Temperate and Mediterranean Forests

T TEMPERATE AND MEDITERRANEAN FORESTS Contents Northern Coniferous Forests Southern Coniferous Forests Subalpine and Boreal Forests Temperate Broadleaved Deciduous Forest Mediterranean Forest Ecosystems Northern Coniferous Forests distinct zones or bands of vegetation. A given vegetation zone tends to be found at higher eleva- C D B Hawkins, University of Northern British tions on drier sites compared to wetter, on south Columbia, Prince George, BC, Canada aspects compared to north, and at southern latitudes & 2004, Elsevier Ltd. All Rights Reserved. compared to northern. Low to mid elevation northern coniferous forests are rich in species diversity while the upper northern coniferous forest is less Introduction complex. The upper northern coniferous forest and lower subalpine have similar species composition The northern coniferous forest or temperate needle- and they are transitional to one another. leaf forest is restricted, essentially, to western North America. It also occurs in small elevational bands on mountain ranges of Europe, Asia, eastern North Distribution America, Mexico, Mesoamerica, and the coastal Western North America plains of the southeastern United States. The northern coniferous forest is conventionally a synonym for the The northern coniferous forest includes the central boreal forest. Depending on the authority, the north- plateaux of British Columbia and isolated Intermoun- ern coniferous forest can be considered a southern tain, mountain ranges between the Cascade–Sierra offshoot of the boreal forest on the Rocky, Coast, ranges as well as the Rocky Mountains. In the Rocky Cascade, Appalachian, Alps, Carpathians, Urals, and Mountains, it extends from the southern Yukon to Himalaya mountain ranges, as well as mountains in south central New Mexico. Some consider it to northern China, Korea, and Japan, or it can be include the Madrean (Mexican) section of the Rocky restricted to montane coniferous forest. Pinaceae Mountains and the Coastal, Cascade, and Sierra (pines, spruces, firs, and larches) are the major Nevada ranges while others consider the Madrean northern coniferous forest family and account for its and Sierra Nevada to be part of the southern economic importance. There are also mixed conifer- coniferous forest. The Sierra Nevada is excluded ous–deciduous stands in the western North American from the northern coniferous forest as: (1) true northern coniferous forest with trembling aspen coniferous forests are relatively rare in the northern (Populus tremuloides) and paper birch (Betula papyri- hemisphere south of 401 N latitude; and (2) giant fera). Compared to the boreal forest, the northern sequoias (Sequoiadendron giganteum) are present in coniferous forest is warmer and more productive: the Sierra Nevada, which some authors consider to be mature trees Z25 m compared to r23 m. This article members of the subtropical mountain system. focuses on western North America because compared to other areas of the world, there are still large areas Rocky Mountains The Rocky Mountain (19–651 N of natural northern coniferous forest. latitude) northern coniferous forest has a subalpine Generally mountains become wetter, colder, and forest above, characterized by subalpine fir (Abies windier with increasing elevation. This results in lasiocarpa), white or Engelmann spruce (Picea glauca, 1378 TEMPERATE AND MEDITERRANEAN FORESTS / Northern Coniferous Forests P. engelmannii), and depending on latitude other rising to 1800 m in elevation above Rocky Mountain conifer species. Species diversity increases moving (western) juniper–ponderosa pine (Juniperus scopu- south from the boreal forest. lorum–Pinus ponderosa) woodlands from 800 to In the Boreal Rocky Mountains (53–651 N lati- 1500 m. It is dominated by cedar (Thuja plicata), tude), the northern coniferous forest is above the western hemlock (Tsuga heterophylla), grand fir boreal forest dominated by aspen, balsam fir (Abies (Abies grandis), and Douglas-fir on the western balsamea), white spruce, and jackpine (Pinus bank- slopes. Western white pine (P. monticola)and siana), with black spruce (Picea mariana) and western larch (Larix occidentalis) are common on tamarack (Larix laricina) in wetter areas (Figure 1). mesic and drier sites as are white–Engelmann The northern coniferous forest is not complex having (interior) spruce hybrids on wetter ecosystems both boreal and subalpine species plus lodgepole (Figure 2). This is the most productive complex of pine (Pinus contorta var. latifolia). White spruce the northern coniferous forest with site indices at 100 dominates at low and mid elevations. Common years (SI100) of 40 m for spruce and 38 m for white broadleaf trees are birch hybrids (Betula spp.), aspen, pine and Douglas-fir. The eastern slopes are less and balsam