Martinborough English Oak
NZ Flax & Cabbage Tree
Sheep excaping the midday
Shelterbelts and Shade
Trees add aesthetic appeal to the farm landscape,
but their advantages go much further with increases
in productivity and better animal welfare when
shelter is provided. Southerly spring storms occur
annually, killing newly born lambs, and while well
planned shelters will not completely solve the
problem, they will go a long way to giving stock
protection from the effects of cold driving rain.
Animal productivity is reduced in cold windy conditions
as energy is used to maintain body temperature,
instead of producing milk, meat and wool. The other
extreme is when animals seek shade in the hottest
part of the day.
Shade provided by single large trees or a shelterbelt,
can reduce the air temperature by 5-10 degrees.
Providing shade against solar radiation and high
temperatures is vital.
Initial planning and good establishment management
is required to obtain the maximum long term benefit.
Take into account prevailing adverse weather conditions,
the noonday sun angle and stock movement from paddock
to paddock. Gateways and non-continuous shelter
can create wind funnels.
Irrigators, especially centre pivot, have their
own special challenges. A farm plan is a useful
tool for planning and recording shelter plantings.
TYPES OF SHELTER
Every farming region has different reasons for
shelter and every property is different in its
requirements. Shelterbelts can be planted as a
barrier, as a wind filter, or a combination of
A barrier type shelter is normally evergreen using
conifers like Pinus radiata, Cedrus or Leyland
cypress, and Phormium (flax) and Pittosporums where
height restrictions apply. The advantage of this
type of shelter is that during adverse weather,
animals can shelter close to the trees; the disadvantage
is that tumbling
air is created in the lea of the shelter giving less benefit downwind .
A semi-permeable shelterbelt can reduce wind speed
by 20-50% over a distance 10-20 times its height.
Moisture losses due to drying winds are reduced,
resulting in greater crop and grass growth.
Deciduous versus evergreen is an important consideration.
Tall evergreen shade creates long winter shadows,
pugging in paddocks and dangerous ice on roads.
Deciduous has the disadvantage of leaf fall resulting
in a more open draughty shelter at ground level.
Regular hedge trimming of some deciduous species
such as Beech cause the leaves to hold on throughout
the winter until new buds emerge in the spring.
A good compromise is to use deciduous to create
the more open upper wind porosity, while using
a native evergreen to provide stock shelter in
the lower third.
New Zealand is fortunate to have a useful range
of native scrubs and small trees suitable for shelter.
Cortaderia, Phormium, Pittosporum, Dodonaea and
Griselinia along with taller Sophora, Plagianthus
and Manuka can be planted together or to compliment
taller growing exotics.
PRINCIPLES OF SHELTERBELTS
- POROSITY -
Ideally 50%, to slow the wind, not stop
- HEIGHT -
Preferably as tall as the situation allows.
Deciduous trees can provide excellent
shade and shelter, with little shading
- SPECIES -
A mix of deciduous trees and native evergreens
has the benefit of the ideal
- SPACING -
Single row shelter 1.2 to 1.5m apart. Multiple
rows and timber belts 1.8 to 2.5m.
Multi row mix of native and deciduous trees
SINGLE ROW SPECIES
Single row shelterbelts tend to be used where
land use or values restrict wider multi-row shelters.
Horticulture and dairying are examples where Italian
alders ( Alnus cordata) or Poplar and evergreens
such as Pinus radiata and Leyland Cypress are trimmed
into formal narrow shelterbelts. However almost
any species can be trimmed into a shelterbelt,
care needs to be taken to form prune early and
not cut beyond live needles in conifers.
The sheltered environment
of a mixed species shelterbelt or woodlot creates
a corridor for migrating wildlife, valuable habitat
for beneficial insects, birds and forage for bees.
WHAT SPECIES TO USE?
Species choice is dependant on local soil and
climatic conditions. Local advice and experience
from tree growers with successful established shelter
is very valuable as conditions vary from region
to region. Macrocarpa, Radiata, Leyland cypress
and Cedrus deodara are traditional faster growing
Deciduous species such as Poplar 'Crows
Nest' and Italian alder, along with a wide
range of other species such as Beech, Hornbeam
and Oaks offer diversity in leaf shape and autumn
and deciduous shelter
Because windbreaks have a long term impact on
the landscape, design and layouts that link with
other farm plantings, such as woodlots and riparian
areas fit more comfortable into the farm scape.
By using natural features, terraces and valleys,
shelterbelts will compliment and appear more connected
to the landscape.
Potential timber species can be planted with the
intention of being pruned to produce a quality
saw log, whilst habitat species form the understorey.
Alternatively, every second tree can be pruned
with the unpruned trees lower branches growing
to fill the gaps. Pinus radiata and Leyland cypress
are species which prune well under these regimes.
Fast growing species such as Pinus radiata and
Poplars can be used to create quick initial shelter
with a slow growing longer term species, either
interplanted or in an adjoining row.
Careful management is important to allow for the
timely removal of the initial shelter species before
it suppresses the slower growing shelter.
Effect of shelter
in wind speed