Threats to Forests - Bugs and Disease

Bugs and Disease

There are always bugs and diseases in the forest making their living by chewing on various parts of the trees.  That’s ok, it’s natural and, to an extent, plays a part in forests’ health. When something in the environment goes hay-wire allowing a particular bug or disease to go epidemic, that’s when there is a problem.  Research and quick forest management actions are the tools people have to stop a disease or insect epidemic in the forest.  We didn’t have the right tools, or they didn’t work, when chestnut blight, Dutch elm disease and white pine blister rust epidemics took off.  These diseases reduced American chestnut, American elm and western white pine populations to a few scattered individuals that survived.  These  events were huge ecological and economic losses.  Sometimes research and management actions can’t stop an epidemic, but they’re the tools we have and we need to constantly improve them and keep trying every time a forest is threatened.

The tussock moth, bark beetle and spruce bud worm are insect threats that from time-to-time have become epidemic, killing large areas of forest.  Forest researchers have developed some techniques to limit the spread of these insects when populations threaten to become epidemic, for example, combating bark beetles usually involves cutting and removing trees that have been attacked.  Harvesting the attacked tree has to be done at the stage in the beetles life cycle when they are still chewing their way through the soft phloem and cambium layers just under the bark.  Cutting and removing an infected trees at this stage of the beetle’s life cycle sends millions of them to a sawmill where they die.  If the tree is left standing in the forest, the beetles dine all winter, then in the spring they burrow outside the bark and fly until they bump into another tree to burrow into and begin eating the phloem and cambium, killing that tree also by girdling it from the inside.  Another year, a whole lot more dead trees, and the cycle escalates, whole forests are threatened.  After a die-off of thousands or millions of trees, they are potent fuel for large, hot fires.

The technique of cutting and removing beetle trees can’t always happen, sometimes the costs are too great, sometimes there is no access, sometimes there is political opposition to cutting the infected trees. 

Probably the biggest factor in preventing insect or disease epidemic is to have a healthy forest, young and middle-aged forests are generally healthy, old forests aren’t - just like people.  Bugs can get a start in old forests, attacking trees with low vigor, once inside the bark they eat, lay their eggs, fly, eat, increase their numbers until there are enough to successfully attack healthy trees.  The epidemic is off and running.   Healthy trees fight a bug attack by sending a rush of sap to a spot where a beetle has burrowed into the cambium.  The sap encases the bug and flushes it back outside the hole it made in the bark - dead bug.  But, evan a young healthy tree can fight off only so many beetle attacks until some make it through and then the tree has lost.

It’s a constant battle for survival out there in the forest, for the trees, the bugs, the fungi and other disease critters.   We people are usually cheering for the trees and doing what we can through research and management to keep the trees healthy, growing and beautiful.

Shore lines on Mount Jumbo from ancient Glacial Lake Missoula