Douglas fir trees have been succumbing to drought in the Willamette Valley. Although there have been individual years of wet conditions over the past two decades, on average conditions have been drier than any other 22-year period in the past thousand years. One may notice the top dieback first, a sign that a vascular issue is not allowing water absorbed by the roots to reach the tree’s upper canopy. Think of this system as an internal pump going back and forth between the roots and the green needles processing sunlight.
If you see this dieback, please call an ISA Certified Arborist first. Do not water it during the summer! The fir is native, and it can be susceptible to root-rot issues. Other management solutions are available and are recommended on a case-by-case basis. Sometimes, the end is inevitable, and removal and replanting of a more drought-tolerant species is the only way to mitigate a risk, replace benefits, or simply remove a dead tree from eyesight.
Another way to have your dead tree, and it doesn’t have to be a fir or even a conifer, live on in a different way is to retain a habitat snag, aka, the Habisnag. Arborists can attempt to mimic nature by carving out broken tops and creating cavities for critters to nest, perch, and feed. We’ve learned from ecologists that a woodpecker is a “Keystone Species” that can indicate a complete circle of the food web and the sign of a healthy forest. Birds from the Black-capped Chickadee and the Brown Creeper to the Piliated woodpecker and Great Horned Owl can utilize this scarce and critical habitat in our urban forests. In addition to Rodentia control and bird-viewing bonuses on your property, bats can keep mosquito populations in check. They prefer morning sun, so east-facing bat-slits can be installed. Upon request, our more artistic-leaning arborists have carved the owner’s requests for heartfelt initials and even lightning strikes!
Habisnags are not for everyone. More formal or sterile landscapes may not want an old tree trunk hanging around, while others have a lower threshold for residual risk. Maybe the location is too close to a structure or high-traffic area. These things must be considered when considering retaining a Habisnag on your property. Left at a predetermined height, an old spar without a windsail has a very low likelihood of failure and can be directionally felled in a few decades if they become unstable.
We’ve had massive successes with this method throughout the Willamette Valley. Colonies of the elusive Acorn Woodpecker have caches and thrive in a backyard in the south hills, while Habisnags at The Cascade Raptor Center house wild birds just outside the enclosures of those being rehabbed. One can expect wildlife activity within a year, and the ecological benefits can extend for future generations. There are some scenarios where a tree is not a good candidate for a Habisnag. Typically, however, a drought-stricken fir still has great structural roots and decomposes slowly from the top- down, which will create a more ideal natural habitat over time. -NL