Illustrating the evidence
The evidence that hardwoods can grow rapidly in the UK is most apparent from situations elsewhere in the world where trees are purpose-grown for specific end-uses, in soils and climates that are broadly similar to the UK's (see York paper for more details). However, some tree plantings in the UK do indicate the potential of certain species. A few such examples from south-east England are illustrated and described here.
Eucalyptus nitens
Eucalyptus nitens (Shining gum) has not been widely planted in UK, but small trials and amenity plantings established since the mid-1980's occur throughout southern England. Stands also exist in Cumbria, Scotland and Eire. The general experience is that the species is vigorous and windfirm, but intolerant of severe cold especially when not cold-hardened. This accords with experience elsewhere in the world. The photograph shows one of six trees at age 16 years that were planted in 1988/89 in Cromer's Wood, near Sittingbourne, Kent. The trees were planted when the surrounding mixed coppice was last cut back. They were fertilised at planting but received no further maintainance. The size of the trees suggests that they experienced little competition from the surrounding coppice, and their form has benefited from the weak competition from the coppice. Thus they are likely to illustrate the growth potential of well-established and well-managed stands of this species in parts of southern England.
Read an article about the shining gums in Cromer's Wood. See also Biomass Trials
West Sussex planting
In 2005, several species of eucalypts were planted on a site in West Sussex formerly planted with conifers. The results to date (September 2007) confirm that excellent establishment and early growth can be achieved, even on an apparently poor (sandy and acidic) infertile site.
Following harvest of the conifers on the site several years ago, the plan for restocking involved encouragement of natural regeneration of larch. This failed, and in 2005 approximately one hectare was planted with eucalypts, to assess their potential as a short-rotation biomass crop. The eucalypts were mainly Eucalyptus nitens, with smaller numbers of Eucalyptus dalrympleana, Eucalyptus nichollii, Eucalyptus subcrenulata and Eucalyptus urnigera. Planting spots were treated with glyphosate herbicide prior to planting, and planting took place in late April 2005. The plants were in treeguards, so that further localised herbicide treatments would be possible, although such treatments were not made.
Most trees grew well in their first year. The growth of some was evidently suppressed either by competition from bracken, or by mature pines nearby. Many of these suppressed trees were killed or badly damaged by cold during the winter of 2005/06. The appearance of these trees suggested that the damage was due to root death, probably associated with low soil temperatures. The trees that were well established were essentially unaffected by this winter.
It quickly became apparent that despite a large population of deer, the eucalypts were unbrowsed. In view of this, re-planting and a little new planting was conducted with E. nitens without treeguards in spring 2006. Survival of these trees has been good; their growth has been very dependant on the degree of competition from nearby vegetation. There is no evidence of browsing by either deer or rabbits.
Further new plantings of E. nitens, E. urnigera and E. glaucescens on 2.5 ha were made in March 2007, on sites prepared by mechanical mulching. On this occasion, the E. nitens and E. urnigera were progressively browsed by rabbits and deer in the weeks following planting, although the E. glaucescens remained unbrowsed. The browsing was probably related to the absence of other vegetation as a result of the mulching, and an unusually dry period following planting.
Eucalyptus nitens in West Sussex, January 2007. The trees just in front of the pines are 21 months from planting, and are in treeguards. The trees in the foreground are 9 months from planting, and were planted without any vegetation control. All the stock was cell-grown, and the trees were approx 15 cm tall at planting. Note the lack of any browsing! The growth of all these eucalypts will have been greatly inhibited by competition from surrounding vegetation.
Eucalyptus nitens and Eucalyptus dalrympleana, West Sussex, January 2007, 21 months from planting. Note the variable but in many cases outstanding growth and form, and the lack of any damage from browsing.
Eucalyptus gunnii
Eucalyptus gunnii (Cider gum) is the most common amenity eucalypt in the UK. Many large trees exist today, and these are likely to be decades old. Thus they are evidently tolerant of harsh winters. A considerable number of very large cider gums occur around Brightlingsea, Essex, and are survivors of those planted there from the late 1887 onwards. Many of the trees noted there in 1947 (see Australian Forestry (1948), Vol 12, pp 63-74) must have survived the severe winters of 1894-95, 1916-17, 1928-29 and 1946-47. The trees that exist today also survived the harsh winter of 1962-63, and their response has been well-documented. The tree illustrated is in the churchyard at Brightlingsea. Because of its location, its form is not representative of those trees in surrounding woodland, or of younger trees in forestry trials elsewhere. Using quality silviculture, the potential yield of this species remains uncertain.
Read more about Brightlingsea's eucalypts, their cold tolerance and their behaviour in woodland.
Birch
Birch is one of the native hardwoods that appears to be a good candidate for rapid growth on short rotations:
- Amenity plantings of birch (and some other species) by the Milton Keynes Parks Trust have responded well to annual fertilisation between their second and fifth year from planting.
- In December 1988, Horticulture Research International at East Malling, Kent established a trial of birch (Betula pendula) that was produced in an EU-funded R&D project on tree propagation techniques. The photograph shows the trees 13 years from planting, having been grown using conditions more analogous to orchard management than traditional forestry. Despite the excellent growth (which met the project objectives), it is very likely that growth conditions were not optimal in several respects. Thus the true growth potential of birch remains unclear.
