No abstract

A study of angiosperm reproductive biology was made in four plant communities in southwestern British Columbia. Species of all four communities have staggered, peak flowering times, resulting in phenolo ical spectra. Anemophily is the major mode of pollination in a salt marsh, while entomopiily predominates in a subalpine meadow. Two sphagnum bogs have more of a balance between wind and insect pollination. There are corresponding differences in the proportions of showy-flowered species in the communities. It is proposed that interspecific competition has greatly influenced the evolution of both species and community flowering strategies.Biotic seed dispersal prevails in the salt marsh and bogs, while most of the subalpine meadow species are wind-dispersed. Species and community modes of dispersal depend on the nature of the vegetation and the relative availability of dispersal vectors, as well as on diaspore morphology.Although vegetative reproduction and self-compatibility are fairly common, the bulk of the flora and vegetation a t all four sites has breeding systems promoting outcrossing. There is little evidence that the physical environments of these communities, all harsh in at least some respects, have selectively favored autogamous or agamospermous species. POJAR, J. 1974. Reproductive dynamics of four plant communities of southwestern British Columbia. Can. J. Bot. 52: 1819-1834. L'auteur a CtudiC la biologie de la reproduction des Angiospermes dans quatre comrnunautCs vCgCtales du sud-ouest de la Colombie-Britannique. Les espkces des quatre communautCs ont une Cpoque de floraison dCcalCe, ce qui donne des spectres phCnologiques. L'anCmophilie est le mode principal de ollinisation dans un marais salant, tandis que 1 entomophilie ~r i d o m i n e dans une prairie sugalpine. Deux tourbikres i sphaignes prksentent plutBt cln Cquilibre entre I'anCinophilie et l'entomophilie.[I existe des diffirences correspondantes dans la proportion des espkces a fleurs voyantes dans les cornmunautCs. L'auteur propose que la compCtition inter-spCcifique a eu une grande influence sur I'Cvolution des stratCgies de floraison aussi bien chez les espkces que dans les communautCs.Dans le rnarais salant et les tourbikres, la dissCmination des graines est surtout biotique, tandis que la plupart des espkces de la prairie subalpine sont dissCminCes par le vent. Les modes de dissemination des espkces et des coinmunautCs dCpend de la nature de la vCgCtation el de la disponibilitC relative des agents de dissimination, ainsi que de la inorphologie des diaspores.Bien que la reproduction vCgCtative et l'auto-compatibilitC sont assez frequentes, la majeure partie de la flore et de la vegetation des quatre sites a des systkmes de croisements qui favorisent a ficondation croisie. Dans toutes ces communautCs, I'environncment physique est sCvkre sous au moins quelques aspects; niamrnoins, il existe peu de donnCes indiquant que ces environnements ont favoris6 ~Clectivemenl les espkces autogames ou agamospermiques.[Traduit par le journal]

In comparison to countries with a tradition of vegetation studies, a comprehensive, hierarchical classification of plant communities in the province of British Columbia has not yet been developed. Such a classification is needed for systematic ecological studies and coordinated conservation of vegetation. As the culmination of fifty years of detailed surveys, tabular and multivariate analyses of 3779 relevrs of natural, old-growth, submontane, montane and subalpine forest communities in coastal British Columbia were used to develop a hierarchy of vegetation units according to the Braun-Blanquet approach. At the highest level, we distinguished seven orders: Quercus garryana, Pseudotsuga menziesii-Mahonia nervosa, Tsuga heterophylla-Rhytidiadelphus loreus, Tsuga mertensiana, Thuja plicata-Tiarella trifoliata, Populus trichocarpa, and Pinus contorta-Sphagnum. Diagnostic table, ordination, and climatic and edaphic regimes were used to show floristic affinities among the orders and to interpret their relationships to regional environmental gradients. Plant communities of each order were briefly characterized by their floristic composition, physiognomy, succession, and environment. The synopsis for all delineated vegetation units (order, suborder, alliance, and association) of coastal British Columbia is included. Table 1. Synopsis of vegetation units distinguished in old-growth forest communities of coastal British Columbia, showing rank, scientific names and abbreviated names.

The historical development of a bog woodland on the north coast of British Columbia is reconstructed using pollen analysis, peat stratigraphy, and 14C dating. The succession spans 8700 ± 210 years in the following sequence: Pinuscontorta Dougl. – Alnusrubra Bong. – ferns/pioneer alluvial forest; Piceasitchensis (Bong.) Carr. – Alnus – Tsugaheterophylla (Raf.) Sarg. – (Thujaplicata) Donn. – Lysichitonamericanum Hulten & St. John – ferns/moist productive alluvial forest on regosols; Thuja – Chamaecyparisnootkatensis (D. Don) Spach – Tsuga – Pinus/scrub forest on peaty mineral soils; Pinus – Chamaecyparis – ericaceous shrubs – Sphagnum L. spp./bog woodland on organic soils. This ecosystem sequence is correlated with changes in paleoclimate reported for southwestern British Columbia and may also be associated with edaphic factors such as changing drainage patterns, the formation of cemented soil horizons, and the accumulation of thick organic surface horizons. The succession from forest to muskeg is contrasted with other evidence for succession from muskeg to forest in north-coastal British Columbia and southeast Alaska. We interpret the regional vegetation and soils as a dynamic complex of ecosystems linked successionally through climatically sensitive pathways. Local site factors such as topography, landform, drainage, and nutrient regime are important secondary factors controlling the direction of succession.

The relationships between the distribution of plant communities and environmental factors were studied in an open peatland – forest complex of the hypermaritime north coast of British Columbia. The entire vegetation gradient, from open through forested peatlands to upland forest, was primarily explained by slope and minimum level of groundwater table. Environmental conditions in the upland Tsuga–Rhytidiadelphus forest were considerably different from those of the other communities; differences were small among the Sphagnum open peatland, the Pinus–Sphagnum woodland, the Chamaecyparis–Fauria forest, and the Thuja–Gaultheria forest. Highest level of groundwater table, conductivity minimum, pH, and dissolved oxygen merely helped distinguish the upland Tsuga–Rhytidiadelphus forest from all other communities. The wet Thuja–Gaultheria forest could be more vulnerable than the upland Tsuga–Rhytidiadelphus forest to local hydrological changes caused by harvesting. Consecutive intraannual measurements of environmental variables are important in clarifying the relationships between distribution of plant communities and environmental variables, especially for communities with peat accumulation.