| Abstract/Description or Keywords |
A considerable body of literature is available on landslide occurrence related to forest development on Vancouver Island. In preparing for results-based management, Western Forest Products Inc. (WFP) began a project in 2004 to com pile over view-level land slide inventories on Tree Farm Licence 6 (TFL 6) to assist with the development of results and strategies under FRPA. One component of the project was a land slide inventory. This paper summarizes the anal ysis of the landslide inventory data covering 1980 km2 of northern Vancouver Island the factors contributing to post-harvest open-slope failures are complex and probably vary from site to site and region to region. However, in this data set, the temporal distribution of slides following harvesting is inconsistent with root strength decay being the major factor. For landslides originating at roads or cutblocks, most slides (both pre- and post-FPC events) are smaller than 0.25 ha. Natural events occur relatively more frequently in larger size classes. The occurrence of landslides from roads on steep terrain built in 1995 and later compared with roads built before 1995 has decreased four-fold. As well, the size of landslides from post-FPC roads tends to be smaller than those on pre-FPC roads. Bearing in mind that recent cutblocks have not been fully tested, there has been almost a two-fold reduction in landslides from cutblocks on steep terrain harvested in 1995 and later compared with cutblocks harvested before 1995. Changed management practices have resulted in fewer landslides for both roads and cutblocks. The greatest frequency of landslides from harvested cutblocks occurred in the first 5 years following harvesting, with 27% occurring in the same year as harvest and some landslides occurring in the first storm following harvesting. This result suggests that root strength decay may not be the most important factor in these types of landslides. |
