All plants which are adapted to allee effects must be of a type which will respond to the operations of severe pruning. Those plants in Group a must have a special adaptation for a spreading habit of growth and yet a compact habit of growth. They must be such plants as will retain their foliage during a considerable period in order to produce and maintain the pleached allee effect. The deciduous and evergreen trees and shrubs shown in Group b of this list are all adapted to types of open allee developments on different scales, to be in keeping with the general landscape effect.

a. Pleached

Acer campestre

European Cork Maple Carpinus caroliniana

American Hornbeam

Carpinus betulus

European Hornbeam

Corylus maxima

Filbert Crataegus oxycantha

May Thorn Fagus sylvatica

European Beech

Quercus laurifolia (South of Washington)

Laurel Oak Rhamnus cathartica

Common Buckthorn

Salix pentandra

Laurel-leaved Willow Ulmus campestris

English Elm b. Not pleached {Open Allees): 1. Deciduous:

Acer saccharinum pyramidale

Pyramidal Silver Maple Acer saccharum monumentale

Columnar Sugar Maple

Betula alba fastigiata Pyramidal White Birch

Crataegus oxycantha May Thorn

Larix leptolepsis Japanese Larch

Populus nigra italica Lombardy Poplar

Quercus robur fastigiata

English Oak Sorbus quercifolia

Oak-leaved Mountain Ash Taxodium distichum

Bald Cypress

Taxus baccaia fastigiata Irish Yew

Ulmus foliacea wheatleyi Wheatley's Cornish Elm

Ulmus glabra fastigiata Columnar Elm

2. Evergreen:

Abies brachyphylla

Nikko Fir Juniperus excelsa stricta

Slender Greek Juniper Juniperus virginiana schotti

Schott's Red Cedar

Picea excelsa columnaris Columnar Norway Spruce

Picea excelsa pyramidalis Pyramidal Norway Spruce

Picea omorika Servian Spruce

Thuja occidentalis lutea Oriental Arborvitae

Thuja occidentalis wareana Siberian Arborvitae

Thuja orientalis (northern grown) Oriental Arborvitae

Thuja plicata Western Arborvitae