. La Canadian field-naturaliste. L'histoire naturelle. Les 150 109 Canadian Field-Naturalist Vol.. La figure 6. La savane à l'association de l'Alvar Foxey Savanna sur l'île Manitoulin. La prairie est dominé par Pa com- pressa, et Geum triflorum Senecio pauperculus dispersés avec Juniperus communis. Les arbres sont le chêne à gros fruits (Quercus macrocarpa). Photo par P. M. Catling, juin 1994. Deux d'entre eux. Par exemple, lorsque le calcaire sous-jacent se dégrade facilement à un matériau de base pour les sols friables le développement Bur Oak-Red Cedar savan- na peut être bien développées, tout en bordure trottoir et de la chaussée association scrub

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. The Canadian field-naturalist. Natural history. 150 The Canadian Field-Naturalist Vol. 109. Figure 6. Alvar savanna association at the Foxey Savanna on Manitoulin Island. The grassland is dominated by Poa com- pressa, Senecio pauperculus and Geum triflorum with scattered Juniperus communis. The trees are Bur Oak {Quercus macrocarpa). Photo by P. M. Catling, June 1994. two of them. For example, where the underlying limestone readily degrades to a flaky parent material for soil development the Bur Oak-Red Cedar savan- na may be well developed, while pavement edge and pavement scrub associations may be non-existent. The larger alvar complexes are the most likely to contain a complete range of potential plant assem- blages. Some good examples of this are the Chaumont Barrens in New York State, and the Cloche and Misery Bay complexes on Manitoulin Island. The more open phases of plateau alvar may be divided into alvar grasslands and pavements (Figures 4, 5 and 7). Belcher et al. (1992) used the terms "meadows" and "rock flats" respectively in refer- ence to these two major divisions. Within each divi- sion several subdivisions are possible based largely on dominance of single species which in turn is associated with moisture levels. The moisture is periodic and even the wettest sites are subject to complete drying out. Communities with trees may be classified as either limestone savannas or pavement ridges (Figures 4 and 6). These, and for that matter the open phases, are all prone to transition zones, which are sometimes extensive. 1. Alvar Grasslands The dominant species in alvar grasslands (Figure 7) are related to both soil depth (1-10 or more cm) and moisture (the latter having to do with elevation as well as soil depth). Belcher et al. (1992) found four subdivisions of meadow in the Burnt lands alvar on the Smiths Falls limestone plain. One was domi- nated by Sporobolus heterolepis, another by Carex crawei, the third by Panic Grass (Panicum ph

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