Pinaceae

Although essentially restricted to the northern hemisphere, the Pinaceae form the largest conifer family with approximately 200 species (about 35% of all conifers); 80-100 of the species, depending on one's taxonomic perspective, are pines (Pinus; Richardson 1998). There are nine other genera; the next largest are the true firs (Abies) and spruces (Picea), with hemlocks (Tsuga) and larches (Larix) following. Douglas firs (Pseudotsuga), true cedars (Cedrus), golden larches (Pseudolarix), Cathaya, and Keteleeria each has only a few or one species (Appendix 1). The genera have been put into either three or four subfamilies over the years (e.g., Melchior and Werdermann 1954-64, Frankis 1989). Four subfamilies are most commonly recognized today. Phylogenetic studies, using molecular analyses based on chloroplast DNA and supported by fossil evidence, generally indicate that the Abietinoideae—Abies, Cedrus, Keteleeria, Pseudolarix, and Tsuga (including Nothotsuga)—are the basal group that appeared during the Jurassic. The Pinoideae (Pinus) and Piceoideae (Picea) follow during the early Cretaceous, and the Laricoideae (Larix, Pseudotsuga, and Cathaya) in the late Cretaceous (Labandeira et al. 2001).

Leaves of all Pinaceae contain terpenoid resin but in some genera resin may be produced only traumatically in the trunk of the tree (e.g., Cedrus, Pseudotsuga, Pseudolarix, and Tsuga). Wu and Hu (1997) thought the distribution of resin ducts in stems and leaves such a "striking morphological character" that it should be used in evaluating relationships of genera in Pinaceae. They thus divided the genera into three groups based on the presence or absence of resin ducts in the wood (Chapter 3). The importance of differences in the kind of secretory structure and quantity of resin produced is elucidated in the contexts of the defensive properties of resin in Chapter 5, and human use in Chapters 7-10.

Paleobotanists such as Miller (1976, 1977) thought that the early evolution of Pinaceae was centered on Pinus. Miller (pers. comm.) has concluded more recently, however, that there are three evolving lines within the Pinaceae and not a central pine group. Pinus today is not only the largest genus in the family but is particularly noted for its great ecological diversity and adaptability. Pines occupy a wide range of habitats from the arid plateaus of western North America, the mountains of Mexico and Central America, to the tropical lowlands of the Caribbean. They also cover large areas across Eurasia into the mountains and tropical lowlands of eastern Asia (Mirov 1967, Richardson 1998). Furthermore, pines are the most widely planted exotic trees because of their adaptability and their large-scale use for timber, paper, and resin. Thus they are found out of their native range in South America, Africa, and Australasia.

Despite fragmentation of large pine forests during the past few hundred years through land clearance and pest introduction, pines continue to be conspicuous components of forests in many parts of the northern hemisphere. For example, Pinus sylvestris (Plate 1), known as Scots or Scotch pine in England and common pine on the European continent, is a complex of many intergrading varieties or subspecies with a range encompassing more than 10,800 km2 (Nikolov and Helmisaari 1992), the widest distribution of any pine. It spans a wide range of environments from the Scottish highlands along the Atlantic to the Pacific coast of eastern Siberia to northwestern Asia, occurring with most of the boreal tree species of Europe and Asia; it also has scattered populations throughout the Mediterranean region (Mirov 1967). The resin has been used by Europeans throughout history (Chapter 7).

Ponderosa pine (Pinus ponderosa) is the widest ranging pine in North America. A drought-tolerant species, it persists in dry environments. Two varieties are recognized, partly related to the difference in the drought seasons in California and the Pacific Northwest versus those in the southwestern United States. In the driest environments, ponderosa pine forms savannas, but in more mesic environments it occurs in mixed stands with various other conifers. For example, it commonly occurs with Douglas fir (Pseudotsuga menziesii) in the Rocky Mountains and with Abies grandis, Calocedrus decurrens, and Pinus lambertiana in the Sierra Nevada. Ponderosa pine and Douglas fir are the two most important western North American timber trees, and their resins have been intensively studied for the protection they provide to valuable timber (Chapter 5).

Lodgepole pine (Pinus contorta) is another pine widely distributed across western North America, with four varieties. Some varieties have cones that are more serotinous (closed, often aided by the gluing effect of resin, until opening because of high temperatures such as those caused by fire) than others. This characteristic is partly responsible for the various ecological roles played by lodgepole pines in diverse ecosystems. In the Rocky Mountains, P. contorta var. latifolia is primarily a pioneer or early forest successional tree in the Picea engelmannii-Abies lasiocarpa forest zone (Plate 3), where infrequent but high-intensity fires occur. Those trees with serotinous cones have little or no seed dispersal in the absence of fire but typically generate dense, even-aged stands following fire. There are other areas, however, where lodge-pole pine is the only tree species that can reproduce with or without fire, and it can become dominant in both early and late forest succession. Most of the late-succession or mature forest stands have lodgepole pines with nonseroti-nous cones, allowing regeneration after disturbances other than fire. The suc-cessional status of resin-producing conifers such as Pinus contorta var. lati-folia has been shown to be related to the characteristics of the resin defense and long-term health of the forest (Chapter 5).

