Planting for shade and shelter

// Animal Welfare // Biodiversity

When planting trees for shade and shelter this winter, it is useful to put together a planting plan taking into consideration the height and porosity (air flow) of the planting.

trees on farm

As well as providing shade and shelter, well-planned plantings could offer other benefits including timber for firewood production, reduced soil erosion, a habitat for native birds, nectar for bees and fodder during drought.

Conversely, poorly designed plantings can result in reduced pasture growth, increased incidences of livestock diseases and problems with drainage and pugging.

Other risk factors to consider when designing a planting plan include fire and wind throw damage.

Planning ahead

When designing a tree planting programme, consider the objectives of the plantings, land use and the needs of livestock at critical times. 

Understand how wind interacts with trees and how this changes the microclimate around the trees. This will help ensure the right trees are planted in the right place to achieve the grower’s objectives.

Height and porosity

The higher the trees the greater the sheltered areas on both sides of the planting. The more porous the planting, the more air will filter through the trees which, to a point, results in a larger but less intensively sheltered zone in their lee.

Dense plantings have short, well-sheltered zones, but create more turbulent air beyond that zone.

If a shelterbelt becomes too porous or has gaps, the wind speed on the leeward side can increase as air funnels through the gaps.

Good design will result in plantings that provide the desired shelter over as much as the target area as possible. Factors such as species, size and location of the planting will depend on individual situations.

Shelter for lambing versus shelter for grazing animals

If the key objective of a planting programme is to provide shelter in a lambing paddock, then a relatively dense shelterbelt orientated to counter problem winds is a good option. This type of shelter could reduce wind speed by up to 90% in a short zone (three to five times the height of the trees) in its lee.

The downsides of this type of shelter include the lack of isolation for lambing ewes, potential snow drifts, lingering frosts and pugging.

Conversely, if the objective is to create a more benign environment for grazing livestock pre-lambing or calving or post-shearing, then either a semi-permeable shelterbelt orientated to counter prevailing winds or widely spaced trees are worth considering.

A shelterbelt with 40-60% porosity throughout its height will reduce wind speed by 20–70% over an area up to 20 times the height of the trees. 

 This results in an extremely sheltered area within which livestock can continue to graze.

Example of a semi-permeable shelterbelt

A semi-permeable shelter planting of fast-growing trees such as poplars or eucalypts could easily reach a height of five metres in five years and up to 25 metres within 15-20 years.

The sheltered area will extend 75–100 metres out from the planting within a few years and around 500 metres at maturity.

A semi-permeable shelterbelt can reduce wind speeds by 50%, increasing the ambient temperature in the sheltered zone. This helps improve both pasture growth and conditions for livestock.

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