by Matie Belle Lakish

As I sit by my fire, mesmerized by the flames, I am struck once again, by the miracle of wood. And trees. If I focus my attention on it, I can vaguely remember the botany classes I took, and the descriptions of the xylem and phloem and the complex passage of nutrients and water along the channels that support leaf growth in spring and senescence in winter. But the real miracle is somehow not described in botanical terms, but as some kind of mystery—how can a plant store so much strength and energy for so long, while providing such amazing service to the animal kingdom on this planet? As I watch the flame fingers twirling about the disintegrating log I marvel at the plan that allows all that energy to be stored so compactly and conveniently, and then be released with enough potency to heat my house and keep me warm. I am so grateful!

Trees are one of the few plants that store large amounts of carbon, primarily in their trunks, for long periods of time. The process by which they do it is still somewhat of a mystery. The photosynthesis process and the basics of plant respiration have been known for a long time, but new facts are emerging all the time, especially as trees have been identified as one of the best potential sinks for the overabundant carbon dioxide that is continuing to be produced by the human reliance on fossil fuels.

Unfortunately, human activity may also be contributing to the death of massive numbers of these savior trees. We, in Colorado, are all too aware of the massive die-offs of spruce and fir as insects and diseases take their toll, at least partly as a result of global warming. There is some good news, however, as research by the University of Arizona, School of Natural Resources and the Environment, which is monitoring two Colorado stands of dead trees attacked by mountain pine beetle, has found that the carbon release is less than anticipated.  “A question we are looking to answer is, ‘How does the carbon dioxide released from the forest into the atmosphere change as you have large scale tree mortality over time?’’’ said Nicole Trahan, a postdoctoral researcher at the University of Colorado, Boulder.    

While researchers thought that the soil organisms that live in and around the roots of the trees, and assist in the tree’s growth, would continue to use oxygen after the trees had died, they found that, “Once the trees are dead, respiration by the trees goes away,” David Moore said. “In addition, if you cut off the carbon that a tree put into the soil while it was alive, you reduce the ability of the soil microbes around the roots to respire.

“After five or six years, there is a buildup of some dead plant material, leaf litter and so on, and that seems to drive the rate of respiration up again. But it never recovers to the point it was before the beetles killed the trees, at least over the span of a decade,” Moore said.

“As long as a tree is alive, it puts much of the carbon it fixes from the atmosphere underground to support its roots and associated microorganisms,” Trahan explained. “When the tree dies, that carbon flow is shut off, and the release of carbon into the soil and the atmosphere goes down, leading to the observed dampening effect on the carbon cycle: As trees die, less carbon is taken up from the atmosphere, but less is released from the soil as well.”

As gardeners, what can we do? Plant trees of course. During this dormant time of the year, when the seed catalogs are arriving daily, is a good time to plan for spring planting. Other research has indicated that two good-sized trees can produce enough oxygen to supply a family of four. While it may take decades to achieve that in our climate, it is a goal to work toward.

Native trees are the easiest to establish and maintain. Piñon and juniper are the natives on the hillsides and can be grown throughout the valley, if tended a bit. Narrow leaf cottonwood is the native along creeks, which is replaced by aspen at higher elevations. Both can be grown as yard trees with supplementary water. Some types of maples and oaks, as well as ash and hawthorn will do well with occasional irrigation. If you purchase a tree through a catalogue, be sure it is hardy to at least zone 4, preferably zone 3. It can be really frustrating to have a tree you have carefully tended die during a hard winter.

My preference, as you may have guessed, is fruit trees. Not only do they sequester carbon and produce oxygen, but they give us nutritious food over a long span of time.

One of the biggest challenges for the production of fruit in our climate are early warm spells that cause trees to bloom early, followed by freezing temperatures that kill the fruit blossoms. To some extent this is a function of living in the mountains, where the thinner atmosphere does less to moderate temperature fluctuations than a thicker atmosphere you would find at lower elevations.

Local critters are also a serious challenge. Mice and rabbits will chew the bark on young fruit trees, girdling the tree and killing it. Deer will eat the leaves and young branches, and bears will happily eat the fruit. Birds and insects will also take a toll.

Given all these challenges, is it worth it? I think it is really a matter of picking the level of involvement you are willing to undertake. If you want to be uninvolved in your tree’s future, choose a native like piñon or juniper. If you are willing to water occasionally and want a little shade, choose a native cottonwood or an aspen or a hardy maple. If you fence, you can add many trees to your list and anticipate a fruit harvest at least occasionally. So, enjoy those catalogues as you sit by your fire, and thank the trees.