Clearing Dead Balsam FirAfter Spruce Budworm

What Spruce Budworm Is

Eastern spruce budworm is the larva of a small moth, and it is native to these woods. It is not a new invader. The Minnesota DNR calls it the most destructive pest of spruce and fir forests in eastern North America. The larvae eat needles in early summer. They prefer balsam fir and white spruce, and they do lighter damage to black spruce, tamarack and some pines. From a distance a stand that has been hit looks scorched, with reddish brown tops where the new growth was chewed off.

It moves in waves. According to the DNR, an outbreak stays in one area for about eight years and then moves on, and thirty to forty years can pass before it returns. Northeast Minnesota has had budworm feeding somewhere in most years since monitoring began in the 1950s. The DNR places most of the current outbreak in northern St. Louis, Lake and Cook counties. That is why clearing dead balsam fir after spruce budworm is on the mind of so many cabin and woodland owners in that country.

How It Kills Balsam Fir

A tree can take a year or two of feeding. The DNR's advice for yard trees says healthy fir and spruce tolerate a couple of years of heavy defoliation, but after three or more years in a row they start to die. Balsam goes first. The top dies back, the needles that are left turn rust colored, and then the whole tree is gray. Where balsam grew thick under popple and birch, entire patches die together.

You cannot mulch your way out of an outbreak. What an owner can control is what stands near the buildings, the driveway and the trails. Look at your balsam in early summer, when fresh damage shows. Trees with green lower branches and a thin top are still alive. Trees with no green at all are finished, and they will not recover.

Why Dead Balsam Is a Fire and Blowdown Problem

Dead balsam is fuel. The DNR says trees killed by budworm create fuels that can add to the spread and intensity of a wildfire. Balsam holds its dead branches nearly to the ground, so a dry stand can carry a ground fire up into the crowns. The DNR also notes that a fir stand hit hard for five or more years in a row is a more severe wildfire risk five to eight years after the trees die. The danger does not pass when the needles drop.

The second problem is wind. Dead balsam rots quickly and does not stand for long. Tops snap off. Whole stems tip over in a storm and hang up in the trees beside them. Give it a few seasons and the patch is a tangle of crossed trunks with new brush growing through it. That blocks trails and driveways, makes the woods hard to walk and puts a deep bed of dry wood on the ground. It is also far harder to clean up than dead trees that are still standing.

How Forestry Mulching Deals With It

A forestry mulcher grinds dead and dying balsam where it stands. The mulching head chews the stem and limbs into chips, and the chips stay on the ground. There is no pile to burn, which matters when the whole point is fire. The work is selective. We leave the pine, spruce, birch, maple and healthy young trees you mark, and we take the dead fir and the brush between them. It is the same brush and underbrush clearing we do anywhere, aimed at one species.

The DNR says a clean-up that removes dead trees reduces the fire risk, and it advises favoring tree species other than balsam fir. Mulching does that on the scale of a home site, a cabin lot or a few acres of woods. It also reopens trails and access lanes that dead fir has started to block, and it is the first step toward defensible space around a home or cabin. Chips on the ground are still wood, but they lie flat, hold moisture and break down. That is a different thing from dry trees standing in the air.

Limits, Timing and What to Do First

There are limits. A mulcher is built for brush, saplings and small trees, and much of the balsam that dies under popple and birch falls in that range. Large dead fir or spruce, and any dead tree that could reach a house, a garage or a power line, is work for a tree service. Calvin sorts out which is which when he walks the property. Old blowdown is slower than standing dead trees, because trunks lying crossed on the ground are awkward for the head. Sooner is easier.

Dead balsam can be cleared in any season. Winter is a good fit, because frozen ground carries the machine into the low spots where balsam often grows. Before you call, walk the place and decide how far out from the buildings you want to go and which trees must stay. If the dead fir is close to a lake or river, shoreland rules may limit what can be removed, so check with the county first. Then ask for a free estimate, or read more about forestry mulching.