Trees
play an integral part in sustainable – or as I prefer, “regenerative” –
agriculture (with all the damage we've caused, we can't afford to simply sustain
anymore). A shelterbelt is a row (or rows) of trees planted across the
prevailing wind direction to slow or deflect the wind. A shelterbelt will alter
significantly the microclimate around your home and gardens or fields.
Trees
(particularly deciduous trees) transpire, giving off huge amounts of water every
day. As the water evaporates, it cools the surrounding area, reducing the stress
on nearby crops. By altering wind patterns and slowing the winds, shelterbelts
reduce the drying effect winds have on your crops. They can also reduce heat
stress on animals and the people working in the fields.
Dense shelterbelts (coniferous trees, thick shrubs such as carragana) protect
the soil from drying out in winter by keeping snow on the ground, which raises
the watertable and reduces the need to irrigate during summer. They also reduce
winter erosion on large fields where cover crops are not practical (experts
estimate that Canadian farmers lose billions of dollars every year due to
erosion). As an added bonus, these shelterbelts keep your house warmer in
winter, reducing your heating expenses.
You might think shelterbelts remove large portions of land from production;
however, research done in Alberta by the Prairie Farm Rehabilitation
Administration (PFRA) showed that increased yields in the sheltered area make up
for this loss of productive land. Levels reach higher than 100 percent of the
original yield from 1.5 to 15 times the height of the shelterbelt, returning to
100 percent from 15 to 25 times the height. Thus, trees 30 feet high will
increase your yields 45 feet away to as much as 450 feet away.
As with all things organic, you'll need to plan before you rush out and plant
a few trees (or shrubs). The PFRA recommends that you review your present
requirements (e.g., erosion control, reducing crop heat stress due to
evaporative water loss), then assess your future needs, estimate the quality of
any existing shelterbelts, and plan new belts for unprotected areas. Map your
home area at one inch = 100 feet (2.5 cm = 30 m); if you have large fields
(e.g., a quarter section), use one inch = 440 feet (2.5 cm = 134 m). Mark the
locations of existing trees, buildings, access roads, powerlines, ponds, etc.
Draw in the prevailing wind directions and where snow accumulates (to eliminate
snow buildup, plant trees at least 100 feet from your buildings and driveways).
Remember that in many areas of the country there are two prevailing winds – the
hot winds of summer and cold winter winds.
Henry Kock of the University of Guelph Arboretum recommends using dense
conifers as winter windbreaks to protect houses, outbuildings and livestock. In
eastern Canada, cedar and white spruce will deflect the wind up and over
buildings; in western Canada, juniper is useful. Henry recommends deciduous
trees and open conifers like white and red pine for use near croplands. The
openness of these trees traps the wind and slows it down rather than deflecting
it over top of the shelterbelt. This results in some air movement along the
ground in the sheltered area, which will protect crops from diseases that
develop in still air. Henry recommends oaks in eastern Canada, although if
you're tight on space, you could create a shelterbelt out of hardy fruit trees
and berry bushes. He also recommends using one densely planted row.
The PFRA recommends planting up to five rows on the north and west sides to
protect from prairie winds; two or three rows are adequate for the south and
east. Around the farmstead, use fast growing, long-lived, tall and dense
species. A dense shrub (preferably fruit-bearing for wildlife) is the outside,
snow trap row. A fast growing species is the second row, and a long-lived
species the third. If you have room for only two rows, one should be dense
shrubs and the other dense trees. Leave sufficient room between the rows for
maintenance equipment.
On prairie fields, the PFRA recommends growing tall trees wherever possible
since the area protected is directly related to the shelterbelt height. If you
have very erodible soils, choose dense-growing trees. The first row should be
less dense to allow even snow distribution across the field. If you grow on a
quarter section or larger, plant shelterbelts every 660 feet across the
prevailing winds.
Henry Kock recommends that you look at nature in your area and learn how
trees function, then plant by nature's example. The PFRA tells its clients to
plant only as many trees as they can care for, as more are killed by grass and
weeds than by any other cause. Also, protect them from livestock by fencing
animals out, and don't grow them closer than 100 feet from any roadway.
Planting trees this fall will not produce much of an effect on your fields
this winter and your crops next summer. However, if you follow these
recommendations and guidelines, in five to ten years you'll have created a farm
or garden that requires fewer inputs and less water, conserves soil and produces
more food, and is beautiful to the eye and soothing to the ear.
Jeff Johnston is a past president of Canadian Organic Growers and a Permaculture
design course graduate. He has worked on conventional and organic farms, and
gardens organically.
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