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Trees can be more than windbreaks

Whether you need a shelterbelt for the yard, a windbreak for cattle, or are working with nature to protect a riparian area, the Agriculture Canada nursery in Saskatchewan has a tree for all reasons.

The breeding program at the Agroforestry Development Centre (ADC) at Indian Head, Sask., concentrates mostly on developing new trees and shrubs for on-farm and other agroforestry applications. Many of the ADC varieties are available through the Prairie Shelterbelt Program (PSP).

The centre, which produces about 28 tree and shrub species, offers conifers, shrubs and deciduous tree species in many combinations to suit different purposes and growing areas. Availability of any particular species can vary from year to year,

The application of these trees and shrubs across Prairie farms and ranchers can vary widely, says agroforestry research adviser Bill Schroeder. The breeding program at ADC considers not only adaptability for different growing conditions, but also the intended purpose. Various plants and/or combinations can be used as shelterbelts, windbreaks and to help rehabilitate riparian or other environmentally sensitive areas on the farm.

WELL SUITED

First and foremost, in tree and shrub breeding, any species needs to be highly adapted to prairie growing conditions, says Schroeder, noting they must be able to withstand variable climatic conditions such as drought or early or late frosts.

Fast biomass accumulation is also important. “We want something that accumulates biomass as quickly as possible,” says Schroeder. “In the case of a riparian buffer zone, for example, we want the tree to be able to capture and intercept as many nutrients as possible and accumulate them in plant biomass. The trees and shrubs are functioning as a bio-filter for nutrients and pollutants such as phosphorus and nitrates.” The greater the biomass the more carbon that can be sequestered, which is increasingly important on farms.

A uniform, non-sprawling growth habit makes for a concentrated row of trees, which is important particularly in making shelterbelts and/or windbreaks more effective.

As more diseases continue to devastate popular varieties, some degree of disease resistance is an important breeding consideration. Biodiversity is another way to help reduce disease risk, he says. In the past farmers would often plant just one variety, like Walker Poplar, but if that variety becomes susceptible to a particular disease it is quickly wiped out because all of the trees are genetically identical.

“So now what we promote is mixed clones or mixed varieties,” says Schroeder. “There will be anywhere from five to eight varieties mixed together in equal proportions. We have tried to make these varieties look somewhat similar in appearance but they have different genetic makeups. It’s a dynamic mix that we change according to a suit a particular region or as new trees come available we may replace one of the poorer performing ones, so it changes from year to year.”

Although there may be slight variations in appearance of these mixed varieties they are providing better functionality and improved longevity for landowners.

Every once in a while the program produces a variety more suited for other applications, like the recently released AC-Sundancer, a new poplar variety which has potential for the Canadian ornamental and nursery trade. Although not available through the shelterbelt program, farmers can find it at their local nursery. This upright columnar landscape tree has similar characteristics to other popular varieties, but is much more resistant to bronze leaf disease — a disease which is threatening other species, such as Swedish Columnar Aspen or Tower Poplar, often found as accent trees in yards and gardens.

The ADC has a number of different mixes designed specifically for different purposes. To help protect a riparian zone they recommend a mix of mainly native species such as Manitoba maple, green ash, balsam and cottonwood poplar, bur oak and shrubs like willows, dogwood, chokecherry, and pin cherry.

On an upland site, for a livestock shelter, or as a field shelterbelt, shrubs such as caragana, villosa lilac or chokecherry, and fast-growing species such as acute willow have a good fit. And long-lived species such as green ash, bur oak or Manitoba maple are often planted together with conifers such as Colorado spruce, white spruce, Siberian larch and Scots pine.

NEW DESIGN

There is also a new school of thought, particularly when it comes to the design of shelterbelts. The traditional design has been to plant a single row of one species such as green ash, willow or caragana.

Four years ago, ADC developed a new design for field shelterbelts, which it calls the eco-buffer . That design has three to five rows with a mixture of trees and shrubs blended together to mimic a natural hedgerow. “It is a mixture of trees, shrubs, fast-growing trees and the slower growing climax trees all mixed together in one design,” says Schroeder.

The advantages of the new design, although a bit more complicated to plant, is better establishment success and a reduced need for weed management. The eco-buffer design is dense enough that it shades out the vegetative ground cover and weeds trying to grow within the buffer.

The final design, however, is decided by each farmer, although the ADC and often local conservation districts can provide technical assistance and advice. There are many online resources to help with the design of riparian buffers and shelterbelts and selection of appropriate tree species at the ADC website. †

About the author

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Angela Lovell

Angela Lovell is a freelance writer based in Manitou, Manitoba. Visit her website at http://alovell.ca or follow her on Twitter @angelalovell10.

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