|Sugar Maple (Acer saccharum)
||Sassafras (Sassafras albidum)
Oak (Quercus falcata)
|Post Oak (Quercus stellata)||American Holly (Ilex opaca)||Persimmon (Diospyros virginiana)|
Why do leaves of trees change colors in the fall?
There are several reasonable ways of answering this question --- some involving plant physiology and others involving evolution and inheritance. However, most people who ask this question are wondering about the physiological causes of the color change. The physiological causes are described here. Although most leaves appear green during the summer because of an abundance of chlorophyll pigments, in fact they contain a variety of pigments. In the fall, the chlorophylls begin to disappear from leaves as existing chlorophylls decompose and the production of new chlorophylls halts. Other pigments in the leaves are then revealed, that were masked by chlorophylls during the summer. In addition, in some species, newly synthesized nongreen pigments contribute to fall colors. In many cases, the pigments responsible for the fall colors are carotenoids, which vary in color from yellow to red. In other cases, the pigments responsible are anthocyanins, which vary in color from red to blue. The brown colors that remain in many leaves after brighter colors disappear --- as seen in oak leaves --- are generally due to the presence of tannins.
Species of trees are characterized by particular leaf colors during the fall. For example, leaves of scarlet oak become scarlet, but leaves of chestnut oak become yellow. The contrast among species can be attributed to different combinations of pigments. Leaves of a species may also proceed through a sequence of bright colors during the fall. For example, leaves of dogwood and red ash first become red or bluish-red, and later become yellow.
The annual timing of the fall color changes is another question, and the underlying mechanisms are not entirely understood. It has been related to a shortening of day-length and cool nights. Individuals of one species may vary in the timing of fall colors, depending on latitude and the amount of stress imposed by the particular site of the tree. Evenso, a species can be characterized by a particular time of color change. In southern New Jersey, species that have a center of distribution in the southeastern states, such as dogwood and sassafras, tend to change colors early in the fall. Species with a more northern center of distribution, such as beech and sugar maple, tend to change colors a few weeks later.
Original Forest of the Campus:
What were the common trees of the original forest on the site of the campus, before it was settled? The forest was probably an oak-hickory community, though very little of the original habitat remains. Some evidence of the original forest remains in the small tract of forest that was adjacent Hwy. 322 and was removed in 2004 to construct new student housing. This habitat fragment is dominated by black oak, chestnut oak, white oak, mockernut hickory, black cherry and sassafras. Other less abundant species in this stand include basswood, black walnut, dogwood, eastern red cedar, hackberry, holly, pignut hickory, pitch pine, post oak, red maple, sour gum, southern red oak and willow oak. Some nonnative species have also become naturalized (established) in this forest, especially norway maple and tree-of-heaven (others are catalpa, black locust, honey locust and white pine). It is possible that the original forest also would have included blackjack oak, beech, chestnut, persimmon, scarlet oak, sweet gum and tulip tree, but no evidence of them remains in this small remnant of habitat.
Reference for Plant Communities of the Region:
Robichaud Collins, B., and K. H. Anderson. 1994. Plant Communities of New Jersey: a Study in Landscape Diversity. (Second Edition). Rutgers University Press. Written in plain English, and the best introduction available for the plant communities of the state.
References for Identification of Trees of the Region:
Elias, T. S. 1980. The Complete Trees of North America. Van Nostrand Rheinhold. Remains the best comprehensive guide for trees of the continent. Includes identification keys, illustrations, distributional maps, and details of the economic utility of trees. This book is out-of-print, but can still be found in used book stores and libraries.
Gleason, H. A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Canada. (Second Edition). The New York Botanical Garden. A technical reference that includes identification keys and concise descriptions of species, but no illustrations.
Holmgren, N. H. 1998. Illustrated
to Gleason and Cronquist's Manual. The New York Botanical
Provides exceptional illustrations of all species in Gleason and
Leopold, D. J., W. McComb and R. N.
Muller. 1998. Trees of the Central Hardwood Forests of
North America. Timber Press.
Little, E. L. 1998. National
Audubon Society Field Guide to North American Trees. A. A.
Knopf. This is a portable book that includes color
photographs, descriptions and
distributional maps. It is relatively inexpensive and can be found in
bookstores. One drawback to this book is that is does not include
Li, H. Trees of Pennsyvlvania.
