Box 93 Relative tolerance classes used to classify the ability of young trees to endure shade

The light intensity ranges given for each class are the lowest amounts of full sunlight that enable the tree species concerned to survive in the understorey. Trees are shown in three columns, the first two being the gymnosperms and angiosperms of the east. There is no such distinction with the major western trees, which are predominantly gymnosperms. (After Spurr and Barnes, 1980. Forest Ecology. Wiley.)

Eastern North America

Western North America

Gymnosperms Angiosperms

1. Very tolerant species can survive when the amount oflight is as low as 1-3% of full sunlight.

Eastern hemlock Tsuga mertensiana Red spruce Picea rubens

2. Tolerant species need 3-White spruce Picea glauca

Black spruce Picea mariana

Flowering dogwood Cornus florida Hop hornbeam Ostrya virginiana Sugar maple Acer saccharum American beech Fagus grandifolia 10% full sunlight. American lime Tilia americana Red maple Acer rubrum

3. Intermediate species require 10-30% full sunlight.

White pine P. strobus Slash pine Pinus elliottii

Yellow birch Betula lutea Silver maple Acer saccharinum Most oaks Quercus spp. Hickories Carya spp. White ash Fraxinus americana Elms Ulmus spp. 4. Intolerant species must have 30-60% full sunlight.

Black cherry Prunus serotina Sweet gum Liquidambar styraciflua American sycamore

Platanus occidentalis Black walnut Juglans nigra

Scarlet oak Quercus coccinea Sassafras Sassfras albidum 5. Very intolerant species need 60% or more full sunlight.

Red pine Pinus resinosa Shortleaf pine Pinus echinata Eastern red cedar Juniperus virginiana Loblolly pine Pinus taeda

Jack pine Pinus banksiana

Longleaf pine P. palustris Virginia pine P. virginiana

Tamarack Larix laricina

Paper birch Betula papyrifera Aspens Populus spp. Black locust Robinia pseudoacacia Eastern cottonwood P.

deltoides Pin cherry Prunus pensylvanica

Western hemlock Tsuga heterophylla Pacific silver fir Abies amabalis

Pacific yew Taxus brevifolia

Spruces Picea spp.

Western red cedar Thuja plicata

White fir Abies concolor Grand fir Abies grandis Coastal redwood Sequoia sempervirens

Western white pine P. monticola Sugar pine Pinus lambertiana

Douglas fir Pseudotsuga menziesii Noble fir Abies nobilis

Ponderosa pine Pinus ponderosa Red alder Alnus rubra

Madrone Arbutus menziesii

Lodgepole pine Pinus contorta

Whitebark pine P. albicaulis Grey pine P. sabiniana

Western larch Larix occidentalis

Cottonwoods Populus spp.

Eastern Hemlock Life Cycle

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