University of Reading Guidance Note on Tree Planting

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UNIVERSITY OF READING GUIDANCE NOTE ON TREE PLANTING

1.0 INTRODUCTION

The University of Reading has many rare and historic trees and is conscious of its duty to ensure the continuing amenity and environmental value of the campus. This can only be achieved by the appropriate selection of species and planting to the highest standards.

The Grounds Maintenance Section is well aware of the potential conflicts that trees can provoke, many of which can be avoided by giving careful consideration to the species selected and the sites that they are planted.

This aims to give practical advice, guidance and references to all those involved with tree planting on University property, with the aim of: • Preventing damage to University property or services • Reducing the need for future maintenance • Reducing future hazards

2.0 SELECTION OF SPECIES

This guide does not intend to discuss the amenity value of tree species, as there are already many books on the subject but does hope to highlight considerations that should be made to ensure the most suitable species are selected for the site.

2.1 TOXICITY There are a number of tree species that are toxic if ingested or their sap can cause contact allergic reactions to skin and eyes. The likelihood of serious poisoning occurring is extremely unlikely because trees are generally unpalatable and are unlikely to be eaten in large quantities. Site assessment should be carried out before known toxic species are chosen.

Species Common Name Toxic Hazard Aesculus sp. Chestnut Ingested fruits Ilex sp. Holly Ingested fruits Laburnum sp. Golden Rain Ingested seeds Ligustrum lucidum Chinese Privet Ingested fruits Rhus sp. R. verniciflua (See Sumach Sap irritant and toxic Toxicodendron) Robinia sp. False Acacia Ingested seeds Sophora japonica Pagoda tree Ingested seeds Taxus baccata Yew Ingested foliage and seed Toxicodendron vernicifluum Varnish Tree Phototoxic

Consideration should be given to those species that could be described as an irritant: Platanus x hispanica (Plane) - Hairs on young foliage can cause irritation of the throat, nose and eyes.

x Cupressocyparis leylandii (Leyland Cypress) - Irritant sap, can cause contact dermatitis. Generally these species only affect those people working on the tree.

2.2 PROPENSITY TO BREAKAGE The incidence of mechanical failure differs greatly between tree species and sometimes between cultivars within the same species. Much of the information listed is based on observation rather than scientific research. The following list may help to make the designer aware of potential hazard associated with species or cultivars which may make its use next to a foot path or road inappropriate.

Species Common Name Potential structural Hazard Abies cephalonica Grecian Fir Forms heavy branches in maturity liable to fail in storm conditions. Cedrus libani Cedar of Lebanon Forms heavy branches liable to failure.

Cedrus libani sub sps. atlantica Blue atlas Cedar Branch failure at point of attachment. var. ‘Glauca’ Failure of trunk in storm conditions. Acer negundo Box Elder Weak wood / frequent failure

Acer saccharinum and Cv. Silver Maple Frequent failure of branches especially in leaf. ‘Pyramidale’ Aesculus hippocastanum Horse Chestnut Failure at forks is frequent. Summer branch drop is common. Ailanthus altissima Tree of Heaven Considered to have brittle wood.

Fraxinus ‘Raywood’ Raywood Ash Failure at forks from a young age.

Liquidambar styraciflua Sweet Gum Top breakage of semi-mature trees.

Liriodendron tulipifera Tulip Tree Top breakage of semi-mature trees and branch failure. Paulownia tomentosa Fox Glove tree Brittle wood

Populus Sps. Poplar Wood of low-density, breakage of tops and branches common. Robinia pseudoacacia ‘Frisia’ Golden Acacia Branch failure common in breezy conditions, during summer. Salix Sps. Esp. S. fragilis Willow Failure often associated with pollarding. S. fragilis sheds its branches and twigs. Tilia cordata ‘Greenspire’ Small leaved Lime A high incidence of weak fork formation and cultivar of resulting failure.

2.3 POTENTIAL PROBLEMS FROM FRUIT, CONES AND THORNS

Tree species should be selected so as to minimise potential future problems from falling fruit, cones, honey dew or thorns. The use of the species listed below should be risk assessed in areas with a high usage to assess their suitability.

