Problems with planted shelter
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.
Artificial shelter for orchards
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.