Nature Notes: Tree Foam

Tree foam looks like bubble bath.

There are many reasons to go hiking during the rain: the solitude, wildlife, scents, and vivid colors to name a few.  But at the top of my list has got to be tree foam.  Also referred to as "stemflow", when rain water drips down the trunks of trees, it picks up impurities and forms bubble-bath looking suds at the base of trees.  Sometimes, the pattern is localized, so that one one or two trees in the forest will have the bubbles.  We've also seen tree foam at the base of nearly every tree in the forest.  Tree foam forms in any season, but seems to be most dependent on the length, duration, and intensity of rainfall.  I find tree foam absolutely delightful and one of the special treats of hiking in the rain.

My Maryland hiking partner and I noticed this tree foam when we were hiking several years ago, and were unable to find an explanation.   For a long time, I would ask everyone I hike with if they'd ever seen tree foam.  I got a lot of blank stares.  One hiking friend actually had seen it, and she calls it "tree spit"!

I finally found some literature about "stemflow" which provides a good scientific description of the process:
www.forestryforum.com/board/index.php?topic=36551.0
As I understand it, rain water dissolves stuff from the treebark as it flows down the stem of the tree.  This changes the surface tension of the water, so that when it drips down towards the base of the tree,  air is introduced due to the turbulence of the water, and foam is formed because of the altered surface tension.

Foam isn't just restricted to trees either.  There is also "rock foam" and one time we even saw "trail foam" as the water was flowing downhill on a leaf-covered trail.

Closeup of the bubbles

On every tree

Big trees

Here is a collection of photos of my favorite big trees I've visited in the last few years.  I've also added a few photos of the hikes to the trees, because they are usually found at some stunning places.

1. Sitka spruce on the coast of Oregon.  I've been visiting this same tree as long as I can remember on the coast of Oregon.  I love how the branches are shaped like giant arms.  This tree is a short distance from an incredible view of the Pacific Ocean.

2. Poplars at Joyce Kilmer Memorial Forest in North Carolina.  Immense trees in a small old growth forest remnant.  This is one of the most beautiful walks because there is such a high concentration of big trees and they give the forest a primeval feel.

3. Gennett Poplar on the Bear Creek Trail in Georgia.  The second largest tree in North Georgia.

4. On the AT near Woody Gap in Georgia.  This tree cracks me up!

5. After I interviewed for a job in Fargo, North Dakota,  I drove over to Itasca State Park.  After stopping to soak my feet at the headwaters of the Mississippi river, I strolled over to this big tree, the largest red pine in Minnesota.  As luck would have it, the showy pink lady slippers were also in bloom.  It was a beautiful area... in JULY!   I'm thankful I didn't take the job, and instead ended up in Georgia.

6. Bristlecone pine.  Cedar Breaks National Monument in Utah.

How I got my Trail Name

Cottony egg sacks of the hemlock adelgid

I was up at Mountain Crossings in North Georgia doing Trail Magic with the Trail Dames, full of excitement and waving my hands around and talking animatedly about the the plight of the Eastern hemlocks.  You see, these beautiful trees are at severe risk of going extinct due to the introduced adelgid, which sap the juice from the needles and rapidly kill the trees.  I was still new to the Trail Dames, and though I can be pretty shy and introverted, get me talking about plants and insects, and I light up like a kid in an ice cream parlor.  I find invasive insects, which I spent nine years studying in grad school, completely fascinating.  North Star, one of the Trail Dames and a very insightful woman, said, "Hemlock! Your trail name should be Hemlock!"  And since then the name has stuck.

This name suits me because, first of all, I love plants and trees.  Especially big, ancient trees.  I'm one of those hikers that will go far out of my way to see the largest (or second largest) tree in the state.  I will run up to it and stretch out my arms to see just how massive the trunk is.  I love imagining what changes they've seen in the world, and what it's like to be rooted to the same spot year after year. 

Eastern hemlocks are tall, graceful trees.  They are a dominant tree in much of the southeastern Appalachians, and are an important part of the forest ecosystem, providing shade to Rhododendrons and streamside plants, and food and shelter for lots of animals.   But the adelgid is changing all of that.  Already, I've seen mountainsides of North Carolina dotted with the gray snags of dead hemlock.  It makes me sad to imagine what the all the forests will be like without hemlocks.  Hemlocks make me think about how fragile ecosystems are, how fragile we all are.

I like the name because it also refers to poison hemlock, a herbaceous plant used to kill Socrates.  So "hemlock" has a dangerous connotation.  Maybe the name will remind me to be tough.