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. 1 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. 2 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 3 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 4 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