Species Common Associated potential problem Name Araucaria araucana Monkey Puzzle Extremely sharp foliage. Tree Ginkgo biloba Maiden Hair Female trees produce foul smelling sticky fruit. Tree Pinus Sps. Especially P. coultrei, P. Pine Shedding of cones can be hazardous. Sylvestris and P. nigra Taxus baccata Yew Sticky fruit.

Acer pseudoplatanus Sycamore Honeydew from aphid infestation.

Aesculus hippocastanum Horse Chestnut Falling fruit (conkers) Children throwing sticks into the crown to collect conkers. Castanea sativa Sweet Chestnut Falling fruit. Crataegus Sp. Hawthorn Thorns. Crushed fruit on footpath

Gleditsia tricanthos Honey Locust Large thorns.

Juglans regia Walnut Falling fruit.

Malus Sp. Crab Apples Crushed fruit on footpaths

Morus nigra Mulberry Very juicy sticky fruit.

Pyrus Sp. Pear Crushed fruit on footpaths

Tilia x europaea Common Lime Honeydew from aphid infestation

2.4 ON MATURITY The following factors should be considered when evaluating the true impact on any new tree:

(a) Mature habit and ultimate size of the tree. Will the tree selected be suitable for the space allocated?

(b) Density of crown / size of foliage. Will the tree selected have such a dense canopy so as to dominate the landscape or shade the building it is meant to enhance?

Further information regarding these subjects and information on appropriate tree species are found in a number of publications (see bibliography)

2.5 THE CAMPUS ENVIRONMENT The following biotic agents may have relevance in species selection, positioning of planting and post planting protection. This is by no means an exhaustive list but does highlight recent pest and diseases whose action may question the future use of the affected species.

Agent Associated Problem Species Affected Students/Public Vandalism/Theft All trees especially Conifers which are taken for Christmas trees Agent Associated Problem Species Affected Squirrels Bark stripping Many, especially: Acer cappadocicum, Acer platanoides, Acer pseudoplatanus, Carpinus betulus and Fagus sylvatica. Sooty Bark Disease Cryptostroma Death of tree Acer pseudoplatanus corticale Bleeding canker Die back leading to death of tree Aesculus hippocastanum A. carnea Coryneum Canker Dieback/death of tree x Cupressocyparis leylandii Seiridium cardinale Rust of Poplar Leaves die and fall with a loss of Some hybrid Populus sps. Melampsoridium betulinum amenity. Willow Scab Leaves shrivel and die leading to Salix sps. Esp. S. babylonica var. Venturia sps. complete defoliation of tree. pekinensis ‘Tortuosa’ Chestnut Leaf Minor Disfiguration of foliage leading to Aesculus hippocastanum, A. flava, Cameraria ohridella defoliation A. indica

Weeping Canker Die back of young trees 10-35 Tilia x euchlora years old

2.6 CLIMATE CHANGE

Summer droughts are likely to continue to be a problem for tree establishment. On high profile landscaping schemes provision for irrigation should be considered at the design stage. Drought tolerant species should be selected where appropriate.

Beech Fagus sylvatica will continue to decline in the south for the next 50 years and so wide spread plantings of this species should be avoided. The likely predicated effects of climate change in the short term can be mitigated by appropriate species selection with planting and aftercare to best industry practice

2.7 DESIRABLE SPECIES

(a) Trees suitable for structure planting: This list is based on the highest percentage of recorded species on the University tree inventory therefore indicating the most successful species. It excludes Horse Chestnut (Aesculus hippocastanum), Beech (Fagus sylvatica) and Sycamore (Acer pseudoplatanus).

Species Common Name Acer campestre Field Maple Acer Platanoides* Norway Maple Alnus glutinosa Common Alder Betula pendula Silver Birch Carpinus betulus Common Hornbeam Castanea sativa* Sweet Chestnut Corylus avellana Hazel Crataegus monogyna Common Hawthorn Fraxinus excelsior Common Ash Ilex aquifolium Common Holly Pinus nigra* Black Pine

Species Common Name Pinus radiata* Monterey Pine Populus tremula Aspen Prunus avium Wild Cherry Prunus cerasifera* Cherry Plum Prunus padus Bird Cherry Rhamnus cathartica Common Buck Thorn Quercus ilex* Holm Oak Quercus robur Common Oak Sorbus aria White beam Sorbus aucuparia Rowan Taxus baccata Common Yew Tilia cordata + Cultivars ‘Rancho’, ‘Streetwise’ Small leaved Lime Tilia x europaea* + Cultivar ‘Pallida’ Common Lime Tilia platyphyllos + Cultivars ‘Rubra’, ‘Streetwise’ Large leaved Lime * Non Native

(b) Trees suitable for specimen planting- This list is based on current successful species and includes species or cultivars the University is keen to add to its collection.

