Southwest. Various techniques
have been used t o q u a n t i f y t h e magnitude of
t h i s t h r e a t . Of t h e techniques used, summarizing timber volume l o s s over a designated time
period appears t o be t h e most e f f i c i e n t . The
y i e l d program SWYLD2 has provided t h e
methodology t o complete t h i s t a s k . Resource
managers can now begin t o a s s e s s , i n a more
f i n i t e manner, t h e o v e r a l l e f f e c t s of dwarf
mistletoe on all resources. Thus, the capa- bility to evaluate impact of southwestern dwarf mistletoe is in the final development stages. LITERATURE CITED Andrews, S. R., and J. P. Daniels. 1960. A survey of dwarfmistletoe in Arizona
and New Mexico. U. S. Dep. Agric., For. Serv., Rocky Mt. For. and Range Exp. Stn., Stn. Pap. 49. 17 p. Edminster, C. B., and F. G. Hawksworth. 1976. User's guide to SWYLD2: Yield tables for even-aged and two-storied stands of southwestern ponderosa pine, including effects of dwarf mistletoe. 1). S. Dep. Agric., For. Serv. Gen. Tech. Rep. RM-23. 8 p. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colorado. Myers, C. A., C. B. Edminster, and F. G. Hawksworth. 1976. SWYLD2: Yield tables for even-aged and two-storied stands of southwestern ponderosa pine, including effects of dwarf mistletoe. U. S. Dep. Agric., For. Serv. Res. Pap. RM-163. 25 p. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colorado.