Ecological analyses of the northernmost population of pitch pine (Pinus rigida)
1997
Meilleur, A. | Brisson, J. | Bouchard, A.
The northernmost population of pitch pine (Pinus rigida Mill.) is located in the St. Lawrence Valley of Quebec in a region of sandstone outcrops. It has been assumed that this population is the extreme in tolerance to climatic rigor acceptable for the maintenance of this species. We studied the population age structure, fire dynamics, and phytosociology of pitch pine to test three hypotheses: (1) along a water gradient, pitch pine is limited to a narrow range of conditions that is most favorable, (2) regeneration is sporadic and restricted to certain years in which a set of presumably favorable climatic conditions occur, and (3) maintenance of the species is dependent on a favorable fire regime. We found that pitch pine colonizes a wide range of edaphic conditions, from dry rock outcrops to peat bogs. Since the last fire (1957), pitch pine establishment has been continuous and abundant. Recent fires are closely associated with spatial position of rock outcrops and peat bogs with little effect on the present distribution of pitch pine. The ecological characteristics of this population appear to be inconsistent with a species that is restricted in its northern expansion by direct climatic limitation to survival or reproduction. We hypothesize that the major factor responsible for the restriction of pitch pine in expanding its distribution northward would be the lack of suitable habitat rather than a physiological response to climate.
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