| BEN |
| BOTANICAL ELECTRONIC NEWS |
|---|
| ISSN 1188-603X |
| No. 220 April 7, 1999 | aceska@victoria.tc.ca | Victoria, B.C. |
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About one-third of the way up the outer coast of Vancouver Island, British Columbia, Barkley Sound is a 35 km2 indentation dotted with hundreds of tiny to moderately-sized islands, with several of the larger over 1 km2 in area. The most isolated islands comprise the Broken Group in the center of the Sound, and are up to about 20 km from "mainland" Vancouver Island. All are continental or landbridge islands, representing hilltops isolated with rising late-Pleistocene sea-levels (e.g. Dawson 1992); from marine charts showing channel depths, the oldest of the present-day islands date from ca. 12,000 yBP, although many (with shallow channel depths of a few meters) are much younger. Very low-lying islands will have re-emerged relatively recently, as continued coastal uplift has dropped relative sea level 3-4 m from maximum rise some 6-7,000 yBP (Friele & Hutchinson 1993). Island substrates are uniformly rocky, composed of mixed Tertiary volcanics and metamorphics (Muller 1983, Yorath 1995); their shores generally rocky, often steep, with a few sandy and many mud/cobble beaches. Most islands are in pristine condition; those in the Broken Group are part of Pacific Rim National Park and several support camping beaches; others are variously private, First Nations, or Crown land. Being exposed and relatively low-lying, the islands are generally dry with shallow soils, and fresh water seeps reaching the beach only on islands >105 m2 in area. The climate (at Bamfield, s. edge of the Sound) is wet maritime, ave. 2950 mm of precipitation/y, but only ca. 10% of the annual total falls in the three summer months Jun-Aug.
Diversity, distribution, dispersal and population dynamics of plant species in from forest to shoreline have been the subject of biogeographic and ecological studies since 1981. Plant surveys on islands in Barkley Sound have continued up to 1997, with ten summer seasons spent in the area (Cody 1992a,b, 1998; Cody & Overton 1996). To date, some 210 islands have been surveyed, many of these repeatedly, often in adjacent or subadjacent years. Surveyed islands cover a size range of about 6 orders of magnitude, and the largest samples sizes are in the range 102-104 m2; nearly 40% of the sample islands are in the center of the Sound, the remainder closer to the mainland (Vancouver Island) coast. All surveyed islands have been accurately mapped by transit at the Fucus line and by elevational contours at 1, 2, 5, 10, 20 and 50 m intervals, with coverage of the major vegetation types superimposed.
The vegetation of the mainland coastal areas and over much of the larger islands is Coastal Coniferous Forest (Klinka et al. 1989, Pojar & MacKinnon 1994; for floristics, I follow Hitchcock & Cronquist 1973). The forests are dominated by Red Cedar (Thuja plicata), Sitka Spruce (Picea sitchensis), and Western Hemlock (Tsuga heterophylla), with occasional firs (Abies grandis, A. amabilis), alders (Alnus rubra), and maples (Acer macrophyllum, A. douglasii). On the islands (only) Douglas fir (Pseudotsuga menziesii) is common, coast pines (Pinus contorta) are found on all shorelines, with Western White pine (P. monticola) on the edges of bogs. The forest understory is composed of mostly ericaceous shrubs such as Arctostaphylos, Gaultheria, Menziesia, and Vaccinium species, ferns, and a few geophytes (Maianthemum, Goodyera, Listera) and forbs (Tiarella, Boykinia). Around the interior forests on islands are concentric rings of first woody shrubs (many Rosaceae, some Caprifoliaceae), second a zone of largely weedy herbaceous, mostly perennial forbs of a wide variety of taxonomic affinities (especially Asteraceae, some Brassicaceae, Onagraceae, Fabaceae), and lastly a shoreline flora of plants specific to rocky shores or sandy, muddy or cobble beaches, many of cosmopolitan distribution.
The flora of the islands is essentially that of the adjacent mainland, since most habitats, even coastal marsh fragments and tiny island bogs, are represented; it currently totals around 300 plant species. Some adjacent mainland species are absent on the islands, mostly wetland species typical of shallow inlets (e.g. Jaumea carnosa, Lilaeopsis occidentalis), extensive sandy beaches (Franseria chamissonis, Carex macrocephala), larger bogs (e.g. Vaccinium alaskense, V. uliginosum, Botrychium sp.), many other freshwater aquatics (e.g. Lysichiton americanum, Carex spp.), and weedy plants, often aliens, typical of roadsides and settlements (e.g. Senecio vulgaris, Medicago, Vicia spp. among others).
But the islands support additional plant species that are rarely or never seen on the immediately adjacent mainland, such as Douglas-fir, manzanita (Arctostaphylos columbianum) and other plants more typical of the inner and drier (NE) coast of Vancouver Island, and additionally various shoreline, rock and cliff plants (e.g. Baeria maritima, Cochlearia officinalis, Carex pansa). Other notable island records include Carex gmelinii, present on a single cluster of islands at the outer edge of the Sound.
The largest islands support around 125 plant species, with species numbers declining with area in the classical manner. The larger islands in Barkley Sound (logA[rea] > 4.25) fit the same regression line:
regardless of isolation. This would indicate that their species numbers (and composition) reflect a pre-isolation state typical of supersaturated non-equilibrial landbridge islands, largely uninfluenced by colonization. Variation in species composition among these islands suggests two lines of enquiry:
On the other hand, small-island groups have species-area curves that differ as a function of isolation distance, with lower species numbers on more distant islands; their differences in diversity, per area, are attributable therefore to differences in the rates of on-going colonization. [Continuation in BEN # 221]
[Benito Tan, a BEN subscriber, posted my note about Archibald Menzies on the bryological discussion list BRYONET-L. This posting triggered an interesting discussion on the role of Dr. Archibald Menzies as a bryologist. I am using two replies originally posted on BRYONET-L. - AC]
From: David Long [D.Long@rbge.org.uk]
In Edinburgh we have Menzies' own cryptogamic herbarium which is one of the most meticulously prepared collections I have seen. He was clearly an extremely eagle-eyed and careful collector and searched hard for sporophytes in the field, and most of his liverworts bear sporophytes. Of course he sent duplicates to William Hooker in Glasgow who published most of the novelties; these holotypes are now in BM (ex K), but the isotypes he kept in his own herbarium are in pristine condition and one of our most prized assets in Edinburgh. The specimens are mounted on small sheets with the data (scanty but usually with place, year and 'AM') on the reverse. Menzies also received many duplicates from James Dickson, Swartz, Schleicher, Schwaegrichen and other contemporaries and was not just a good collector but a serious student of cryptogams.
Further information on Archibald Menzies is to be found in:
From: Allan Fife [FifeA@landcare.cri.nz]
There are two other references that those with an interest in Menzies might wish to consult:
The spring gathering to remember Chess Lyons (see BEN # 212) will take place on Sunday, April 11, 1999 at Freeman King Nature House, in GOLDSTREAM PROVINCIAL PARK from 2:00 to 4:00 p.m., NOT in "Freeman-King Park," as previously stated.