0785-B1
A. A. Hopkin[1], P. De Groot, D. Pitt, A. Carroll, H. Ottens and E. Caldwell
Integrated pest management (IPM) is important to the future of Canada's intensively managed forests. It involves the use of products and strategies that are effective but benign to the environment. Techniques such as silviculture and planning can be used to reduce the risk to pest losses. Examples of real, and potential IPM systems are given for control of the mountain pine beetle (Dendroctonus ponderosae), the eastern spruce budworm (Choristoneura fumiferana) and for weed species.
Canada's forests are central to its economic, environmental, and social well-being. Forests filter the air we breathe and the water we drink, and provide habitat for countless species of plants and animals. They also offer a multitude of spiritual and recreational values. In Canada, 41% of the productive forested land is commercial, providing jobs for 880,000 Canadians. In 1998, forest products contributed $31.7 billion to Canada's trade balance (Natural Resources Canada, 1999). There has been a significant shift towards setting aside forest land for non timber uses (e.g., habitat, biodiversity, recreation), resulting in a reduction of the commercial forest land base. These trends, coupled with increasing demand for wood fibre, have resulted in the need to manage forests on the reduced land base more intensely.
Without protection from insects and diseases, and weed species, gains made through intensive forest management can be lost. In Canada, insects and diseases are estimated to cause growth loss and mortality that can amount to 70% of the harvest (Hall and Moody 1994). Although less visible, and more difficult to quantify than insect or disease damage, losses to competing vegetation can be equally significant, particularly in conifer production (Walstad and Kuch, 1987).
Prior to the 1940's, large-scale forest insect control efforts were not undertaken in Canada. Pest control, where it was practiced, relied on silvicultural techniques such as sanitation, pruning, or thinning, or the application of insecticides to high value stands. After 1945, improvements in aircraft spray technology and the discovery of DDT, resulted in major control programs against forest insects, most notably the eastern spruce budworm. Following the 1962 publication of Rachel Carson's "A Silent Spring", there was a change in public attitude towards the use of long lasting synthetic pesticides. Out of this came the development of less harmful insecticides such as
B.t. (Bacillus thuringiensis). However increased focus on environmental issues by the public (Kates 1994), and the reluctance to use chemical pesticides has created a need for effective alternative and more benign control strategies. More thought is now being given to integrated pest management (IPM) in forestry.
The process of IPM attempts to protect resource values from pests while at the same time minimizing the effect on non-target species. The approach is based on ecological knowledge of the crop and potential pests, and seeks to maximize the use of natural control agents, and silvicultural practices. The concept does not exclude the use of pesticides, but permits the judicious use of them, as well as consideration of alternatives. Combining and integrating chemical insecticides with the use of insect parasitoids, predators or natural pathogens (biological control) was formalized as "integrated control" in agriculture in the 1950's (Stern et al. 1959). However, integration of biological control with the application of pathogens is rarely practiced in forestry in Canada.
There are many definitions of IPM in forestry and agriculture. Some definitions clearly emphasise the importance of ecology and maximizing the use of natural regulating factors, while others emphasize the importance of optimizing pest control and maximizing economic returns. One of the most often-quoted in forestry is that by Stark and Waters (1985) who define IPM as a process of synthesis where all aspects of the pest-host system are studied and evaluated to provide the resource manager with an information base for decision-making. One conceptual element of IPM, that is under-appreciated in forestry, is that IPM is a component of total resource management. It is worth quoting Waters (1974) here, who wrote: " It is implicit that the actions taken [pest management] are fully integrated into the total resource management process - in both planning and operation. Pest management, therefore, must be geared to the life span of the tree crop as a minimum and to a longer time span where the planning horizon requires." Two important components that Waters identified are that IPM must start with planning and it must be part of the whole forest cycle. These practices and strategies must be built into overall forest management planning. Too often pest management tries only to deal with pests after they become problems. All too often, pest management is seen as an entity separate from forest management, a practice that usually spells problems.
There have been some IPM success stories in recent years such as the "slow the spread" program to control the gypsy moth in the United States (Sharov et al. 2002). However, as noted by Volney and Mallett (1998) the Canadian situation is somewhat unique in that forest management costs must be low and yet at the same time environmentally benign. Although IPM does not receive the attention it deserves in Canadian forestry, it is our contention that sufficient knowledge exists for the implementation of IPM systems. In the case studies that follow, we show how these programs are working towards integration into forest resource management and how pro-active, or preventative pest management strategies, are being integrated with other strategies.
The Mountain Pine beetle (Dendroctonus ponderosae (MPB) is considered the most destructive insect of pines in western Canada, causing extensive mortality (Fig 1). In 2000 alone, the MPB affected 475, 000 ha of forest in British Columbia, causing a loss of 17 million m3 of timber. The basis of the MPB control program is built on the basis of ecological and silvicultural studies. The risk of infestation has been established and quantified (Shore and Safranyk, 1992), and the approach to dealing with MPB is well established (B.C. Ministry Forests 1995). As with any IPM system, a number of options are available to the practitioner when outbreaks occur, including, suppression, adjustment of harvest schedule, salvage (Fig. 2a). A key component of the MPB control program is an annual survey to pinpoint outbreaks so that control operations can be considered. A number of tactics have been developed to deal with this destructive pest when management of the insect is undertaken. Damage can be reduced through direct control, including, sanitation logging, burning of infested trees (Fig 2b), insecticide injection and use of insect attractants (pheromones). Since the selection of strategies and tactics is complex, due to the need to consider both temporal and spatial aspects of both insect and forest, a decision-support system has been developed to assist land managers with control decisions (Shore et al 1996). Efforts have also been undertaken to reduce the likelihood and severity of beetle attack using forest management that reduce stand susceptibility This includes hazard rating of stands, accelerated harvest to remove damaged trees, spacing and thinning, as well as shortened rotation to reduce losses in new stands (Whitehead et al. 2001).
