Eucalyptus nitens trial in Kent - yields and comment
It is evident from the photographs that the Eucalyptus nitens established and has grown very well.
The two provenance types have performed similarly.
At 47 months from planting (May 2005) the trees were 12m tall, with a standing stem volume of 93.5 m³/hectare.
Overall survival was 81%, with most of the losses due to windthrow in the first winter (the site is quite exposed).
Stocking at this time was 1975 stems/hectare. Assuming the average basic density of the wood plus bark at this age was 420 kg/m³, this represented an annual increment of 10 oven-dry tonnes (odt)/hectare/year.
In June 2005 half the area of E. nitens was thinned, removing 50% of the volume/60% of the trees.
This was done to examine the response of the stand to thinning, and to demonstrate that a useful yield of woodfuel logs could be obtained after 4 years.
A further assessment was carried out in September 2009, 8.33 years from planting.
The mean annual increments (MAI) for the unthinned and thinned areas at this time were 40.1 and 37.4 m³/hectare/year respectively.
Assuming the average basic density of wood plus bark at this age was 450 kg/m³, these figures equate to 18 and 16.8 odt/hectare/year respectively.
The part of the stand left unthinned at 4 years was thinned by 50% in September 2010, as this was judged silviculturally necessary.
The intention is to maintain the stand as an amenity block, thinning it periodically for further firewood.
The stand was undamaged in the recent severe winters.
Further points concerning the trial include:
- The yields obtained are world-class for Eucalyptus nitens, and show that short rotation forestry is technically possible in parts of the British Isles.
The growth rate is likely to be the highest ever recorded for any forest plot in the UK.
- Compared to parts of the world where E. nitens is grown commercially, the rainfall in Kent (around 500mm per annum) is low.
It seems likely that faster growth and shorter rotations would be possible in similarly mild areas having higher rainfall.
- The trees remaining in the part of the stand thinned at 4 years evidently responded to the thinning by growing substantially faster than the trees in the unthinned area.
The cumulative yield (the yield at 4y combined with the yield at 8y), was higher than that of the unthinned stand at 8y.
This finding is likely to be generically applicable, and thus points to a possible management option.
- Growth of Eucalyptus gunnii in the trial is also very good by the standards of UK forestry, but as expected was substantially less than that of the E. nitens.
The form of the E. gunnii is poor.
- The harvested logs dried rapidly.
Those harvested in June 2005 were fully air-dry within 4 months.
Further comments on eucalyptus as fuel wood are available in the Advice section.
- The economics of the trial have not been evaluated, and it would be inappropriate to attempt this for a single atypical site.
- Direct extrapolation of these results to other species, regions and site types is not straightforward.
In particular, it is emphasised that Eucalyptus nitens not sufficiently cold tolerant to be an appropriate choice of species for colder parts of the UK and Ireland.
The issues involved are discussed in the Advice.