The Plants and Birds of Cape Roger Curtis

Cape Roger Curtis, the south-western tip of Bowen Island, probably contains the richest coastal bluff habitat on the east coast of Georgia Strait.

By Terry Taylor

Published in Discovery Magazine, Spring 2005

The narrow strip of land along the island’s shore is an eastward extension of the rainshadow created by the Vancouver Island mountains. Although the rainshadow is less pronounced than on the Gulf Islands and eastern Vancouver Island, the flora is similar, but with less diversity. There are, however, a few sites where seepage, soil nutrient levels, and southern exposure produce conditions approaching those of Vancouver Island. This is true to such an extent that the south coast of Bowen Island is the best example of that environment on this side of the strait. At the same time, its vegetation is also partly that of the Vancouver area. The Cape is the place where all these factors come together to create the richest coastal site in the Lower Mainland.

The shoreline here is transitional between two ecological zones. The drier sites around Victoria and its environs are classified by ecologists as the Coastal Douglas-fir Biogeoclimatic Zone (CDF). It is dry and sunny enough in this zone for Garry oak (Quercus garryana) to flourish, and for Douglas-fir (Pseudotsuga menziesii) seedlings to grow under a canopy of mature Douglas-fir trees. Above the CDF and along most of the mainland coast is the Coastal Western Hemlock Biogeoclimatic Zone (CWH). This is the zone which occupies the lower slopes of our North Shore mountains. In this habitat Douglas-firs actually grow larger than they do in the zone which bears their name, but the shade and humidity is too great to allow their seedlings to grow under the parent trees. Western hemlocks (Tsuga heterophylla), however, grow quite readily under such conditions. If no disturbance occurs to remove the original forest, the hemlocks take over. That is why most of our conifer forests are dominated by hemlock.

Cape Roger Curtis lies between these two ecological zones, within what is referred to as the Very Dry Subzone of the CWH (CWHxm). It is enriched by species from both Douglas-fir and western hemlock sites. These steep, rocky slopes receive ample moisture during the winter, but rapidly dry out during the summer, and the thin soil is not able to retain this moisture for very long. A few places, however, receive seepage from the wetter uplands, and it is in these moist spots that most of the rare plants are found. All of these factors have come together to produce this very special place, but it is also a very fragile place. Since few people come here it is relatively free of the weed species which have been introduced to many similar sites such as Lighthouse Park. Extensive trampling or disruption of the early season seepage sources could rapidly destroy this unique ecology.

Herbaceous plants in Mediterranean-type habitats use two basic methods of survival. The first is to grow as a perennial, but possess a large bulb or corm big enough to supply the nutrients required to take the plant through the rest of the year, until it can renew itself next spring. Daffodils do this. Camas uses this strategy, and those at Cape Roger Curtis may be the only native population still surviving on this side of Georgia Strait. The other method is to grow as an annual—germinate and flower very rapidly while there is still sufficient soil moisture, then produce seeds which wait until the spring of next year. The blue-eyed Mary is a familiar member of this group. These types of annuals are sometimes called ephemerals. The seeds germinate about March, and the plants shrivel and die in June!

There is also a special tree at the Cape, even more special than the arbutus trees that also cling to these rocks. This is the Rocky Mountain juniper which, as its name implies, grows in the Rockies. It is also found at the coast, but not usually on this side of our inland sea. Other species observed at Cape Roger Curtis that are common on Vancouver Island, but very rare over here are: blue toadflax, hairy honeysuckle, yerba buena, slender plantain, slender sandwort, Menzies’ larkspur, Indian’s-dream fern, and dwarf owl-clover.

The botanical diversity of Cape Roger Curtis is actually much greater than indicated by this list. Only a cursory investigation was made of mosses, lichens and fungi. Also, the plants shown are those which were observed on just two survey days, both of which were in May, one in 1991, the other in 1993. More extensive studies, including non-vascular plants and fungi, carried out at other times of the year, are required to actually show the true diversity of the site.

Both surveys were conducted in May, and although this is when most of the rare and ephemeral species are evident, obviously the list of plants is only preliminary. But it is an inventory sufficient to show that this is indeed a unique and ecologically significant area. If the wildflowers and special ecology of Cape Roger Curtis are lost they will be lost forever. The decisions made in the near future will decree whether this will or will not be the case.