Neil K. Dawe1,5, W. Sean Boyd2, Ron Buechert3, Andrew C. Stewart4
1Canadian Wildlife Service, retired; 438 Temple Street, Parksville, B.C. V9P 1A3; e-mail: email@example.com
2Environment Canada, Science and Technology, 5421 Robertson Road, Delta, B.C. V4K 3N2
3761 Laburnum Road, Qualicum Beach, B.C. V9K 2J8
41921 Doran Road, Cobble Hill, B.C. V0R 1L5
Abstract: We document significant, negative changes to the native marsh vegetation of the Little Qualicum River estuary and strongly infer that resident Canada Geese are the principal cause. Twenty-four of 56 marsh species showed significant changes in either frequency or mean cover values and, of those, 14 increased in frequency and/or mean cover while 10 decreased. Decreasing species had a significantly higher proportion of known Canada Goose dietary items while increasing species had a higher proportion of species with high salt tolerance. Impacts to the Carex-channel edge community, dominated by C. lyngbyei, suggest that the detrital food web of the estuary is losing at least 17 tonnes dry mass from this community every year. In addition, at least 5 tonnes dry mass per year are being lost from the Deschampsia-flats community. Other vegetation changes and evidence suggests a concurrent change in the salinity regime of the estuary, perhaps through a reduction of the freshwater hydraulic head, which is allowing salt water intrusion to occur. This may be caused by increasing water withdrawal from the aquifer to meet the needs of a growing human population in the area. This change in the salinity regime may also be working synergistically with the geese to increase the effect of some of the impacts; however, the geese appear to be the primary agent of change. Cursory examinations of other estuaries on the east coast of Vancouver Island, including Nanoose-Bonell creeks, Englishman River and Campbell River estuaries, suggest that these systems are experiencing similar negative impacts from resident geese. These similar impacts, and the common fact that Canada Geese have increased in abundance at all the estuaries, further suggest that the geese are the primary driving force behind the changes to the vegetation. We discuss the implications of these changes and possible management options to mitigate them, including significantly reducing the number of geese and rehabilitating the marsh.
Key words: Branta canadensis, Canada Goose, Carex lyngbyei, Deschampsia cespitosa, grazing, grubbing, impacts, Little Qualicum River estuary, resident geese, salinity changes, Vancouver Island.
Dawe, N.K., W.S. Boyd, R. Buechert, A.C. Stewart. 2011. Recent, significant changes to the native marsh vegetation of the Little Qualicum River estuary, British Columbia; a case of too many Canada Geese (Branta canadensis)? British Columbia Birds 21:11-31.
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