Canopy Project: Conservation of Arthropod Biodiversity In Coastal Sitka Spruce Forests
Neville N. Winchester and Richard A. Ring
|General information and editorial notes||The biodiversity crisis in ancient northern
temperate rainforests continues to be accelerated by habitat loss and consequent
extinctions of floral and faunal species assemblages that cannot adjust to rapid habitat
alterations, especially those of large scale. In an effort to record arthropod biological
diversity in these forests we have studied canopy arthropods in a number of Vancouver
Island rainforest types since 1992 (Fig. 1). We constructed fixed canopy access systems in
three ancient forest sites and initiated four additional studies where single rope
techniques are used to access the high canopy. To date, the most intensive study of
arthropod biodiversity has focused on the Carmanah Valley on Vancouver Island, British
Columbia. Since 1992, we have systematically collected an estimated three million
Fig.1. Location of the canopy research sites established on Vancouver Island, British Columbia
Our canopy research has centred around a main objective to establish structured arthropod inventories of the unique and previously unnamed species that inhabit ancient forests. These studies rely on information at the level of species (see Danks 1996), which are the fundamental units needed to gain insights into ecosystem interactions. The development of our canopy research program has relied on over 40 taxonomic experts for identifications; their contributions are invaluable and form the framework for understanding arthropod biodiversity in these ancient forests.
The study of forest canopies and their contribution to the structure of arthropod assemblages, as well as knowledge of the systematics of canopy arthropods, has increased rapidly during the last 20 years (see Stork et al. 1997 ). Canopies of natural forests in temperate regions contain largely undescribed and little understood assemblages of arthropods, the new knowledge of which has expanded regional estimates of the total number of insect-arthropod species (Schowalter 1989; Behan-Pelletier and Winchester 1998; Winchester 1997a,b).
In 1993, a cluster of five Sitka spruce trees taller than 60 m was identified and incorporated into the Carmanah canopy access system. Access to the canopy is by means of a 2:1 mechanical advantage pulley system. Four wooden platforms strapped onto the branches and trunk of the main tree provide consistent heights (31 to 67 metres) from which to sample (Fig. 2). A series of burma bridges provides access to four other Sitka spruce trees (Ring and Winchester 1996). At the inception of this study this station was the only permanent access system of this type available for long-term work on arthropods in the canopy of northern temperate rainforests.
Fig. 2. Fixed canopy access system, Carmanah Valley. Researcher on platform (45 metres from ground) adjacent to a suspension bridge used to connect adjacent Sitka Spruce trees. (photo credit, Bob Herger)
Coastal Temperate Rainforest Invertebrate Fauna
Our knowledge of canopy invertebrates in this challenging research environment continues to evolve as we record an extraordinarily diverse and largely undescribed fauna. Most of the arthropod taxa from the forest floor have representatives in the canopy on foliage, bark and branches, or are associated with suspended soils that have accumulated up to 80 cm deep (Fig. 3). Taxonomic distinctness among canopy species is most pronounced in suspended soils. For example oribatid mites are members of a distinct arboreal community that is not just a random sub-set of the ground fauna and is markedly different from the arboreal communities of younger forests, indicating that a specialized arboreal fauna exists in the ancient forest (Fig. 4). Comparisons between the high canopy and adjacent ground sites indicate that overall, species percent similarity is low. Thirty and 28 species of oribatids were recorded from two canopy sites, of which 12 species were canopy specific. We conclude that oribatid mites can be used as a surrogate for other ancient forest soil microarthropods, and predict that arboreal specificity will be pronounced in these taxa too.
Across all study sites, arthropods associated with the branches in the canopy were dominated by individuals in the phytophagous, predator and parasitoid guilds (Winchester 1997a). Individual trees and seasonality both contributed significantly to the proportions of species in the phytophagous and predator guilds. Vertical partitioning was not a significant factor influencing the proportions of species in the different guilds. The documentation of high predator loading (e.g. Carmanah Valley, 32 arachnid species) in a functionally diverse, historically old and structurally complex ecosystem such as the ancient rainforest canopy is in concert with previous studies. It supports the conclusion that the amount and kinds of plant material lost to herbivory are never extreme because epizootic outbreaks are prevented by a series of checks and balances, provided by natural enemies, that have developed over a long period of time.
Although some arboreal invertebrates are vagile dispersers with widespread ranges (e.g. Oribatida, Tectocepheus velatus), several species are strictly arboreal, are isolated from their ground counterparts and have low dispersal capabilities (e.g. Oribatida, Scapheremaeus n. sp.). Limited geographic ranges have been observed in forest floor invertebrates (Olsen 1992) and have been recorded in our study where several taxa from the forest-floor litter appear to be restricted to microhabitats that are found only in ancient forests (e.g. Staphylinidae, Tanyrhinus singularis).
