The short scrubby jack pines Bob shows in Michigan are characteristic of the south (from the point of view of the boreal forests, Michigan is 'the south'). In the boreal forest it is a tall slender tree, as shown in these pictures in northern Minnesota ('the north').
Mature jack pine forest in the Boundary Waters, MN, Photo by Bud Heinselman
190 year old jack pine being invaded by cedar (olive green along water edge) and black spruce (photo Lee Frelich). Forests this old are unusual and succession is starting to occur.
Here is the interior of a mature jack pine boreal forest with feather moss about 10 inches deep on the forest floor.
And, since this is a fire dependent forest type, with high intensity crown fires every 50-150 years (unlike the scrubby jack pines further south which are not serotinous), here are pictures after the fire. Note the cones on the lower branches (look like small knobs) and high in the crowns, which create considerable density in the crown even after the needles have fallen off. (Photos by Bud Heinselman).
Here is a jack pine forest 3 years after fire (Photo Bud Heinselman). Note that the forest came right back from a black moonscape to dense regeneration.
Non-boreal (Bob's pictures from Michigan) and boreal jack pine (these pictures) are very different in growth form, ecological function, and adaptation to fire. The forest Bob showed probably has open cones, more frequent fires and more variety of jack pine tree ages.
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