Trees and heritage
The trees in this category have very high conservation value, either owing to their great age and historical associations, or because they provide a setting for similarly historic buildings. Public sentiment is typically strong, as are the statutory constraints, requiring sensitive treatment. A common technical problem in this context is the management of ivy, whether on trees or on masonry, and this section concludes with a note on this topic.
Summary of example report
The yew, believed to be about 2000 years old, is a prominent visual feature from the main approach to the [ancient monument]. The main stem is now in the form of an open ring, which is weak relative to the weight of the crown, so that the crown has subsided close to ground level on the north side.
The tree should be conserved for as long as possible, and has to be made safe for pedestrians on the path to the monument. Two possible actions, or a combination of the two, will achieve these aims by relieving the loading on the main stem: bracing the crown with cables or pruning to reduce the size of the crown.
Braces require periodic inspection, they may be regarded as unsightly and it may be difficult, given the complex nature of what is left of the main stem, to be sure that structural integrity has been restored. Crown reduction may be unpopular because it changes the appearance of the tree.
Crown reduction is more likely to secure the long-term conservation of the tree, and at present the tree is over-large for its function as a setting for the monument. Yew responds well to pruning: the consequent wounds are resistant to decay and the residual crown is invigorated.
Management of ivy
Ivy obscures defects at inspection and may create a microclimate which promotes decay. It has the potential for strangulation but is not parasitic. It increases wind resistance, competes for water and may suppress the aerial part of the tree. Senescent trees may become dominated by ivy, hence suppressed, so that they die earlier than they otherwise would. Ivy provides roosts/nesting sites for bats and birds, and is otherwise advantageous to wildlife.
Ivy may penetrate mortar if soft, or will at least pull soft mortar with it if torn from a masonry structure. Ivy tends to insulate buildings and may soften lines. If desired on a building, it should be pruned every one or two years. Ground ivy also facilitates access to the ground by birds after snow.
Management of ivy
Work to ivy is best begun in late summer/early autumn, whether pruning or operations to kill it. At this time, disturbance is avoided to hibernating bats (winter) and nesting birds (spring/summer).
Pruning ivy on masonry will prevent progressive damage. The roots of the ivy, colonizing the mortar and any interstices in the masonry, will otherwise increase progressively in size, ultimately exerting high disruptive forces. Prune back to the clinging stems.
Killing ivy is difficult. Begin by severing the main stems near ground level. The severed aerial part will wither and decay over a year or two. Its grip is loosened as its clinging roots decay, and it will eventually disintegrate or fall from its support under its own weight. Two herbicides are recommended for killing ivy.
Root-out (ammonium sulphamate) is applied to the cut stumps and is translocated to the roots. It can also be watered into a root volume if not occupied by other (desired) plants.
Roundup or Tumbleweed (glyphosate) is sprayed on foliage, but ivy leaves are waxy and penetration is poor. Spraying re-growth from the stump is better, especially if most of the crown was inaccessible prior to severance. Leaves can be abraded/crushed by hand prior to spraying to aid penetration. A wetter could also be added (eg. 1% soft soap), but is said to be illegal in U.K. Two sprays are advised, end-August and mid-September.
Late summer/early autumn is best for both herbicides because active translocation from aerial part to roots is taking place at this time. Treatments over more than one year may be necessary.