February 2001
Now that we are in the height of summer, I am thankful that I do not have to work outside all day in the full sun. My weekday job is inside, but not in an air-conditioned building, so it still gets uncomfortably hot. On holidays and at weekends, I try to stay out of the sun during the heat of the day. My sheep and cattle also avoid the hot sun as they have plentiful shade to retire to.
The Animal Welfare Act of 1999 produced codes of welfare for many aspects of animal husbandry, but not specifically relating to shade and shelter on pastoral farms, because it was said to be too complex to legislate for. However, there is some legislative teeth in a general statement relating to protecting the physical health and behavioural needs (of animals) in accordance with good practise. This is directly linked, among other things, to providing adequate shelter.
I imagine that it is a rare event for farm stock to die of heat stress in NZ, but there is ample evidence that they do suffer from heat stress and productive performance and health (farm profits) are adversely affected. Shade and shelter are not just a matter of animal welfare, they are also sound farm economics.
It is still common to see animals locked in paddocks with no shade or only a single tree. I recently saw lambs seeking shade in the shadow of a power pole.
Too small an amount of shade can create problems as many animals camping under the same tree can cause fertility transfer or increased risk of fly strike. The answer is that more well spaced and well chosen trees are required, not fewer.
A few well chosen deciduous trees in each paddock not only provide shade to improve animal welfare and performance, but their shelter may improve the growth rate of near by pasture as well as providing forage through leaf fall or cut branches. In general the trees should be narrow crowned so as not to discourage summer grass growth and to make the stock move as the shadow shifts. A pruned bottom log on open spaced trees also allows light and rain to the soil around the trunk which supports grass growth. Pruned poplar and other hardwood logs could well be a valuable timber resource too.
AgResearch near Woodville have been experimenting with poplars and willows integrated with pastoral farming on hill country blocks. They have taken advantage of the wide range of polar and willow clones available from neighbouring HortResearch at Aokautere. Research leader Alec Mackay enthusiastically promotes poplars but admits they are still discovering the details of effects on soils, pasture performance and stock performance. Never the less, they now have encouraging results from several years of research to back their enthusiasm.
One of the principal concerns of farmers is "Do poplars suppress grass growth?" The issue is complex to measure, as the control pasture adjacent to the test site may benefit from shelter. Available evidence so far is that there is a modest decrease in pasture production near large older trees, but this can be minimised by choosing narrow crowned forms, wide spacing, pruning, and ensuring stock are present to eat leaf litter at times of heavy leaf fall. Freshly fallen leaves still have nutritive values similar to pasture, but this rapidly deteriorates. The leaf fall and shelter offsets losses in pasture production.
Another major benefit of poplars on sloping sites is soil stabilisation. Slips and soil disturbance through animal trampling and pugging are major causes of soil loss on hill country. Poplars can greatly reduce the probability of slips occurring, and also improve the structural properties of wet soils, making them less susceptible to pugging. All this helps to retain soil fertility on the hills.
Loss of topsoil from the hills must surely be one of the great threats to sustainable agriculture. Intensive grazing with wet soil conditions by either sheep or cattle can cause 1-3 tons/ha/year soil loss. Just figure out what that means over a mere hundred years or so and add that to the number of slips which occur on steep sites.
Poplars, even though they are deciduous, have a considerable drying effect on wet soils which extends for at least two months after leaf fall. Evergreen trees would have an even greater effect as they continue to transpire water throughout the winter months. It makes sense to stabilise winter wet pastures with trees or chose dry soils as sites for feeding out supplementary forage.
Many areas now will be experiencing seasonal shortfalls of pasture as summer heat browns grass off. Farmers should consider using willows and poplar, among other trees, as supplementary forage. It may take a little work to cut down, but stock will thrive on it. It is also free of pasture fungal spores which often cause illness to stock in late summer.
Poplars and willows are not the only desirable farm shade trees. Alders, ash, chestnut, elm, honey locust and plane trees are other possibilities with ash, chestnut and elm also having highly sought after timber for furniture making
So there are many beneficial elements to mixing trees with pastoral grazing systems. Among the benefits are aesthetics, animal welfare through shade and shelter in both winter and summer, forage supplements during times of pasture shortage, soil conservation and hardwood timber. Each element alone would warrant planting more trees, and the sum is surely a compelling reason.
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http://www.treecrops.org.nz/knowl/archives/cairnse/pastoral.html
Wednesday, 27 August 2003 - Updated: 2007 August 11