Douglas-fir, douglas pine

Scientific name: Pseudotsuga menziesii

Douglas fir

Douglas fir

Douglas fir seedling

Douglas fir cone

Douglas fir cone
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Large evergreen tree with branches occurring in irregular whorls
  • Can reach up to 60 m in height in New Zealand
  • Young branches are angled upwards but older branches tend to droop
  • Young trees have dark-grey bark. As trees mature, the bark turns a deep brown colour  and becomes corky in texture
  • Leaves are dark bluish green often with two pale strips running their length. Long and narrow, flattened with a blunt tip, 1.5–3 cm long and 1.5 mm wide. Arranged singly in spirals but often lie flattish on either side of the shoot
  • Female cones are medium size (4-10 cm long and up to 5 cm wide) and hang near the ends of branches
  • The cone’s scales are soft, rounded and overlapping, with three pointed bracts protruding from between the scales
  • Male cones are catkin-like and about 1 – 2 cm in length.

Origin and habitat

  • Douglas fir escapes from plantations and can become a problem in extensively grazed pastures
  • Native to western North America
  • Second most important plantation softwood timber species in New Zealand after Pinus radiata. Douglas fir plantations cover 106,557 ha in New Zealand, approximately 5% of the total plantation area
  • Thrives in areas with a mild and humid climate but with a dry summer period. Needs a moderately high rainfall (1000 – 1500 mm of rain annually)
  • Prefers well drained soils of sedimentary or volcanic origin with a low pH (5.0 – 5.5) and moderate fertility
  • Late spring or summer frosts can cause damage or mortality to young trees.

Life-cycle

  • Douglas fir produces two seeds from each cone scale. Each seed has a large wing and is spread by the wind
  • Viable seed production begins after about 12-15 years of growth. It is therefore important to control young regenerating trees before this time
  • Each tree can produce 20,000 seeds, but seed production is highly variable between trees, sites and years. Seed is easily spread by wind because the cones are on the periphery of the crown, the seeds are small and have large wing. Seeds remain viable for only a relatively short time under natural conditions (approx. 2-3 years)
  • Douglas-fir can regenerate under partial shade conditions and can be found as understorey of open Douglas-fir stands. Browsing or dense canopies can limit Douglas-fir regeneration.

  • Douglas fir is spreading in some high country areas where increasing seed-rain is occurring and site conditions are favourable for establishment (open ungrazed or sparsely-grazed short tussock grasslands and open shrublands)
  • As seedlings establish close to a seeding tree or stand, Douglas-fir can spread to form dense stands
  • Larger Douglas-fir wildings can reduce grazing potential of grassland and can shade out native and exotic grasses in the long term.

Benefits

  • Douglas fir is the second most important softwood in New Zealand, after Pinus radiata, and provides large export returns and high quality durable building timber. Douglas fir is a good alternative to Pinus radiata on sites with higher snow-fall and where farming might become increasingly un-economic
  • Used for structural purposes in engineering and construction.

  • Grazing can control Douglas fir when it is young and grazing pressure is high
  • Initial low density infestations of young seedlings are best controlled by hand-pulling
  • Handsaws, scrub cutters or chainsaws can be used to cut off stems of larger trees as close to ground level as possible (below ground level if able) and glyphosate, metsulfuron-methyl, picloram or triclopyr applied to the cut stumps to prevent re-sprouting
  • Basal spraying with herbicide mixes containing ingredients such as triclopyr (X-Tree) can be used for denser infestations and fringe spread. Good timing of control action should prevent tall dense stands from establishing. However, such stands can be boom-sprayed with herbicides, although control is inconsistent (see the NZ Wilding Conifer Management Group’s website at www.wildingconifers.org.nz)
  • Individual trees are best controlled by drilling holes in the trunk and injecting glyphosate or metsulfuron into the holes.