Power Down

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The greenest battery in the world

If shelterbelts conjure up a vision of regimented Japanese cedars pruned into 5m high green walls, please rethink this. What I am talking about are mixed hedgerows that are attractive, productive, provide habitat and food for birds and bugs (and you and your stock), and are effective windbreaks.

Shelterbelts should filter the wind. Filter is the operative word. A solid wall across the wind creates a vacuum on the leeward side and causes the wind to fall over it and dump down almost immediately.

Conversely, a porous wind filter that slows the wind can provide shelter for up to 20 times its height on the leeward side, and even provide protection on the upwind side.

I favour a layered shelter with a dense base of feijoa or flax that stock can tuck into, inter-planted with tall, porous upright trees to filter and slow the wind.

Even the uprights can be multi-purpose. You can plant quick-growing trees for (almost) instant shelter, nitrogen-fixers for your soil, fruit, nut or fodder trees, or firewood options you can coppice.

If you only have a small property, consider a 3-5m high hedgerow on your windy side rather than large shelter trees.

The longer your shelterbelt, the better, as the wind will whip around the edges and funnel through the gaps.

Place your shelterbelt across the prevailing winds (west and south in my area) but not high across the northern side as you don’t want to block the sun.

Think carefully if planning to put your shelter along a boundary. Shelter is effective on both sides, and in future you may want access to both sides for maintenance. It’s useful to put in a driveway or a race to access the paddocks around the outside of your property, and have your shelter on the internal side of that race.

Take into account the contour of your land. Cold air sinks. A low, dense shelter on a slope can trap a ‘pond’ of cold air on the uphill side. In that case it is better that the lower growth is permeable to allow the cold to seep away.

Conversely, planting on top of a slope naturally increases the height and effectiveness of the shelter as the wind is already being directed upward by the contour of the land.

Fencing and protecting your shelterbelt from stock can be pretty cheap. Two parallel fences can protect a lot of trees. I prefer a solid netting fence with an electric outrigger to stop stock reaching over as I have pushy calves and I plant tasty trees. But I have seen mature cattle separated from natives with as little as two electric wires (see picture, top right).

The best shelterbelt is porous, not solid

When shelter is a narrow, solid barrier, wind hits it, then immediately falls over it, swirling as it does so and offering little respite. A more porous, wider line of trees means no swirling or dumping and the area sheltered is much larger, on both...