Download How tree planting helps prevent erosion

How tree planting helps
prevent erosion
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P
lants and trees need land to grow on and the constantly
changing climate is providing a number of challenges,
including erosion. One of the many benefits of tree planting is
that it can help minimise erosion.
Soil erosion costs New Zealand around $100-200 million per year
through loss of productive capacity, damage to infrastructure and
degradation of waterways.
Tree cover – as opposed to pasture – helps to mitigate erosion
through two main functions, the first of which is removing water
from the soil profile. Up to 60 per cent of the water that falls in a
water catchment is not transported downslope if tree canopy cover
is in place: 30% is removed by tree cover (leaves of tree) intercepting
the rain; 30% is used by the tree, making best use of the water
from its roots and passing out into the air as vapour. Removing this
amount of water from the soil profile particularly during storm events
significantly reduces the probability of slope failure (erosion).
The other important function relates to the tree roots’ ability to
hold the soil together. Roots in the soil provide structural integrity
(similar to reinforcing steel in concrete). Trees have deeper, stronger,
more extensive root systems than pasture plants, which help to
reduce mass movement erosion.
The Ministry for Primary Industries (MPI) runs a number of
programmes to encourage landowners to plant trees on erodible
land. These programmes include the Afforestation Grant Scheme,
Sustainable Land Management Hill Country Erosion Fund and the
Erosion Control Funding Programme.
These programmes are designed to ensure that crown investment
achieves the best result from taxpayer dollars. They consider;
• all erosion types present and their severity (slump, earthflow,
landslide, etc.)
• that prevention is better than cure (early treatment of potential
erosion, can prevent intense treatment later on)
• whether the treatment area is sufficient (mid-slope boundaries
to be avoided)
• suitable species to grow (will they grow, how quickly, what are
their roots and canopy like)
• the right amount of trees in given area (want to achieve rapid
root reinforcement and canopy cover/rain interception)
• risk of site failing prior to successful establishment of control
(high-risk sites require faster establishment results, or risk of
failure is high)
• risk of treatment not establishing well (failures are expensive,
consider all options)
• potential pest issues, including farm animals
• ongoing maintenance/management
• time (all afforestation treatments take time before they become
effective, some much longer than others)
• longer-term effects (harvesting on steep land, effective riparian
setbacks)
Typically, poplar and willow are used on less severe erosion or
erodible features, which allow pastoral farming to continue. These
trees are very quick and easy to grow in varying conditions. For
more aggressively eroding or erodible sites trees such as Radiata
pine, eucalyptus, manuka and Douglas fir are used. Native reversion
(replanting with native species) is also an effective treatment option
for which funding is available.
So, if you are suffering from erosion on your land, consider
tree planting as a eco-friendly alternative. You’ll also enjoy the
numerous, health and wellbeing, social, environmental and
economic benefits.
Kiwi Gardener
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