Figure 1. Extensive mortality to pines resulting from the mountain pine beetle.
Fig. 2a. Harvesting lodgepole pine after MPB attack
Fig 2b. Burning of trees infested with MPB
The eastern spruce budworm (Choristoneura fumiferana (SBW) is the most damaging insect of spruce fir forests in North America and causes growth loss and mortality to balsam fir and white spruce (Fig. 3). Unlike the MPB, where silvicultural strategies were developed to manage populations, the approach to SBW usually involves aerial spraying of biological (B.t) insecticides. Spray programs are supported by extensive monitoring to delineate the area of forest affected, and by population forecasts using weather based models (Regniere et al 1995). Assuming populations are increasing, B.t. is applied to areas considered at risk. The development of a computer-based decision support system (DSS) for the spruce budworm (MacLean et al. 2001) allows for the integration of monitoring with knowledge of stand vulnerability, and economic impacts, to determine the relative need for, and benefits of spraying (Fig. 4), or for adjustments to the harvest schedule, to remove accessible forest at risk.
A good deal is known about the population dynamics of this insect (Regniere and Lysyk 1995), and the role of insect parasites, and their application in controlling the SBW (Smith et al. 2002). Mature spruce-fir forest is most vulnerable to attack making silvicultural options to reduce losses is theoretically possible. Work conducted on stand vulnerability (MacLean 1980) has shown that reducing stand age (harvest of mature trees) and/or increasing the hardwood component could reduce damage by the spruce budworm. Large-scale conversion to a less susceptible forest is seldom practical, however, on stand-by-stand basis such an approach is possible. Recently, Carter (2003), and the QMRN have attempted to summarize potential approaches, to IPM of the SBW based on our understanding of the insect and host ecology
Figure 3. Dead balsam fir trees after an outbreak of the eastern spruce budworm.
Fig. 4. Use of the Spruce budworm DSS to determine losses due to defoliation and potential growth loss reduced through aerial application of B.t.
Vegetation management, normally involving herbicides, is essential to conifer regeneration in Canada. The public have expressed concern over reliance on chemical control (Wagner 1993) and in response, a search for alternatives to herbicides, has been undertaken under initiatives such as the Vegetation Management Alternatives Program (Wagner et al. 1994). Manual cutting is the most practical available alternative to chemicals. To enhance this, a biological control agent that consists of a naturally occurring fungus, Chondrostereum purpureum, has been developed, that prevents re-sprouting (Pitt et al. 1999; Harper et al. 1999). Another enhancement to manual cutting involves optimisation of the timing and height of cutting. Bell et al. (1999) found that cutting just after full leaf out, at a height just below live crown, minimized the suckering and sprouting of aspen.
A number of ongoing research initiatives show promise for integrated vegetation management. A fungal biological control tool is being pursued for Calamgrostis canadensis, a competitive grass that rapidly invades western boreal sites after harvest (Mallet 2000). As proactive measures for enhancing crop establishment success and early growth, researchers have looked at the use of plant growth regulators in Douglas fir (Scagel and Linderman 2001) and nutrient loading of black spruce planting stock (Imo and Timmer 1999, Malik and Timmer 1997) with some success. Other alternatives such as mulching, cover cropping, and livestock grazing have been experimented with but, excepting use of the latter in western Canada (Comeau et al. 1999), these have seen little operational application. Nevertheless, these alternatives, coupled with existing tools, and the knowledge gained from current research efforts, should place foresters in a good position to practice integrated vegetation management, as we move into an era of intensive forest management.
Fig. 5. Application of the fungus Chondrostereum purpureum as a biological control to prevent resprouting of woody species following cutting.
Integrated pest management is considered a motherhood issue that is difficult to argue with in principle, the practice of it is somewhat more difficult. Unlike agriculture, forests in Canada are managed over extensive and often remote areas, with difficult access and high management costs. They are usually naturally regenerated, and are highly diverse areas with varying topographies. Land ownership is usually public while stewardship is often private. The time between planting and harvesting is usually between 60 and 100 years. In Canadian forestry, IPM must often be considered at the landscape level. Fortunately the improvements in Geographical information systems allow for analysis and decision-making at this level. Many of the IPM approaches in forestry must be developed and improved with this in mind. Above all though, IPM is a way of approaching forest management. Consideration must be given to economic thresholds and future pest impacts. Growing a tree species that is likely to be affected by a pest, in a manner that increases the likelihood of damage is not unusual, but goes against the principle of IPM. Strategies to avoid, reduce or mitigate pest impacts are usually both possible and practical in a managed forest.
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| [1] Natural Resources Canada,
Canadian Forest Service, Great Lakes Forestry Centre, 1219 Queen St. E.
Sault Ste. Marie, ON. P6A 5E2, Canada. Email: [email protected] |