Pest Damage and Integrated Control
INTEGRATING DWARF MISTLETOE William E. Waters-2/
Abstract: A broader, more comprehensive concept of forest pest management is needed to make it a really integral part of forest resource management. A generalized model structure of a forest pest management system is presented, and the major com- ponents are discussed briefly. Predictive models are the primary mechanism of information flow to decision and action in the sys- tem. General considerations affecting the kind and number of these models are discussed, with particular reference to the dwarf mistletoes. The whole-system approach to dwarf mistletoe management is urged. The focus of this symposium is on dwarf mistletoe control. Each of the symposium sections - - including this, the last - - has the
word control in its title. The various papers
presented thus far have covered the relevant biology of the mistletoes, their ecological relations with host trees and stands, their effects on growth and yield and some damage statistics for different host types and geo- graphic regions, and various control techniques for prevention or amelioration of the damage to be expected. The term management has
crept in at times, and this has been expanded to integrated management in several contexts.
The nature of dwarf mistletoe effects on for- ests has made the use of these terms fairly common, in fact. But what do we really mean by integrated pest management, or integrated management of dwarf mistletoes? The concept of forest pest management - the notion that destructive diseases (and insects) are an integral part of forest eco- systems, that they have both ecological and economic impacts on those ecosystems and the resource values involved, and that somehow their effects have to be kept at tolerable levels in ways compatible with forest manage- ment objectives and practices - - is not new
Ñ'presente
at the Symposium on Dwarf Mistle- toe Control Through Forest Management, Berke- ley, Calif., April 11-13, 1978. Ñ'~rofessor Departments of Forestry and Con- servation and Entomological Sciences, College of Natural Resources, and Entomologist in the Agricultural Experiment Station, University of California, Berkeley. (Meinecke 1916; Hopkins 1909). However, the concept has little reality in practice. The attitude of forest managers and administrators generally has been to play the game of "wait and see," followed by seat-of-the-pants deci- sions on action when a pest becomes obvious, intrusive, or intolerable. This attitude has affected research priorities, time schedules, and methodology accordingly. If we better understand the full meaning of integrated pest management - - its spacetime dimensions, the complexities and interac- tions of its ecological and economic components, and the social and political factors that in- evitably have a part in planning and decision- making -- perhaps we can better set our sights
on the research now needed and improve the odds of getting forest resource managers and admin- istrators to put our collective knowledge and technology to work. Our real goal should be a forest protection system that incorporates dwarf mistletoe control -- and control or
regulation of all other destructive agents that may be involved -- into the total resource
management process on a long-term, continuing basis. Let us look at the basic components of a forest pest management system. Figure 1 shows a generalized model structure of such a system (Waters and Cowling 1976). There are four basic components (enclosed by the dotted lines): (1) the population dynamics and epidemiology of the insects and diseases involved, (2) the dynamics of forest stand development, (3) the socioeconomic impacts of pest-caused damage on resource values, and (4) the treatment strate- gies. Each component is a complex subsystem in itself; each requires detailed analysis and Treatments
RESEARCH
AND DEVELOPMENT
1
Treatment
strategies
-------
I forest conditions I
L
F i g u r e I - - G e n e r a l i z e d model s t r u c t u r e o f a f o r e s t p e s t management system.
understanding t o provide t h e p a r t i c u l a r pred i c t i v e models c a l l e d f o r i n t h e o p e r a t i o n a l
system. The h e a v i e r a r r o w s show t h e p r i m a r y
linkages, o r information flows, i n t h e plann i n g - d e c i s i o n p r o c e s s . The f o c a l p o i n t o f
t h e system i s t h e b e n e f i t / c o s t i n t e g r a t i o n ,
whereby t h e b e n e f i t s ( v a l u e s s a v e d o r g a i n e d )
and t h e c o s t s o f a l t e r n a t i v e t r e a t m e n t s o r
actions a r e assessed.
F i g u r e 2 shows t h e same g e n e r a l model i n
a d i f f e r e n t c o n f i g u r a t i o n (Campbell and McFadden 1977). T h i s emphasizes t h e d i f f e r e n t
r e s o u r c e v a l u e s and management o b j e c t i v e s
t h a t may b e a t s t a k e .
