Managing a kahikatea forest fragment
Existing and newly-created kahikatea forest fragments need to be carefully managed and protected if they are to survive. Kahikatea forest fragments mainly need:
- fencing from stock
- plant and animal pest control
- protection from ‘edge effects’
- retaining or slowly restoring water levels
- planting if heavily grazed
- legal protection.
Fencing out stock
Stock - especially cattle - eat many native plants and trample seedlings (wiping out the next generation). Kahikatea fragments are particularly vulnerable because they are generally on flat land, so stock can easily move through. Often where stock regularly visit kahikatea fragments the only understorey plants are weeds, such as the poisonous Jerusalem cherry.
Fencing to exclude stock is essential if fragments are to survive in the long term. A single hotwire will deter most cattle, but it is best to complete a full wire fence to protect the forest. Leave a 3-5 meter gap between the fence and the forest edge to provide space to plant a protective buffer. Some councils and the Queen Elizabeth II National Trust may help with fencing costs. Be ready to tackle weeds as soon as the last stock are out, you may find the weeds ‘take off’ when grazing stops.
See our forest fragment fencing tips.
Weed and pest control
Perennial plants like privet, hawthorn, arum lily, wild ginger,, ornamental cherry, ivy and wandering dew pose a serious threat unless they are removed. Plants that are spread by birds will continue to establish unless seed sources in nearby gardens are also removed. It’s important not to use kahikatea fragments as dumping grounds for garden or domestic rubbish, even lawn clippings, because these often contain weeds.
Some common weeds of grazed kahikatea fragments such as Jerusalem cherry or inkweed are less of a problem. They are only there because of the degraded condition of the remnant and will eventually disappear once the natural understorey recovers after fencing. However, Jerusalem cherry may persist for 15 or so years, particularly in light gaps and near the forest edge, or if stock get into the fragment. Very wet kahikatea stands may also be invaded by reed sweet grass (Glyceria maxima) which forms dense mats and smothers native plants.
Contact your local plant pest officer for information on how to control problem weeds.
Animal pests can also be a problem for native plants and animals. Possums, stoats, ship rats and wild cats are everywhere in the Waikato. They have a disastrous effect on wildlife. Eight out of every 10 eggs laid, or chicks hatched by a native bird, are killed by possums, rats or stoats. Possums can also severely damage plant species like lowland ribbonwood, mahoe and titoki.
Exposure to prevailing winds can damage sensitive species on the edges of fragments and dry out the forest interior. This is a particular problem with kahikatea fragments, because they usually occur on flat ground, well away from the shelter of hills.
To reduce this problem, you can:
- Plant a ‘hedge’ around the fragment’s edges using fast-growing, hardy species such as:
- karamu (Coprosma robusta or C. lucida)
- manuka (Letospermum scoparium)
- swamp flax (Phormium tenax)
- kawakawa (Piper excelsum)
- mapou (Myrsine australis)
- round-leaved Coprosma (Coprosma rotundifolia).
- Put up a shade cloth barrier along a fence line as an instant, but temporary, solution.
Learn more about how ‘edge effects’ and isolation threaten forest fragments.
Keeping their feet wet
Kahikatea is often thought of as a swamp tree, but it can live in a range of sites. Laboratory research has shown that kahikatea seedlings survive best in moderately wet soil. Kahikatea are more abundant in wet soils because they can cope with waterlogging better than other species, particularly broadleaved trees which out-compete kahikatea in drier conditions.
If wet kahikatea forest sites are drained:
- plant species commonly found in kahikatea swamp forest, such as swamp lily, swamp maire, swamp coprosma and mudfish may not survive
- weeds are more likely to invade
- broadleaved trees such as tawa and titoki will replace the kahikatea over time.
Most of the kahikatea fragments in the Waikato are on land that was drained for farming. In rare cases, it may be possible to restore the water table to its original level by blocking drains that run through or around the fragment. However, any change in water table should be gradual, or all of the plants could die. Seek expert advice before making any changes.
Activities on land next to kahikatea forest may affect the health of the forest:
- Take care with fires (for example, grass stubble burning) and spray drift (especially of broadcast herbicide).
- Fertiliser drift or enriched runoff may encourage weeds or change the mix of native species in a block. For the same reason, kahikatea stands should not be used for effluent disposal.
- Adjacent woodlots, organic orchards or shelterbelts may help reduce the effects of adjacent land use.
Dense young kahikatea stands are often bare underneath and it may be tempting to underplant them. This may be a waste of time because planted seedlings may die from root competition or dense shade from the established trees. However, it’s worth trying the following:
- If native seeds don’t pop up on their own within a year or so after you have fenced your stand, you may wish to plant small-leaved shrubs like Coprosma areolata, and shade-tolerant native grasses such as the hook sedge (Uncinia) that can cope with shade and root competition.
- Plant a ‘hedge’ around the outside of the stand to shelter it from edge effects.
- Plant grassy areas and large gaps inside the fence.
When planting edges or grassy areas, spot spray the grass with a glyphosate herbicide. Plant large potted seedlings of short-lived ‘nurse’1 species like mahoe or karamu around edges. In gaps plant long-lived trees, including kahikatea and pukatea.
See our kahikatea forest fragment planting guide and list of species.
Many kahikatea forests are located on flat land, so they are generally not covered by regional council rules that are designed to maintain soil and water quality by protecting hill-country vegetation. Local council rules may also not protect kahikatea forests. Local rules vary from district to district, and may change when the councils review their plans. To protect kahikatea fragments from clearance by future landowners, consider placing a private covenant over them. Contact the Queen Elizabeth II National Trust, Nga Whenua Rahui, Department of Conservation, or your local council for more information.
Find out more about legally protecting forest fragments.
There are many organisations and books that can offer practical advice and help with your forest fragment restoration project. Some nurseries specialise in native plants and can supply advice as well as providing plants. See our fragment information and contacts for more details, and find out more about managing forest fragments in the Waikato region.
Check out our case studies to find out how forest fragment restoration and protection can be achieved alongside sustainable land management.
Find out about how combining the restoration, creation and protection of forest fragments into sustainable farm management practices has been recognised in our annual Farm Environment Awards.
If your kahikatea stand is a swamp forest you can create your own wetland management plan using our template and its completed example as a guide.