It reaches within 100 km of the Pacific Ocean in the Skeena Valley, overlapping with the range of Sitka spruce ("Picea sitchensis" [Bong.] Carr.), and almost reaching the Arctic Ocean at latitude 69° N in the District of Mackenzie, with white spruce up to 15 m high occurring on some of the islands in the Delta near Inuvik. The wide variety of ecological conditions in which 4 Quebec conifers, including white spruce, are able to establish themselves, was noted by Lafond (1966), but white spruce was more exacting than black spruce. In the United States, the range of white spruce extends into Maine, Vermont, New Hampshire, New York, Michigan, Wisconsin, Minnesota, and Alaska (Sargent 1922, Harlow and Harrar 1950), where it reaches the Bering Strait in 66°44′ N" at Norton Bay and the Gulf of Alaska at Cook Inlet (Nienstaedt and Zasada 1990). Southern outliers have been reported in southern Saskatchewan and the Cypress Hills of southwestern Saskatchewan (Scoggan 1957, Nienstaedt and Zasada 1990) and southeastern Alberta, northwestern Montana (Munns 1938, Harlow and Harrar 1950), south-central Montana (Munns 1938), in the Black Hills on the Wyoming–South Dakota boundary (Munns 1938, Fernald 1950), on the Manitoba–North Dakota boundary (Munns 1938), and at Shushan, New York (Cook and Smith 1959). 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 . Its northern distribution roughly correlates to the location of the tree line, which includes an isothermic value of 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 is generally found in regions where the growing season exceeds 60 days annually. The southern edge of the zone in which white spruce forms 60% or more of the total stand corresponds more or less to the July isotherm of around the Great Lakes; in the Prairie Provinces its limit is north of this isotherm. During the summer solstice, day length values range from 17 hours at its southern limits to 24 hours above the Arctic Circle. One of the hardiest conifers, white spruce in parts of its range withstands mean daily January temperature of and extreme minimum temperatures as low as ; minimum temperatures of are general throughout much of the range except the southernmost and southeasternmost parts (Fowells 1965).