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Indicator 2.3 - Area of forest disturbed by fire, insects, disease, and timber harvest core indicator 
Disturbance from natural causes is a fundamental process in Canada's forests and helps to promote the natural functioning of the ecosystem and maintain biodiversity. In addition, a small proportion of Canada's forests is disturbed each year through harvesting, which also usually helps to renew forest stands. Because disturbance is an integral part of the functioning of the forest ecosystem, large reductions in the amount of disturbance may be as undesirable as large increases. Many scientists and forest managers believe that the amount of disturbance needs to be maintained within some acceptable level. In the past decade, there has been considerable scientific debate about defining a "natural" range of variation. This concept has been adopted, with varying success, by several jurisdictions throughout the world, although in general it needs more development. In Canada, some jurisdictions are going through a process of defining an acceptable level of disturbance. Interpretation of this indicator should be related to those jurisdictional efforts. However, even before these various processes are completed, this indicator will provide important information at a national scale, helping Canadians to engage in discussions on topics as diverse as fire suppression or wood supply. The data available on the different disturbances described in this indicator come from various sources and apply to different land bases. The data on forest fires and insect infestations are purported to cover the entire territory of Canada, although some fires or insect infestations in very remote areas may remain undetected and therefore unreported. Harvesting occurs only in areas that support the growth of trees of commercial interest-a much smaller land base than that affected by fires and insect infestations. There are unfortunately no national data to evaluate the impact of forest disease outbreaks to support this indicator. Forest fires have always been an integral part of Canada's forest ecosystems. Although they may seem to be only a destructive force, as portrayed in the media coverage of the 2003 blazes in British Columbia, they are actually an essential element of forest renewal. They help control insect and disease damage and eliminate litter that has accumulated on forest floors. Some species of trees actually require the intense heat generated by forest fires to release their seeds. Finally, fires can help reset the successional clock of forest ecosystems by removing the forest canopy and allowing sunlight to reach the ground, promoting the growth of shade-intolerant pioneer trees. Forest fires in Canada from 1975 to 2005 vary considerably in number and in size of forest area burned (Figure 2.3a). Typically, human error is responsible for the largest number of fires annually while lightning strikes cause the largest fires by area, especially in remote northern areas. There is a great fluctuation in fire activity both among provinces and territories in a given year and within a given province or territory over the years. There is no notable trend in either the number of fires or the area burned from 1975 to 2005. 
Figure 2.3a Number of forest fires and area burned in Canada (1975-2005). (Source: CCFM 2006, Johnston 2005) Updated Data: PDF | Excel In 2005, 7438 fires burned a total of 1.7 million ha in Canada. On average over the past ten years, around 7384 fires have burned about 1.9 million ha per year. The year 2003 was particularly challenging for fires in British Columbia. Nearly 2500 fires in the province were attacked by a force of more than 10 000 firefighters and support personnel, and burned approximately 265 000 ha (John Parminter, British Columbia Ministry of Forests and Range, Sept. 27, 2004, personal communication), the largest area burned in the province since 1982. Several factors can play a role in a fire crew's ability to control a fire. For instance, getting to a fire early, before it has an opportunity to gather energy, provides the best chance to extinguish it. Winds can fan flames, and accumulated forest litter can provide fuel for the fire. In British Columbia, the combination of cumulative drought and difficult terrain resulted in unprecedented fire behavior in 2003 and made fire suppression almost impossible in some circumstances. Extinguishing fires is difficult at best, despite Canada's world-class fire protection systems. This is why early detection and prevention also play an important role in Canada's forest fire management strategy. Because of the role fires play in forest ecology, not all fires should be suppressed. A sustainable forest management approach advocates preserving ecosystem diversity to conserve the habitat of the majority of living organisms. Knowledge of natural dynamics associated with forest fires and other disturbances is essential to implement such an approach. Understanding forest fires will make it possible to use their positive effects for forest management. Overall, the area disturbed by insects declined from 1975 to 2004, the last year for which national data are available (Figure 2.3b). Spruce budworm, prevalent across the country, remains at levels well below the major infestations that occurred in the early 1970s. Forest tent caterpillar defoliation is also less severe than the devastating defoliation of the early 1990s. Overall, insects damaged approximately 13 million ha of forest across Canada in 2004, and British Columbia and Ontario recorded the largest disturbances. 
