Riparian Margins

Water quality and the environment for native fish and aquatic insects can both be improved by fencing off waterways. If these are planted as well, not only is the property made more attractive, but birds and insects are given habitats, and stock are provided with shelter and shade along the outer fence.

This information, based on more than twenty years of successful planting by the Yellow-eyed Penguin Trust, sets out how to plant a riparian strip with natives. Suitable species, with deep and widespread roots, include ribbonwood, cabbage trees and Pittosporum. These require little maintenance, whereas exotic species like poplar and willow need far more attention.

If possible, choose locally grown plants which are suited to your conditions, and which come from seed collected in your area.

Native plant nurseries such as the Yellow-eyed Penguin Trust Nursery, which grows plants from seeds gathered from the Catlins to North Otago, and inland to Macraes, will give good advice.

Your first step is to visit the nursery, find out what species it stocks, their cost, and how many you can order at a time. Often, plants have to be ordered in advance, sometimes up to one or two years.

Fencing

Requirements and cost

The Yellow-eyed Penguin Trust booklet, From Field to Forest: a guide to revegetating southern coastlines, sets out the method for estimating permanent fencing requirements and their cost. Copies of the booklet are available through the Yellow-eyed Penguin Trust office.

If the riparian area is flood-prone, a one- or two-wire electric fence may be easier to restore after floods, but the base of the fence needs to be kept clear to prevent shorting.

Width of strip

The longer and steeper the slope feeding into a waterway, the wider the protected margin needs to be to provide minimal water quality.

In New Zealand, for gently rolling land, a width of one to three metres per 100 metres is ideal.

On steeper slopes and poorly draining soils, a margin of 10 to 15 metres per 100 metres of adjacent slope is recommended.

For self-sustaining bush with minimal weed management, a strip of at least 10 metres on the paddock edge is needed.

If you need access to the waterway for cleaning, you may decide to plant only one side. Adjust the width of the other side accordingly.

Native fish like cooler water, so if you want to reduce the temperature of the stream, your strip will need to be at least 200 metres long.

Plant maintenance

Plant maintenance needs to be carried out for three years, so fence off the area that you can afford to plant in any one year. Don't forget the labour costs to keep it free from pests and weeds.

The planting plan

Don't start planting until the fencing is completed, otherwise stock can rapidly devastate the tasty and expensive seedlings.

What to plant where

Think of the planting area as three zones: fringe (zone A), mid-bank (zone B) and high bank (zone C).

Alongside the watercourse, in zone A, use plants such as grasses, sedges, flax, toetoe and tussock which can tolerate wet or flood conditions. This is particularly important where bank erosion is a problem: the zone should be wide, and shading should be avoided.

On higher ground, in zone B, plant shrubs such as Coprosma and Pittosporum species closer to the waterway, with taller trees such as ribbonwoods and cabbage trees behind.

On a higher bank, zone C, include a grass or sedge width of at least one metre on the paddock edge if you want a water quality filter to deal with surface runoff.

Plant spacing

As a general guide, allow spacing of one metre for sedges and grasses, and between one and a half to two metres for bushes and trees. However, modify this for factors such as the size of the plants, how big they will grow, and expected survival rates.

Preparation for planting

Removal of competing species

Remove invasive species such as broom or gorse.

Kill unwanted trees, such as poplars and willows, by painting stumps with herbicide immediately after cutting. See regional council publications for effective methods of removing willows.

Young native plants can't compete for nutrition and moisture against imported grasses, especially cocksfoot. Therefore, before planting, remove pasture grass and other vigorous species such as thistles, either by chemical means or manually.

Glyphosate herbicides are the safest to use beside waterways. Use only the recommended rate. Spray in one metre square patches where each plant is to go. It is best for the new plant to do this about three weeks before planting. Also, unwanted plants will have time to decompose and be easier to remove or plant through.

Manual turfing - with a spade, grubber or scrub bar with cutting blade - is an alternative, but it is labour intensive.

Managing weeds in riparian strips

Weeds need to be controlled for approximately three years before the native plants are self-sustaining.

Before you plant, decide how to stop the rapid regrowth of weeds and rank grass. Chemical spraying is one alternative. Another is to place a cover or weed mat around each plant.

Mulch should be placed around, but not quite touching, the plant.

