Popular plants can be overplanted in the landscape. Two examples of overplanted tree species in most communities includes ornamental pear varieties, such as Bradford pear, and red maple. Planting lots of one specific plant not only gets monotonous, but can lead to problems.
Low diversity plantings, consisting of only a few species, should be avoided for several reasons.
- All susceptible trees of one species are affected by any new insect or disease, resulting in widespread damage or death. We have seen this scenario play out in the past decade as pine wilt killed most of our Scotch pines and we are seeing it again now with Japanese beetles.
- Trees have varying levels of tolerance to urban pollution and environmental stresses. When fewer tree species are used, overall mitigation of environmental stresses declines.
- Low diversity in trees enables pest populations to grow larger than would occur in a more diverse planting.
- High levels of tree diversity increase populations of beneficial predatory insects and spiders, which help keep under
- Low diversity in trees is also less valuable to beneficial insects and wildlife, including birds and pollinators, especially considering the many seedless tree cultivars often used in urban areas. Did you know - a single nesting pair of black-capped chickadees feed their young 6000-9000 caterpillars before they fledge, a period of about 16 days. After fledging, their young are fed for up to three more weeks. A mind-boggling number of insects! Good tree diversity is important to support this level of necessary insect populations.
Diverse plant populations, which are created by mixing many tree species, can withstand insects, disease, and environmental problems better than a single type of plant. Planned properly, diverse plantings are also much more attractive.
Dutch Elm Disease – A Lesson in Diversity
Dutch elm disease and the decline of the American elm is a classic example. Rows of American elms lined the streets of many towns across the country in the early 1900s up to about 1950. Then along came Dutch elm disease, a fungus which kills elms very rapidly and readily spreads from tree to tree. Once the disease got started, little could be done except watch one mature elm tree after another die. Streets that were once lined with beautiful shade trees suddenly became barren.
We will soon be experiencing the same phenomenon as emerald ash borer kills our ash trees and, unfortunately, many communities have a high percentage of ash trees in their overall tree canopy.
Planting a variety of tree species provides protection from this type of devastation. Keep this in mind when planning landscapes and windbreaks. One guideline commonly discussed in forestry circles is 10-20-30; no more than 10% of a single species, no more than 20% of any genus and no more than 30% of any tree family. Diversity is key!
Diversity in the Lawn
These same principles apply to lawns. Consider using a mixture of turfgrass species in a lawn, such as Kentucky bluegrass AND turf-type tall fescue. Each grass brings its best attributes to the lawn and minimizes the impact of any single disease or insect pest. This results in a lawn with overall greater tolerance to pests and environmental extremes.
Also important is the use of turfgrass cultivar blends. A blend is the combination of different cultivars (cultivated-varieties) of a single species. For example, most quality packaged bluegrass seed contains 3-4 cultivars.
Using mixtures and blends when seeding turf areas helps assure a diverse population that withstands most problems or stresses that may occur.
Diversity in the Landscape
When planning flower gardens, groundcovers, and other landscape plantings, keep these ideas in mind. There are significant differences in weather stress tolerance, disease & insect resistance and value to wildlife & insects in all types of plants.
The Nebraska Statewide Arboretum is one place for great recommendations on a variety of trees, shrubs and perennials well-adapted to our state’s challenging weather conditions. Visit them at PlantNebraska.org and click on “Resources & Events” then “Tips, Help and How-tos". There's still time for fall planting!
Bringing Nature Home
Want to learn more about the importance of diversity and plant selection to increase wildlife habitat in your landscape? Plan to attend Wachiska Aubudon Society’s program with Doug Tallamy on “Bringing Nature Home”. This free program will be held Sunday December 3, at 3 p.m., at Nebraska Innovation Campus. Registration opens October 15 at WachiskaAudubon.org. This event is sponsored by the Wild Bird Habitat Store and the Nebraska Statewide Arboretum.
Images
- Corneliancherry dogwood, Cornus mas, is a small tree which blooms very early in spring, providing an early food source for emerging insects. It's also very beautiful and is a great replacement for crabapple or redbud, Cercis canadensis. Image by Denise Ellsworth, The Ohio State University, Bugwood.org.
- The flower if a cornelian cherry dogwood tree, Cornus Mas that blooms in early spring. Image by Richard Webb, Bugwood.org.
- American beech is an underutilized tree for Nebraska landscapes. Image by Rob Routledge, Sault College, Bugwood.org.