Monday, December 2, 2013

Rethinking Shelterbelts



Justin Evertson

        Since the first settlements in the region more than 150 years ago, trees and shrubs have been planted to protect people, livestock and soils from the harsh Great Plains climate.  Although shelterbelts are typically associated with farms and ranches, they are also used to protect and improve important community features such as parks, schools, large public properties, acreages, subdivisions and commercial areas.  Shelterbelts also provide habitat for wildlife, they help reduce snow drifting and help screen unsightly views. 
        Shelterbelts became very common in the Great Plains during and immediately following the Dust Bowl years of the 1930s.  Such plantings were promoted by state and federal governments to help prevent soil erosion and improve crop production.  The shelterbelt design has changed little from that era.  Most still consist of just a few species of plants, including a row or two of evergreens, planted in straight lines. Time has proven this traditional method of design to have several shortcomings:

  •  A lack of plant diversity can lead to large sections of a shelterbelt dying quickly when certain diseases, insect pests or weather events impact a planting.  Recently, this has become a very serious problem in southeast Nebraska with the sudden loss of many Scotch pines (Pinus sylvestris) from Pine Wilt Disease (see article on back). Scotch pine has become the most commonly planted tree around farms and acreages and it is possible that millions of trees in the region could die in the coming years
  • Evergreens planted tightly in rows can suffer from several needle blight diseases in the more humid air of eastern Nebraska.
  • Species choices often do not reflect soil and topographical changes that occur within the planting line of many shelterbelts.

        To help improve the long-term success of shelterbelt plantings in and around communities, the Nebraska Statewide Arboretum has developed the following design recommendations.

  • Shelterbelts should contain a broader diversity of trees and shrubs than they have in the past.  This does not mean planting one of everything, but rather the use of several species in complementary groupings.  A good rule of thumb is to limit any single species to no more than 20 percent of the total planting. 
  • In the more humid air of eastern Nebraska, evergreen trees are often more prone to foliar diseases.  This is especially true where trees are planted tightly together, as in many older shelter plantings.  For this reason, new shelterbelts in eastern Nebraska should never be a solid wall of evergreens, but should include many deciduous trees and shrubs.  In fact it is very possible to have an effective shelterbelt here with no evergreens at all.
  • In the more arid western Nebraska, evergreens are less prone to foliar diseases and in general are better able to survive the frequent drought conditions than most deciduous types.  As such, evergreens will likely be a larger component of a shelterbelt in the western part of the state. 
  • Several species of deciduous trees and shrubs hold their leaves well into winter or have denser branching that allows them to block more winter wind.   
  • Species selections should better reflect soil conditions. More specifically, species selection should change when soils move from dry uplands to wetter bottom areas. Many shelter plantings extend up and down on slopes with no change in species.

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