The Raised Bogs of South-Eastern Labrador, Canada: Classification, Distribution, Vegetation and Recent Dynamics

Abstract

(1) The mires of Labrador form a distinct geographical zonation: concentric raised bogs occur at low altitudes along the southern coast, excentric and plateau bogs extend inland to slightly greater altitudes and higher latitudes, and patterned fens occupy most of the interior north to the tundra. (2) The zone boundaries parallel contours and climatic isopleths, and the zonation is explained in terms of the effects of moisture surplus, soligenous water flow and physiography on mire development. (3) The raised bogs are similar to oceanic mires, with an extensive ground cover of Cladonia spp., absence of trees on the mire expanse, and pronounced surface patterns of broad peat hummocks and open-water pools. Three floristic noda are recognized in the phytosociological table: Cladonia stellaris-C. rangiferina-Kalmia angustifolia nodum on raised hummocks and Sphagnum rubellum-Scirpus cespitosus and Sphagnum lindbergii-Scirpus cespitosus noda in hollows. (4) As a result of the extensive cover of lichens the hummock vegetation readily burns during lightning fires, which are prevalent on the uplands. Examination of a chronosequence of stands burned in 1898, 1931, 1959 and 1975 documents the rapid resprouting of most vascular species and a gradual succession of Cladonia spp. and bryophytes. (5) The recent history of the hummock vegetation involves the alteration of Cladonia stellaris and Sphagnumfuscum, as documented by the presence of recurrence surfaces in short cores, peat monoliths, and long cores. Local factors, including fire and the lowering of the water table through pool drainage, are frequently responsible for changes in the ground cover and the degree of peat humification, and they may confound the stratigraphic interpretation of climatic change.