Norbury Park

Norbury Park.

On Friday 21^st  July 2023 Small Woods members collected early in the overflow car park at the BIFoR FACE facility. We were welcomed by refreshments and good weather, before cramming into as few cars as possible for the drive to the Long Barn. A 1740’s threshing barn that has been renovated as a beautiful conference hall. We were each greeted with a copy of Jo Bradwell’s book “Norbury Park, An estate tackling climate change”. Jo Bradwell gave us a presentation of his approach to woodland management.
Professor Bradwell explained his non-agricultural background and how a desire to offset his “Carbon Guilt” had led to the acquisition of Norbury Park. Starting from a position of “I don’t know what to plant so I’ll plant everything”. His initial aim was to maximise carbon sequestration, in the established woods, newly planted woods and later on the arable land. The farm moved from arable to mixed grasses for silage and then to complex herbal lays. Increased production has long been shown for mixed pastures, particularly when nitrogen fixing legumes are included. The increased carbon in the soil accounted for half the over 5,000 tonnes net of CO2 sequestered by the estate in 2020 mainly by the farm soil.
In the woodlands he has developed a novel woodland management system. It is based on four principles. 1: Individual species are more productive in intimate mixtures, than in monocultures. 2: Greater leaf area in the maximum amount of light allows greatest growth. So, choose the trees you wish to favour early and remove the crowns of competing trees, hence Halo-Pollarding. Allowing the pollards to keep sequestering carbon. 3: As Nitrogen is often the limiting nutrient in biological systems, include nitrogen fixing trees in your mixtures.  4: Control pests particularly those that you can. Infection rates are reduced in intimate mixtures. Deer and squirrel numbers are kept as low as possible.
Non-anecdotal evidence for increased productivity in tree mixes is lacking in the U.K. but scientific papers were referenced showing it in natural and plantation stands abroad. There appear to be three main causes. Greater variety and depth of the canopy and understory enabling more light to be utilised. Greater variety in the depth that roots can extract water and minerals from, and possibly most significantly reduced pests and diseases. Though there is a wider range of pathogens and pests there is a wider range of predators and further between potential hosts. Species variety is considered key to reducing infection rates.
The presentation included examples of trees from the estate. A section of an 11 year old Hybrid Larch and 33 year old one of similar size from an estate monoculture were handed round. Powerful evidence for competition removal, but not necessarily for mixtures without knowing the thinning history of the monoculture. It is not known how the Forestry Commission had thinned the stand.
Professor Bradwell went on to explain the paucity of European species following the ice ages. Species failed to return across East-West aligned obstacles like the Mediterranean, the Pyrenees and the Alps. He advocated considering non-native species.
The presentation lasted about 35 minutes. There were many questions, several about carbon accounting. The major downside appears to be the complexity of the management and the extra labour required.
 
We then set off into the woods. The first stop was by an example of a squirrel trap that was being developed. It was table mounted and based on the lethal Kania spring bolt squirrel trap. The estate had believed vertically mounted bolt traps tended to have unacceptable bycatch rates.  The new trap was inclined to the horizontal, at 20 degrees. A feed hopper allowed corn bait to trickle out. There was also a trap door triggered after the bolt was sprung. This allowed any catch to fall to the floor and be scavenged, eliminating the necessity of daily inspection. The estate spends £16,000 a year on squirrel control, mainly because the 100 traps are inspected daily during the summer when trees are most at risk. It is hoped that after further trials and tweaks the trap will be made commercially available.
Our second stop was at the first of the mixed plantations from 2009. The diverse species range was immediately apparent. It lacked non-commercial conifers or nonnative broadleaves. Though the later were seen in later plantings. Examples of winners were obvious because of their girth and an orange band! Most of these were surrounded by trees that had been pollarded. Pollarding keeps the regrowth above deer foraging and allows carbon sequestration in the trunks and roots. It will be interesting to see the timber crop in 20 or 30 years. We did see an impressive Hybrid Larch. It was next to a Larch stump of nearly equal proportions, a slice of which was placed nearby and measured at 13” diameter. As a first planting it was very impressive and will have provided valuable lessons for the later plantings. There was plenty to inspire anyone thinking of woodland creation.
Driving back past bits of mature woodland and small patches of different planting dates, it was apparent non-native hardwoods were now being planted. Our tree ID skills were challenged. Then there was another chance to admire the Long Barn again over our lunches.
I have independently come to approach woodland management in much the same way as Prof Bradwell but think his case is not as strong as he tries to make it appear.