Distribution
White spruce is the northernmost tree species in North America, reaching just north of 69°N latitude in the Mackenzie River delta. It grows between sea level and an elevation of 1,520 metres (4,990 ft). Its northern distribution roughly correlates to the location of the tree line, which includes an isothermic value of 10 °C (50 °F) for mean temperature in July, as well as the position of the Arctic front; cumulative summer degree days, mean net radiation, and the amount of light intensities also figure. White spruce generally is found in regions where the growing season exceeds 60 days annually.
The southern distribution corresponds to the July isotherm of 18 °C (64 °F) around the Great Lakes; in the Prairie Provinces its limit is north of this isotherm. During the summer solstice, photoperiod values range from 17 hours at its southern limits to 24 hours above the Arctic Circle.
Read more about this topic: Picea Glauca
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