P r e d i c t i v e models a r e t h e p r i m a r y mechanism o f i n f o r m a t i o n f l o w t o d e c i s i o n and
a c t i o n i n a n o p e r a t i o n a l system (Waters and
Ewing 1 9 7 5 ) . We must have t h e c a p a b i l i t y t o
a n t i c i p a t e t h e o c c u r r e n c e , abundance, and
t r e n d s i n p e s t p o p u l a t i o n s . We must be a b l e
t o e s t i m a t e t h e i r p o t e n t i a l e f f e c t s on s t a n d
growth and y i e l d and o t h e r s t a n d p a r a m e t e r s o f
concern, and t o p u t t h e s e i n t e r m s o f t h e v a l u e s
t h a t w i l l be a f f e c t e d . And we have t o be a b l e
t o s p e c i f y i n advance t h e e x p e c t e d outcomes o f
d i f f e r e n t t r e a t m e n t s o r management a c t i v i t i e s ,
i n c l u d i n g no a c t i o n , n o t j u s t i n t e r m s o f t h e
e f f e c t s on t h e p e s t ( s ) b u t i n t e r m s o f v a l u e s
l o s t , s a v e d , o r g a i n e d a s w e l l . T h i s lookahead f e a t u r e i s a major d i s t i n c t i o n between
p e s t management and p e s t c o n t r o l .
The k i n d and number o f p r e d i c t i v e models
i n t h e system depend i n p a r t , o f c o u r s e , on
t h e p e s t o r p e s t complex i n v o l v e d . But some
general considerations apply i n a l l cases, i n c l u d i n g t h e management o f dwarf m i s t l e t o e .
These a r e :
(1) The time-span o f t h e t r e e l l c r o p l l - c u t t i n g c y c l e s and r o t a t i o n a g e s
w i l l d i f f e r with t r e e species,
l o c a t i o n , and management o b j e c t i v e s .
This i s a f a c t o r c e r t a i n l y with
RECREATION
INVENTORY
TIMBER
WATER
FIRE
HAZARD
PROJECTED VALUE FOR EACH
RESOURCE SUBSEQUENT
TO APPLICATION OF
CONTROL ALTERNATIVES b
STAND
INVENTORY
MAKER
DOUGLAS -FIR
TUSSOCK MOTH
INVENTORY
11 Projected values subsequent to exercising the "no control" alternative will provide a base line for estimating benefitlcost ratios.
Figure 2--Information inputs, flows, and outputs in the Douglas-fir tussock moth research and development program (from Campbell and McFadden 1977). dwarf mistletoes, considering the
wide range of situations in which
they are involved.
(2) The phenology of the tree(s) rela-
tive to the life cycle and activity
of the pest--the extent to which
critical stages of the pest, such as
establishment and infection, are
dependent on being synchronized with host plant development. This may not be very important with the dwarf mis- tletoes. (3) The annual number of generations and seasonal abundance of the pest-- whether the pest has one, two, or more generations or cohorts a year; the rate of increase in each cohort; and the potential for increase in suc- cessive years. As I understand it, there is some variation in this fac- tor among the dwarf mistletoes over the range of hosts and conditions in which they occur. (4) The manner of spread and dispersal capability of the pest~whether spread or dispersal is active or pas- sive, short- or long-range, random or contagious (dependent on direct con- tact of infected hosts), regular or irregular in frequency, etc. This factor, along with host conditions, determines the pattern and rate of spread of infection or infestation in stands or areas. It certainly is an important consideration with the dwarf mistletoes. individual tree selection, or some other silvicultural system, and the frequency of operations related to these; the products or product mix and other uses and values intended. These considerations establish constraints on all components of the system - - on the
stand dynamics and impact models parti- cularly. This all sounds complicated - - and it can
be. We don't, in fact, have all the pieces for any major pest. But some simplifications -in methodology, not in the overall concept -can be made as a start. Where do we stand with the dwarf mistletoes, for example? Firstly, all of the current knowledge of dwarf mistletoe biology and epidemiology -and this is well summed up at this Symposium -- can be wrapped up in two models which express (I) the conditional probabilities of (5) The kind and rate of damage inflicted dwarf mistletoe occurring in individual stands --whether the effect on stands is qual- or management units based on tree and stand itative (i.e. cosmetic) or quantita- characteristics, proximity of infection sources, tive; whether outright tree mortality, and other quantifiable variables, and (2) the growth loss, or some combination of rate of increase in mistletoe damage, including these is involved; the age-size dis- mortality, by tree species, age class, a spa- tribution of trees affected; the tial index, infection level, and, again, other relation between rate of damage and quantifiable variables determining predictive loss and pest numbers or infection accuracy and precision. An approach to develop- sources; and the shifting interplay ing such models for disease management, util- between measured damage and loss and izing a logical simulation of the processes of management objectives, expressed as disease establishment and buildup, has been thresholds for action. All of these described by Waggoner (1976). Stage (1973, factors are involved in the prediction 1975) has provided a computerized, algorithmic of damage and loss due to dwarf mis- basis for putting expectations of pest inci- tletoes in particular situations. dence and damage into projections of stand growth and development for forest management (6) The kind and frequency of treatments planning. A more detailed exposition of the --whether bioloeical,