Broadleaf Species Common Name Acer cappadocicum Cappadocicum Maple Acer carpinifolium Hornbeam Maple Acer diabolicum Horned Maple Acer grosseri Snake Barked Maple Acer macrophyllum Oregon Maple Acer maximowiczianum Nikko Maple Acer opalus Italian Maple Acer saccharum Sugar Maple Alnus cordata Italian Alder Alnus rubra Red Alder Alnus x spaethii Hybrid Alder Arbutus x andrachnoides Hybrid Strawberry Tree Betula albo-sinensis var. septentrionalis Chinese Birch Betula ermanii Erman’s Birch Betula maximowicziana Large leaved Birch Betula nigra River Birch Betula papyrifera Paper Birch Betula utilis var. pratttii + Var. jacquemontii ‘Jermyns’ Himalayan Birch Carpinus betulus ‘Pendula’ Weeping Hornbeam Carpinus x schuschuaensis Hybrid Hornbeam Carya cordiformis Bitter Nut Carya laciniosa Shell Bark Hickory Carya ovata Shagbark Hickory Carya tomentosa Mockernut Catalpa ovata Yellow Catalpa Catalpa speciosa Northern Catalpa Celtis australis Nettle Tree Cornus controversa Table Dogwood Crataegus coccinioides Scarlet Hawthorn Cydonia oblonga Common Quince Drimys winteri Winters Bark Fraxinus americana American Ash Fraxinus angustifolia Narrow leaf Ash Fraxinus excelsior ‘Diversifolia’ One Leaved Ash Fraxinus latifolia Oregon Ash Fraxinus ornus Manna Ash Broadleaf Species (Cont’d) Common Name Fraxinus velutina Arizona Ash Gleditsia tricanthos Honey Locust Gymnocladus dioica Kentucky Coffee Tree

Ilex x altaclerensis cultivars especially: ‘Balearica’ Highclere Holly ‘Camelliifolia, ‘Golden King’ and ‘Hodginsii’ Ilex aquifolium cultivars especially: ‘J.C. Van Tol’, ‘Handsworth New Common Holly Silver’, ‘Aurea Marginata’ Ilex x koehneana ‘Chestnut Leaf’ Holly Ilex latifolia Tarajo Ilex perado Azorean Holly Juglans cathayensis Walnut Juglans nigra Black Walnut Juglans regia and cultivar ‘Laciniata’ Common Walnut Koelreuteria paniculata Golden Rain Tree Laurus nobilis Bay Laurel Ligustrum lucidum Chinese Privet Liquidambar Styraciflua ‘Lane Roberts’ Sweet Gum Magnolia acuminata Cucumber Tree Magnolia denudata Lily Tree Magnolia kobus North Japanese Magnolia Magnolia officinalis Magnolia salicifolia Willow Leaf Magnolia Malus floribunda Japanese Crab Malus baccata Siberian Crab Malus transitoria Chinese Crab Morus alba White Mulberry Morus nigra Black Mulberry Nothofagus dombeyi Southern Beech Nothofagus procera Southern Beech Nyssa sinensis Chinese Nyssa Nyssa sylvatica Tupelo Ostrya carpinifolia Hop Hornbeam Parrotia persica + Cultivar ‘Venessa’ Persian Ironwood Paulownia tomentosa Foxglove Tree Phellodendron amurense Amur Cork Oak Picrasma quassioides Picrasma Platanus x hispanica London Plane Platanus orientalis + insularis ‘Digitalis’ Oriental Plane Populus x canadensis ‘Robusta’ Black Italian Poplar Populus lasiocarpa Chinese Necklace Poplar Prunus avium ‘Plena’ Double Wild Cherry Prunus Kusar Japanese Cherry Prunus maackii Manchurian Cherry Prunus ‘Okame’ Japanese Cherry Prunus padus ‘Watereri’ Bird Cherry Prunus ‘Pandora’ Japanese Cherry Prunus sargentii Japanese Cherry Prunus ‘Tai Haku’ The Great White Cherry Pterocarya fraxinifolia Caucasian Wing Nut Pyrus elaeagrifolia Pear Pyrus ussuriensis var. hondoensis Manchurian Pear Quercus acutissima Saw Tooth Oak Quercus canariensis Algerian Oak Quercus castaneifolia + Cultivar ‘Green Spire’ Chestnut Leaved Oak Quercus coccinea + Cultivar ‘Splendens’ Scarlet Oak Quercus dentate Daimyo Oak Quercus ellipsoidalis Northern Pin Oak Quercus frainetto + Cultivar ‘Hungarian Crown’ Hungarian Oak Quercus x hispanica ‘Lucombeana’ Lucombe Oak Quercus ilex Holm Oak Broadleaf Species (Cont’d) Common Name Quercus nigra Water Oak Quercus palustris Pin Oak Quercus phellos Willow Oak Quercus robur ‘Fastigiata Koster’ Cypress Oak Quercus suber Cork Oak Quercus x turneri Turner’s Oak

