Shelter from wind and weather is a primary need for humans – and for animals and plants. Protection from extremes of weather helps them to survive and grow. Farmers often plant shelter belts – rows of trees positioned across the prevailing wind. Artificial windbreaks or clumps of native bush are also sometimes used to provide shelter for crops or animals.
New Zealand’s temperate climate is warm enough for grass to grow all year round, except in the most southern or high-altitude regions. Farm animals are grazed in open pasture throughout the year – unlike in Europe and North America, where domestic animals are often housed indoors during the cold winter months.
Despite its mild climate, New Zealand is windy compared with many other countries, mainly because it lies in the path of the westerly airstream that circles the southern hemisphere in the 40s latitude.
Of the main centres, Wellington has the highest average wind speed – 22 kilometres an hour. Auckland is second at 17 kilometres a hour. The strongest measured wind gust in the North Island was 248 kilometres per hour at Hawkins Hill in Wellington, in July 1962. The South Island’s strongest gust was 250 kilometres per hour, in South Canterbury in April 1970.
On pioneer farms, after homesteads were built, one of the first priorities was to plant shelter for buildings and stock yards. Tree planting was encouraged from earliest settlement – by 1900, over 20,000 acres (8,093 hectares) of Canterbury alone had been planted in shelter belts.
Planted shelter belts slow down the wind. This reduces moisture loss from soil and plants in summer and autumn, and helps delay the effects of drought. It limits buffeting of fruit, shoots and flowers by strong wind, and makes it easier for insects to pollinate plants.
The large number of shelter belts in Canterbury were mostly planted against the South Island’s famous nor’wester wind, which blows across the Canterbury Plains from the Southern Alps. The westerly airstream rises over the mountains, increasing in speed as it descends onto the eastern plains. The dry land warms the wind in summer and autumn, so it is often strong, dry and hot, and can cause soil erosion.
Depending on crop type, soil moisture levels, rainfall and wind speed, sheltered crops may produce 5–15% more than those without shelter. Shelter belts around orchards also help reduce drift of horticultural sprays to about 12% of that from unsheltered areas.
Shelter can also reduce soil erosion by wind.
Shelter is generally beneficial to livestock. Animals gather in shade during hot weather, and take refuge from cold winds. Sheltered animals need less feed to maintain physical condition, and their winter growth rates improve. Sheep and cattle can comfortably withstand lower temperatures than humans, because they generate internal heat through biological activity in the rumen (first compartment of the stomach), as long as they are well fed.
The domestic animals most vulnerable to hypothermia are newborn lambs and recently shorn sheep – but these are more likely to seek shelter than older lambs or woolly ewes. Shelter has been shown to reduce spontaneous abortions and lamb losses from hypothermia. Ewes prefer to lamb in isolation from the flock and will seek out shelter to do this if it is available.
Cattle are less susceptible than sheep to hypothermia in cold weather. But shelter from the sun during hot weather can improve milk production and conception rates in dairy cows, and the growth rate in fattening cattle.
Deer benefit from reduced wind speed in cold conditions, and shade in hot weather. They also use shelter to hide their fawns and to provide secluded mating sites. Trees in a paddock have a calming effect on deer, reducing their tendency to run along fencelines and create tracks that become eroded.
Dogs also need good shelter. In order to rest adequately and stay healthy, they should have water- and wind-proof kennels which are kept clean and dry.
In serious droughts, the foliage from shelter belts (such as poplar and willow species) can be harvested and used to feed stock. Use of appropriate tree species may encourage bees, especially in early spring, and predators or parasites of crop pests. Shelter belts also provide habitats for birds, and native trees may attract native birds.
Māori developed techniques that allowed them to grow tropical plants such as kūmara (sweet potato), taro and yam (which they had brought from Polynesia) in New Zealand’s temperate climate. They built low stone walls, and added sand and gravel to soil to form mounds and to help warm it. These ‘stone fields’ are evident today in archaeological sites.
In the early days of European settlement, shelter for livestock on most farms was provided by remnants of native forest, left after the land was turned into pasture. These were clumps of native bush or individual trees scattered across a farm, especially in gullies of hill-country properties. Most have disappeared, and it has been largely up to farm forestry advocates, and more recently regional councils, to encourage farmers to use native bush for shelter.
The New Zealand Farm Forestry Association was formed in 1957. In the early 2000s it had about 3,000 members in 29 branches. Members own or manage up to 100,000 hectares of forest – radiata pine, cypresses, eucalypts, Douglas fir, blackwoods, poplars, other hardwoods and native trees.
Canterbury has New Zealand’s largest expanse of farmland planted with shelter belts. After Europeans settled there, the landscape was transformed from a droughty, treeless plain into a patchwork of paddocks edged by hedges and rows of trees. One of the earliest forms of shelter was gorse hedges planted on low sod walls. However, gorse spread and became a weed, and hedges needed work to maintain them. By the 1940s, many were being removed and replaced with post-and-wire fences and tree shelter belts. Still, in 1993 Canterbury had almost 300,000 kilometres of hedges and shelter belts.