cultural. chem- rationale and mathematics of integrating for- ical. or an integrated mix of methods est pest dynamics and stand dynamics into the are to be employed, and the time management decision-making process has been sequence in which they will be applied given by Stage and Long (1976). The incorpor- (within a given year and over succes- ation of earlier whole-stand models of lodge- sive years). For every pest or pest pole pine and ponderosa pine infested by dwarf complex, including dwarf mistletoes, mistletoe (Myers et al. 1971, Myers et al. every alternative will have a differ- 1976) into a new computer program by Edminster ent expectation of outcomes in terms (1978) covering a wider range of stand condi- of protection afforded and cost. tions is a significant step in developing the practicable kind of input needed on mistletoe incidence and effects over time. These ap- (7) The scope and objectives of the pest management program--the space-time proaches, and the models and computerized pro- frame of the program; whether preven- cedures to utilize them, combine in effect the tion, suppression, long-term regula- information contained in the pest population tion, or some combination of these is and stand dynamics boxes of the general model. intended. This determines the dimen- sionality of the entire set of predic- The assessment and projection of potential tive models in the system. impacts of destructive insects and diseases - their cumulative net effects on the productiv- (8) Silvicultural considerations and ity, usefulness, and value of a tree species management objectives--whether the or forest type with respect to different stands are to be managed under an resource uses and management objectives - - is
even-aged, 2-storied, group selection, an area which forest pathologists (and ento- mologists) have usually avoided. Properly so. choice is made based on some utilitarian cri- The ecological, economic, and social complica- terion such as maximum benefit per unit cost tions of this aspect of pest management were (Valentine et al. 1976). The limitation to dissected and reconstructed at a U.S. Forest this approach is that the risks of a bad choice Service-sponsored work conference at Marana may be quite high depending on the caliber of Park, Arizona,in 1972. The report of that the data and the assumptions used in constructing conference did much to clarify terms and to the decision-tree. A more serious shortcoming distinguish explicitly between the measurement is that it cannot be incorporated easily into and prediction of changes in stand parameters a forest management model. Numerous decision- brought about by the activities of diseases trees may be needed for a given pest or pest and insects and the effects of those changes complex, and the variables and criteria in terms of values affected (U.S. Forest Ser- used may be more or less unique for the situation vice 1972). The ecological and economic com- involved. Regardless, this approach has a plications, research and applied approaches to strong appeal as an interim procedure, at impact evaluation, and data requirements in an least, and it undoubtedly would be useful for operational system, have been more fully sum- many dwarf mistletoe situations. marized by Waters (1976). I believe we now have a clear communication link with forest In the longer view, there is good reason economists and forest managers and, importantly, to set our sights on a complete management sys- a better basis for mutual understanding of tem for the dwarf mistletoes - - and, ultimately,
where and how value judgments should be on total protection systems against all des- entered into the general model for planning tructive agents affecting the coniferous forests and decision. Specifically, in the case of of the Western United States. The long-range dwarf mistletoes, it would seem that the cur- program goals of the Renewable Resources Plan- rent values and related economic parameters of ning Act of 1974 and the mandate of the National managed stands of most, if not all, of the Forest Management Act of 1976 both give protec- host tree species are well enough known and tion of our forest resources high priority. sufficiently amenable to simulation for a rea- The environmental benefits to be derived also sonable number of years ahead that this com- support this view. There is an opportunity for ponent of the dwarf mistletoe management model the dwarf mistletoes to serve as the prototype could now be filled in. for forest disease management on the scale envisioned here. I, for one, believe we should Similarly, from research and management get at it. experience, it should be possible to develop reasonably accurate estimates of the costs and LITERATURE CITED effectiveness of silvicultural treatments, or management practices, for prevention or ame- lioration of dwarf mistletoe damage for a Campbell, R. IT. , and M.W. McFadden.
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