Managing tree health can cover many areas, from fungal pathogens to new pests and diseases arriving from overseas.
Trees are not removed lightly, so the option to continue to manage trees in the collection is always explored where appropriate.
The arboretum is divided into three zones for inspection during autumn. Zone one contains high usage areas, near to paths and busy visitor areas, which are inspected annually each autumn. Zone two covers medium usage areas which are inspected every five years, and zone three contains low usage areas which have no formal inspection plan.
In addition to the different inspection zones, the team focuses on around 100 trees for individual inspection each year. Trees on the list require special attention due to identified physical hazards including bracing or decay. Location is also considered if the tree is close to pathways or busy visitor areas.
Visual inspections take place to investigate the type, position and size of fungus or pest on the tree. For example, some fungal fruiting bodies appear around the roots or buttresses whilst others appear on the trunk of the tree. The team also look at the tree’s crown condition and search for any structural defects.
A closer look
Often it is only the fungal fruiting body that can be identified visually, which means the tree team cannot necessarily see how far the pathogen has affected the tree internally.
If the team want to investigate the problem more, they use technology to scan the trunk to get a visual picture of the tree’s health. The picus sonic tomograph (www.tree-surveys.com) uses sound waves to create a picture of how developed the decay has become.
The picus sonic tomograph is just one example of equipment that is available and may be used in conjunction with other pieces of kit such as the resistograph. The resistograph drills into the tree to measure the wood’s resistance, therefore measuring the depth of decay.
Removal or maintenance?
Many trees can continue to be managed and monitored in the tree collection for several years. However if the tree is deemed too hazardous and is seen to be a health and safety risk to visitors or other specimen trees, it will be removed.
This decision to remove a tree can be an emotive one as the trees being felled are often old, original Holford plantings. We always try and explain to our visitors why we remove trees; a process which in itself is highly skilled and carefully planned.
Tree removal is important for the health and ongoing development of the tree collection. The numbers in the tree collection are maintained by planting around 300 new specimens each year.