Quercus variablis Chinese Cork Oak Quercus velutina + cultivar ‘Rubrifolia’ Black Oak Robinia pseudoacacia Common Acacia Salix alba Var. sericea Silver Willow Salix x sepulcralis ‘Chrysocoma’ Golden Weeping Willow’ Sorbus alnifolia + Cultivar ‘Skyline’ Sorbus aria + Cultivars ‘Magnifica’, ‘Majestica’ Whitebeam Sorbus aucuparia + Cultivars ‘Edulis’, ‘Sheerwater Seedling’ and Rowan ‘Streetwise’ Sorbus commixta + Cultivar ‘Embley’ Japanese Rowan Sorbus domestica Service Tree Sorbus hupehensis Sorbus x hybrida + Cultivar ‘Gibbsii’ Sorbus intermedia Swedish Whitebeam Sorbus latifolia Service tree of Fontainebleau Sorbus sargentiana Sargent’s Rowan Sorbus thibetica ‘John Mitchell Whitebeam Sorbus x thuringiaca + Cultivar ‘Fastigiata’ Bastard Service Tree Sorbus torminalis Wild Service tree Sorbus vestita Himalayan Whitebeam Tetradium daniellii Euodia Tilia americana American Lime Tilia dasystyla subsp. caucasica Caucasian Lime Tilia henryana Henry’s Lime Tilia heterophylla White Bass Wood Tilia mongolica Mongolian Lime Tilia tomentosa Silver Lime Toona sinensis Chinese Cedar Zelkova carpinifolia Caucasian Elm Conifer Species Common Name Abies cephalonica Grecian Fir Abies concolor Colorado White Fir Abies forrestii Forrest’s Silver Fir Abies grandis Grand Fir Abies nordmanniana Caucasian Fir Abies pinsapo Spanish Fir Abies procera Noble Fir Calocedrus decurrens Incense Cedar Cedrus atlantica + ‘Glauca Group’ Blue atlas Cedar Cedrus deodara Deodar Cedar Cedrus libani Cedar of Lebanon Chamaecyparis lawsoniana + Cultivars Lawson Cypress Cryptomeria japonica + Cultivar ‘Elegans’ Japanese Cedar Ginkgo biloba Maidenhair Tree Metasequoia glyptostroboides Dawn Redwood Picea asperata Dragon Tail Spruce Picea omorika Serbian Spruce Picea orientalis Oriental Spruce Picea smithiana Himalayan Spruce Pinus aristata Bristlecone Pine Pinus armandii Armand’s Pine Pinus ayacahuite Mexican White Pine Pinus bungeana Lace Bark Pine Conifer Species (Cont’d) Common Name Pinus cembra Arolla Pine Pinus coulteri Big Cone Pine Pinus halepensis Aleppo Pine Pinus heldreichii Bosnian Pine Pinus x holfordiana Holford’s Pine Pinus jeffreyi Jeffrey Pine Pinus ponderosa Western Yellow Pine Pinus sylvestris ‘Edwin Hillier’ Scots Pine Cultivar Pseudolarix amabilis Golden Larch