1972. University of Pennsylvania Press.
Martine, C. 2000. Trees of New
Jersey and the Mid-Atlantic States. 4th Edition. New Jersey
Rhoads, A. F. and T. A. Block.
2000. The Plants of Pennsylvania. University of
Pennsylvania Press. Although the campus is outside the geographic
scope of this flora, most trees of the
campus are included in this book. Includes identification keys
finely-detailed illustrations of many species.
Samuelson, L. J. and M. E. Hogan.
2003. Forest Trees. A Guide to the Southeastern and
Mid-Atlantic Regions of the United States. Prentice Hall.
What is a tree?:
Although many plants are obviously trees, in some cases plants that are shrubs are nearly trees. For this list, a tree is defined to be a plant that: 1) is woody at maturity; 2) has a single trunk at ground level; and 3) is more than 15 feet tall when mature. By contrast, a shrub is a woody plant with several stems at ground level, and is usually less than 15 feet tall at maturity. Shrubs are excluded from this list.
Names in the List:
Each species may be correctly identified by either a common (vernacular) name and a Latin name. The list below includes both common and Latin names, but is arranged alphabetically by common name. In some cases, a group of species are widely known by a common name referring to the whole group (for example: maples, oaks or pines). In these cases, the individual species are listed below under the broader common name.
Partial List of Trees of the Campus (a work in progress):
This list includes the trees within the Glassboro Campus of Rowan University. In general, this includes the property bound by Carpenter Street, Whitney Avenue, Girard Avenue and Bowe Boulevard. More than 60 species and of trees are found on the campus.
Red Ash (Fraxinus pennsylvanica)
White Ash (Fraxinus americana)
American Basswood; Linden Tree (Tilia americana)
European Basswood (Tilia cordata)
Black Cherry (Prunus serotina)
Black Walnut (Juglans nigra)
Black Willow (Salix nigra)
Catalpa (Catalpa species)
Atlantic White Cedar (Chaemacyparis thyoides)
Eastern Red Cedar - see Juniper
Northern White Cedar; Arborvitae (Thuja occidentalis)
Chinese Fir (Cunninghamia lanceolata)
Dogwood (Cornus florida)
Douglas Fir (Pseudotsuga menziesii)
American Elm (Ulmus americana)
Balsam Fir (Abies balsamea)
Ginkgo; Maidenhair Tree (Ginkgo biloba)
Hackberry (Celtis occidentalis)
Mockernut Hickory; White Hickory (Carya tomentosa)
Pignut Hickory (Carya glabra)
Hemlock (Tsuga canadensis)
Holly; American Holly (Ilex opaca)
Horsechestnut (Aesculus hippocastanum)
Japanese Pagoda Tree (Styphnolobium japonicum)
Japanese Temple Tree (Cryptomeria japonica)
Juniper; Eastern Red Cedar (Juniperus virginiana)
Larch; European Larch (Larix decidua)
Black Locust (Robinia pseudoacacia)
Honey Locust (Gleditsia triacanthos)
Mulberry (Morus alba)
Southern Magnolia (Magnolia grandiflora)
Mimosa (Albizzia julibrissin)
Box Elder; Ash-leaved Maple (Acer negundo)
Japanese Maple (Acer palmatum)
Norway Maple (Acer platanoides)
Red Maple (Acer rubrum)
Silver Maple (Acer saccharinum)
Blackjack Oak (Quercus marilandica)
Black Oak (Quercus velutina)
Chestnut Oak (Quercus prinus)
Northern Red Oak (Quercus rubra)
Pin Oak (Quercus palustris)
Post Oak (Quercus stellata)
Scarlet Oak (Quercus coccinea)
Southern Red Oak; Spanish Oak (Quercus falcata)
White Oak (Quercus alba)
Willow Oak (Quercus phellos)
Osage Orange (Maclura pomifera)
Persimmon (Diospyros virginiana)
Pitch Pine (Pinus rigida)
Red Pine (Pinus resinosa)
White Pine (Pinus strobus)
Sassafras (Sassafras albidum)
Sour Gum (Nyssa sylvatica)
Blue Spruce; Colorado Blue Spruce (Picea pungens)
Sumac (Rhus species)
Sweet Gum (Liquidambar styraciflua)
Sycamore; Plane Tree (Platanus occidentalis, and Platanus x acerifolia hybrids)
Tree-of-Heaven (Ailanthus altissima)
Tulip Tree; Tulip Poplar (Liriodendron tulipfera)