Douglas-Firs and Sap Streams: Natures Defense

Douglas-fir sap stream
Douglas-fir sap stream

The evergreen!  How beautiful, how welcome, how wonderful the evergreen.

—Jane Austen (1775-1817) from Mansfield Park, 1814

🌿  🌿  🌿  🌿

The day dawned gray and cloudy, the kind of mountain weather that often leads to dulled photographs, but it wasn’t raining, and it wasn’t cold.  In fact, conditions were above average, and in Northwestern Oregon that’s a plus!  We opted for a hike, and so Chris and I headed to Brightwood to hike a trail known mostly to locals. 

Along the trail
Along the trail

At the muddy parking area, we shouldered our packs, and crossed a dry culvert into the dimly lit woods.  The smell of evergreen spiced the air; a smorgasbord of intoxicating green fragrances that made me to breathe fast and deep for want of more.  

Salal
Salal (Gaultheria shallon)

In the distance, the sounds of the river were like a whisper.  The woods were peaceful, almost too peaceful, and seemed empty of life.  Of course, nothing could be further from the truth.  Animal sign told of their comings and goings that revealed these woods are a busy place.  At trailside, piles of dirt the size of cow pies revealed the ambitious work of the Townsend’s mole—the Northwest’s largest mole.  Cedar trunks, with their numerous carvings were telling signs that the pileated woodpecker prospers in these woods.  Non-animal signs told stories of their own like the wind-felled Douglas fir with its upturned root wad.  What a sound this big tree must have made when it fell!  Root wads, while not the most attractive sight, provide habitat for various plants and animals.  Also notable were snags, both living and dead.  They too are important in that they provide forage, shelter, and nesting sites for birds, bats, flying squirrels, insects, and other creatures.  

Pileated woodpecker holes on western red cedar
Pileated woodpecker holes on western red cedar
Douglas-fir and snag
Douglas-fir healing from an old wound with wild grape in the foreground

Not far in to our hike, I saw something that stopped me in my tracks.  Chris had gone on ahead, but came back moments later wondering what had happened to me.  I showed him a Douglas-fir that was seeping heavy amounts of sap.  Not the usual trickling sap we often see, but thick rivulets.  It is what is called a “sap stream” or “pitch stream” that a Douglas-fir releases to usually combat insects, namely the Douglas-fir bark beetle (Dendroctonus pseudotsugae); a destructive wood-boring beetle that attacks trees weakened by drought, fire, and/or disease.  While most beetle outbreaks are short-lived, the damage they cause is often significant, and can result in the loss of hundreds of trees.  

Douglas-fir sap stream
A closer look at a Douglas-fir sap stream

So how do sap streams work?  When a tree is under attack, it releases large amounts of sap that (if all goes well) plugs the insect holes, thus trapping and drowning the insect.  If infestations are too significant, sap streams are ineffective, and the tree will die.  

It was unclear what caused the sap stream.  There were no dead needles in the canopy, and no sawdust to suggest an infestation.  To my eyes, the fir looked healthy enough, as did its neighbors.  What I did notice, however, was what looked like dirt in and around the sap.  Unfortunately, it was too high on the trunk to look at more closely.  So what had caused this reaction?  Insect?  Injury?  Or was it something else?  

I recorded my findings in my journal adding them to an ever-growing list of questions that might or might never be answered.  On the ground lay a sprig of leaf lichen.  I picked it up, attached it to my pack strap, and started down the trail.  

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Copyright 2013.  All rights reserved.

8 thoughts on “Douglas-Firs and Sap Streams: Natures Defense

  1. I have three tall mature Dougs on the top of a steep hill. I want the trees healthy for their aid in holding up the bluffl and preventing erosion. Per the discussion above one or more of these trees are under distress, sap streams and all of them are raining sap down on our deck, getting worse every year. We have an epidemic of Mountain Beavers just below the trees on the hill. Can Mountain Beavers be feeding off the root system of the Dougs distressing the trees?

  2. We have 7 fir trees on our property–all over 150 ft. high. Just about all are weeping something fierce. No other trees have fallen so as to damage any of the trees. They “appear” to be healthy except for an enormous amount of pinecone droppings that we’ve not had in past years (we’ve been here over 10 years). Many years ago, we had the trees sheared up at least 50 feet as the branches were blocking out the sun to the pools of two of our neighbors and were cutting off much needed sunshine to the lawns and shrubs around the trees. Every now and then a very large “widow maker” comes down after a storm. The dirt/grass around each of these giants is extremely dry due to our not having rain in our area for several weeks. When we did get rain several weeks ago, it wasn’t much to write home about. The trees are original to this area and were not planted by man. Their bases are huge. Any suggestions for how we can help these gentle giants? We are located in Portland, Oregon. Thank you for your time. Barbara Howard

    1. Hi Barbara,

      It’s hard to know without seeing them, but from your description I’ll tell you what I can. Unless the branches are sparse of needles, there shouldn’t be a problem. Douglas-firs shed their needles, sometimes quite heavily. Mature trees should be watered during droughty periods so that the soil is wet, but not soggy. Fertilizing can also maintain their health, making them resistant to pests and disease. As for the cones, Douglas-firs release seed crops approximately every 7 to 8 years. Some years, these cone drops can be very heavy. (Our Douglas-firs are dropping a lot of cones this year, and shedding a lot of needles. But their crowns are still full and green.) Sap streams are common, and occur for a number of reasons, but are usually nothing to be alarmed about.

      Thank you for your questions. I hope you’ve found my answers helpful. However, if you still have concerns, I would probably contact an arborist that can examine them more thoroughly.

      Best of luck!
      Julie

  3. It appears, from the photo, the sap may be emanating from an elongated scar on the tree. ( The edge of a scar is usually a slightly darker colour than the rest of the bark ). These scars can often be seen where falling trees have grazed standing trees. The falling trees can occur because of wind, age or sloppy human fallers ( fellers ). The scars can be more or less conspicuous and may be buried far inside the current bark surface. The sap can protect the tree and eventually the tree may grow around the scar – or not as appears to be the case here. Why this stream is running so prolifically can, as you have said, can be due to a variety of factors.

    1. Thanks, T.L., for stopping by, and for your insight about sap streams. So many theories to consider, and very difficult to pinpoint the exact cause, but fascinating nonetheless.

  4. Bark beetle attack was a secondary stress to the fir. It is possible that the roots have begun to rot. Insects are typically a result of stress, not the cause, although they aid in the decline of any tree species.

    1. Hi Jason, Thank you for your comment. In my article, I do not say that insects are the cause. What I said is that trees weakened by drought, fire, and/or disease are vulnerable to insect attack. And while most beetle outbreaks are short-lived, the damage they cause is often significant. Thank you for reading Nature Chronicles.

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