method to repair a semi-girdled to completely girdled main trunk or other stem in which scion wood is grafted above and below the injury to reconnect the vascular cambium.
A bridge graft is used to supply nutrients to the rootstock of a woody perennial when the full thickness of the bark has been removed from part of the trunk. This is because the innermost layer of the bark, called the phloem, is living tissue that is required to transport the sugars produced by photosynthesis down to the roots.
This wound is often caused by rabbits or other rodents, stripping the bark away and girdling the tree. The inability of the plant to transport food manufactured in the leaves down to the root system causes the root system to die after they have used up any stored nutrients. The lack of a root system causes the upper portions of the plant to die. Where one-quarter or less of the trunk circumference has been girdled, it may not be necessary to use this technique. It is also difficult on small caliper tree trunks. A bridge graft uses scions to 'bridge' the gap. Each scion is taper cut in order to accommodate the need for matching the cambium layers of the scion with those of the tree to which it is being grafted. It is also vital that the scions be placed so that the end which was closest to their own roots before they were cut is at the bottom of the graft, and the end which was closest to the growing tip is at the top. If they are not placed this way the cells in the scion are upside down and it will eventually die. Once in place the graft wounds must be completely sealed. This is both to prevent moving of tissues which would inhibit them from joining together and infection of the site which would lead to the death of the scions.