Research in the Nelson Forest Region has demonstrated a net loss of range to forest encroachment, mainly in the Ponderosa Pine and Interior Douglas-fir zones.[52] Prescribed range burning and wildfires may limit the extent of this problem.
Weed inventory, monitoring, mapping and research must increase to improve identification of problem species and to plan and implement weed containment program, so that potential threats to Crown forage and biodiversity from non-native weed species are minimized and controlled.
Figures 4.16-4.20 show the present provincial distribution and relative occurrence (low, medium, high) of the five major rangeland weed species:
The current weed infestation is then inventoried, digitized and overlayed on the map of potential spread. Figure 4.21, an example output of this process, was created to assist in planning weed management activities in the Boundary Forest District.
One crucial step in a biological weed control program is to determine whether a candidate organism can be introduced to control a weed without also threatening desirable plants. The provincial government, through the Ministry of Agriculture, Fisheries and Food and the Ministry of Forests, has historically supported weed biocontrol development by providing funding to the International Institute for Biological Control (IIBC) in Switzerland and to Agriculture Canada in Lethbridge, Alberta.
Significant progress has been made to bring the two knapweed species — diffuse and spotted knapweed — under biological control. Presently, 12 biological control agents, including seven seed-head agents and five root-feeders, are at various stages of establishment and redistribution. The seed-head gall flies (Urophora affinis and U. quadrifasciata), first released in 1970 and 1972 respectively, are now distributed throughout the entire knapweed infested area. Several insects such as Larinus obtusus are still at the early introduction and establishment stage. The root-feeding beetle (Sphenoptera jugoslavica), which attacks diffuse and spotted knapweed in hot, dry habitats, is close to being fully distributed but has not yet reached high enough population levels to significantly affect the knapweed populations.
The successful introduction and establishment of the seed-head weevil (Rhinocyllus conicus) and root-boring weevil (Trichosirocalus horidus) have added nodding thistle to the list of weeds considered under biological control in the province. The biological control program for weed species such as hound’s tongue, dalmation toadflax and leafy spurge is still in its early stages.
The release sites for the three major knapweed biological control agents — Agapeta zoegana, Sphenoptera jugoslavica and Cyphocleonus achates — are shown in Figures 4.22-4.24. A summary of all release sites for biological control agents released throughout the province between 1970 and 1992 is shown in Figure 4.25.
In several areas the combined use of range by livestock and wild ungulates has led to serious declines in range condition. The condition of these ranges must be evaluated and realistic wildlife population and livestock AUM goals set to properly partition and allocate the Crown forage land base. Moreover, forage allocation must meet more than the forage demands of livestock and large ungulates. Forage allocation must ensure that vegetation provides forage and habitat (structure) for all animal species present on the site. It must also ensure that vegetation provides sufficient cover to protect soils from erosion, to contribute to nutrient cycling, to reduce evaporation and to function effectively as a key component of the hydrologic cycle. The East Kootenay Trench Wildlife Agriculture Committee (EKTWAC) is attempting to resolve these problems in the Cranbrook and Invermere Forest Districts.
Closer cooperation is required between range and forest tenure licensees to reduce the potential for conflicts associated with livestock damage to conifer seedling plantations, range degradation from harvesting and site preparation activities and the removal of natural livestock barriers during harvesting.
Studies in B.C. indicate that tree seedling mortality by livestock can range from negligible to 56% depending on the site and livestock management.[58] Other factors, such as poor planting stock, site conditions, planting methods and rodents, also contribute to seedling damage and mortality.
Livestock can adversely affect forest regeneration by trampling and browsing seedlings.[59] Most commonly, livestock damage trees through incidental trampling, but these scars are generally about 25% of the stem circumference and located near the base of the seedling.[60] Occasionally scars may be larger, but they rarely girdle the tree seedling completely.
Newman and others (1991) reported that livestock rarely browsed lodgepole pine seedlings (less than 2%) when other forage species were available. This study also found that 18% of lodgepole pine seedlings were damaged before livestock were introduced onto three plantations near Kamloops. In one pasture, 77% of all trees were damaged by voles — some trees were completely girdled and defoliated. McLean and Clark (1980) concluded that livestock can be compatible with conifer regeneration, provided that the number of livestock and length of grazing period are strictly controlled.
Resource overlaps occur on virtually all Crown land areas grazed by livestock in B.C. Integration of forage and livestock management on Crown land with other recognized values such as timber production, wildlife, watershed values and recreation will continue to challenge resource managers in British Columbia. In the past, interaction with timber and wild ungulates was the principal concern. Greater emphasis on environmental issues and conservation will occur in the future.
