|Forest Investment Account|
|Abstract of FIA Project|
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Blue grouse habitat on Haida Gwaii/Queen Charlotte Islands
|Author(s): Doyle, Frank||Imprint: Telkwa, BC : Wildlife Dynamics Consulting, 2004||Subject: Blue Grouse, British Columbia, Forest Investment Account (FIA)||Series: Forest Investment Account (FIA) - Land Base Investment Program|
For many years on Haida Gwaii/Queen Charlotte Islands (Haida Gwaii), there has been local concern that the population of Blue Grouse (Dendragapus obscurus) was declining. In addition, scientists working with the threatened Queen Charlotte Goshawk (Accipiter gentilis laingi) are concerned that the reduction in grouse, one of the goshawks main prey items, was threatening the ability of the islands to maintain a viable goshawk population. Other research on Blue Grouse has linked population trends to the age of the forest (recent harvested – old growth), and within the central part of the islands only 14% of the original mature-old growth forest remains. This study therefore set out to determine if grouse were being impacted by harvesting, and to do this grouse survey transects were set up across the spectrum of available harvested landscape types, to establish if and when harvesting was impacting densities of birds. In all three transect were established within each landscape type, resulting in a total of 27 transects which were surveyed at least three times, culminating in a total of 866 grouse survey points. The number of birds singing was recorded at each station, and both an in-field, and GIS landscape analysis of the available habitat was then conducted. Independent from harvesting impacts, the survey results indicate that the density of grouse on Haida Gwaii is at least seven times lower than observed in similar habitats (old growth with recent harvesting) on the adjacent islands to the north in SE Alaska, and on Vancouver Island and the Gulf Islands to the south. However, historical accounts suggest grouse densities on Haida Gwaii were likely far higher in the past, and the introduced deer has been identified as a probable factor in the reduction in the numbers of grouse, as it directly competes with the grouse for forage plants. In addition, introduced nest predators, such as the raccoon are also likely to be impacting the success of breeding birds. Grouse densities were highest in the central, most productive portion of the island, the Skidegate Plateau Ecosection, and this is also the area with the highest area of harvesting. However, at a landscape scale (2 km radius of a survey station) the larger the area of mature-old growth in the landscape the more birds that were heard. At a finer scale (<300m radius of a survey station), the highest number of birds were heard in the recently (<15 years) harvested areas, but this density then declined sharply as the stands aged. The area of alpine and alpine forest present within 2 km of a survey transect, was also positively linked, such that the larger the area of alpine the more grouse that were heard. No other habitat type was significantly linked to the number of grouse singing. In addition, tree species composition in the landscape, as represented by the leading species within Forest Cover polygons, was also not correlated to the number of birds heard singing. Grouse may also be impacted by introduced species on Haida Gwaii, but the pattern in the density of birds with habitat type was consistent with other studies, suggesting that this rather than the impact of these species was the main factor behind the observed population decline. Based on the size and spatial arrangement of the area harvested, grouse populations have probably declined in the 50 years since intensive harvesting was initiated, even though populations may benefit from some recent harvesting, as new openings (<15 years) are used by breeding birds. This decrease in grouse may have substantially impacted the viability of the threatened goshawk population, with near to 50% of known and predicted goshawk territories impacted by an area of harvest that is likely reducing the densities and availability of grouse. However, it is also probable that island wide impacts from introduced species on the numbers of grouse, is severely impacting the ability of the landscape to support a healthy goshawk population. This impact may be such that independent of forest management practices goshawk healthy goshawk populations can only be maintained by managing for a reduction in the impact by the introduced species. To provide for the best opportunity to successfully manage for a healthy grouse and goshawk population will therefore probably require a combined approach. This would see the implementation of forest management practices that support high grouse populations, and access to the grouse for goshawks, taking place while at the same time reducing the direct and indirect impacts of introduced species on grouse populations, in particular by the deer. The results from this work have been submitted to all provincial and Haida Gwaii land management groups, including local conservation and hunting associations. In addition the information has been presented to the Goshawk Recovery Planning Team and to the provincial Land Use Planning forum, so that the information can be incorporated within the long term landscape management objectives for Haida Gwaii/Queen Charlotte Islands, which include the maintenance of a healthy ecosystem.
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Updated August 02, 2006
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