Hornby Island is within an ecological region unique in Canada. The Coastal Douglas Fir zone is one of the smallest biogeoclimatic zones in British Columbia, occurring only on the Gulf Islands, southeastern Vancouver Island and small portions of the Sunshine Coast and Fraser Delta. It is a region of exceptionally high biodiversity but also one that has been profoundly and adversely affected because of its accessibility for logging and suitability for settlement. Less than 1% of this ecosystem remains relatively undisturbed; 12% of provincial ecosystems is generally considered a minimal protection target to achieve ecological representation. Even if all the remaining remnants of old-growth forest can be preserved, areas of older second-growth forest must also be protected and allowed to recover to an old-growth state to ensure adequate representation of this forest type in the future.
The original Coastal Douglas-Fir forests had a relatively open canopy dominated by gigantic Douglas-Firs, which can live more than 750 years. About 100 species of other trees, shrubs, vines, herbs and mosses are indigenous to these forests.
On Hornby only about 104 hectares (260 acres) of relatively undisturbed stands of older forest has been identified. This is about 3.5% of the island’s area. However, there are also at least 572 hectares (1330 acres) of older second-growth forest (19% of the island). As these recovering forests reach about 80 years old they start to develop a structure and composition that allows much of the natural biodiversity to become re-established. These areas can provide important connectivity, allowing the movement and dispersal of forest plant and animal species. Within the Coastal Douglas Fir zone, Garry Oak Woodlands cover about 0.6% of the landscape. They often occur on south-facing slopes where summer moisture is low and shallow soils are common.
These open woodland ecosystems support a very high biodiversity of plants. Less than 5% of the historic Garry oak woodlands remain and many of these are seriously degraded. The woodlands provide habitat for a variety of birds, rare moths and butterflies and the Northern Alligator Lizards. This ecosystem includes 93 species at risk.
On Hornby, the Garry oak ecosystem is near the northern extremity of its range. There are about 16 hectares (40 acres) of woodlands, the principal sites being west of Helliwell Park and above the Ford Cove Hill. There are many other smaller stands of Garry oaks.
Terrestrial herbaceous ecosystems (natural grasslands rich in wildflowers) are found in rocky, exposed areas near the shoreline and above coastal bluffs. Hornby has about 24 hectares (60 acres) of these sensitive ecosystems. They contain many rare and uncommon plants-and also support other species, such as the endangered Taylor’s Checkerspot Butterfly. However, they are very susceptible to disturbance and degradation because they occur in areas that attract residential development and recreation.
Indigenous human communities have been part of this area’s ecosystems as they evolved through shifting climatic conditions since the last ice age. Settlement communities have brought change, not only through logging, development and recreational use but also by interrupting preexisting processes (such as periodic fire) and by introducing invasive non-native species that displace native vegetation. In the 1980s the non-indigenous Virginia opossum was introduced to Hornby and is likely having a significant impact upon the preexisting ecology of the Island.
The waters around Hornby support a high diversity of marine life including a variety of sponges, anemones, sea stars, nudibranchs crabs and fish. A unique feature of the marine ecology is the presence of six-gilled sharks, normally a deep-water dweller, at relatively shallow depths near Flora Islet.
The Hornby-Denman area is the site of the largest and most consistent herring spawn in British Columbia. This spawning is important to a variety of species, including Stellar and California sea lions (that spend the winter in these waters using rocks and islets to the south-east of Hornby as haul-outs), the estimated 10,000 bald eagles that congregate here each spring and the West Coast’s largest concentration of Harlequin ducks.
Several species of groundfish are present, including quillback, copper, black, Puget Sound and yelloweye rockfish, lingcod, kelp greenling and cabezon. Rockfish and lingcod are now in serious decline throughout the Strait. There are areas of kelp-covered terrain and eel grass around Hornby that provide excellent habitat for juvenile rockfish. Salmon populations have declined significantly and whales, once fairly common, are now rarely seen.
Hornby has large inter-tidal areas which have a particularly rich ecology. The health of these areas is likely supported by the waters around Hornby being relatively pristine compared to other areas of the Strait, but the accessibility and development of Hornby’s shoreline also make it vulnerable to disturbance.
Coastal areas of the island are important for the well-being of many species that are part of the marine ecosystem. Pelagic cormorants roost on rocky bluffs; bald eagles depend on large trees around the island for perching or nesting; herons require a suitable stand in which to establish a heronry; salmon spawn in Beulah Creek; river otters use much of the coastline; Harlequin ducks and other sea birds are susceptible to disturbance from on-shore activity. Pollution originating on land (including from septic seepage) can contaminate bivalve shellfish. Thus there is a strong connectivity between the terrestrial environment and the marine environment of Hornby.
The natural setting of Hornby Island is rich, varied and of provincial importance. Despite heavy impacts from human use over the past century or so, a significant representation of natural ecosystems remains intact, though at risk from development and recreation pressures. The island’s year-round population seems to have stabilized but, if Hornby continues to be a popular location for tourists and seasonal residents, protecting these remaining ecosystems-and restoring those already degraded-will be a crucial challenge.
Because Hornby Island has a self-contained hydrological system, fresh water is a critical element of its natural setting. Wetlands are extremely productive ecosystems, supporting a large number of species. They are also holding areas for fresh water which can incrementally recharge surface and groundwater systems during the dry season. Hornby, in common with most of the Gulf Islands, has few wetlands. Many of these have already been drained or damaged as a result of logging, agriculture, road-building and landscaping.
Three of the largest wetlands are on the “bench” above Lambert Channel, near Ford Cove and north of Helliwell Park. There are also significant wetlands in the upland Crown land. The only sizable lake on Hornby is in Strachen Valley; it was established in the 1990′s by beaver activity resulting in a significant increase in biodiversity in the area and a more consistent year-round flow in Ford Creek. Surface drainage is generally through many small seasonal creeks. Only Beulah Creek and Ford Creek (both draining the eastern escarpment of Mount Geoffrey) are fish-bearing. Riparian areas, along the margins of streams, lakes and marshes, are very important in providing habitat for a variety of species and maintaining the productivity of fish-bearing streams. Many of these areas have been affected by logging, road-building and settlement.
Groundwater on Hornby is found in open fractures or breaks within the sedimentary rocks underlying the entire island. These openings occupy less than 1% of the rock volume and allow the water to move from one part of the island to another. About 20% of Hornby’s annual precipitation of approximately 34″, which occurs principally in the fall and winter, infiltrates the subsurface to replenish the groundwater supply.
This is the only source of groundwater recharge. This recharge generally takes place on the higher areas of the island and in stream beds. Outflow is to wetlands, creeks and the ocean. Groundwater is the major source of potable water on the island. In 1989 it was reported that in the main residential areas the demand has reached more than 80% of the available water. Since then, the summer population of the island has expanded to several thousand people. Excessive draw down of aquifers in coastal areas can lead to saltwater intrusion or replacement by contaminated run-off. Over-development, inappropriate land use practices, inadequate waste treatment and improperly constructed or abandoned wells can all have an impact on the quantity and/or quality of groundwater. Most water, used or unused, eventually reaches the ocean and any contamination can negatively affect marine life.
Copyright © 2014 · All Rights Reserved