Apart from timber harvest, fires and pathogens - including insects and various kinds of diseases - are two disturbances that affect forest ecosystems over large areas. Although damages from wind throw, winter kill, and other physical damage, such as browsing by deer, are often important locally, on a provincial or regional scale the damage is low.

Throughout British Columbia, about 15 different insect species cause the mortality and growth loss of about 5,886,999 cubic metres of timber per year (Wood and Van Sickle, 1994). Fires are less harmful, causing about 1.8 million cubic metres. Fires and insects are normal components of healthy forests, and are essential to biodiversity. Insects feed birds, for example, and fires create openings, structural diversity and specific habitat elements, such as standing snags and large woody debris that are home to many species of animals, plants, fungi and other organisms. For a forest to remain healthy, however, the disturbance regimes must be in balance with natural regrowth over the landscape. Therefore, the trends in fires and insect infestations are as important as how much timber was affected in a given year.

Insect Infestations

Province-wide, insect pest infestations have fluctuated markedly in the last two decades (the period of reliable record), rising sharply for some species (especially Mountain Pine Beetle and the two species of Spruce Budworm) until about 1989, and then dropping. The peaks in their populations were not synchronous (did not occur at the same time), and therefore can not be associated with a single event, such as weather patterns or forest practices. No dramatic outbreaks have been recorded this decade, although trend data have not been published since about 1994.

Quantitative data on infestations in the Columbia Basin are scarce because comprehensive surveys are not a regular part of forest management, and public reporting lags behind completion of the surveys that are done. For example, the 1996/97 Ministry of Forest Annual Report tables for (a) Area Under Attack by Forest Pests, (b) Timber Damaged by Forest Pests, and (c) Bark Beetle and Defoliating Insect Control Activities, all gave "Data Incomplete" or "Data Not Available" for the Nelson Forest Region.

Results of a Nelson Region survey completed in 1994, the most recent published, showed that:

One aspect that concerns forest managers and ecologists is the incidence of insect infestations in young, replanted forests. Because many defoliating insects favour young trees, and new plantations following clearcut logging are of uniform young age, the potential exists for unnaturally high insect infestations in these stands. Therefore during 1991-1995 the federal and provincial forest agencies studied insect and other damage in young forests (Nevill et al., 1996). They found that:

The authors concluded that if the forest health guidelines of the new (at that time) Forest Practices Code are implemented assiduously, pests would not adversely affect regenerating stands. They also noted, however, that more research is needed to determine exactly how various forest practices and silvicultural (management of specific stands or harvest blocks) prescriptions affect forest pest populations, which will have to be in balance with other disturbance regimes and timber harvest if the forests are to remain healthy in the long term.

Wildfires

Fires are natural components of forest (and other) ecosystems, and in some forest types more than others. Ponderosa pine and Lodgepole pine, for example are fire-maintained ecosystems; without periodic fire they could not exist. Ponderosa pine is resistant to fire, but needs fire to clear away the underbrush and other species of trees (especially Douglas-fir), which without fire would soon dominate the forest. Fire is what give ponderosa pine stands their open, park-like look with a grassy understory and plenty of wildflowers. Keeping the grassy understory by periodic burning also benefits livestock. More information on prescribed burning in the Columbia Basin is in the Grasslands page.

Lodgepole pine succumbs readily to fire, but needs it to reproduce: the cones open and seeds germinate readily after a fire, regenerating the pine stand. This is good for the pine, and for commercial timber values (because the pines grow quickly, reaching merchantable age sooner than other tree species) but it is not necessarily good for other forest values, such as biodiversity. As lodgepole pines age, their densely-spaced canopies choking out the sunlight and their needles turning the soil acidic, the productivity of the understory declines and with it the number of plant and animal species.

Even in other forest types where fires are less frequent and not necessary for the forest as a whole, fires still play an important role by creating structural diversity (openings, younger-aged patches) and providing habitat for species (such as dead snags for woodpeckers) that could not thrive in an old, unburned forest. Indeed, the degree of "patchiness" is an attribute of forest ecosystems for which managers are striving to find a good measure, and to optimize in forest ecosystem management.

Overall, in British Columbia and in the Nelson region, during the period of reliable records (since about 1950), the frequency of fires has been increasing, but the area burned has been decreasing, because of effective fire suppression (Harding, 1994). Most fires are natural; in 1996 (the last year of published data) fewer fires burned considerably less area than average in the Nelson Forest Region. It is proving a challenge to provide a mix of fire suppression needed to protect commercial timber, while at the same time allowing fire to function naturally for the benefit of biodiversity. In the East Kootenay, the purposeful use of fire to improve wildlife habitat and other non-timber values is progressing beyond the experimental stage and may eventually become fully developed tool in modern forest management.

References

Hall, P.J., 1996. Forest insect and disease conditions in Canada 1994. Canadian Forestry Service, Ottawa.

Harding, Lee, 1994. Threats to diversity of forest ecosystems in British Columbia. In L.E. Harding and Emily McCullum (eds.), Biodiversity in British Columbia: our changing environment. Environment Canada.

Nevill, R., N. Humphreys and A. Van Sickle, 1996. Five-year overview of forest health surveys in young managed stands in British Columbia.

Van Sickle, G.A., 1995. Forest Insect Pests in the Pacific and Yukon Region. Chapter 6 in J.A. Armstrong and W.G.H. Ives (eds.), Forest Insect Pests in Canada. Canadian Forestry Service, Ottawa.

Wood, C.S. and G.A.Van Sickle, 1994. Forest insect and disease conditions, British Columbia and Yukon - 1994. Pacific Forestry Centre Information Report BC-X-354.

Forest Ecosystem Topics