Use Shelterbelts to Avoid a Momentary Lapse of Season
by George Powell
I’m gazing out my window at the ever increasing snow banks that are still growing under the latest winter flurry (thank you La Nina). And, it is hard to imagine spring will ever arrive. But watching the patterns of snow drift in and among openings and patches of trees and shrubs has reminded me of how important shelterbelts can be to capturing water for the next growing season. And indeed, capturing and storing winter precipitation can become a make or break proposition for crops or livestock watering later on in the dog days of a summer drought.
Shelter For Water Storage
Even in a year of very abundant snowfall, there can still be water shortages in the growing season. Especially if you can’t successfully capture and store that water resource. Loss of snow cover becomes an ever present possibility as we move through the fringe of the winter season and inch towards April showers and May flowers.
As the sun gains back strength, a momentary lapse in the winter season that comes from a rapid warming period can bring on a quick melt. And the freshet flows stream over the frozen ground below. That once mounding store of snow is then no longer a reserve for your next crop. Nor does it seep into the ground water reserves to be drawn later for livestock watering or irrigation. And this highlights the important role tree and shrub cover on farms. In shelterbelts, timberbelts, hedgerows and conservation reserves, they can conserve winter precipitation for later use.
Shelterbelt Design is Key
Snow distribution patterns can be controlled with properly designed and maintained shelterbelts and hedgerows. And larger conservation reserves of trees and shrubs can also serve to moderate spring temperature rises. This allows for a more controlled melting of the snow pack. And slow melting snow infiltrates into thawed ground, and decreases the amount that melts and flows overland.
Detention ponds are also an option to capture the overland flow of snow melt. But they come at a cost. Your must be willing to sacrifice a large production area to store melt water. Or, you have to go through the costs and regulatory hoops of building deeper dam structures (if your topography even practically allows this). Your cheapest and largest storehouse, therefore, is usually keeping moisture in the ground.
Tree Orientation and Density
Both planted or retained trees that are oriented against the prevailing wind will reduce wind speeds. And, in doing so, will diminish the capacity of the wind to carry snow. Snow dropped from the slowing wind is thus retained.
Tree density is also an important consideration in trapping the snow. Denser plantings will provide for greater wind reduction over short distances. And this is good for preventing snow drifts where you don’t want them (e.g. roadways, livestock wintering sites, farmsteads). More open shelterbelts and tree plantings, however, will create a snow drop over a greater distance. Therefore, they are more suited, therefore, to capturing snow on fields to feed next year’s crops.
Mind the Gap
Research and practical experience has also shown that a gap in the bottom of shelterbelts can improve snow distribution. Shelterbelts or hedgerows with an opening (either naturally occurring or created by pruning) will let wind to move through the lower part of the tree or shrub row. Wind speeds and turbulence are reduced. And this carries snow out further beyond the shelterbelt’s edge before being deposited.
The same design principles can be used for blocks of trees and shrubs next to dugouts and irrigation pond. Capturing snow increases the yield of snow trap and melt water captured.
But whether for field or dugout capture, using shelterbelts, or other tree and shrub retention for snow capture and controlled melt is yet another example of why agroforestry is conservation that pays.
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