In June 2018, Professor Claus Mattheck visited the UK for the final time. Claus is regarded as one of the founding fathers of modern arboriculture. His Visual Tree Assessment (VTA) inspection methodology is now recognised as the basis of assessing tree condition. When news of his visit began to circulate, bookings flooded, such that the original one-day event became a five-day tour.
I was able to attend days two and three, both being lectures. Those familiar with Mattheck lectures appreciate how much he gives, and the volume of information provided. As I began my review, I reached the end of a section of notes assuming that these represented the end of the first day. It then dawned on me that this was only the first morning coffee break, and just ninety minutes of content. A single review cannot do justice to the event.
Claus started the second session with an interesting observation: if we prune a tree, this will usually help! If a tree is not pruned by us, it will often prune itself but not in a good way, leaving it vulnerable to pathogens. He suggested using the dome shape as a basis, but not worrying too much if an individual branch doesn’t fit the dome. It is important to keep the leader.
The slide show included an over-extended branch using a pile of soil for support and being propagated. This is natural layering and forms a new tree. Slenderness can be a problem, he cautioned. When the height over diameter ratio exceeds 50, the tree can struggle to sustain itself, with the range 40-60 being critical. The tree usually fails before it reaches 60, with uprooting being common. Apparently, in Singapore, this happens at a ratio as low as 25%, which could be something to do with local Geography.
When decay occurs with smooth swelling, there are no notches and we get hosepipe kinking, and the hazard beam. With butt rot, the failure is longitudinal and the trunk will split before it breaks. Structural kinking will initiate failure. Claus has identified that latewood, which tends to be softer, can be particularly vulnerable to decay.
Claus then explored how trees can naturally regenerate. A benefit of this is that the slenderness of the tree is reduced, which is beneficial. He cautioned against seeing a leaning tree as being automatically dangerous. In his view, a branch that is leaning is simply one that is attached to the trunk and not the soil! When there is crown shortening, we should wait for this to happen before diagnosing the condition of the tree. All of this was accompanied by a slide show showing many illustrations. Having had a full morning of information, it was time for a welcome lunch break. We were again encouraged to not eat too much food but to drink plenty of coffee to sustain us for the afternoon!
In the afternoon, Claus explored the issue of tree grafts. This is the only way to propagate some trees. In appearance, a good graft can seem similar to a poor one. However, a poor graft can develop included bark. If half of a graft cracks, trunk failure can be expected. He asked how a poor graft can survive, being loaded with compression. He suggested that a leaning grafted tree is safer, with no fusion. A graft lower on the trunk is safer.
He moved on to explore the hazard beam. This is when a curved structure is straightened by wind. We don’t need to remove this, we can prune it. A hazard beam is not found on a straight branch. There can be internal stresses due to cracks leading to tension and high growth stress. Interestingly, a hammer doesn’t detect the stress. Claus nearly felled a healthy tree when the hammer indicated it was hollow. He cautioned that if we are considering felling, use a decay detecting borer, don’t do it based on the hammer!
Exploring the properties of tension wood, Claus identified that wood is four times stronger under tension than compression wood. If wood is put under tension when newly formed, it will undergo optimisation which strengthens it. We then moved on to what can be predicted. All Horse Chestnut have spiral grain which can be serious. Should we fell them all? This would not be proportionate! It is very reassuring to hear such endorsement of a realistic management approach. When safety is an issue, Claus is clear that we should intervene. He is also clear when we should step back and ponder.
The review will continue next month.