AgPest » Contorta pine

Contorta pine

Growth habit ranges from a stunted (contorted) bush with twisted branches, to a tree 25 m or more in height
Young trees have a narrow cone-shaped crown which becomes more rounded and dense as the tree ages. Older trees are often a darker green than Pinus radiata
Branches grow in clearly defined whorls almost to ground level. New branches are initially green but become brown and more rigid as they age
In young trees the bark is smooth in texture and relatively thin but as the tree ages the bark becomes reddish brown (although grey on the surface), thicker, rougher and often deeply furrowed
Needles are yellowish-green to dark green, rigid and 2 – 7 cm in length (quite short). They are in pairs on short shoots (fascicles). They are often twisted and point forward in dense clusters
Rough, brown cones are usually present from an early age and occur in pairs or are solitary and are persistent. They are asymmetrical in shape and 0.5 – 6 cm long. One of the more important diagnostic features is that each cone scale has a fine spike
Pinus contorta seeds are small, 3 – 5 mm long and 2 – 2.5 mm wide with a 7 – 15 mm wing. Seeds are generally black although infertile seeds are often mottled, paler in colour or reddish brown. Seeds can be carried for considerable distances in strong winds.

P. contorta originated in the Western United States, extending from Baja in California to the Yukon in Canada (latitude 31^o to 64^o N). It is notable among the pine species as its habitat includes ecological extremes; it grows from sea-level up to an altitude of 3,350 m. Four subspecies are present in New Zealand, but the most vigorous spreading variety is Pinus contorta subsp.contorta
First introduced to New Zealand in 1880 in seed lots from an unknown source
Spread to Taita, Wellington by 1896 and in 1902 it was first used in state forests. By 1907 it was well established in Greendale, Canterbury and was introduced into central North Island State Forests in 1908
Has been used for shelterbelts and around farmhouses for wind-protection in the high country and other areas in New Zealand
The species is no longer used for forestry in New Zealand
In New Zealand it inhabits a wide range of habitats subject to climatic extremes (including heat, cold, damp, dry and windy environments and soils of low or high fertility)
Can grow at higher altitudes than New Zealand native trees and could be a threat to alpine habitats.

Contorta pine trees start to produce cones and viable seeds early in life. Such trees are often physiological older “cut-backs” that have been controlled, but low-growing green branches were missed which enabled plants to regrow
Most cones do not release seeds until the trees are 4 -5 years old
Seeds are very light and easily spread for long distances by the wind, spreading far from trees on ridge-tops and from sites with strong winds and upward eddies
New plants can be very dense around “mother trees”. The resulting in-fill leading to a closed canopy relatively quickly
Seeds can also be spread by floating on the surface of streams, rivers and lakes
P. contorta growth habits often reflect site conditions. In harsher environments single trees become shrub-like and stunted. Trees grow taller and larger when conditions are more favourable or higher stand densities are reached.

P. contorta is the most targeted “pest” conifer species in New Zealand, as shown in Regional Pest Management Strategies
It is the most vigorous spreading conifer species in New Zealand and threatens landscape values, biodiversity and farming productivity by out-competing pasture areas and forming dense stands, even above the natural tree-line.

P. contorta was once used to re-vegetate high country areas in the South Island with the intention of stabilising erosion prone slopes
The intention was that trees could serve as a nurse crop for other species in harsh environments once the canopy opened up.

Hard grazing can control Pinus contorta when it is young and palatable
Single smaller trees can be removed by hand, with loppers or chainsaws. The cut must be below any green foliage – otherwise the stump will regrow and the control will be unsuccessful. Herbicide mixtures can also be applied to the cut stump
Larger trees need to be cut by chainsaw, scrubcutter or by hand at or below ground level to ensure no green foliage remains. Applying herbicide to the cut stumps improves control in case some green tissue was not noticed
Drilling holes in the stems and pouring suitable herbicides into the holes is the most reliable method of killing individual trees. Metsulfuron is probably the best herbicide
Foliage spraying and basal application have shown good results on smaller trees, if applied properly. Various herbicides and spray mixes have given some effective results
Larger very dense stands might require foliage spraying carried out via helicopter. New herbicide mixes and application standards developed by DoC are now used and show a fairly good success rate
Go to the New Zealand Wilding Conifer Management Group website for more information on control of wilding pines.

Further detailed information on how to identify, control and manage wilding pines like Contorta pine can be found on the website: New Zealand Wilding Conifer Management Group (accessed 1 August 2014).
Ledgard NJ 2009. Wilding control guidelines for the control of wilding conifers. New Zealand Forest Research Institute Limited, Christchurch, New Zealand. 46p.
Ledgard NJ, 2009. Wilding control guidelines for farmers and land managers. New Zealand Plant Protection 62: 380-386.
Ledgard NJ, Paul TSH 2008. Vegetation succession over 30 years of high country grassland invasion by Pinus contorta. New Zealand Plant Protection 61: 98-104.
Miller JT, Ecroyd CE 1987. Introduced forest trees in New Zealand: recognition,r Role and seed source. 2. Pinus contorta Loudon. Contorta pine. Forest Research Institute Bulletin No. 124, Ministry of Forestry, Forest Research Institute, Rotorua, New Zealand.
Salmon JT 2000. The trees in New Zealand. Exotic trees: the conifers. Reed Publishing (NZ) Ltd., New Zealand. V.2 159 p.
Weedbusters, 2016, Pinus contorta Factsheet (accessed 14 October 2016)

Thanks to Scion for contributing to this Pinus contorta information.