{"id":539,"date":"2013-04-27T19:02:12","date_gmt":"2013-04-28T02:02:12","guid":{"rendered":"http:\/\/blogs.oregonstate.edu\/treetopics\/?p=539"},"modified":"2015-08-03T13:07:31","modified_gmt":"2015-08-03T20:07:31","slug":"bugs-the-good-and-bad-dead-wood-revisited","status":"publish","type":"post","link":"https:\/\/dev.blogs.oregonstate.edu\/treetopics\/2013\/04\/27\/bugs-the-good-and-bad-dead-wood-revisited\/","title":{"rendered":"Bugs, the good and bad (dead wood revisited)"},"content":{"rendered":"

In response to last week\u2019s post on the value of dead wood in the forest<\/a>, I received this e-mail from a landowner:<\/p>\n

\u201cWe’ve never left much on the ground in the way of dead wood…not during logging, but wind damaged, etc.\u00a0 Our thought has always been that these rotting logs increase the insects in the forest, both good and bad. Is this a valid concern and if so, where is the balance between bugs and wildlife?\u201d<\/i><\/p>\n

He raises a point worth exploring. While calling an insect \u201cgood\u201d or \u201cbad\u201d is a matter of perspective, for the purposes of this discussion let\u2019s assume that \u201cbad\u201d insects are those that cause economic or environmental damage, and \u201cgood\u201d insects are those that don\u2019t. The vast majority of insects that inhabit western Oregon forests fall into the \u201cgood\u201d category\u2026with a few notable exceptions.<\/p>\n

One of these \u201cbad\u201d bugs that the e-mailer might have in mind is the Douglas-fir beetle. This time of year, the adult beetles are flying around in search of Douglas-fir trees where they lay their eggs underneath the bark. Their favorite targets are large diameter, freshly downed logs\u2014or standing trees that are weakened from another cause (root disease, soil compaction, etc.). Through the summer and winter, the eggs hatch and the larvae grow as they tunnel around under the bark (this activity is what kills the tree). The following spring, they have become adult beetles, and they fly away in search of new homes. If they can\u2019t find another weak tree or fresh log, they will go after a healthy tree.<\/p>\n

\n \"Douglas-fir\n
reddish bark dust in bark crevices is a sign of the Douglas-fir beetle (Photo: Elizabeth Willhite, bugwood.org)<\/figcaption>\n <\/figure>\n

Healthy trees can withstand a low-level Douglas-fir beetle attack, and in normal circumstances there are rarely enough beetles around to cause concern. The problem arises when the beetle population builds up and lots of them infest a healthy tree at once. When does that happen? In situations where there is a lot of freshly downed or damaged wood on the ground for them to target initially \u2013 like after a winter windstorm.<\/p>\n

Here\u2019s a true story for illustration.<\/p>\n

In fall 2009, a landowner in the Coast Range was hit hard by beetle kill to his otherwise healthy, 100+ year old forest. Why? Here\u2019s how we think this may have played out.<\/p>\n