Facilities Management Directorate Grounds Maintenance

GROUNDS MAINTENANCE GUIDANCE NOTE ON SELECTION

1.0 INTRODUCTION

The University of Reading has many rare and historic on land managed by the University of Reading Facilities Management Directorate Grounds Maintenance Section. Grounds Maintenance 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 tree and planting to the highest standards.

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

This Guidance note 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. Trees which have known to cause poisoning are listed in Table 1 below

Table 1 Potentially Toxic Tree Species Species Common Name Toxic Hazard Laburnum sp. Golden Rain Ingested Rhus sp. Sumach Sap irritant and toxic Rhus verniciflua Varnish Tree Sap irritant and toxic Yew Ingested foliage and

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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 in table 2 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. Table 2 Species with Propensity to Breakage 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 atlantica ‘Glauca Blue atlas Cedar Branch failure at point of attachment. Group’ Failure of trunk in storm conditions. Acer negundo Box Elder Weak wood / frequent failure

Acer saccharinum and Cv. Silver Frequent failure of branches especially ‘Pyramidale’ in . 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 cultivar and of resulting failure.

2.3 POTENTIAL PROBLEMS FROM , 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 these species should be assessed in areas with a high usage or within areas of hard landscaping to assess their suitability.

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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.

2.5 THE CAMPUS ENVIRONMENT The following biotic agents described in table 3 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.

Table 3 Biotic Agents within the Campus Environment Agent Associated Problem Species Affected Students/Public Vandalism/Theft All trees especially Conifers which are taken for Christmas trees Squirrels Bark stripping Many, especially: Acer cappadocicum, Acer platanoides, Carpinus betulus and Fagus sylvatica. Coryneum Canker Dieback/death of tree x Cupressocyparis leylandii Seiridium cardinale Hornet Moth Basal damage of bark/cambium Populus sp. Sesia apiformis Rust of Poplar die and fall with a loss Some hybrid Populus sps. Melampsoridium betulinum of amenity. Willow Scab Leaves shrivel and die leading Salix sps. Esp. S. babylonica Venturia sps. to complete defoliation of tree. var. pekinensis ‘Tortuosa’ Chestnut Leaf Minor Disfiguration of foliage leading Aesculus hippocastanum Cameraria ohridella to defoliation Bleeding Canker Cambium death to death of Aesculus hippocastanum, tree 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.

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2.7 DESIRABLE SPECIES

(a) Trees suitable for structure planting: The list at Table 4 below 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) which we would not consider a viable species and Sycamore (). It should be noted that Acer, Fraxinus and Tilia species establish well at Whiteknights

Table 4 Trees Species Desirable for Structure Planting 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 Fagus sylvatica Common Beech Fraxinus excelsior Common Ash Ilex aquifolium Common Holly Pinus nigra* Black Pine Pinus radiata* Monterey Pine Prunus avium Wild Cherry Prunus cerasifera* Cherry Plum Prunus padus Bird Cherry Prunus spinosa Blackthorn Quercus ilex* Holm Oak Quercus robur Common Oak Sorbus aria White beam Sorbus aucuparia Taxus baccata Common Yew Tilia cordata Small leaved Lime Tilia x europaea* Common Lime Tilia platyphyllos Large leaved Lime

* Non Native

(b) Trees suitable for specimen planting are listed in table 5 below. The list is based on current successful species and includes species or cultivars that Grounds Maintenance is keen to add to the Whiteknights landscape.