Pseudotsuga menziesii Douglas Fir Sciadopitys verticillata Umbrella Pine Sequoia sempervirens Coast Redwood Sequoiadendron giganteum Wellingtonia Thujopsis dolabrata Hiba Tsuga heterophylla Western Hemlock Wollemia nobilis Wollemia Pine

3.0 DAMAGE BY TREES

Trees planted in inappropriate places can lead to a number of different types of damage in the short or long-term future. This damage may be caused by the direct or indirect action of trees as follows:

3.1 DIRECT ACTION Two mechanisms for damage are common: (a) Direct physical damage By roots, e.g. the lifting of paving slabs or damage to lightly loaded structures e.g. boundary walls from expanding roots or trunk or direct contact of expanding crown to building.

Consideration should also be given to the trip hazard potential of expanding roots and future maintenance problems e.g. Cherry trees planted in a lawn. Species associated with this kind of damage include: Fraxinus, Tilia, Aesculus, Quercus, Acer esp. A. pseudoplatanus, Betula, and Prunus.

In areas of hard landscaping the risk of damage can be reduced if trees are grown in a planting strip with exposed soil rather than planting pits. The use of root direction bags can dramatically reduce distortion of pavements. Tree grills should be specified where pedestrian damage to the rooting area is likely. The use of structured soils will increase the load bearing capacity of the area allowing hard landscaping over the rooting area of the tree. Sufficient space should be allowed for trunk and root expansion.

(b) Damage to drains and underground services Water leaking from damaged drains, sewers or water mains encourages localized root growth. Roots are then likely to enter through the defect and proliferate, causing blockage and enlarging of the initial defect. Trees planted over an existing drain or service run may make use of the backfill as a rooting medium, this could result indirect pressure or leverage forces been applied to the service

Tree species associated with root invasion include Populus, Salix, Aesculus, Acer pseudoplatanus, Platanus and Betula.

Recommended minimum distance between new planting and drains to avoid direct damage Diameter of tree stem at 1.5m above ground level at maturity Drains & underground services <30cm 30-60cm >60cm

<1m Deep Minimum distance from tree 0.5m 1.5m 3.0m >1m Deep Minimum distance from tree - 1.0m 2.0m

B.S. 5837 (2005) Trees in relation to construction Table 3 gives a more detailed account of minimum planting distances between trees and structures.

3.2 Indirect action On sites with shrinkable clay soils consideration should be given to the water demand of individual species and an appropriate planting distance should be kept between trees and existing buildings. On new developments it might be appropriate to increase the foundation depth when trees are to be planted close by and so the advice of a structural engineer should be sought. NHBC Standard Buildings near Trees, Chapter 4.2 gives advice on the avoidance of indirect damage by trees to structures

High water demand species include: Eucalyptus, Populus, Quercus, Crataegus, Salix, Sorbus (simple leaved), Cupressus, Chamaecyparis, x Cupressocyparis, Sequoiadendron

4.0 SITE SELECTION Trees must not be planted if they would: • Disrupt the view of road users. • Block the light from streetlights. • Cover road signage • Obscure CCTV coverage • Obstruct the passing of vehicles or pedestrians

It should be noted that the highways authority would enforce the pruning of such trees and it is an offence to plant a tree within 5m of the centre of the carriageway.

5.0 MATERIAL SELECTION Many tree defects originate in the nursery. The following Specifications are required for new planting: • The highest quality nursery stock grown to BS 3936 Nursery Stock part 1: Specification for trees and shrubs1992 • Trees are correctly labelled and are true to type • Trees are transported and handled according to HTA Plant Handling Code. • Container grown stock has not outgrown its container. • Containerised stock has sufficient roots to fill the container. • Trees grown in “air pots” when available

Trees that are of poor quality or form will be rejected. Native trees must be of a suitable local provenance, as defined in Forestry Commission Practice Note Number 8, ‘Using local stock for planting native trees and shrubs’

6.0 PLANTING

Faulty planting is often responsible for the development of instability in trees, as well as poor growth and is the main reason for tree failure. An appropriate site specific specification should be produced for each planting scheme. Staff carrying out tree planting should be trained and competent.