Are Native Trees Always the Best Choices?
by Michael Kuhns, Extension Forestry Specialist
Across the country people are becoming interested in using native plants in their landscapes, or in maintaining native landscapes as they build homes or businesses. This is leading to problems, however, as people plant inappropriate trees due to a false notion of what "native" means, good well-adapted trees that are non-native get overlooked, and homes built in existing native landscapes are subjected to dangerous fires.
The roots of this native plant trend are in the renewed interest in the environment that has come about over the last several years. Plant-people in educational institutions, nurseries, garden centers, and horticultural societies are also advocating the use of locally-adapted native plants. This makes sense because these plants often require lower inputs of water, minerals, and pesticides than exotic plants.
In the Intermountain West this native plant trend is also taking hold. For example, interest in xeriscaping, often incorporating native plants, is increasing as people become more concerned about limited water supplies. The increased interest in all types of native plants has of course increased interest in landscaping with trees native to our region.
The concept and practice of using native trees in home and business landscapes in our region has some problems. By definition, a "native" plant is one that is living, growing, and reproducing naturally in a particular region. The key idea here is how we define a region. Quaking aspen (Populus tremuloides) and singleleaf pinyon (Pinus monophylla) are trees that are native to the region we call the Great Basin or Intermountain West. However, each grows in a much different habitat, with aspen found on higher wetter sites in the mountains, and singleleaf pinyon growing at lower elevations with very little moisture.
Simple acceptance of the idea of planting native trees would lead to either of these species being planted anywhere in the region. This is not appropriate, however, since aspen planted on a dry site where little supplemental moisture is available will die. And planting of pinyon on naturally wet sites or sites where we water heavily will also lead to failure. The focus in using native trees should be on trees that are native to the region and that are well-adapted to the specific site where they will be planted.
This of course means that native trees aren't even an option for the sites where most people in our region live, since most of us live at the bases of the mountains on sites where there never were native trees. The fact that we can see aspens on the cool, moist mountainsides from our kitchen windows in the dry, hot valley doesn't mean that planting aspens in our yards is appropriate. And, in fact, aspens tend not to do very well in many of the places where we live because of the un-natural stresses they experience.
So, if we live on what is naturally semi-desert shrub land does this mean that our landscape should consist of plants native to such areas? If we care about the environment must we forget about having trees for shade and wind protection since trees aren't native for many of us? This is partly a philosophical question you need to answer for yourself, but practically speaking there are some environmentally responsible alternatives.
If we want trees in our naturally treeless landscapes then we need to pick natives from our region that are appropriate for specific planting sites. I think it also makes sense to consider the use of locally-proven non-natives such as bur oak (Quercus macrocarpa) and hackberry (Celtis occidentalis) that can help accomplish the goals of reducing maintenance and inputs while having a desirable landscape. Any use of non-natives must be done with care, of course, to avoid the introduction of aggressive species that can become pests like tamarisk (Tamarix spp.) and Russian-olive (Elaeagnus angustifolia).
Problems are also associated with saving native trees when we build into wooded areas. Construction activities often kill native plants directly, and landscape maintenance practices such as establishing well-watered bluegrass around drought-tolerant pinyon or juniper trees can kill indirectly.
Many western forests are naturally adapted to regular fires that clean out dead material, kill competing plants, or even kill all trees and make way for a new forest. Examples are coniferous forests, oak-maple woodlands, and pinyon-juniper woodlands. Many of the most desirable home sites in our region are in such forests. Saving the native vegetation may seem desirable, but homes and lives are likely to be lost when these areas burn.
Firewise landscaping, where plant fuels and other landscape elements are designed and managed with fire in mind, and proper construction techniques and home placement can reduce fire hazards in such areas. Ultimately, though, we may find that the risks and costs to society of developing some of these areas are unacceptable.