4 Table 5 Tree Species Desirable for Specimen Planting Broadleaf Species Common Name Acer macrophyllum Oregon Maple Acer opalus Italian Maple Acer saccharum Sugar Maple Alnus cordata Italian Alder Alnus rubra Red Alder Arbutus x andrachnoides Hybrid Strawberry Tree Betula albo-sinensis var. septentrionalis Chinese Birch Betula ermanii Erman’s Birch Betula papyrifera Paper Birch Carya cordiformis Bitter Nut Carya laciniosa Shell Bark Hickory Carya ovata Shagbark Hickory Carya tomentosa Mockernut Catalpa speciosa Northern Catalpa Celtis australis Nettle Tree Cornus controversa Table Dogwood Fraxinus americana American Ash Fraxinus angustifolia Narrow leaf Ash Fraxinus excelsior ‘Diversifolia’ One Leaved Ash Fraxinus latifolia Oregon Ash Fraxinus ornus Manna Ash Fraxinus velutina Arizona Ash Gleditsia tricanthos Honey Locust Gymnocladus dioica Kentucky Coffee Tree Ilex x altaclerensis cultivars especially: ‘Balearica’ ‘Camelliifolia’, Highclere Holly ‘Golden King’ and ‘Hodginsii’ Ilex aquifolium cultivars especially: ‘J.C. Van Tol’, ‘Handsworth Common Holly New Silver’, ‘Aurea Marginata’ Ilex x koehneana ‘Chestnut Leaf’ Holly Ilex latifolia Tarajo Ilex perado Azorean Holly Juglans cathayensis Chinese Walnut Juglans nigra Black Walnut Juglans regia and cultivar ‘Laciniata’ Common Walnut Koelreuteria paniculata Golden Rain Tree Ligustrum lucidum Chinese Privet Liquidambar Styraciflua ‘Lane Roberts’ Sweet Gum Magnolia denudata Lily Tree Magnolia salicifolia Willow Leaf Magnolia Malus baccata Siberian Crab Malus transitoria Chinese Crab Morus nigra Black Mulberry Nothofagus procera Southern Beech Nyssa sinensis Chinese Nyssa Nyssa sylvatica Tupelo Parrotia persica + Cultivar ‘Venessa’ Persian Ironwood Paulownia tomentosa Foxglove Tree Platanus x hispanica London Plane Platanus orientalis + insularis ‘Digitalis’ Oriental Plane Prunus sargentii Japanese Cherry Prunus ‘Tai Haku’ The Great White Cherry Pterocarya fraxinifolia Caucasian Wing Nut Pyrus elaeagrifolia Pear Quercus canariensis Algerian Oak Quercus castaneifolia Chestnut Leaved Oak Quercus coccinea Scarlet Oak Quercus dentate Daimyo Oak Quercus ellipsoidalis Northern Pin Oak Quercus frainetto Hungarian Oak

5 Broadleaf Species (Cont’d) Common Name Quercus x hispanica ‘Lucombeana’ Lucombe Oak Quercus nigra Water Oak Quercus palustris Pin Oak Quercus robur ‘Fastigiata Koster’ Cypress Oak Quercus suber Cork Oak Quercus x turneri Turner’s Oak Quercus velutina Black Oak Sorbus alnifolia + Cultivar ‘Skyline’ Sorbus domestica Service Tree Sorbus intermedia Swedish Whitebeam Sorbus latifolia Service tree of Fontainebleau Sorbus sargentiana Sargent’s Rowan Sorbus thibetica ‘John Mitchell Whitebeam Sorbus torminalis Wild Service tree Sorbus vestita Himalayan Whitebeam 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 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 procera Noble Fir Calocedrus decurrens Incense Cedar + ‘Glauca Group’ Blue atlas Cedar Cedrus deodara Deodar Cedar Cedrus libani Cedar of Lebanon Ginkgo biloba Maidenhair Tree Metasequoia glyptostroboides Dawn Redwood 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 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 Sequoia sempervirens Coast Redwood Sequoiadendron giganteum Wellingtonia Thujopsis dolabrata Hiba Tsuga heterophylla Western Hemlock Wollemia nobilis Wollemia Pine

6 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, 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 deflectors can dramatically reduce distortion of pavements. Tree grills should be specified where pedestrian damage to the rooting area is likely. The use of below ground cell systems within hard landscaping allow the successful establishment of trees while retaining sufficient load bearing properties 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 0.5m 1.5m 3.0m tree >1m Deep Minimum distance from - 1.0m 2.0m tree

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

7 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 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.

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