I have fallen love with a tree – it is Douglas Fir (Pseudotsuga menziesii) – the branches and needles have such a spicy sweet resinous
scent somewhere between grapefruit and Christmas pudding. And it is our great fortune to have several self-sown young Douglas fir trees at Holt Wood, presumably arising from seed of mature trees on neighbouring land (Figure 1). However, in real life, a mature Douglas fir is a giant of a tree, the second tallest conifer in the world after the coastal redwood according to Wikipedia, long-lived and easily reaching up to 60 m. So, can we keep these gorgeous things at Holt Wood?
The wonderful aroma of the foliage (Figure 2) is due to chemicals which are largely about preventing insect damage. The main constituents of the aromatics in Douglas fir have been investigated for their variation through the seasons, and Zou and Cates (1995) showed increasing concentrations of terpenes, especially inαpinene, camphene and bornyl acetate while monomeric phenolics and tannins decreased in the earlier summer period – and they suggested the observed changes related directly to budworm larvae, a defoliating pest. More recent research also shows changes in terpene release in foliage attacked by Douglas fir beeetles (Giunta et al., 2016). The green bark of young trees is laden with blisters full of sticky resin, all designed to protect from damage.
So many uses
Having pollarded a Douglas fir in December, we have had an abundance of foliage and branches to use. So many uses spring to mind for this wonderful tree. Seasonally, the foliage is ideal for sprigs of needles in a wreath – as seen on our front door, the best ever Christmas garland we have made (Figure 3. Douglas fir mixed with Rhamnus alaternus, a variegated form of Italian buckthorn). We are also drying the branches to see if the aromatic blister-filled resinous bark slices will make drawer fresheners! The best use so far has been making an infusion of the fresh needles which is a very pleasant drink for a cold. Looking up in the Native American ethnobotanical database (http://naeb.brit.org), there are over 170 recorded uses for needles and bark, and many of these are medicinal, including tea as a tonic and for colds.
Growing Douglas fir
Douglas fir is usually grown in UK and Europe for its magnificent wood, strong and durable, which is how it has become partly naturalised. The Forest Research website (http://www.forestry.gov.uk/fr/infd-8cyjvj) suggests that this tree will have more use in a warming climate, provided sites are not too exposed and have sufficient soil moisture. So the tree is ideal for us if we can find a way to harvest branches from it regularly but control the overall size. Realistically, pollarding our Douglas firs is the only way we can keep them as, like many conifers, their growth is too fast and too big. Our young trees at Holt Wood were self-seeded and we do not want to lose them. But pollarding should be done with caution on a conifer as the growth is not usually replaced (exceptions might be Yew and Thuja species). If pruning is to be done, it is best when the conifer is dormant, and selectively applied as cutting all back to bare wood is unlikely to be successful since new shoots will not form. Once cuts are made, the tree is extremely vulnerable to infection so the usual advice on clean sloping cuts is most important. We pollarded one Douglas fir tree several years ago (Figure 4.), cutting above a number of side branches, and it lives on, so we are trying another and have yet to see how our pollards develop. Hopefully, our love affair with the Douglas fir will not have to end too soon.
Zou J and Cates R. (1995) Foliage constituents of douglas fir (Pseudotsuga menziesii (Mirb.) Franco (Pinaceae)): Their seasonal variation and potential role in douglas fir resistance and silviculture management. J Chem Ecol 21: 387-402.
Giunta A, Runyon J, Jenkins M, et al. (2016) Volatile and within-needle terpene changes to Douglas-fir trees associated with Douglas-fir beetle (Coleoptera: Curculionidae) attack. Environ Entomol 45: 920-929.