with an estimated average lifespan of 250 to 300 years. Slow-growing trees in rigorous climates are also capable of great longevity. White spruce high on the shore of Urquhart Lake, Northwest Territories, were found to be more than 300 years old. Bark The bark of mature white spruce is scaly or flaky, grey-brown or ash-brown, but silvery when freshly exposed. Resin blisters are normally lacking, but the Porsild spruce Picea glauca var. porsildii Raup has been credited with having smooth resin-blistered bark. White spruce bark is mostly less than 8 mm and not more than 9.5 mm thick. Chemistry Isorhapontin can be found in spruce species such as the white spruce. Distribution White spruce has a transcontinental range in North America. In Canada, its contiguous distribution encompasses virtually the whole of the Boreal, Subalpine, Montane, Columbia, Great Lakes–St. Lawrence, and Acadian Forest Regions, extending into every province and territory. On the west coast of Hudson Bay, it extends to Seal River, about 59°N, "from which the northward limit runs apparently almost directly north-west to near the mouth of the Mackenzie River, or about latitude 68°". Collins and Sumner reported finding white spruce within 13 km of the Arctic coast in the Firth Valley, Yukon, at about 69°30′ N, 139°30′ W. It reaches within 100 km of the Pacific Ocean in the Skeena Valley, overlapping with the range of Sitka spruce (Picea sitchensis), 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, 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, where it reaches the Bering Strait in 66°44′ N" at Norton Bay and the Gulf of Alaska at Cook Inlet. Southern outliers have been reported in southern Saskatchewan and the Cypress Hills of southwestern Saskatchewan and southeastern Alberta, northwestern Montana, south-central Montana, in the Black Hills on the Wyoming–South Dakota boundary, on the Manitoba–North Dakota boundary, and at Shushan, New York. White spruce is the northernmost tree species in North America, reaching just north of 69°N latitude in the Mackenzie