If you are planting a conifer species, you need to think about the risk of spread of seed and seedlings outside the planted area.
What are wilding conifers?
Wilding conifers are trees that have established naturally outside the planted area mainly because of seed spread. Local conditions such as wind and temperature will determine how easily these can spread.
Wilding conifer spread in New Zealand is an increasing problem. It is expensive for regional councils and landowners to control. We want to make sure we do not add to the problem by putting the wrong tree in the wrong place.
The main conifer species with risk of wilding spread are:
- Douglas fir (Pseudotsuga menziesii)
- Scots pine (Pinus sylvestris)
- Lodgepole or contorta pine (Pinus contorta)
- Dwarf mountain pine and mountain pine (Pinus mugo and P. uncinata)
- Bishop pine (Pinus muricata)
- Maritime pine (Pinus pinaster)
- Ponderosa pine (Pinus ponderosa)
- Corsican (black) pine (Pinus nigra)
- European larch (Larix decidua)
- Radiata pine (Pinus radiata)
How to identify your risk of wilding spread
If you are planting more than 1 hectare of trees for harvest, then you need to comply with the National Environmental Standards for Plantation Forestry. You will need to assess whether the species you are planting is at risk of spread. This must be done:
- by someone qualified or experienced in silviculture
- using the wilding tree risk calculator.
The New Zealand Institute of Forestry has a list of registered forest professionals.
Wilding tree risk calculator
The wilding tree risk calculator helps to identify the risk of future spread when deciding where to plant conifers.
The calculator assessment requires risk scores for 5 categories:
- tree species growth and spreading vigour
- palatability of tree species to grazing stock
- siting of planting site in relation to prevailing winds
- downwind land use – grazing
- downwind land use – vegetation cover.
If the calculator score is 12 or higher then you need to get resource consent from your council to plant.
What to do if your trees start to spread onto nearby land
Trees themselves are not the problem. The problem is the spread of seedlings on neighbouring land which are not removed before they become established and self-perpetuating. To prevent this:
- monitor for any spread from your forest
- remove saplings that have established outside of planted areas, before they develop seed cones
- work with neighbours to control wilding conifers that have spread across property boundaries.
The Ministry for Primary Industries has information on wilding conifer control and what forest owners can do to help.
The NZ Wilding Conifer Group has more information on their website, including new plantings and control practices.