Canadian Forest Service Publications
Effects of fire return rates on traversability of lodgepole pine forests for mountain pine beetle and the use of patch metrics to estimate traversability. 2006. Barclay, H.J.; Li, Chao; Benson, L.; Taylor, S.W.; Shore, T.L. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, BC. Mountain Pine Beetle Initiative Working Paper 2006-01. 32 p.
Issued by: Pacific Forestry Centre
Catalog ID: 26243
CFS Availability: PDF (download)
A Monte-Carlo simulation was used to examine the effects of fire return rates on the equilibrium age structure of a one-million hectare lodgepole pine forest (Pinus contorta var. latifolia Englm. Ex S. Wats; Pinaceae). A mosaic of ages over the one million hectares was produced for each fire regime modelled. These were used to generate mosaics of susceptibilities to mountain pine beetle attack. This susceptibility is related to the age distribution to calculate the mean susceptibility of the forest. Susceptibility maps were produced for two timber supply areas in British Columbia, as well as for the whole of B.C. In addition, we defined a quality, called traversability, which describes the ability of a beetle population to disperse across a landscape according to defined rules of susceptibility and maximum distance for dispersal through unsuitable habitat. Using each of 40 combinations of susceptibility classifications and dispersal limits, the landscape was categorized as traversable or non-traversable. This represents the suitability of a landscape to allow an incipient beetle population to spread unimpeded across the landscape under consideration. It was found that (i) long fire cycles yield an age structure that is highly susceptible to beetle attack; (ii) fire suppression reduces the frequency of fires and yields an age structure highly susceptible to beetle attack; (iii) harvesting one age class reduced the mean susceptibility to mountain pine beetle attack, and this reduction decreased with increased harvest age and increased fire cycle length. When fires were limited in size to less than 100 ha, the area was always traversable. For larger fires, traversability declined and for the largest fires (up to one million ha) the area was often not traversable. Harvesting reduced the mean susceptibility and traversability, often substantially. Traversability was calculated for the whole of British Columbia in blocks of about one million ha using B.C. Ministry of Forests and Range inventory data for the year 2000. The area most traversable was the area in Tweedsmuir Park and the Lakes Timber Supply Area, where most of the present outbreak is centred. FRAGSTATS patch metrics were calculated for each of the simulations and these were related to traversability using discriminant analysis. This was then applied to the B.C. inventory; the concordance was high with 93.3% of conditions being correctly classified.