Shelter lowers stock stress
It’s winter again, the time of year that is best for tree planting on farm.
Using trees for stock shelter is one of the ways farmers can lessen the climatic stress animals feel during winter.
Normally an animal living in its natural habitat would find its own shelter but farmed animals may not be provided with sufficient options, especially if they are in a field of grass surrounded only by a wire fence.
Planting a shelter belt is the option open to some livestock farmers for reducing the adverse effects of wind.
Artificial windbreaks also play a part in protecting livestock where cost allows and rapid protection is essential.
When establishing a shelter belt, careful consideration needs to be given to site selection and the tree species that are to be used.
An understanding of the terrain and local weather conditions is important, along with an appreciation of the interaction with livestock behaviour.
Strategic planting is likely to be more worthwhile than blanket planting and because of the longterm commitment, a careful decision should be made.
Besides protecting stock, the traditional view has been that the shelter belts help to reduce evaporation of soil moisture and transpiration from the grass. Strong winds in particular enhance transpiration rates from the grass and, if the water absorption rate by the roots is lower than the transpiration rate, the plant develops an internal moisture deficit.
The reduced growth rates were reflected in reduced dry weight, leaf area, and height but leaf area was much more sensitive to wind than growth of whole plant weight, which supports the concept that leaf cell expansion is specifically limited.
Wind can cause physical damage to grasses, leading to stunting or desiccation. At higher wind speeds, grass blades knock and rub together, bend over, and frequently rotate about their longitudinal axes. Such movements could produce permanent lateral fractures as well as wilting and desiccation of the leaf tips.
In addition to environmental benefits such as erosion control and soil conservation, shelter can have complementary effects by achieving multiple goals for both the landowner and the environment.
Recent research reports reveal that sheltering and feeding ewes before lambing has a major impact on reducing lamb losses.
The reports also say that sheltering and feeding ewes two weeks before lambing has a bigger effect on lamb survival.
The types of species used in the shelter belts will make a difference in the number of invertebrates.
Broadleaf shelter harbour more ground-living spiders than conifer shelter belts and there will be a greater variety of native species of spiders and beetles in shelter belts made up of native species.
These spiders and beetles can play an important role on pastoral farms by helping to reduce the numbers of pasture pests.
Roots hold the soil together, providing significant reinforcing.
Root tensile strength is important, but differs between species.
The effect of trees in reducing erosion is a function of tree size, tree stocking per hectare, root tensile strength, and rate of decay after harvest.
Shelter trees can be a haven for birds, give shelter for homes and buildings, stock yards, be aesthetically pleasing, and increase the tree species in an area.
This is one of the largest ways of increasing biodiversity.
Shelter can also screen noise and reduce odours associated with livestock operations.
The use of native plants, particularly those naturally occurring in the locality, help to preserve the local character and provide forage for bees.
Shelter belts control the removal of top soil by the wind, when the establishment of shelter is undertaken simultaneously with other sustainable land use practices such as minimum tillage.
Good shelter improves the microclimate of plants and soil by improving plant water relations and conserving heat and reducing physical damage. It is very important to know that the principles of shelter and the techniques of establishing windbreaks as a sustainable land management practice.
There are four main contributing factors or principles relating to effectiveness of shelter – orientation, permeability, length, and height.
Shelter is most effective when sited at the right angles to the eroding wind.
The wind barrier should be sited directly across the most harmful wind to give maximum protection.
If east-west belts are required they should include deciduous species to lessen the winter shading of pastures.
Porosity of the shelter belt determines the wind behaviour on the leeward and to a some extent on the windward side.
Practical experience has shown clearly that belts of medium porosity (about 50 per cent) produce a much more even wind flow over a much wider area.
Good porosity can be achieved by correct species choice and subsequent management.
When porosity is low, the wind profile is changed; turbulence occurs at a factor of about five times the shelter height.
It is important that shelter filters the wind to avoid turbulence.
This is achieved by planting at pre-determined spacings and pruning.
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 shelter belt 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.
Because of the nature of wind patterns through the gaps it is extremely difficult to fill them in later.
Any early failure must replaced as soon as possible.
Height of the shelter directly influences the area of wind reduction on the leeward and windward side.
The greater the height greater the area influenced.
Generally, good wind shelter is provided for 15 times with some effect up to 20 times the shelter height on the leeward side and up to five times on the windward side, where a high degree of protection is required.
Tall shelter gives the most economic protection as the area protected is directly related to the height of the windbreak
For further details and advice, please call Bala Tikkisetty at the Waikato Regional Council on 0800 800 401.