With its soft top and low height, flax can provide shelter
that fits under irrigation booms, forestry expert Nick
Ledgard says. Photo from Allied Press files.
Farmers are planting shelter belts to assure lucrative
export markets that they take animal welfare seriously.
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
Workshop co-ordinator Harriet Palmer encouraged participants
to plant more trees.
''The right trees in the right places are part of a holistic
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
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
Then there were those that would tolerate moderate exposure
and could be planted ''in behind the front line'', such as
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
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
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
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
''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