December 27th, 9 am.
It is the last week in December and the evenings have brought freezing temperatures between the small rainstorms. This morning, the frost is thick on the ground and the temperature gauge in the car reads 29 degrees. The frost makes beautiful crystals on the grass, reflecting rainbows into the air. Above the fog I can see blue sky and know it will warm up as soon as the sunshine can come through. As I head out along Davis Creek the tree silhouettes stand out against the brightening blue sky. Being able to distinguish different tree species based on their silhouettes is fun to do.
Along this gorgeous riparian corridor there are not many different species of trees. The main ones are willows, alders, cottonwoods, ash, and a few oaks. These are all deciduous, meaning they have all lost their leaves for the winter. These are the trees I am observing and noticing how their unique shape and branching patterns set them apart from one another. Of course, if one looks at the bark color and texture there are more distinguishing characteristics to go on, but today I am just looking at the overall form of the tree to inform me what species it is.
Starting with the red willow, Salix laevigata, the largest willow along this creek, I can see a few large specimens. This tree can reach 50 feet high and 50 feet wide. It is an outstanding tree with a form that is variable because it often grows from multiple winding trunks. Some branches grow unevenly and straight up, with more growing out horizontally far away from the base and laying along the creek bottom before growing upwards again. I can see the bark looks gray and furrowed, and the red tips of the branches give this tree its signature red hue. I think it is aptly named red willow.
Right near these red willows are other willows that have bright yellow to orange stems. These grow more shrub-like and look like thickets. There are many small branches shooting out of the ground with no real main trunk. This is the arroyo willow, Salix lasiolepis, which is a short-lived, fast-growing multi-stemmed shrub or small tree. It grows 10-30 feet and has smooth bark with yellowish to dark brown twigs. It is easy to tell these two willows apart in the winter just looking at their silhouettes.
The other tree that stands out today has silver-gray bark and majestic growth, the white alder, Alnus rhombifolia. It can grow up to 50 feet high but does not spread out like the red willow. The main trunk of the tree is somewhat straight. The branches have twigs that are lacey with small orange brown catkins that cause the ends to droop down. This tree is related to the birch tree and looks similar, but we don’t have any native birch trees in our area so can’t get them confused.
The fourth riparian tree species we will cover is always easy to recognize because it generally has seeds hanging down and a lot of lichen all over it. It has an opposite branching pattern which means that each branch has a branch opposite of it on the stem. Mature Oregon ash, Fraxinus latifolia, attains heights of 60 to 80 feet and may live up to 250 years. In forest stands and riparian corridors such as this, Oregon ash develops short narrow crowns with small branches on long, straight stems. Trees growing in the open have broad, rounded crowns with large limbs on stems. We have several of these majestic open-crowned Oregon ash trees out in the grasslands. All along the fence lines ash grows in what looks like straight rows. I am often asked, “Did someone plant those trees like that?” The answer is no, the winter flooding floats the seeds across the pastures where they end up pressed against the fence lines. They drop and sprout up, and with a little protection from that fence, they are more successful than in the middle of the fields. No matter where these trees grow out here, whether in the grasslands or in the riparian areas, they are almost always covered with lichens and moss. The lichen hangs down like hair from the branches, giving these trees a light green cast. This is like the valley oaks that grow in the grasslands but because the ash are smaller trees, the effect is more dramatic.
With just a little observation and perhaps a small guide to our native trees like the Pacific Coast Tree Finder book, you can get to know the trees in the valley in winter and in spring.