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 Riparian plantings

New Zealand Tree Grower, August 2005
Allan Kirk
This article is written about riparian planting for the less stable soils of the Manawatu. The planting advice for more stable soils will be a bit different

Oil was the much-coveted natural resource of the 20th century. Water is quickly becoming the sought after natural resource of the 21st century. Human life can be sustained for over a month without food, but only about three days without water.

Water is fundamental for the life of both our stock and consumers, and the quality of the water our stock consumes determines their health.

Bearing in mind the importance of water now and into the future we need to preserve current water quality levels. The future of the farming industry and our grandchildren’s health will be determined by our actions today.

Riparian areas have long been recognised as one of the components of preserving our water quality. They are simple in construction and follow some easy guidelines and give benefits to both to the farm and the wider community.

Significant benefits

The farm benefits most importantly from an improvement in capital value. Little else enhances a property put up for sale than a well fenced, managed riparian area. It will offer future landowners recreational uses such as duck shooting or swimming opportunities, and intangible benefits associated with owning a small paradise for your own personal enjoyment. The careful planting of trees can benefit stock health with shade, shelter, and improved pasture growth.

In addition to these benefits there are improvements to water management, with appropriately spaced trees storing excess water, reducing stream bank erosion and stream bed degradation. These factors all reduce the risk to farm infrastructure, which again is part of managing the capital value of your property.

The wider community also benefit greatly from these riparian areas. Ecologically the riparian area is a major benefit for our environment. The shrubs and trees offer a food source for the invertebrates from their fruits seeds and leaves. They also shade and cool the water that enhances oxygen levels in the stream. All these factors promote New Zealand’s native fish and the ability of other animals to survive in the streams and waterways.

Another important benefit is bird corridors, allowing birds to move between small blocks of native bush.

How do we create the riparian area?

We start with the fundamental of fencing. This can vary from property to property dependent on stock type, intensity of stocking, contour and soil type. At the basic level a fence has to exclude grazing animals from the immediate flood plain.

The immediate flood plain is defined as where high flows are contained. Fences are best value when they are permanent, ranging from eight-wire post and batten for sheep to a five-wire fence for most dairy farms. Electric fences have their place but require maintenance and this tends to have a low priority in management.

The basic set-back zone of only including the immediate flood plain is too small to accomplish future protection and enhancement of water quality. For total effectiveness the set back riparian area should be extended another four to six metres, equating to 10 to 12 metres on each side of the waterway. This allows the development of an effective riparian area between the land and the water.

In any normal farming system there is run-off of nutrients, effluent or soils into waterways. The riparian area needs to be developed to act as a buffer against this normal flow of materials, thereby reducing the effect on adjacent waterways. To be effective we need to recognise a number of zones within the riparian area.

• Zone 1 the immediate flood plain
• Zone 2 from 2 to 4 metres 
• Zone 3 from 4 to 9 metres 
• Zone 4 from 9 to 10 metres.
  

Zone 1 The immediate flood plain

This area needs species with good lateral root development but without adding weight to the stream banks. The plants also need to allow the high water levels to pass quickly and not have their flows impeded. Only grass-like species should be used such as flax or toi- toi to give immediate bank protection while adding no weight to a fragile area.

No trees or shrubs should be allowed in this zone. Trees shrubs add weight and debris to the waterway and also shade out the important grass species.

Zone 2 Approximately two to four metres from the waterway

This is generally in the path of most flood events so is also a zone where no trees can be planted. The rules can be relaxed slightly to allow shrubs if flood events are likely to be of a minor nature. Shrubs up to the level of two metres in height and no closer than three metres between them should be the heaviest stocking applied. It is important not to shade out the grasses.

Zone 3 The tree zone four to ten metres from the waterway

The trees in this zone need to perform a secondary purpose, such as protecting the stream exit or entry points, the bends and the shelter retirement areas. The trees should be chosen from species such as manuka, lancewood and cabbage trees. These are trees that will allow the passage of any extraordinary floods and still allow light down to the ground level for the grasses. They will not become too big or need lots of maintenance to ensure they are still effective. They have quite large and deep root systems, anchoring the soil and buffering against major floods. Their roots have the ability to store reservoirs of water, acting like natural detention dams.

Zone 4 The first metre inside the fence

This is the first metre inside your riparian zone from the fence to the buffer zone. It should just be grass. The most effective are Carex, Astelia or Festuca species. This buffer zone could also include introduced grasses such as poa or cocksfoot.

Grasses are an integral component of any riparian area as soaks for phosphates and nitrogen fertiliser washed off the land.

What some of the problems could be

Noxious weeds growing and spreading within a riparian area have long been cited as reasons for not fencing off the streams or waterways. Weeds can spread from these areas, trap stock and can be unsightly. However weeds are not a problem within the riparian areas. They will certainly grow, but if stock are excluded from the riparian area and good pasture management is maintained on the rest of the property, this should not be a concern.

Weeds will succeed only where conditions are right. Gorse survives in nitrogen deficient soils and blackberry in damper soils. But if gorse establishes itself, native shrubs and trees will grow through. So with the exception of old man’s beard, the rest of the noxious weeds are only a problem if they jump the fence into the right conditions.

Cost and other concerns

Finance can be an impediment to establishing a riparian area. When times are tough I would concede that riparian fencing might not be highest on the priority list. However if you are looking at a capital asset, or financing succession plans, the benefits of a well-tended riparian area are significant.

Trees and their branches can create dams in waterways, another often mentioned reason for not establishing a riparian area. But if the trees have been selected, sited and maintained carefully then they are unlikely to be a problem.

A solution for the future

Riparian areas are a generational issue. We need to adopt solution that is effective for our great grandchildren – it is not just about now. Riparian areas benefit everyone. Responsibility for their establishment needs to be shared. Regional councils, Fish and Game, and the Department of Conservation, all have free advisory services that will assist in developing appropriate riparian areas.
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Allan Kirk is the Land Management Officer Soils with Horizons Regional Council, Wanganui Office.