Description
Pinus banksiana ranges from 9–22 m (30–72 ft) in height. Some jack pines are shrub-sized, due to poor growing conditions. They do not usually grow perfectly straight, resulting in an irregular shape similar to pitch pine (Pinus rigida). This pine often forms pure stands on sandy or rocky soil. It is fire-adapted to stand-replacing fires, with the cones remaining closed for many years, until a forest fire kills the mature trees and opens the cones, reseeding the burnt ground.
The leaves are in fascicles of two, needle-like, twisted, slightly yellowish-green, and 2–4 centimetres (0.79–1.6 in) long.
Jack pine cones are usually 5 centimetres (2.0 in) and curved at the tip. The cones are 3–5 cm (1.2–2.0 in) long, the scales with a small, fragile prickle that usually wears off before maturity, leaving the cones smooth.
Unusually for a pine, the cones normally point forward along the branch, sometimes curling around it. That is an easy way to tell it apart from the similar lodgepole pine in more western areas of North America. The cones on mature trees are serotinous. They open when exposed to intense heat, greater than or equal to 50 °C (122 °F). The typical case is in a fire, however cones on the lower branches can open when temperatures reach 27 °C (81 °F) due to the heat being reflected off the ground. Additionally, when temperatures reach −46 °C (−51 °F), the cones will open, due to the nature of the resin.
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