The Gulf Islands are underlain by folded and highly faulted sedimentary rocks. This area of southwestern British Columbia is seismically active, overlying a tectonic subduction zone. On the islands, north-south headlands and high ridges of erosion-resistant sandstone/conglomerate are separated by narrow valleys and bays underlain by more easily eroded shale.
Glacial ice as much as a mile thick carved the landscape over two glacial periods, with the ice most recently receding 12,000 years ago. Deposits of glacial sand and gravel form Sidney Island, and striated and fluted bedrock are common evidence of past glaciation throughout the islands. Although sea levels have remained the same for the last 5,000 years, they have fluctuated, in the more distant past, up to 150 metres higher than the present level.
Many plants in the Gulf Islands are at the northern extreme of their range, and are not found elsewhere in Canada. Garry oaks and arbutus trees—with their smooth red bark and evergreen leaves—are unique to this small area of British Columbia. Garry oak associated-ecosystems support many of Canada's species at risk.
The dominant ecosystem of the southern Gulf Islands supports Douglas fir, Balsam fir and Western red cedar forests. Most of the islands' forests have been logged in the past, with only pockets of old growth forest remaining. On the drier rocky ridges, there are open wildflower meadows and grassy hilltops, usually interspersed with Garry oak, arbutus and Douglas fir woodlands. Coastal bluffs represent another sensitive ecosystem, one in which plants face disturbance from wind, heat dessication, storms and salt spray, and must sustain themselves on very shallow soils.
Many invasive introduced species such as Scotch broom, Himalayan blackberry and gorse are displacing native species in many areas of the Gulf Islands and present a significant challenge to the sustainability of park ecosystems. Agronomic grasses from Eurasia dominate many sensitive ecosystems today.
The wide variety of terrestrial and marine habitats mean that the wildlife found in the Gulf Islands is diverse. Orcas, porpoises, sea lions, seals and otters call the surrounding waters home; eagles, falcons and turkey vultures soar overhead. Hundreds of resident and migratory species of seabirds, shorebirds and waterfowl thrive on the bounty of the nutrient-rich ocean waters.
On land, large predators are uncommon, causing significant alteration to island ecosystems as prey species multiply unchecked. Overabundant deer populations reduce the forest understory in their search for suitable food plants. This not only changes the composition of the forest plants but also changes the structure and habitat features so important to other species. Overall, the Gulf Islands have 15 COSEWIC-listed Endangered species, 10 Threatened species and 13 species of Special Concern. These species run the gamut from butterflies to snakes, from shellfish to ferns, and from bats to killer whales. Sharptailed snakes are just one of the endangered species currently being monitored in the national park reserve.
ATTENTION: It's seal pup season!