Participants at the Trees on Farms workshops being held around the South Island were asked why they were there.
Canterbury University School of Forestry lecturer Nick Ledgard told the Pleasant Point workshop on April 30 that there was an increasing concern with overseas consumers' perception that Kiwi farmers exposed their livestock to the elements.
Workshop co-ordinator Harriet Palmer encouraged participants to plant more trees.
''The right trees in the right places are part of a holistic plan.''
With good information and advice, farmers could gain ideas about using trees for cash, animal welfare, water quality, soil conservation, aesthetics, and access to premium markets for their livestock, she said.
The objective of shelter on farms was to reduce wind velocity and thereby minimise the risk of soil erosion, damage to buildings, lowered crop or pasture production, and livestock discomfort.
From the outset of settlement in Canterbury, conifers were the best option for shelter, Mr Ledgard said. Amenity value was not so important - settlers wanted quick growth.
Shelter was needed for animals, especially recently shorn sheep and newborn stock.
Late April's southerly storm could have resulted in stock deaths without shelter, he said.
In terms of hardiness, the toughest trees that usually had no failures to become established were conifers, Mr Ledgard said.
Then there were those that would tolerate moderate exposure and could be planted ''in behind the front line'', such as birches.
The next level was ''almost garden trees'' that had amenity value and could sometimes be used with irrigation systems.
Farmers should consider trees' use when choosing them, Mr Ledgard said.
There were two main types of shelter: dense, for protecting stock, which forced the wind up and provided shelter for one to two times the trees' height across the paddock; and permeable, which filtered the wind.
Fifty degrees of porosity was needed for the latter, to give a greater area of wind reduction. More species would serve this purpose, including cedars and poplars.
Lombardy poplars needed very little maintenance and did not suffer much from rust in this part of New Zealand, he said.
''Too many people put trees too close to fences because they begrudge losing any grazing. It allows greater ease of management with more space.''
He recommended two-row planting, to safeguard against failures. If there were any gaps in a shelter belt, ''the wind goes through twice as fast''.
On his own property, he had oaks underplanted with rhododendrons that had to be well watered to become established. The sheep rushed to feed on the acorns when they fell.
If farmers wanted to reduce windblow, they needed to reduce trees' ''sail area'', Mr Ledgard said. Pruned trees had their sail area right at the top, so they could be more susceptible to wind damage.
Where irrigation was used, the height of shelter belts was limited to what fitted under the booms. A radiata hedge would grow taller every time it was pruned and could cause problems, he said.
Now, farmers were planting around the periphery of paddocks with Lombardy poplars, but that left a large area in the middle with little wind reduction.
On some farms, cypress hedges had gaps allowing centre pivots to pass through.
Some native shrubs could be suitable for use under pivots. Flax was one, with its soft top and low height. However, ''it tends to push at fences''.
He recommended riparian planting with natives to manage sediments and filter out nutrients.
''With large rivers, we've got no choice but to use willows and poplars. They have fine roots and survive when they're knocked.''
There was no doubt shelter would become increasingly important in the future, Mr Ledgard said.
''Unfortunately, most farmers are unfamiliar with trees because they have a history of clearing trees to create farmland.
''By the time they get to management level, they've got no experience of trees.
''Trees are an integral part of sustainable management.''
Farmers' No1 resource was soil, Mr Ledgard said. The topsoil, particularly, was essential to grow pasture.
''But trees use the whole soil profile. They punch out the same productivity each year, no matter what the weather.''
- by Sally Brooker