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Bala Tikkisetty is a sustainable agriculture advisor at Waikato Regional Council.
Bala's back this week with some useful stuff on shelterbelts, and how they can help you, your property, and the environment.
With the winter tree-planting season just around the corner, it’s timely to look at the many figurative farming fruits they can provide (besides any real ones).
Those benefits include providing shelter for stock and supporting pasture growth.
Clearly animals suffer in bad weather. Stock farmed in paddocks, in particular, don’t always have access to natural shelter so planting of shelterbelts is a useful way of helping protect them.They cut exposure to wind, rain and cold in winter, as well as reducing heat stress at hotter times of the year.
Besides protecting stock physically, reducing animal stress helps ensure better feed intake and farm production.
Shelterbelts also help reduce evaporation of soil moisture and transpiration from the grass, particularly helpful in protecting grass growth during droughts or prolonged dry spells. An important factor in this is the reduction of wind-induced agitation of the grass.
Wind can cause physical damage to grasses, leading to stunting or desiccation. The wind speed threshold for physical damage in herbaceous plants in general is often stated as being about six metres per second. At higher wind speeds, grass blades knock and rub together, bend over, and frequently rotate about their longitudinal axes. Such movements may produce permanent lateral fractures, desiccation and wilting of the leaf tips.
Shelterbelts also provide additional environmental benefits such as erosion control and soil conservation.
And shelter trees can be a haven for birds, provide shelter for homes, buildings and stock yards, be aesthetically pleasing, and increase the diversity of tree species in an area. They can also screen noise and reduce odours associated with livestock operations.
The use of native plants for shelterbelts, particularly those naturally occurring in the locality, help to preserve local character and provide forage for bees.
Strategic planting is likely to be more worthwhile than blanket planting and, because of the long-term commitment, careful decisions should be made.
There are certain principles that we need to remember while planning for shelterbelts.
Shelter is most effective when sited at the right angles to the prevailing wind. The wind barrier should be sited directly across the prevailing wind to give maximum protection. If east-west shelterbelts are required they should include deciduous species to lessen the winter shading of pastures.
The density of the shelter belt determines the wind behaviour on the leeward and to some extent on the windward side. Practical experience show belts of medium porosity produce a much more even windflow over a much wider area. Good porosity or permeability of shelterbelts can be achieved by correct species selection and subsequent management including pruning and training. When permeability is lower than say 50 per cent, the wind profile will be changed and turbulence occurs.
The longer the windbreak the better the protection. Short plantings have a disproportionate edge effect, where wind slips around the ends reducing the area of protection. Gaps in a shelterbelt cause the wind to funnel through at excessive speed. This can happen where there are missing trees or when there is a draughty space at ground level.
Tall shelter gives the most economic protection as the area protected is directly related to the height of the windbreak.
For further site specific advice, you can contact Waikato Regional Council on 0800 800 401.