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A phytosociological study of fir and spruce forests on the plateau of Cape Breton Island, Nova Scotia Smith, Richard T.

Abstract

The present study was designed to: a) employ phytosociological methods to characterize the major spruce and fir forests of the Cape Breton Plateau, b) measure specific climatic and edaphic factors and relate these to the forest vegetation and c) assess the boreal nature of the Plateau forests through comparisons with boreal forests in neighbouring regions of eastern Canada. Climatic measurements were made from June to late August during a two year period. These included continuous recordings of temperature and wind and weekly measurements of precipitation. Daily maximum and minimum temperatures and weekly precipitation were used for climatic characterization of the area and for comparison with D.O.T. meteorological data at Cheticamp and Ingonish Beach in the lowlands of Cape Breton. Soils were sampled, where possible, in each forest stand. Profiles were described and samples were taken for quantitative analysis of texture, nitrogen, phosphorus, carbon, pH, available water, and exchangeable calcium, potassium, magnesium and sodium. Vegetation study resulted in the recognition of three forest associations. The most widespread of these is the Abies balsamea - Diyopteris spinulosa - Hylocomium umbratum. or upland fir association. This is the most productive of the three associations. It forms the climatic climax of the area, and occurs on the better-drained soils of low ridges. Stands of this type have relatively closed tree canopies in which Abies balsamea is predominant and Betula papyrifera occurs frequently but with low densities. Shrub layers are poorly developed because of poor light conditions, and the herb and bryophyte layers are moderately to well developed. The Picea mariana - Pleurozium schreberi or black spruce association is common, and develops both on poorly-drained organic soils in low lying areas, and on thin stony soils on ridges. Tree growth is very poor in these areas. Stands of this type lack a well-defined tree canopy and are chracterized by dense growths of stunted, wind pruned Picea mariana which rarely exceed 3 m in height. Low shrub species, many of which also occur in raised bogs, are abundant, while herb and bryophyte growth is poor. The third forest type recognized is the Abies balsamea -Osrrunda cinnamomea - Sphagnum cavillaceum or swamp fir association. This has a rather limited distribution and occurs low lying sheltered areas, on poorly drained organic soils. Site conditions here are poorer for tree growth than are those of the upland fir association, and Abies balsamea, the dominant species, forms an open canopy with lower densities and higher numbers of standing dead trees than in upland fir stands. Beneath the open canopy, light conditions are favourable, and the shrub, herb and bryophyte layers are well developed. The forest soils studied are acid and have low levels of total nitrogen and exchangeable calcium, sodium, potassium and magnesium. Although differences among the soils of the three associations for the chemical factors analysed were few, the organic soils beneath the swamp fir and the black spruce stands of low lying areas have high moisture contents and probably are poorly aerated. This could be responsible for poor tree growth in these areas. Earlier workers have noted that the coniferous forests on the Plateau differ from the mixed climatic climax forests of the lowland areas of Cape Breton, and have suggested that climatic rather than edaphic factors are responsible. In the present study, comparisons of climate for the two areas corroborated this view, indicating that summer maximum and minimum Plateau temperatures are several degrees lower than those of the lowland areas. A second opinion is that although the Plateau forests have been classified as similar to those of the remainder of Nova Scotia, they are more boreal in nature. In the present study the Plateau forest associations were found to be floristically richer than boreal forests in Newfoundland and southeastern Quebec, but because they contain most of the major species of the boreal forest types, it is concluded that they should be considered a southern extension of the boreal forest.

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