Manage weather damage to your forest

Protect your forest from wind

Wind is generally considered the greatest risk to forestry in New Zealand. Damage can vary from major storms causing stem breakage or uprooting, to less obvious wood defects which reduce value. Tree lean resulting from wind can cause compression or tension wood. This can lead to problems with drying and seasoning sawn timber and veneer. Resin pockets in the timber of Radiata pine can also result from the stress of strong wind.

The best way to avoid these situations are to choose the correct:

• species
• site
• maintenance routines.

Reduce wind damage

You can reduce the main effects of wind by encouraging root development. Establish your forest by using good quality seedlings that are well planted. Thinning at appropriate times also helps root growth by reducing competition between the trees.

Wind stress on individual trees increases with wider spacing. There can be a significant mutual shelter effect with closer tree spacings. You should consider this when deciding on thinning regimes for windy sites.

The likelihood of wind damage also increases with tree height. Avoid thinning older stands in areas exposed to strong winds. Otherwise, thinning’s should be very light and more frequent. Remove a few trees at a time, without creating major gaps in the canopy.

Protect your forest from snow

Snow damage can be significant in the South Island and in higher altitude North Island forests. Radiata pine is susceptible to snow damage, especially on the lee of ridges away from prevailing wind. Here snow tends to be dumped and its weight can break branches. In these situations, it's recommended to plant alternative species which can shed snow, such as radiata hybrids or Douglas fir.

Reduce snow damage

You should control brush weeds, particularly broom, on sites that are prone to snow. Brush weeds can catch snow. These then drift, causing tree or branch breakage or tree toppling, especially in young trees.

You can control these by:

• shading (keeping the trees close together)
• grazing
• applying herbicides.

Protect your forest from frost

Frost, especially when out of season, can affect most commercial timber tree species, particularly at higher altitudes. While frost is more of a problem during establishment, it can also cause damage during management. Repeated heavy frosts can stunt tree growth to affect the timing of silviculture.

Reduce frost damage

You should leave frost hollows unplanted unless:

• a very frost-hardy species is available
• you are using special establishment techniques.

Get advice from forestry consultants with local knowledge if your area is susceptible to heavy frosts.

Protect your forest from drought

Drought is an ongoing risk in drier parts of the country. Seedlings and restoration plantings are vulnerable as developing root systems of smaller plants do not have access to deep soil water stores. Mulches, such as bark, old carpet and sheep wool, can help to retain moisture. For well established trees, reduce drought stress by manipulating the stocking through thinning. This will help reduce wind flows through the stand and drying out effects.

Reduce risk of falling trees damaging powerlines

Falling branches or trees can damage transmission lines. This can lead to power blackouts and fires which can be an expensive problem.

Prevent this by:

• including safe setbacks when planting
• undertaking regular inspections and treeline maintenance in consultation with your local power companies.

Who is responsible for trees growing near powerlines?

The Electricity (Hazards from Trees) Regulations 2003 set out tree owners’ obligations for keeping trees free from power lines. They define when the lines company must give notices, and the information they need to include.

Your lines company website will have more information, including:

• the dangers posed by contact between trees and electricity lines
• the distances trees should be from electricity lines
• the dangers of cutting and trimming trees near lines
• a list of offences that tree owners could commit and their penalties.

Our manage fire risks page has more information.

Reduce storm damage to neighbouring properties

Reduce slash damage

Forestry slash is scrap timber, branches and offcuts left behind in the forest after the trees have been harvested.

A lot of slash can be left on the ground after a forest is harvested, and it can take years to break down. If a large storm hits at the wrong time, slash can be washed into streams and rivers, and have damaging consequences for rural communities and local environments. It can cause costly damage to infrastructure like roads, bridges and culverts, and land and fences downstream. Slash can eventually end up on riverbanks or beaches.

The key to preventing slash damage is to make sure the slash doesn’t wash off the land in the first place. Streams and creeks need to be left clear as much as possible, and slash should be put somewhere stable that will not be reached by a 20-year flood.

Any slash that gets into a waterway should be caught by slash traps. The Forest Owners Association has published guidance on managing slash and slash traps, including where to use traps, and how to design, build, and maintain them.