A Hike in the Santa Fe National Forest, New Mexico

My hike with my daughter and her boyfriend, at about 11,600 feet elevation north of Santa Fe, showed me that I can still push my body to limits that most people my age cannot attain. It felt brutal at the time but almost immediately afterwards the memories were shimmering and beautiful. Here are some of the things we saw.

The trail started off in the douglasfir (Pseudotsuga menziesii) zone and quickly reached the subalpine zone. I didn’t quite make it into the tundra on top of Santa Fe Baldy.

Decades ago, there were large fires, and aspens (Populus tremuloides) quickly filled the spaces. But since there have been, to all appearances, no fires for a long time, the aspens have grown quite large. Each clump of aspen, covering perhaps much of an entire mountainside, is a genetic individual: one tree with hundreds of trunks. These aspens, whether due to age or genetic differences, had tan-colored bark rather than the white bark I have seen so often in the Black Hills. The bark is thin, translucent, and has a layer of green photosynthetic cells under it.

There were many species of subalpine wildflowers. Columbines (Aquilegia) were rare in the shade, and camass lilies (Zigadenus) were more common out in the meadows.

There were lots of mushrooms and mushroom pickers. The pickers were all smart enough to avoid the deadly Amanita:

A huge storm chased us back to the car for the last few hundred feet of our trip.

I have seen montane and subalpine forests in California, Arizona, Nevada, Washington, Montana, South Dakota, Colorado, and Utah; they all have many features in common but each is unique. We cannot save wild places by just fencing off a token forest or two.

My Fun Evolution Trip Part Six: Adaptations and Stories

We saw a couple of really interesting plant adaptations in the Black Hills. The first is the white buttercup, which filled some of the shallow ponds of Little Spearfish Creek.

The underwater leaves were finely dissected, which increases their surface area for absorbing dissolved carbon dioxide. Terrestrial leaves could also absorb more carbon dioxide this way but would lose too much water, which is not a problem for an aquatic plant. The flowers, however, float on top of the water where insects can find and pollinate them.

Another set of adaptations is represented by the quaking aspen, Populus tremuloides. When you see a whole clump of aspens, perhaps covering several acres, it may be a single genetic individual that has spread by underground stems. All of the aboveground stems are the same height. The resulting genetic uniformity has its risks: diseases can spread rapidly not only because of the genetic monoculture but because of whichever underground connections may remain intact. But the connections help to stabilize the massive clone: the stems (ramets) growing in favorable locations can help to support the ramets growing in unfavorable locations, very much like the phalanx of an army. Many plants have this adaptation, but aspens are famous because they have such massive clonal growth.

Other aspen adaptations sound more like just-so stories. The first is the ability of their leaves (as well as those of cottonwoods, which are in the same genus) to quake in the slightest breath of wind. They do this because of their flat petioles. The standard explanation is that this allows the leaves to absorb more carbon dioxide. I am confident that this is true, but I can only ask why, if quaking is such a wonderful adaptation, that more plants do not employ it?

The second is a nearly unique bark adaptation. The bark looks greenish and is capable of carrying out photosynthesis. Underneath a tight white layer of tissue, there is an intensely green layer, at least in the Black Hills populations. Apparently the photosynthesis in this layer is less inhibited by cold temperatures than in leaves and might benefit the tree in early spring or late autumn. I could not readily find references about what aspens might do with the sugar their bark produces; perhaps they load it directly into the adjacent phloem and send it down to the roots and underground stems. Apparently this layer was actively producing sugar, for an ant quickly found the shallow wound that I made in the bark.

I do not doubt the value of the adaptation, but once again I ask, if it is such a great adaptation, why don’t other trees have it? Of course, many young stems do have it. We cut down a mulberry tree in our yard, which was inconveniently disturbing the foundation of our house, and hundreds of thick green stems immediately sprouted back. Even older mulberry stems have a green layer—but not, to my knowledge, the trunks, as in aspen.

I would think that green trunks, like quaking leaves, would be easy to evolve, and should be more common, if our facile adaptive just-so stories were entirely correct. It appears to me that a few plants have evolved great adaptations within evolutionary constraints.