The tree has developed a mutualistic
relationship with a bird, the Clark’s
nutcracker. The tree is dependent on this bird for reproduction,
and the seed of the tree is a major source of food for the
bird. Whitebark pine cones do not open and cast seed when
they are ripe. The cones remain closed until the nutcracker
comes along, pries the cone open with its bill, and stores
the seed within a pouch beneath its tongue.
The bird then caches the seed to be used later
as a food supply. Some of these seed caches are forgotten,
or are not needed and the tree reproduces.
Incidentally, the Clark's nutcracker is a
member of the Corvid family of birds along with jays, ravens
and crows. This is the most intelligent family of birds in
North America.
If you think about it, the nutcracker not
only has to remember where it has cached its seeds, but also
whether it has consumed that particular food supply. The bird
has been observed burrowing through several feet of snow to
retrieve a cache of seeds.
The red squirrel
also uses whitebark pine seed as a food supply. The squirrel
cuts the cones from the tree and caches large groups of cones
in middens. Interestingly, these middens are often raided
by bears, in particular the grizzly
bear relies on these middens for up to 1/3 of its food
supply.
Unfortunately, the whitebark pine is in trouble.
A fungus, the whitepine blister rust, was introduced from
Europe around the turn of the century. This fungus attacks
the stem of the tree, kills it and girdles the tree. It is
estimated that 80% of the whitebark pine in Glacier National
Park have died in the last 20 years. The fungus has now also
spread to the Helena National Forest, but it has not been
reported in Yellowstone Park yet.
The tree is also being affected by advancing
forest succession due to fire suppression. More shade tolerant
trees are growing in the shade of the whitebark pine forests
and overtopping the tree. A lack of fire also means there
are less open areas for the tree to reproduce.
What can be done? The first step to aid the
whitebark pine is to understand the problems it faces. Foresters
can create openings with timber harvest and prescribed fires
to provide places for the Clark’s nutcracker to cache
seed and encourage the tree to reproduce. Foresters can also
try to collect seed from trees that appear resistant to the
white pine blister rust. It is estimated 5% of the trees are
resistant to the fungus. Cone collections from apparently
resistant trees have begun on the Forest with the objective
of testing the trees grown from this seed for fungus resistance
and the goal of eventually planting fungus resistant seedlings.
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