Pines of the coastal plain of southeastern North America (e.g., Pinus elliottii, Figure 7-2; P. palustris; and P. taeda), occurring in widespread savannas, and those around the rim of the Mediterranean Basin (e.g., P. halepensis) have been some of the most heavily used for resin. Today, however, pines native to the Asian tropics (e.g., P. kesiya, P. massoniana, and P. merkusii) are among the most productive for the naval stores industry (Chapter 7). Numerous pines also cover midelevations of mountains in Mexico (e.g., P. mon-tezumae, a variable complex of subspecies; Figure 7-6) into Central America

(e.g., P. oocarpa) and much of the Caribbean (e.g., the P. caribaea complex). These pines have a long history of human use.

In many cases, species of different genera of Pinaceae either codominate or are prominent components over vast expanses of boreal and high-elevation forests in mountains. It is assumed that resins probably provide defensive properties for these important forest trees, some of which have been heavily used by humans (Chapter 5). Examples include the boreal spruce-fir forests across North America (with Picea glauca and Abies balsamea, Plate 2 and Figure 2-1), the subalpine spruce-fir zone in the Rocky Mountains (dominated by P. engelmannii and A. lasiocarpa; Plate 3), and the ponderosa pine-Douglas fir zone in the Rocky Mountains. In the Sierra Nevada, Douglas fir occurs in a zone with Pinus jeffreyi (Plate 4), a close relative of P. ponderosa. Large areas in the arid southwestern United States and northern Mexico have a low open forest or woodland characterized by mixed species of pinyon pine (e.g., P. edulis and P. monophylla) and juniper (e.g., Juniperus monosperma and J. scopulorum, Plate 5). The resins from these trees have long been used by Native Americans (Chapter 10), and pinyon pines were once tapped for their resin on a small scale. Desert junipers also could be used as a basis for small cedarwood oil industries (Chapter 7).

The true cedars (Cedrus) consist of only three or four species that occur naturally in the western Mediterranean in North Africa to the western Hima-

Figure 2-1. Abies balsamea, balsam fir, an important balsam-producing tree of North American boreal forests (see also Plate 2).

laya. Differences between the species are slight, and Melchior and Werdermann (1954-64) considered their nearest relatives to be the deciduous larches (Larix). The name Cedrus is from kedros, used by the ancient Greeks to designate a resinous tree. General use of this name by the Greeks may have led to trees other than Cedrus being called cedars, as discussed under Cupressa-ceae. The leaves of true cedars are resinous, and resin exudes from young cones (Plate 6). Resin that accumulates in the heartwood gives the wood its fragrant odor and is distilled as cedarwood oil (Chapter 7). Cedars of Lebanon (C. libani) are highly resistant to pests and also were the most massive trees known to the ancient Israelites, who used them to build the temple and palace of Solomon. Other ancient potentates exploited C. libani so intensively that only small remnant populations remain.

Larix, a cool northern hemisphere tree, is the most abundant deciduous conifer and occurs in some of the most extreme environments, above the northern and elevational limits of most conifer growth (Gower and Richards 1990). The American larch or tamarack (L. laricina), a tree of the cooler northern hemisphere, produces an economically valuable resin, as does the European larch (L. decidua), that is similar to Canada balsam from Abies balsamea (Chapter 8). Pseudolarix, with only one species, P. amabilis (Plate 7), is indigenous to a very limited area in the coastal mountains of eastern China. Considered to be closely related to Larix by Melchior and Werdermann (1954-64), Pseudolarix is also deciduous. Before dropping, the leaves change to a rich golden yellow, hence its common name, golden larch. On the other hand, Frankis (1989) considered Pseudolarix more closely related to Abies and Cedrus than to Larix. Despite its restricted distribution today, Pseudolarix fossils indicate the genus was widely distributed in mid- to high latitudes of Asia, North America, and Europe during the Cretaceous and Tertiary (Le Page and Basinger 1995). Pseudolarix resin forms amber and may be related to the producer of Baltic amber because it is one of the rare conifers with resin that contains succinic acid (Chapter 4).

Members of the North American and Asiatic genus Tsuga are called hemlock in North America and hemlock-spruce in the British Isles. Despite the name, they are not relatives of the poison hemlock (Conium maculatum, Api-aceae, or Umbelliferae) used by the ancient Greeks to poison Socrates among others. Species of Tsuga are either small or large trees in northern coastal or subalpine forests. Hemlocks are considered by Melchior and Werdermann

(1954-64) to be close kin of firs (Abies) and spruces (Picea) and often are confused with them. Hemlock leaves are resinous, but like Abies, Cedrus, and Pseudolarix, Tsuga only produces resin in the wood following injury (Chapter 3).

Since species of Pinaceae tend to occur in high density, dominating forests that cover vast areas, there are probably more individuals of these northern temperate zone dwellers than other resin-producing trees; however, resin-producing angiosperm trees of the tropics have a far greater diversity of taxa.

Was this article helpful?

0 0

Post a comment