Decline and mortality in eastern white pine is being attibuted to moisture extremes during the late 1990's, followed by stress-dependent insects and diseases. Lack of proper thinning practices may also be a key factor contributing to eastern white pine mortality. Some unthinned white pine plantations are declining, but damage has not been reported on thinned plantations or mixed species plantations which have thinned themselves. A similar decline in white pine was observed about 10 years ago.
Affected trees are generally 20-30 years old and growing in groups or pockets within pure white pine plantings. We think the droughts of 1988 and 1991 mark the beginning of the domino effect resulting in white pine pocket mortality. Resinosis (heavy resin or sap flow) just below the live crown was evident on many affected trees. Drought stress predisposed the trees to extremely heavy pine bark adelgid infestations. Infestations were so heavy, especially on the more protected side of the tree and just below the live crown, that the trunks of trees appeared white-washed and the cambium was damaged. Cambium damage opens the door for infection by a variety of opportunistic secondary fungal pathogens.
Many bark beetles are also attracted to these stressed trees. Their boring activity kills additional cambium and can cause rapid decline and death in trees that are already extremely stressed. This complex of factors results in weakened trees, which often causes the trunk to break just below the live crown. Mortality is also caused by restriction of fluid movement through damaged cambium and blocked vessels.
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| Vigorous Natural Regeneration in Pine Stand Opening (White Ash) |
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In unthinned stands of pure white pine, trees will stagnate and become stressed before they thin themselves. This stress from overcrowding predisposes the trees to insects, pathogents, etc., which do not normally affect healthy trees. You cannot control droughts (or other climatic conditions), insects, or diseases. The one stress factor you can control is overcrowding. In many cases alleviating this one stress factor is enough to break the chain of events that results in tree mortality. I'm sure there are exceptions -there always are in nature- but at least, if faced with drought or some other stress, vigorous stands will suffer much lower mortality.
White pine stands in Ohio should be thinned by age 20 to maintain health and vigor. The obvious advantages to this approach are that you control how many trees are removed, which trees remain as part of your stand, and how removals are spread throughout the stand.
If you have questions about a forest pest call your local forester.