Ecology of a Black Spruce (Picea mariana) Clonal Population in the Hemiarctic Zone, Northern Quebec: Population Dynamics and Spatial Development

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Abstract
In northern Quebec, black spruce (P. mariana [Mill.] B.S.P.) occurs throughout the hemiarctic zone along with white spruce and larch. Black, spruce reproduces mostly vegetatively by layering. Population study of a clonal stand located in the Lake Minto area, northern Quebec, was undertaken to provide a better understanding of these populations. The smooth straight line trend of age, height and diameter distributions indicated a stable population. The inverse J-shaped depletion model suggested by the population structure was similar to those described for southern stable tree populations. The inverse exponential model which best described the population implied a constant death rate through time. Clonal population growth was little disturbed by climatic change. Small variations (statistically not significant) that were still apparent in the growth curve could be related to more or less favorable growth periods. In the forest tundra, where disturbances are mostly linked to climatic changes, the opportunistic use of both vegetative and seed reproduction constituted an important asset for black spruce populations. Spatial growth pattern of the black spruce clone was determined using cartographic data related to above- and belowground components of the population. Because it reproduced mainly by layering, the black spruce clonal stand displayed a radial development. Older individuals were found near the middle of the stand while regeneration was most active on the border. Few living ramets occurred in the immediate center of the clonal stand while rotten roots and stems were found buried in the soil organic layer. These rotten structures were probably the remains of individuals that gave birth to the clone. Spatial distribution of above and belowground structure showed three units that resulted from the decay of branch connection between layerings. If the population were to expand, these units would be expected to develop either towards stability or towards extinction depending on topography and space available.