Most farm shelter belts are planted with exotic species, usually radiata pine (Pinus radiata) or macrocarpa (Cupressus macrocarpa). Native species such as lemonwood (Pittosporum eugenioides) or ngaio (Myoporum laetum) are fast growing and also provide very effective shelter. It is important to select species that are adapted to the local conditions. Shelter may also be provided by pampas grass (now considered an invasive pest plant) or other scrub species.
The most commonly used trees for orchard shelter are alders, eucalyptus, poplar, willow and casuarinas.
Generally shelter belts do not produce good timber, and trees pruned for timber do not provide good shelter. However, trimming a shelter belt will improve its effectiveness and help it live longer.
A hedge is a narrow band of low, dense, shrubby vegetation that separates fields or paddocks. Hedges are usually a single row, and in New Zealand are often gorse or barberry. A shelter belt is a line of trees planted as a windbreak, and may be single- or multi-rowed. They are usually radiata pine or macrocarpa.
The ideal shelter belt reduces wind speed by 50–80% out to a distance of up to five times its height, and by 30–50% for a distance of up to 10 times its height. To do this, it should have about 40% porosity or air passage space, so some of the wind goes through. This is more effective than an impermeable wall, which creates wind turbulence on the downwind side. To provide an effective buffer zone from snow, shelter should reach from ground level to at least 15 metres in height.
Shelter belts may be a single row of trees, a double row or more. Wide shelter belts usually provide more effective and rapid shelter, but occupy more land. Single-row shelter belts are normally of one tall species that will grow to the final effective height. Double-row shelter belts may have a low-growing, bushy species as the second row. This provides early, effective shelter, and if planted on the windward side, will shelter the taller species while it gets established.
The shelter belt should be as long as possible to minimise ‘end’ effects where the wind comes around the ends of the belt. The length should be at least 12 times, and preferably up to 24 times, the height.
In orchards or gardens, the shelter belt should be at least twice as high as the plants it is protecting.
To be most effective against wind, the shelter belt should lie across the direction of the prevailing wind. But to minimise shading of pasture, it should be oriented north–south. North–south-oriented shelter protects against dry north-westerly winds, and east–west shelter protects against cold southerlies. Shelter belts are usually planted along existing fence lines.
Newly planted shelter belts must be fenced to exclude grazing stock, so the trees can grow to maturity undisturbed.
Shelter belts can adversely affect the associated crop or pasture – usually because of the trees’ vigorous root growth into the adjacent area. Willow (Salix matsudana), which was widely planted on many kiwifruit orchards, is one of the most troublesome. Willow roots can grow 10 metres or more within three to four years of planting, and compete with the orchard crop for soil moisture and nutrients. Some growers attempt to prune roots using blades or trenches close to the trees.
Tall shelter may shade a crop and reduce flowering and growth.
In grazed pasture, shelter-belt tree roots also compete with pasture species for soil moisture. Areas close to trees may become bare of pasture because of dryness and trampling, and because animals may rest there and leave their dung and urine.
Some trees are poisonous to stock and can lead to spontaneous abortions. Macrocarpa (Cupressus macrocarpa) poisoning is the most common, partly because it is one of the most widely planted species. Pinus ponderosa, which is less widely used in New Zealand, has the same effect. Shelter belts may also harbour unwanted animals, such as possums or other pests.
On irrigated dairy farms many shelter belts have been removed to make room for the very long arms of the large-scale pivot overhead sprinklers.
In the early 2000s, a new form of shelter was appearing on the market and being used on some intensively stocked dairy farms – a large shed where stock can be housed and fed. In winter and spring, these allow cows to be removed from pasture for part of each day. This helps reduce overgrazing and ‘pugging’ (heavy trampling of the soil and pastures), which can slow down grass growth. In summer these shelters help to reduce heat stress in animals.
Dairy shelters allow farmers to allocate feed more accurately to each cow, resulting in faster growth of yearling dairy animals in winter. Overall, dairy production increases of 20% are common as a result of increased pasture growth and cow contentment and efficiency.
Most horticultural crops in New Zealand require shelter from wind. An alternative to planted shelter is artificial shelter using tall posts and windbreak material, usually a polyethylene fabric, strung on wire. This can also form a roof for the crop, to prevent damage by birds.
Gregory, N. G. ‘The role of shelterbelts in protecting livestock: a review.’ New Zealand Journal of Agricultural Research 38 (1995): 423–450.
Price, W. L. ‘Hedges and shelter belts on the Canterbury Plains, New Zealand: transformation of an antipodean landscape.’ Annals of the Association of American Geographers 83, no. 1 (1993): 119–140.