As I gaze out my window at the ever increasing snow banks that are still growing under the latest winter flurry (thank you La Nina) 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.
Even in a year of very abundant snowfall, there can still be water shortages in the growing season 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 freshet flow 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 in shelterbelts, timberbelts, hedgerows and conservation reserves can play in conserving winter precipitation for later use.
Properly designed and maintained shelterbelts and hedgerows can be used to control snow distribution patterns. And larger conservation reserves of trees and shrubs can also serve to moderate spring temperature rises, allowing for a more controlled melting of the snow pack that infiltrates into thawed ground, and decreasing the amount that melts and flows overland.
Detention ponds that capture the overland flow of snow melt are also an option, but come at a cost. And unless you are willing to sacrifice a large production area to store melt water, or go through the costs and regulatory hoops of building deeper dam structures (if your topography even practically allows this), your cheapest and largest storehouse is usually keeping moisture in the ground.
Both planted or retained trees that are sited 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 snow retained. Tree density is an important consideration in trapping the snow. Denser plantings will provide for greater wind reduction over short distances and are 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 and are therefore more suited to capturing snow on fields to feed next year’s crops.
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 which, in turn, decreases wind turbulence and carries snow out further beyond the shelterbelt’s edge before being deposited.
The same design principles can be used to utilize blocks of trees and shrubs next to dugouts and irrigation ponds to increase 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.