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Reducing canopy size stresses the tree because of the cuts required. Unlike a thinning cut, a drop-crotching cut does not cut back to a natural boundary, this means that decay can spread quickly inside cut branches, for this reason it is best not to perform crown reduction if at all possible.
This is a more extensive and severe form of pruning and is used to:
1. Reduce the weight of potentially dangerous limbs.
2. Balance a misshapen tree, for example, following storm damage, or after bad pruning.
3. Prevent trees obstructing or damaging buildings and property.
4. Prevent trees from interfering with overhead telephone and power lines.
In many instances, canopies cannot be properly reduced in size to the extent desired and certain species such as Beech do not lend themselves to crown reduction.
Over pruning of the trees to create the desired effect can initiate decay in the trunk or branches and stimulate rapid epicormic growth that fills in the canopy as it quickly grows to it’s original size.
Removal and replacement with a smaller maturing plant may be the choice that minimizes the input of resources. When a customer wishes to reduce the height, crown reducing is much preferred to topping.
Crown reduction should not be used to reduce the chances of the tree blowing over in a storm. Crown Thinning is the preferred method to minimize storm damage of an otherwise structurally sound tree.
Crown reduction can be considered when the root system of a large maturing tree has substantial decay making it potentially hazardous or on a tree with a high rating.
How is crown reduction achieved?
The objective is to make cuts so that the foliage is left intact on the outer edge of the new, smaller canopy ideally, pruning cuts should not be evident when you stand back from the tree after pruning.
Topping, shearing, tipping, and rounding over are not appropriate techniques for reducing the size of the tree because they compromise the tree’s structure and can cause decay.
We would recommend when removing more than 30% of the foliage, that you consider dividing the job into 2 sessions, around 12 months apart to minimise sprouting and starch removal from the tree. To reduce the size of a tree with drop-crotch cuts, we shorten the branches that extend beyond surrounding branches. This maintains the approximate original shape of the tree. The tree is simply made smaller.
The longest portion of the main branches will be cut back to an existing, smaller lateral branch that is large enough to assume the role of the branch. This is normally a third to half the diameter of the removed branch.
Excessive sprouting accompanied by die back or decay often occurs if you cut back to a branch that is too small. It is unreasonable to expect more than about a 15-20% reduction in size of canopy from a properly executed crown reduction.
This is a time consuming technique and is more an art than a science. It requires substantial talent to perform this operation. Of course this is a temporary measure because the tree will quickly revert to its natural size.
Crown Reduction Case Study – English Oak
This ancient English Oak (Quercus robur) was showing signs of advanced die-back in the crown, small leaf size and low vigour. Examining the base of the tree revealed extensive damage by livestock in the past. This had significantly reduced the vascular tissues of the tree, and allowed decay fungi to begin affecting it’s health. Sadly the tree is now in decline, but provides a huge source of habitat and great aesthetic value to the area.
Our key values include managing the landscape for as rich a diversity of healthy habitat as possible. Ancient Oak’s whether alive, or dead and decaying, can be maintained safely by reducing the weight loading to prevent collapse.
Deadwood was removed from the crown to avoid potential damage from falling debris, the crown was reduced in size by about 15-20% and shaped to improve the trees appearance. By reducing the crown, risk of major limb failure is minimised, and should allow the tree to safely resize its crown whilst in decline.
Removing live tissue from a stressed tree should not be advised as it is this photosynthetic material that is helping to sustain the tree. Therefore as much foliage as possible is maintained throughout this process.
This phase of works allows us to track further decline in the tree and assess any risks as they arise. Further reduction in the size of the crown may be necessary until the tree reaches a size that can be sustained, or the tree dies. This process of a phased decline helps to maintain these historic trees for as long as possible.
Veteran trees may be pruned with ‘Coronet Cuts’ to increase the habitat diversity provided by the tree’s presence. These cuts simulate natural fractures on stems to encourage the production of regrowth from dormant buds further down the branches, and provide habitat for wood boring insects.
It is always our aim to complete the best possible remedial work for the health of the tree, and local environment.
All waste is responsibly disposed of, and recycled wherever possible.
For more information about Heritage Arboriculture Ltd or to book an appointment to discuss your trees, please call us on 01234 720801.
Heritage Arboriculture ltd
Creating a Healthy and Beautiful Environment