History
A pollard is a tree cut 2-3 m above the ground, which develops a crown of branches which can be cropped repeatedly. The height of the boll prevents stock browsing the young shoots.
It was therefore particularly suitable for trees in wood-pasture, parks, commons and Royal forests; and was also used for trees on riverbanks, woodland and district / parish / ownership boundaries. The bark of the lopped branches, and if cut in summer, the foliage of deciduous species, could also provide some food for livestock.
Rotations varied between 10 - 35 years and seemed quite irregular in an area.
Complex systems of rights evolved with pollarding on commons and in Forests. Generally, the landowner owned the unpollarded trees and the bolling (trunk) of the pollard. The commoners sometimes had rights of lopping branches from the pollards - so they wanted to continue to lop and create new pollards, whilst landowners were keen to restrict the establishment of new pollards and removed for their own use bollings which had died.
Which species?
Almost all species of broadleaved trees will pollard - many very readily if started when young and regularly lopped. In wood-pasture the species least palatable to stock predominate; hornbeam, oak and beech. Other species frequently pollarded are ash, willow, field maple, elm, crab apple, hawthorn, whitebeam and black poplar.
Why pollard?
1. Longevity: Repeated, regular pollarding increases a tree's lifespan. It also prevents the crown becoming top heavy which would de-stablilize a riverside tree, causing bank erosion and the build-up of trash behind a fallen trunk. A heavy crown may even split the boll, where rot will invade and kill the tree.
On the other hand, water is often retained in the top of the boll which probably makes the pollards more liable to rot and at younger ages than standard trees of the same species.
2. Historical importance: In terms of perpetuating some features of the wildwood, and in nature conservation interest, wood-pasture complements coppice and high forest in ancient woodland; and maintains environmental conditions intermediate in some ways between high forest and open ground.
3. Wildlife: Pollards are a unique habitat. Different invertebrates are found in standing dead wood when compared to dead wood on the ground. The pollard bolling is a long-lived source of standing dead wood. Epiphytic bryophytes and lichens are found on extremely old bollings in pollution-free areas.
Old crowns and hollow trunks provide roosting and breeding sites for owls, duck, bats and otter bolts.
4. Wood: Willow pollards provide withies (1 year's growth), rods (3-5 years) and all provide firewood (10+ years).
5. Landscape and historical importance: To many these striking trees are very beautiful and give clues to the past system of land and tree management. These old trees carry in their tree rings a record of their treatment superimposed on the changes in climate and other factors affecting their growth.
The current problem
Regular lopping and creation of new pollards declined about 50-100 years ago and can probably be attributed to a general decline in local firewood demand during the Industrial Revolution; and various common lopping rights were extinguished.
The problem now is: (a) no new pollards are being created to replace the old and dying and (b) old, neglected and sometimes dangerous pollards which are unlikely to be re-pollarded without more awareness of the need, and possibly some incentive to do an uneconomic task.
The October 1987 storm damaged recently re-pollarded trees less than unstable, neglected pollards. Storm-damaged trees may well recover through self-pollarding, with or without tree surgery to tidy them up.
Morphology and physiology of pollarding
Pollard branches, coppice regrowth and epicormic shoots all arise from the same stock of long-dormant buds (augmented in the case of pollarding and coppicing by adventitious buds). The difference between these three types of growth depends on the part of the tree involved, the extent of the growth (often slow part of the tree involved, the extent of the growth [often slow or limited in epicormic shoots] and what stimulated growth [ie total loss of crown or shoots, environmental factors]).
Roughness of bark and especially burrs ("bird's eyes") indicate a high density of dormant buds, which tend to be concentrated around present or former branches. Dormant buds appear to be very abundant on oak, hornbeam and sweet chestnut but less so in other broadleaves. The longevity of these buds is variable, but up to 100 years in oak, averaging 60 years in hornbeam and chestnut, less in beech and still less in birch and willow.
Thus the fact that young bark seems better at producing new branches than old bark could be because the initial stock of buds has had less time in which to decline or the thinner bark is easier for buds to break through.
Adventitious buds develop in the callus formed on the rim of the cut surface. Again, there are differences between tree species in the readiness to form adventitious buds.
Most pollard branches come from dormant buds in oak and hornbeam, in beech a high proportion probably arise from adventitious buds and in lineage elm they all do.
Pollarding removes the entire crown while leaving the bolling and roots untouched. Such a severe alteration of the shoot and root balance must be reflected in the physiology of the tree, but little about this is known.
Successful re-growth consists of many shoots arising in a vigorous bushy mass at the top of the bolling. These shoots self-thin so that as the branches become larger there are correspondingly fewer of them.
Pollarding is an extremely traumatic treatment to the physiology of the tree. There must be substantial root death after lopping, thus providing much fungal resource and allowing entry into the heartwood. The cut surfaces and water-holding hollows of the bolling also encourage fungal entry and growth. Subsequent entry of specialised wood-feeding invertebrates can be tolerated for centuries and is not indicative of imminent death.
