Classification and Management of Rare Ecosystems in British Columbia

This paper reports on the progress in developing a field reference for the identification, description, and assessment of rare ecosystems in British Columbia for the Conservation Data Centre (CDC). To this end, a review of plant community classification concepts is provided. Concepts discussed include (1) the relationship between the plant community and the plant association, (2) vegetation classification concepts used in the biogeoclimatic ecological classification system, (3) clarification of classification concepts and the B.C. CDC’s Redand Blue-listed plant communities, and (4) plant community rarity—the nature of the threat. Management implications and recommendations are outlined as a starting point for further discussion. Donald S. McLennan Oikos Ecological Services Ltd. 3855 Second Avenue, Box 985, Smithers, BC, V0J 2N0, Canada [email protected] Irene E. Ronalds Oikos Ecological Services Ltd. 3855 Second Avenue, Box 985, Smithers, BC, V0J 2N0, Canada M C L E N N A N A N D R O N A L D S 114 Proc. Biology and Management of Species and Habitats at Risk, Kamloops, B.C., 15–19 Feb. 1999. environmental gradient is more gradual, such as on long slopes in mountainous terrain. In these cases, identifying where one plant community changes to another is much more difficult. Whereas the plant community refers to real assemblages of plants in nature, the plant association is a classification concept that groups similar plant communities, often for environmental description and ecosystem-based land management. In the Braun-Blanquet approach, which is the basis of the plant community classification in the biogeoclimatic ecosystem classification (BEC), plant communities are sampled using réléve analysis, and the floristic data are analyzed so that similar plant communities are grouped together, following the rules of vegetation classification (see MuellerDombois and Ellenberg [1974] or Shimwell [1971]). Using this approach plant communities are considered part of the same plant association if they meet certain criteria for frequency of occurrence and percent cover of indicator species. The CDC has recently updated its terminology so that rare plant associations, rather than rare plant communities, are the elements of conservation (B.C. Conservation Data Centre 1999). Ecosystems can be defined as the system that includes the total assemblage of living organisms, together with their nonliving environment, over some particular area (Kimmins 1992). The nonliving component of the ecosystem includes factors such as climate, physiography, and soil, and are together considered as site component of the ecosystem. The plant community is the plant component and, with animals, makes up the biotic component of the ecosystem. Thus plant community and ecosystem should not be considered synonyms. The size of an ecosystem is not included in the definition, and is determined by scale of interest. In the BEC system local forest ecosystems are defined as areas of the landscape uniform in soil polypedon, vegetation composition, and vegetation structure (Pojar et al. 1987). These are also the criteria used when selecting the location for a plot to conduct releve sampling of a plant community. Rare plant associations are thus used as labels for defining and identifying rare ecosystems that include identified rare plant communities. The rare ecosystems that support listed rare plant communities should be the focus of conservation to ensure the coarse filter approach to conservation of biodiversity. APPLICATIONS OF THE PLANT ASSOCIATION CONCEPT IN BIOGEOCLIMATIC ECOSYSTEM CLASSIFICATION The concept of the plant association is central to the classification of ecosystems in BEC at the chronological (successional), regional (subzone), and local (site association) levels of the system (Pojar et al. 1987). Within BEC, changes in plant communities and their plant associations across the landscape are used as bio-indicators to interpret important ecological gradients, and for determining the location of important ecological boundaries. For example, plant communities change over time on the same site as vegetation succession proceeds following stand replacing disturbance. Forest stands develop in a continuous and relatively predictable manner that has been classified into a number of structural stages (Initial, Herb, Shrub-Herb, Pole Sapling, Young Forest, Mature Forest, and Old Forest, following RIC [1998]). Plant communities, and the plant associations that circumscribe them, also change along disturbance chronosequences, and floristically unique plant associations along this time gradient are referred to as seral associations. A structural stage may have many seral associations within, especially in the Initial, Herb, and Shrub-Herb stages, or the same seral association may include more than one structural stage. This latter situation occurs primarily in midsuccessional forest structural stages, such as the Pole Sapling and Young Forest stages, where subcanopy plant species diversity is often low. Another important application of the plant association Table 1 Conservation Data Centre ranks and definitions for element rarity. 1. Critically imperilled extremely rare (≤5 extant occurrences or very few remaining individuals) or some factor(s) make it especially vulnerable to extirpation or extinction. 2. Imperilled rare (typically 6–20 occurrences or few remaining individuals) or some factor(s) make it vulnerable to extirpation or extinction. 3. Rare or uncommon typically 21–100 occurrences; may be susceptible to large-scale disturbances, such as loss of extensive peripheral populations. 4. Frequent to common >100 occurrences; apparently secure but may have a restricted distribution or future threats may be perceived. 5. Common to very common demonstrably secure and essentially ineradicable under present conditions. Table 2. B.C. Conservation Data Centre criteria for Redand Blue-listed plant communities. Status Significance CDC rank Red-listed endangered plant communities with or threatened ranks of 1, 2, 1–2, 1–3 Blue-listed vulnerable plant communities with and at risk ranks of 2–3, 3, or 3–4