poplar (Populus balsamifera). The diverse and not as productive. Aspen and paper birch northern limit is marked by the absence of lodgepole are the dominant broadleaf species and are usually pine and subalpine fir. The southern boundary is the found in seral mixed species stands. The subalpine transition between the Peace and Fraser River forest, in addition to Abies and Picea, has whitebark drainages. This roughly corresponds to Engelmann pine (Pinus albicaulis), limber pine (P. flexilis), spruce and Douglas-fir’s (Pseudotsuga menziesii var. mountain hemlock (Tsuga mertensiana), and sub- glauca) northern distribution limit. alpine larch (Larix lyallii). The Central sector is The Central Rocky Mountain (45–531 N latitude) defined by the distribution of whitebark pine. northern coniferous forest is a rich productive forest Ponderosa pine parklands in the Southern Rocky Mountains (33–451 N latitude) are below two northern coniferous forest zones. The lower is a Douglas-fir forest with white fir (Abies concolor) and Colorado blue spruce (Picea pungens) and the upper is a lodgepole pine forest. Aspen is the primary broadleaf species. The subalpine, in addition to spruce and fir, has bristlecone pine (Pinus aristata). The Madrean (19–351 N latitude) northern coniferous forest has complex topography and flora. About half of the world’s pine species occur in Mexico. Fir forests (Abies concolor, A. religiosa, and A. guatemalensis) with codominant Pinus, Quercus, Pseudotsuga, and Cupressus species usually occur below Pinus hartwegii forests. Douglas-fir associated with P. flexilis and Abies concolor occurs below the fir-dominated forests. A ponderosa pine parkland is Figure 1 Boreal Rocky Mountain northern coniferous forest Figure 2 Central Rocky Mountain northern coniferous forest at rising above the boreal forest at 591 N. 541 N; mixed wood stands dominate recent cutovers. TEMPERATE AND MEDITERRANEAN FORESTS / Northern Coniferous Forests 1379 below the Douglas-fir forest and above a mixed pine– A. religiosa continue southwards from Mexico and oak (P. edulis, P. cembroides–Quercus arizonica, dominate the high mountain, perhumid forests of Q. gambelii) chaparral in southern regions and a northern Mesoamerica. pinyon–juniper (P. edulis–Juniperus spp.) pygmy conifer woodland in northern regions. Coast and Cascade Mountains In the Coast and Cascade Ranges (43–49.51 N latitude), the northern Plateau The Nechako and Fraser Plateaux comprise coniferous forest starts immediately above the much of central British Columbia. The western temperate coniferous forest. Along the western portions are in the rainshadow of the Coast slope of the Cascades and in the Coast Range, the Mountains and are less productive than more east- northern coniferous forest has a lower amabilis fir erly portions (Figure 3). Rain shadow areas are (A. amabilis) zone and an upper mountain hemlock dominated by lodgepole pine with interior spruce zone. These forests are nearly as productive as those occurring on rich, moist soils. The primary species, of the Central Rocky Mountains. The northern moving east away from the rainshadow, are interior coniferous forest consists of a ponderosa pine forest spruce and subalpine fir with Douglas-fir occurring often with Douglas-fir, and a mesic Abies or on drier sites. Lodgepole pine is a seral species on mountain hemlock forest above 1500 m, but below much of the plateau but it may be the climax species the subalpine on the eastern Cascade slopes. of the rainshadow region. Other Northern Coniferous Forests Intermountain From 371 to 451 N latitude, between Appalachians Above the elevational limit of the the Rocky Mountains and the Cascade–Sierra com- deciduous forest along the Appalachian chain plex are mountain chains, isolated like islands, in an are dense, even-aged, red spruce (Picea rubens) otherwise very arid, high elevation environment. stands. Abies increases in abundance with elevation Above a pinyon–juniper woodland from 1500 to (A. balsamea in the north, A. fraseri in the south). 2500 m is the northern coniferous forest. A white fir Pure subalpine stands can form if the mountain has montane forest with lodgepole pine, ponderosa pine, sufficient elevation. In mixed spruce–fir stands, fir is and Douglas-fir on mesic sites characterizes the shorter-lived and faster-growing than spruce. The region. The subalpine is dominated by limber pine, Appalachian northern coniferous forest has been subalpine fir, and the intermountain bristlecone pine severely impacted by acid rain, woolly aphid, and (Pinus longaeva). On very arid ranges, the subalpine unknown mortality agents over the past 25 years. is absent and pinyon pine covers the slope. Southeastern USA Pre-European settlement pine Mesoamerica Low mountain pine forests

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