Responses of tree species
Oak: variable. Hatfield - 90% of trees that had not been pollarded for 15- years died. Killerton (Devon) - 85% re-pollarded well. Response varies according to many factors.
Beech: usually dies. However, Epping Forest - 44% survival.
Ash: responds well.
Hornbeam: considered to be the most successful. Epping Forest - 97% survived.
Lime (small and large leaved): thought to respond well, judging by urban pollarding of hybrids.
Wych and smooth-leaved elm: variable response. In Suffolk, not good.
Willows: excellent response.
Black poplar: good response.
Field maple: good response.
Hawthorn: good response
HINTS, TIPS AND RECOMMENDATIONS FOR RE-POLLARDING NEGLECTED TREES
1. Tree species and genotype
Burry, twiggy trees (oak, hornbeam) respond best to re-pollarding.
Burrs are probably genetic in origin and indicate a local concentration of buds keeping up in growth with the bark. Burry oaks (such as self-pollarded, gale-damaged specimens in Staverton Park) are much more likely to succeed than smooth-barked ones. Smooth-barked ash are less likely to succeed than rougher ones.
2. Age of bolling and branches
It is difficult to say how age of branches or time since last lopped, effect success. There does seem to be a marked decline in the abilities of dormant buds to grow after a certain time - varying with species. As a rough rule, once past the normal rotation age (say about 40 years at the most), for some species the success rate of re-pollarding declines quickly to a low level.
3. Size of bolling
Large oak trees, well over 1 m diameter at breast height, hollow, with branches up to 45 cm in diameter have responded well. Similarly with ash. This factor may not have a great deal of effect.
4. Fungal infection
Variable in different trees and difficult to assess.
5. Time of year to pollard
Lopping for foliage must have taken place in the summer, but is nowadays preferred in the autumn and winter. Better success rates are achieved by lopping in January and February (stopping when the sap starts to rise), than November to December. (This may be because, like winter pruning, negligible callus growth results over winter, allowing more time for fungus, etc., to invade.).
6. Method of pollarding
(a) The need for younger bark from which more buds may grow out and the general toleration of heart-rot, may justify leaving branch stubs 15-60 cm long which seems to result in better re-growth.
(b) Re-growth arises from adventitious buds formed in the callus and from dormant buds in the bark below the cut. Cutting branches on a slant increases the perimeter of cut bark from which at least some shoots arise. Lopping higher up the crown, so that more, smaller branches are removed may increase the amount and vigour of the callus formed. Slanting surfaces shed water and may decrease fungal infection.
(c) Although there may seem little point in using wound dressings to reduce fungal infection, dressings might play a useful role in encouraging callus growth by slowing dehydration of the cut surface, eg Arbrex, or by direct chemical stimulation such as a preparation containing thiophanate methyl.
(d) Clean cuts on the bark may be left by edge tools so that callus formation is easier and there is less risk of the bark being detached. Others believe this does not have any effect.
(e) Leaving one branch only uncut for one year (two or three if re-growth is slow), whilst the others are pollarded, so that this branch will provide some photosynethate during the first year when the new shoots are growing. To preserve the stability of the tree a single, near vertical branch near the centre of the trunk would be preferred (although this would be the most difficult to cut later on).
7. Shade
Although light may not be the main stimulus to the emergence of epicormic shoots, it encourages growth once they have appeared. A re-pollarded tree is in a fairly delicate state for the first year or two and shading by taller, more vigorous neighbouring trees undoubtedly adversely affect re-growth.
8. Other site factors
Soil, wetness and other factors may all affect re-growth success but this is not yet clearly understood.
CREATING NEW POLLARDS
New pollards should be created to replace old, dying pollards not only for landscape and historical reasons, but to minimise the distance for organisms to travel to find a suitable substrate. Start many new pollards to give a balanced age-structure to the population and to allow for failures.
Which trees?
Normally young maiden trees (from natural regeneration or planting) will be available for pollarding, but coppice stems can also be used. Mis-shapen trees, or those with "weak forks" and likely to cause problems later, or storm-damaged trees may be easier to "sacrifice" for those who find it difficult to pollard a lovingly planted tree!
How young?
Create new pollards when young trees are as young as 2 m in height and between 10 - 30 cm diameter breast height:
- "very young" for oak
- younger than 15 years for beech (said to be difficult)
- 15 years for hornbeam
- 12 years for yew
How high?
Pollarding should be done at least 30 cm above the reach of whatever browsing animals are envisaged, ie 1.8 m for fallow deer, 3 m for horses (Giraffe-pollards [4-5 m high] exist at Windsor and Sherwood). At least 30 cm branch stubs should be left.