Weed mats must have the corners spaded in or have U shaped wire pegs to hold down the corners. Different types of weed mat include:

• Newspaper, first moistening the layers and then spading them in the corners to fasten them down
• Old wool bales, cut into squares, with a slit into the centre on one side for placing around the plant
• Sacks, water permeable and preferably biodegradable. Jute sacks, often available from coffee roasters, are ideal, but need to be doubled to reduce light. Place the top one with the cut from the centre on the alternate side to the bottom sack.
• Carpet, cut into squares, with a slit into the centre on one side. Place upside down.
• Commercial felt mats which come with cages and pegs included.

Herbicides include

• Glyphosate herbicide is generally used on competing weeds, especially exotic grasses, but it needs careful individual application so that growing plants aren't affected. An upturned bucket with its bottom cut out is sometimes used to protect smaller plants.
• Alternatively, grass-selective herbicides, such as Gallant, can be used to overspray both plants and competing exotic grasses. This is an attractive alternative, especially on large-scale projects, as it is much quicker than traditional spraying and can be done while driving along outside the fenceline. Care however needs to be taken to avoid over-spraying desirable monocotyledons such as native grasses and sedges (in Zone A) and cabbage trees (which may be in Zone B).

Managing animal pests

Just as a strong stock-proof fence is essential, a reliable method to prevent damage from pukeko, rabbits, hares and possums is also important. In general, deterring pests is safer and more efficient than trapping or poisoning, but you may need to combine some of the following methods:

• Physical barriers around each plant. The Yellow-eyed Penguin Trust has had success with a wire-netting protector held down by three #8 wire pegs. (Tip 1: Cut the ends at an angle to get a point. Tip 2: 3.15mm MILD fencing wire is easier to bend if you have to buy new wire). The pegs can be removed after two or three years.
• Rabbit proofing. To deter rabbits burrowing under the fence, lay rabbit netting attached halfway up the fence, with the remaining section laid on the surface of the ground and pinned. A layer of turf or sticks placed along the outside of the fence is also effective, but not all sites would have this option. Repellents, such as Treepel and Plantskydd or a home made egg repellent. Because the repellent needs to be reapplied every so often, particularly after rain, this method is more labour-intensive and expensive.

  Egg paste repellent

  (Recipe from Otago Regional Council's Environmental Considerations for Clean Streams: a guide to managing waterways in Otago)

  One litre of the egg paste repellent will cover about 50 seedlings.

  The repellent will deter rabbits and hares from chewing seedlings.

  Use either of the two recipes listed below.

  80g whole egg powder
  800 ml water
  150 ml acrylic resin (available from paint shops)
  OR
  5 fresh eggs
  600 ml water
  150 ml acrylic resin

  Mix eggs with water, then add resin. (If using egg powder, mix with a little warm water to form a paste before adding remaining water and resin). Pour through a strainer into the applicator. Spray approximately 20-30 ml of the mixture over and around each seedling immediately after planting. Thoroughly clean equipment with water following use. Left over mixture can be stored in a deep freezer until needed again.

• The use of larger plants can deter hares and pukekos. The latter can nibble and uproot flax and sedge plantings under 40cm high.
• Trapping. Timms traps are very useful for possums and, as they kill the animal, they do not need to be checked daily like non-lethal traps.
• Pesticides are very effective, but usually require licensed operators. You also need to think about the effect of poisons on the environment.

Planting

Planting is an exciting time, but successful planting is the result of thorough preparation along the lines set out above.

When to plant

May to August is best, allowing the plant to establish before growth begins in spring. As well, winter is generally wetter and there will be no need to water.

How to plant

• Dig a good hole, at least 100mm deeper than the base of the plant and at least 100mm wider.
• Place in it a slow release fertiliser pellet.
• With minimal disturbance of the roots, get the plant out of the bag with as much of the soil as possible.
• While zone A plants may come in root trainers, most native plants will come in planter bags (PB3 to PB5). It is important to get the root trainer plants into the soil quickly before they dry out.
• Place the plant with the top of the root ball level with the ground, and cover with loose soil. Tramp this down firmly.
• Ideally, cover with mulch, newspaper or weed mat.

For detailed information on planting riparian strips, contact your regional council. For example, the Otago Regional Council has produced an excellent booklet, Environmental Considerations for Clean Streams: a guide to managing waterways in Otago.

Download brochure (PDF)