Dynamics of the Boreal Forest in Northwestern Ontario

Abstract

-Histories of stand establishment and development in seven boreal forest types, dominated by Picea mariana, Pinus banksiana, Populus tremuloides and Abies balsamea, are analyzed. The initially established tree cohort in the stand appears to be the major determinant of compositional development. The short fire interval accounts for the preponderance of young communities and prevents deterioration of stands. Spruce budworm infestations are a possible factor in the perpetuation of Abies balsamea forests. INTRODUCTION In spite of relative compositional and structural simplicity and apparently uncomplicated vegetation-environment relationships, the course and mechanisms of successional development in central Canadian boreal forest are poorly understood. A few recent studies (Shafi and Yarranton, 1973a, b; Carleton and Maycock, 1978) have described the dynamic status of forests in eastern Ontario. Temporal changes in jack pine (Pinus banksiana) forests were examined by Yarranton and Yarranton (1975), Carleton (1982) and Kenkel (1986), and those in black spruce (Picea mariana) communities by Carleton and Wannamaker (1987) and Taylor et al. (1987). Gregory (1979) provided data on tree reproduction in the southern portion of northwestern Ontario, whereas Cogbill (1985) analyzed forest development in the Laurentian Highlands of western Quebec. No comparable data on forest dynamics exist for northwestern Ontario. Consequently, the goal of the present study is to address problems of tree establishment, early community development and indications of expected compositional changes in boreal forest communities in this region. STUDY AREA The region of study is roughly circular, ca. 700 km in diam (Fig. 1). The western limit is the Ontario-Manitoba border, and the southern is the shore of Lake Superior and the Ontario-Minnesota border. The northernmost sites are located at Big Trout Lake; from there, the eastern limits pass through Kasabonika and Webequie, S to White River and Lake Superior. The region has warm, short and relatively wet summers, and very cold, long and dry winters (Chapman and Thomas, 1968). A N-S gradient of increasing temperature is superimposed on a W-E gradient of increasing moisture. The landscape, except for the rugged shores of Lake Superior, is composed of gently rolling knobs of Precambrian rocks, extensive boggy plains, and various glacial deposits (Zoltai, 1961, 1963, 1965). Mineral soils are coarse and thin, while peat deposits are substantially thicker. Podzols and organic soils (fibrisols and mesisols) are the most characteristic and widespread types. I Present address: Acres International Ltd., 5259 Dorchester Road, P.O. Box 1001, Niagara Falls, Ontario L2E 6W1, Canada. 289 This content downloaded from 157.55.39.209 on Sun, 11 Jun 2017 18:33:43 UTC All use subject to http://about.jstor.org/terms 290 THE AMERICAN MIDLAND NATURALIST 124(2) 96' 95' 96' 9392' 91' 90e9' e8' 87' 66' 65' 8 8' 82