Visit to the Earth Trust in Little Wittenham, Oxfordshire with the Royal Forestry Society, Dr.Jo Clark the scientist in charge there showed us around.
Compared to other major crops the idea of selecting and cross pollinating populations of elite broad leaf ‘plus trees’ for timber is a fairly recent development from the 1990’s onwards. Some of the trials are planted at the Earth Trust (formerly the North Moor Trust in Oxfordshire).
My notes cover climatic variation and tree trials – of greater interest is the ‘nurse crop effect’ of nitrogen-fixing trees and shrubs on the growth of walnut trees. Key message to foresters for timber in the UK from what I can gather is ignore the provenance of your trees at your peril! Imported saplings may be a false economy if they are not geographically adapted. Also as a bit of a counter argument – local isn’t always best adapted and best to grow – because of a variety of reasons including changing climate. The recommendation may be to hedge your bets and
1, Use some locally adapted trees. (Though as far as provenance of local trees is concerned I understand wind-pollinated trees produce tree seed pollinated from some considerable distance away)
2, Some that are likely to be adapted to future climatic conditions. Foresters have reported that trees are adapting well when moved north in the Northern Hemisphere.
It is obviously not straight forward. Any helpful comments would be welcome.
The trials we discussed.
Before we were shown a progeny trial of ash trees we had our boots sprayed with disinfectant as a precaution against the risk of spreading ash die back. It was a trial of seedlings from elite timber trees replicated in different locations in the UK. Growth and straightness of the trunk were measured at the different sites; the best families were kept based on results from all sites and the overall worst performing families at all sites were cut down. The trial was planted in the ’90’s and they were just ready to collect seeds in 2012 when Ash die back was found in the UK and there was an embargo on moving ash. One interesting thing is that apparently there appears to be a link to early leaf fall in ash and ash die back resistance. From discussion it appears there is greater diversity in ash in the UK than there was for elm – so there is hope that trees with resistance will be found, partially as a result of identifying likely survivors in affected areas.
We saw a couple of other interesting trials one was a trial of four blocks of ash from Eastern Europe, Wales,Oxfordshire and Yorkshire and you could see the difference in growth. The Eastern European trees which represent what has been commonly imported in recent years appeared to show differences in relation to leafing up and I think had a less desirable tree form for timber production in comparison.
Jo Clark talked about a reciprocal trial of ash seedlings from Inverness down to Southern France – carefully grown in local soil. She found ash from the local site was not the best performers and trees from good ash tree growing sites performed better and trees from southern latitudes were doing well when transplanted north because of climate change.
Then we heard about the oak trial which contains two timber species (which I think can cross-pollinate). The problem of shake in Oak trees (also occurs in sweet chestnut) was highlighted – this is related to presence of large conducting vessels in the living part of the trunk which can result in fractures emanating later with the potential to devalue the timber. It can be affected by growing conditions but has a strong genetic component. There is a link between large conducting vessel size and trees coming into leaf late in the spring – allowing for selection for trees that come into leaf earlier which will have smaller conducting vessels in the living tissue of their trunk. I think this highlights the need for cautious selection by foresters of their planting material – continental material often widely planted in recent years – from areas such as Eastern Europe, though straight stemmed, may be later into leaf and more prone to shake linked to associated larger vessel size in the living tissue of the trunk.
One problem with selected oak tree trials highlighted is the relatively small amount of seed that can be produced from a nursery compared to other species like ash.
We were shown two trials – one planted around 1998 where the walnut trees grown from seed had not grown very well (typically up to about 6-7′).
The trial adjacent to this planted in around 2002 was flourishing because it had been planted with nurse crops of Russian Olives Elaeagnus angustifolia and Italian alder Alnus cordata nurse crop that fix nitrogen which benefits the walnut trees establishment. The Italian alder make a gap in the sky for the walnuts to poke their heads through the Russian Olive bushes and are then cut down.
Russian Olives have been planted in the first trial more recently and are having a beneficial effect on the regrowth of the walnut trees .
Other tree species mentioned
We touched on beech, if climate predictions are right beech will decline in Southern Britain in the future. We also saw an English cherry tree trial selected for timber with several replicates of each tree – originally produced by East Malling Research.