|Sound looking wood, but dead all the same.|
Note the pollarded, but still living, poplar behind.
It's good when people ask why, because I get a chance to write yet another blog.
Please forgive the following lecture; I’m an ex-teacher and I love this stuff!
This week's topic for discussion is tree-felling. In particular the felling of a seemingly health poplar tree on the big bend of the Great Ouse, along the side of the Great Meadow where our windpump is situated.
Hornet Clearwing Moth
Several years ago we found that all three of the trees on the riverbank had been attacked by the moth, but they were not coping as well as the other poplars on the reserve. We think this is due to several wet winters that flooded the path and encouraged a fungal infection to develop in the base of trunk at ground level. The first sign was a die back of some branches. At this stage, the trunks and lower branches looked perfectly healthy.
Exit holes made by the moths and rot at ground level
due to fungal infection.
We decided to pollard the dead branches and hoped that the trees would be able to recover. Of course, we had just treated the symptoms, not the cause, but at least no-one was killed by a falling limb. We marked the trees with metal discs and continued to monitor them on our rounds.
|Health and Safety nightmare!|
In a situation like this, the precautionary principle applies; if a tree is likely to come down on a path in the next year, we fell it. If we can save it by pollarding, we try that first.
Tree surgery is expensive, by the way. We have probably spent over £600 on trying to save these three poplars alone.
As a rule we leave the trunk in big pieces to benefit wildlife, but we are not allowed to do this by the river because the next flood might carry the logs away and cause no end of damage to boats and weirs.
There is good news though. These poplars grow back from succours on the roots and so we do not have to replant them. Of course, once they reach maturity, the moths attack again, and so the cycle continues. It’s not unlike the situation with Dutch Elm disease. Near the River Viewpoint you can see elms sprouting every year, but they get attacked by elm beetles as soon as they have enough girth. We don't have to fell them because they never grow big enough to be a problem.