Figure 2.3b Area disturbed by selected insects in Canada (1975-2004). "Total" includes various insects in addition to the three species shown separately. "Forest tent caterpillar" includes an undocumented estimate of the area affected by forest tent caterpillar in 1980. (Source: CCFM 2006) Updated Data: PDF | Excel Insect outbreaks tend to be cyclical with peak populations occurring in particular years and certain regions of the country. As Figure 2.3b shows, there have been three outbreaks of forest tent caterpiller between 1975 and 2004. In the past few years, the mountain pine beetle has been particularly devastating in British Columbia and its impact is described more fully in the adjoining case study. Other insects have also had significant outbreaks. For example, the large aspen tortrix has caused significant damage in Alberta since 2002 and a spruce bark beetle outbreak has affected about 400 000 ha in the Yukon in recent years and continues to grow. The spike in total area disturbed by insects in 1991 and 1992 is attributable largely to hemlock looper and gypsy moth. Most of Canada's forests are even-aged, which means that trees reach maturity at about the same time. As mentioned before, this is due to major disturbances, such as fires, that reset ecological succession of forest ecosystems. Management of these forests for wood production attempts to mimic the natural life cycle through some form of clearcutting that will allow sunlight to reach the ground and help sprout pioneer tree species. Selection harvesting is commonly used in unevenaged forest stands. Under this type of management, relatively small openings are created in the forest canopy to maintain an uneven-aged structure with trees of all ages and sizes. The area disturbed by harvest fluctuates over time (Figure 2.3c). After peaking in 1987, it fell by 1991 to a level approximately equal to the earlier peak of 1979-1980. Since then, harvest levels have been fairly constant and currently stand at about 900 000 ha per year, or slightly more than 0.5% of Canadian forests that are accessible and most likely to be subject to forest management activities. This represents a significantly smaller area than that disturbed by natural disturbances. Indicators 2.5 and 5.3.1 provide additional information on harvesting. 
Figure 2.3c Area of forest disturbed by harvest in Canada (1975-2004). (Source: CCFM 2006) Updated Data: PDF | Excel CASE STUDY: Mountain pine beetle (Dendroctonus ponderosae) in British Columbia The mountain pine beetle attacks lodgepole pine, ponderosa pine, and, more rarely, white pine. Lodgepole pine, the predominant commercial species in the province, accounts for more than half of the growing stock in the interior of British Columbia. While bark beetles play a natural role in the forest ecosystem, the activity of the mountain pine beetle in the central interior over the past several years has been very significant. Mild winters and abundant mature lodgepole pine have enabled beetle numbers to reach unprecedented levels. Furthermore, hot and dry summers have drought-stressed the host trees and made them more susceptible to beetle attack than under normal summer conditions. Many years with below average area burned in the province have increased the proportion of older forest that would otherwise have burned and subsequently regenerated to form a younger forest. It is believed that British Columbia may have up to three times more mature lodgepole pine than it did about a century ago; there are large areas of mature pine forest on the landscape that arose after wildfires in the late 1800s and early 1900s. The beetle has killed approximately 330 million m3 of commercial timber (24% of the mature lodgepole pine) by the end of 2004. The beginning of the current infestation can be traced back to about 1994 and has expanded to cover 8.7 million ha in 2004, up from 165 000 ha in 1999. Over the next decade, the beetle could infest up to 80% of all lodgepole pine in the interior if not halted by cold weather. Management strategies to stem and curtail the infestation include aerial and ground detection, pheromone baiting to attract the beetles, felling and burning of infested trees, and a variety of harvesting techniques. Every precaution, through tight controls on hauling, milling, and storage, is taken when transporting salvaged logs to ensure that the beetles are not spread to new areas. British Columbia continues to conduct research on the mountain pine beetle in conjunction with the Canadian Forest Service and other organizations. |