Fig. 3. Moss core sampling in the high canopy of a Sitka Spruce in the Carmanah Valley. (photo credit, Bob Herger)
Habitat changes that occur through logging of ancient forests have been well documented, but the effect of this type of habitat alteration on arthropods has been addressed only to a limited extent and we are aware of no studies that have looked at impacts of forest conversion on functional responses of arthropods. For example, arthropod dispersal can affect the resident canopy fauna by adding significant pulses of individuals from adjacent habitats (i.e. tourist guild inputs). Of the 27 species of Trichoptera (adults) recorded from the Carmanah project, several species were collected in the canopy only for a limited period, reflecting species-specific emergence patterns, raising questions about how changes in habitat would affect this normally rapid and significant input of biomass into the canopy.
Given the fact that only a small percentage of the total number of specimens in our studies have been identified to species it is likely that the number of new species recorded (to date, 300) represents only a small part of the total number of new species. Habitat specificity is well documented for the staphylinid beetles; examples include Pseudohaida rothi, which represents the first record for Canada (Campbell and Winchester 1994), and Trigonodemus fasciatus, which is endemic to British Columbia (Scudder 1994). Eight new species of staphylinid beetles of the subfamily Omaliinae appear to rely on ancient forests as a source area to maintain reproductively viable subpopulations (Campbell and Winchester 1994).
Even though taxonomic information is not complete these trends are apparent in many other groups such as the mycetophilids (fungus gnats), where a large number of new species have been recorded (e.g. Anacliliea vallis Coher and A. winchesteri Coher: Coher 1995). Most other dipteran groups contain several undescribed species that are restricted to habitats contained in ancient forests (e.g. Minilimosina n. sp., Phthitia n. sp., Sphaeroceridae: Marshall and Winchester, in prep.). Given the striking ancient-forest habitat associations of the new species recorded in this study, we suggest that many ancient-forest arthropods are candidates for Centinelan extinctions: extinction of species unknown before their demise and hence unrecorded (Winchester and Ring 1996).
Although Canada signed the Rio Convention on Biological Diversity in 1992 and the ecological, economic and social importance of sustaining forest ecosystems has been clearly outlined in several documents (e.g. Canadian Biodiversity Strategy 1995), current policy has not fostered the development of sustainable forestry that is inseparably coupled with the maintenance of biodiversity (form and function) in our ancient forests. In order to meet the stated goals of sustainable management and retention of biodiversity, an extensive plan of ecological research that includes arthropods is needed to catalogue species assemblages and address dynamic processes such as dispersal and the effects of fragmentation in ancient forests. These are the future challenges for policy makers and for the entomological research community.
Fig. 4. An example of the oribatid mites that are members of a distinct arboreal community. (phot credit, Drs. Valerie Behan-Pelletier and Henri Goulet)
Behan-Pelletier, V.M. and N.N. Winchester. 1998. Arboreal oribatid mite diversity: colonizing the canopy. J. Soil Ecol. (in press).
Campbell, J.M., and N.N. Winchester. 1994. First record of Pseudohaida rothi Hatch (Coleptera: Staphylinidae: Omaliinae) from Canada. J. Ent. Soc. Brit. Columbia 90: 83.
Canadian Biodiversity Strategy. 1995. Canadian Biodiversity Strategy. Canadas Response to the Convention on Biological Diversity. Minister of Supply and Services Canada, Ottawa.
Coher, E.I. 1995. A contribution to the study of the genus Anacliliea (Diptera: Mycetophilidae). Ent. News 106 (5): 257-262.
Danks, H.V. 1996. How to assess insect biodiversity without wasting your time. Biol. Survey of Canada, Doc. Series No. 5.
Ring, R.A. and N.N. Winchester. 1996. Coastal temperate rainforest canopy access systems in British Columbia, Canada. Selbyana 17: 22-26.
Schowalter, T.D. 1989. Canopy arthropod community structure and herbivory in old-growth and regenerating forests in western Oregon. Can. J. For. Res. 19: 318-322.
Scudder, G.G.E. 1994. An annotated systematic list of the potentially rare and endangered freshwater and terrestrial invertebrates in British Columbia. J. Ent. Soc. Brit. Columbia. Occasional Paper 2.
Stork, N.E., J. Adis, and R.K. Didham (Eds.). 1997. Canopy Arthropods. Chapman and Hall, London.
Winchester, N.N. 1997a. Canopy arthropods of coastal Sitka spruce trees on Vancouver Island, British Columbia, Canada. pp. 151-168 in N.E. Stork, J.A. Adis, and R.K. Didham, (Eds.), Canopy Arthropods. Chapman and Hall, London.
Winchester, N.N. 1997b. Arthropods of coastal old-growth Sitka spruce forests: Conservation of biodiversity with special reference to the Staphylinidae. pp. 363-376 in A.D. Watt, N.E. Stork, M.D. Hunter, (Eds.), Forests and Insects. Chapman and Hall, London.
Winchester, N.N. and R.A. Ring. 1996. Centinelan extinctions: extirpation of Northern temperate old-growth rainforest arthropod communities. Selbyana 17(1): 50-57.
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