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8.2: Conifers

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    8.2 Conifers (Phylum Pinophyta)

    Conifers are the most diverse group of gymnosperms, with 629 species worldwide (Christenhusz and Byng, 2016). A large number of conifer species are native to the Northern Hemisphere where they are an important part of native ecosystems, providing forest structure with many organisms depending on them for survival. The majority of conifer species are trees with secondary growth (wood formation) and are evergreen, not shedding their leaves seasonally. Leaves on most species are adapted to cold climates and snowy conditions by growing in a needle-like shape, which prevents snow from accumulating on the tree and eventually breaking it. Instead, the snow falls through the needles and releases the pressure caused by its weight. Another advantage of the needle-like leaf shape is resistance to desiccation in the cold dry winter. All species of conifers are wind pollinated, with some species having male and female plants (dioecious), while others have male and female cones on the same tree (monoecious).

    There are several economically important species of conifers such as pines, cedars, and junipers, which are used for lumber and paper making. Conifers are the main source of raw material for paper products in North America, with numerous species grown in timber lots and constituting a big part of the world’s economy.

    Culturally, many species of conifers are important and are used during the holidays for decorations or as part of celebrations. For example, several species of Christmas trees are grown on tree farms, and pine cones and juniper foliage are used for wreaths and other seasonal decorations (Figure \(\PageIndex{1}\)). Another example of how conifer species are used by people is the harvesting of juniper berries to make gin. The berries are female cones, not real fruits, that are used to flavor the alcoholic beverage. The seeds of two Araucaria species are also eaten in Chile and Australia by indigenous peoples.

    Christmas trees.jpg
    Figure \(\PageIndex{1}\): Washington Christmas tree farm. A) Holiday ornaments, and B) Field of Christmas with trees. By Washington State Department of Agriculture is licensed under CC BY-NC 2.0 via Flickr.

    Pine trees are the most iconic group of conifers (Figure \(\PageIndex{2}\)). They are considered by many as the most important genus of trees, as they have been used extensively by humans and their range of distribution occupies a vast area that extends from subtropical areas to subarctic zones. Pine trees grow in the coastal plains of Florida, mid-elevation forests in Mexico, and the boreal forests of Canada (Richardson et al., 2007). Pine “nuts,” which are pine seeds, are very nutritious and are harvested from 29 species of pine trees in different parts of the world, including most of the Mediterranean, Asia, and the Middle East (Awan and Pettenella, 2017), as well as in the Southwestern United States.

    White pine by DutraElliott.jpg
    Figure \(\PageIndex{2}\): White pine (Pinus strobus) native to the Eastern United States. A) Needle like leaves, B) Female cone, and C) Four year old seedling. By DutraElliott is licensed under CC BY-NC-SA 4.0 via Flickr.

    Redwood trees, Sequoia sempervirens, and Sequoiadendron giganteum, are important species in the conifer group in California (Figure \(\PageIndex{3}\)). These trees are the tallest trees on Earth and can reach up to 110 meters (330 feet) in height and 11 meters (33 feet) in diameter. They can also live up to 2,200 years (Watson, 1993). These trees depend on humidity carried by fog for survival and can absorb water directly through their leaves (Burgess and. Dawson, 2004). When fog or light rain occurs, the xylem reverses its direction, absorbing water directly from the leaves and transporting it to other places in the plant such as stems and sometimes to the roots (Burgess and Dawson, 2004). This impressive mechanism is important for the survival of the California redwoods because during the summer months when droughts are common, fog coming from the ocean is still commonly present (Limm et al., 2009).

    Figure \(\PageIndex{3}\): Sequoia sempervirens in the Big Basin Redwoods State Park, California. By Allie_Caulfield, CC BY 2.0, via Wikicommons.

    Douglas fir (Pseudotsuga menziesii) is a conifer native to the Pacific Northwest (Oregon, Washington, and British Columbia). It has been used extensively by native peoples, who eat the seeds, harvest and consume crystallized sugar from the branches at certain times of the year, and use the sap for medicine. This species has been logged for over 160 years (late 1800s to today) in the Pacific Northwest, and is one of the most important US timber exports (Cubbage et al., 2020; Walter and Maguire, 2004). Its wood is used to make poles, plywood, and railroad ties, among many other things. This tree can live up to 1,300 years and it is an integral part of the ecosystem where it is native (Figure \(\PageIndex{4}\)). Several mammal and bird species depend on its seeds as a source of food and the structure of the forest created by these tall trees allows a high diversity of plant and animal species in these areas.

    Douglas fir by DutraElliott.jpg
    Figure \(\PageIndex{4}\): Pacific NorthWest Douglas fir (Pseudotsuga menziesii). By DutraElliott is licensed under CC BY-NC-SA 4.0 via Flickr.

    There are no native gymnosperms in Hawai`i, but conifers can be found in different parts of the islands as introduced species. Several conifer species were introduced in experiment plots. In the 1920s and 1930s, approximately 15 million trees were planted by different organizations as an experiment to reforest degraded areas (Woodcock, 2003). If you go hiking in a forest reserve, you will likely see stands of these species in their original plots as well as naturalized species that escaped cultivation. The following are some of the species that were planted in O‘ahu: Sugi (Cryptomeria japonica; 499,000 trees), Monterey cypress (Cupressus macrocarpa; 216,000 trees), maritime pine (Pinus pinaster; 173,000 trees), redwood (Sequoia sempervirens; 130,000 trees), Monterey pine (Pinus radiata; 121,000 trees) and several Araucaria species, including Cook’s pine (Woodcock, 2003). Araucarias are native to the Southern hemisphere and they eventually became naturalized in Hawai‘i after being introduced as part of these experimental plots. Now these areas have trees growing and producing seedlings that compete with native species (Figure \(\PageIndex{5}\)).

    Araucaria by DutraElliott.jpg
    Figure \(\PageIndex{5}\): Araucaria experimental plot on the windward side of O‘ahu. A) Female cone, B) Cone dispersing seeds and C) Araucaria mature trees. By DutraElliott is licensed under CC BY-NC-SA 4.0 via Flickr.

    This page titled 8.2: Conifers is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Daniela Dutra Elliott & Paula Mejia Velasquez.

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