At the event, which took place on 20 June, Johnston predicted there will be more cuts in the public sector, resulting in redundant tree officers becoming consultants in competition with those in the private sector.
Duncan Slater, a chartered forester and former local authority tree officer who is studying for a PhD at the University of Manchester whilst lecturing at Myerscough College, spoke about the study of branch forks and the understanding of their mechanical properties. He is convinced the strength of forks has been underestimated, maintaining they are natural and do not need to be ‘medicalised’. He went on to speak about bark inclusions, saying they give better conductance of sap and are probably caused by phototropism.
The problem is often created by humans, he suggested. He believes we grow upright cultivars close together, shelter them when young and do not thin woodland early enough. Inclusions occur and then we complain when the junction snaps. Bark inclusions can be weak, but we must look at our practices in order to minimise the problem, he added.
He said that much arboricultural science is of a low quality and urged more arboriculturists to go into scientific research in the hope of improving it.
Philip van Wassenaer, principal consulting arborist and founder of Urban Forest Innovations and Urban Forest Solutions in Toronto, Canada spoke on "Testing Tree Stability using Engineering-based Tree Pulling Tests: Research meets Practice".
Of the two types of root failure, hinge failure is common and due to the roots themselves, while rotational failure is much rarer and due to a failure in the soil in which the tree is growing.
To calculate the likelihood of a tree breaking or becoming uprooted we must first calculate its wind load and then conduct a ‘pull test’ on it to measure the inclination, simulating the action of the wind, he said.
Once the data has been entered, the result can be calculated. Following a visual assessment and pulling tests, the results can be expressed as a percentage of safety. A figure of 150 per cent is acceptable, while one of 100 per cent suggests the stability of the tree is compromised.
The conference’s main speaker was Ed Gilman, Professor of Environmental Horticultural in the College of Agricultural and Life Sciences at the University of Florida, USA.
His presentation "Pruning in Urban and Suburban Landscapes". He said trees with two stems may break easily, but this is easily prevented by pruning. He also questioned thinning as a regular practice and does not recommend topping either.
The professor sees the three main aims of pruning as a means of reducing failure, to provide clearance beneath a tree and to improve its general appearance. He believes that interior branches should be retained. Objectives of formative pruning are to reduce the growth rate of lower branches and to reduce the occurrence of upright stems competing with the leader. The questions which need to be asked before pruning are: Where is the leader? Where is its competiton? Where should the competition be cut?
The habit of pruning a tree at planting is a good one, he feels, because most trees will probably not receive much aftercare.
In his afternoon session Gilman looked at how root growth and our management of it can impact on the health and stability of a tree. In 1989 the nursery trade in Florida got together to write a ‘standard practice’ document for the top growth of trees. This task took nine years to complete. Since then it has had quite an impact The trade is now turning its attention to root growth.
Lateral surface roots grow when a tap root reaches a soil zone which is not suited to growth. In well-drained soil roots grow both outwards and downwards. Gillman stressed a visual inspection of young trees is crucial because the depth to the first root impacts on survivability, anchorage and establishment. The depth of the first large root tips is also important.
He also told delegates that he does not like to see soil over a rootball and that he is against the use of mulches. In his experience, recently dug field trees are the first to die when transplanted, followed by those in containers, while stock which has been root-pruned and hardened off in the field is usually the last to die. The smaller the nursery stock the quicker it generally establishes:
"We have to start managing roots at an earlier stage than we currently do", he said.
He said he felt that slicing the rootball may be a step in the right direction, and he also believes that root pruning at planting has no adverse impact on a tree’s growth.
He finished his second session by looking at staking trees. Having tested guying systems and rootball anchoring, he believes that pieces of untreated timber offer young trees the best support, rotting away gradually once their work is done. His research has also shown that the anchorage of both staked and unstaked trees is the same a year after planting. His final advice was to water early and often to promote good establishment.
The Barcham Trees’ Big Barn Conference has a DVD is available at £10 per copy. Contact Natasha Hutchison firstname.lastname@example.org for details.