The effect of strip-harvesting on fuel moisture and loading in lodgepole pine stands

Abstract

Fire and insect outbreaks are the two leading natural disturbance factors affecting Canadian forests. Over the last 20 years Mountain Pine Beetle (Dendroctonous ponderosae Hopkins) has killed more than 50 percent of western Canada’s merchantable lodgepole pine (Pinus contorta) forests and spread beyond its historical range. The outbreak has affected forests and communities throughout British Columbia and Alberta and has prompted investigation into forest harvesting and modification management strategies to reduce likelihood of outbreak and impact of infestations. For these treatments to be successful they must not only account for effect on insects, but fire as well. This study examined how progressive strip cut harvesting affected fuel moisture and loading. Stands were treated with alternating parallel clear cut five-meter-wide machine corridors and fifteen-meter-wide thinned retention strips. Fuel moisture content and fuel load was sampled from both treatment types and compared against unaltered control sites. Fine fuel moisture content was significantly different between each treatment, though interestingly the thinned treatment sites were drier than the cleared sites. Duff moisture content was not significantly different from control in either of the altered sites, though again thinned site moisture content was significantly lower than in the clear treatment. Fine fuel load was not significantly different from control in either of the altered sites, though the cleared treatment had significantly higher fuel load than the thinned treatment. Total site fuel load was not significantly different between the control and thin but was considerably lower in the clear treatment. These findings suggest that thinning affects fuel moisture content in a manner not accounted for in standard fuel moisture models. Increases in fine fuel moisture content leads to increased flammability, however the dramatic overall reduction in fuel load and duff moisture content indicate a reduction in difficulty of control.