Conifers are trees and woody shrubs, which are members of the plant class Gymnospermae (Gymnosperms). Gymnosperms are characterized by having naked seeds in contrast to the Angiosperms which have seeds enclosed in an ovary (Harlow and Harrar 1950). This diverse and extremely valuable group of higher plants is generally considered to consist of three botanical orders under the class Gymnospermae: the Coniferales, the Taxales and the Ginkgoales. Within these orders are eight families, 55 to 65 genera and more than 600 individual species (Rushforth 1987, Vidakovic 1991).
Conifers receive their name from the shape of the fruit or "cones" produced by many species within this group, especially members of the families Araucariaceaeand Pinaceae (order Coniferales). The term "conifer" is also descriptive of the conical crown form which is characteristic of many trees in this class of plants. Other characteristics include the presence of needle-like or scale-like foliage and a preponderance of species with evergreen foliage (exceptions - Larix, Metasequoia and Taxodium). The conifers include the world’s oldest known trees (Pinus longaeva) and the world’s most massive trees (Sequoiadenron giganteum) (See textbox) (Figs 1.1, 1.2).
Figure 1.1 The world’s largest conifer, the
General Sherman Tree, Sequoia - Kings Canyon
National Park, California (USA)
Figure 1.2 Pinus longaeva in California’s White Mountains (USA) are the oldest known trees
Various species of conifers, principally members of the family Pinaceae (e.g. Abies, Larix, Picea, Pinus) are often the dominant forest cover over extensive areas of boreal and temperate forests of the northern hemisphere. Conifer forests, principally Pinus spp, are also the dominant forest cover over much of Mexico and the northern portions of Central America. Extensive forests of Juniperus spp., Cupressus spp. and Pinus spp. dominate semi-arid forests in western North America, Mediterranean Europe and the Near East. In other parts of the Northern Hemisphere, conifers are frequently found in association with broad-leaf trees. In the Southern Hemisphere, conifers tend to have more restrictive natural ranges but are equally varied. Species of the genera Araucaria and Agathis are locally abundant and important. In other areas of the Southern Hemisphere, the genus Podocarpus and several members of the family Cupressaceae (e.g. Australcedrus, Callitris, Widdringtonia) are locally abundant (Fig 1-3).
Many conifers have exceptionally wide natural ranges. Juniperus communis, for example, has a circumpolar distribution and is found across Asia, Europe and North America. Pinus sylvestris is distributed from the British Isles across the European and Asian continents to Siberia, while the natural ranges of Larix laricina, Picea glauca and P. mariana extend across the boreal forests of the North American continent from the Atlantic Ocean to the Pacific Ocean.
Because of their many uses and relative ease of planting, conifers have
been widely established in forest plantations. Many species, such as cupressus
lusitanica, pinus elliottii, p. Radiata, p. Taeda, and p. Patula
have been established over large areas outside of their natural ranges.
The genus pinus is the second only to eucalyptus in terms
of area of plantations established in the tropics (4.49 million ha as of
1990) (fao 1993). Chile and New Zealand each have in excess of 1.5 million
ha of pinus radiata plantations.
The world’s oldest known tree is the bristlecone pine, Pinus longaeva, a species which occurs near the summits of high, arid mountain ranges in eastern California and Nevada, United States. A forest of bristlecone pines near the summit of the White Mountains of the Inyo National Forest, California, contains the Methuselah Tree which has been documented to be at least 4 600 years old. This stand also contains at least 17 more trees in excess of 4 000 years (Menninger 1967).
The world’s most massive living tree is a giant sequoia, Sequoidendron giganteum, known as the General Sherman Tree. This tree is located in a grove of giant sequoias in the Sequoia-Kings Canyon National Park in the Sierra Nevada Mountains of California, United States. This tree has a height of 83.8 meters, a circumference at ground level of 31.3 meters and a trunk volume of 1486.6 m3 *.
Ironically, the world’s oldest and the world’s most massive trees are located within an air line distance of 100 km of each other.
Information obtained from Sequoia-Kings Canyon National Park, USDI, National Park Service, California, United States.
Throughout human history, conifers have provided a wealth of products beneficial
to human society. The wood of many species has been used for structural
lumber, production of paper and related products, fuelwood, posts, poles
and myriad other products. Conifers have also provided a wide range of
beneficial non-wood products including essential oils, resin, fragrant
and attractive foliage, ornamental plants, decorative objects, edible seeds,
flavourings and medicinal products. In many cases, both wood and non-wood
products from conifers have been over-exploited to the point where extensive
damage or loss of forest area has resulted. On the other hand, conifers
have been revered by many human cultures and have been used as both religious
and political symbols. They are also the subject of a rich mythology and
folklore and are well represented in arts.
Figure 1.3 Natural conifer forests:
A. Juniperus procera, Maralal, Kenya,
B. Pinus brutia,Isle of Rhodes, Greece,
C. Araucaria araucana, Conguillio National Park, Chile,
D. Pinus roxburghii, Uttar Pradesh, India