The Earth’s Terrestrial Biomes

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Natural Vegetation Natural vegetation is a plant cover that develops with little or no human interference. It is subject to natural forces of modification and destruction, such as storms or fires. Natural vegetation still occurs in some remote areas, such as the arctic and alpine tundra or parts of the wet equatorial rain forests. In contrast, much of the land surface in midlatitudes has been totally affected by human activities, through intensive farming or urbanization.

Structure and Life Form of Plants Plant geographers are often less concerned with individual species and more concerned with the vegetation as a whole. In describing g the vegetation, g p plant g geographers g p refer to the life form of the plants, which emphasizes their physical structure, size, and shape. This method of classifying plants can provide information on the relationship between the species and their environments.

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Terrestrial Ecosystems – The Biomes Terrestrial ecosystems are directly influenced by climate and interact with the soil. At the global scale, the largest recognizable subdivision within terrestrial ecosystems is the biome. biome

Terrestrial Ecosystems – The Biomes There are five principal biomes (which can be subdivided into smaller vegetation units, called formation classes based on plant life forms). The forest biome is dominated by trees, which form a closed or nearly closed canopy. The savanna biome is transitional between forest and grassland. It supports an open cover of trees with grasses and herbs beneath. The grassland biome develops in regions with moderate shortages of soil water.

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Terrestrial Ecosystems – The Biomes The desert biome includes organisms that have adapted to the moderate to severe water shortages that occur for most, if not all, of the year. The tundra biome is limited by cold temperatures - only small plants that grow quickly when temperatures rise above freezing during the short growing season can survive.

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Terrestrial Ecosystems – The Biomes Forest Biome Within the forest biome, there are six major formations: lowlatitude rain forest monsoon forest subtropical evergreen forest midlatitude deciduous forest needleleaf forest sclerophyll forest

Terrestrial Ecosystems – The Biomes Low-Latitude Rain Forest Low-latitude rain forest, found in the equatorial and tropical latitude zones, consists of tall, closely set trees. The crowns of the trees are generally arranged in two or three layers.

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Terrestrial Ecosystems – The Biomes Low-Latitude Rain Forest Low-latitude rain forest, found in the equatorial and tropical latitude zones, consists of tall, closely set trees. The crowns of the trees are generally arranged in two or three layers.

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Terrestrial Ecosystems – The Biomes Monsoon Forest The monsoon forest of the tropical latitude zone differs from the tropical rain forest because it is deciduous. Most of the monsoon forest trees shed their leaves during the dry season as a result of moisture stress. The monsoon forest is usually open, with patches of shrubs and grasses interspersed among the trees.

Terrestrial Ecosystems – The Biomes Subtropical Evergreen Forest The subtropical evergreen forest is found in regions of moist subtropical climate, where winters are mild and there is ample rainfall throughout the year year. There are two forms of this forest, broadleaf and needleleaf.

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Terrestrial Ecosystems – The Biomes Midlatitude Deciduous Forest The midlatitude deciduous forest is the native forest type of western Europe, eastern Asia, and eastern North America. It is dominated by tall, tall broadleaf trees that provide a continuous and dense canopy in summer but shed their leaves completely in the winter.

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Terrestrial Ecosystems – The Biomes Needleleaf Forest Needleleaf forest refers to a forest composed mainly of conifer trees with comparatively short branches and small, narrow, needle-like leaves. Most are evergreen, retaining their needles for several years before shedding them. When the needleleaf forest is dense, it casts a continuous and deep shade; lower layers of vegetation are sparse, except perhaps for a thick carpet of mosses. Species diversity is generally low, with large tracts of the needleleaf forest overstorey consisting almost entirely of only one or two tree species.

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Terrestrial Ecosystems – The Biomes Sclerophyll Forest The native vegetation of the Mediterranean climate is adapted to survival through the long summer drought. Shrubs and trees that can survive these annual droughts are characteristically equipped with small, tough leaves that resist water loss through transpiration; this is the characteristic leaf form of sclerophyll vegetation. Sclerophyllous leaves are also considered to provide an adaptive advantage in areas of high light intensity and nitrogen deficient soils, which are characteristic of the Xeralfs of this region.

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Terrestrial Ecosystems – The Biomes Savanna Biome The savanna biome is usually associated with the tropical wet-dry climate of Africa and South America - has a distinct dry season during the low-sun period when at least one month receives less than 60 mm of rain. In most of the savanna regions regions, mean annual temperature never falls below 24 °C, with maximum temperatures normally occurring at the end of the wet season under cloudless skies. Precipitation varies from about 250 mm in drier areas to 1,500 mm or more, but water shortages develop during the dry season throughout this biome. Regional differences in precipitation are reflected in the diversity of the savanna biome, which includes vegetation formation classes ranging from woodland in the moister areas to grassland.

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Terrestrial Ecosystems – The Biomes Grassland Biome The grassland biome includes two major formation classes — tall-grass prairie and short-grass prairie or steppe; between these lies a broad transition known as mixed prairie. The grasslands are concentrated mainly in North America and Eurasia. In the southern hemisphere they are represented by the Pampas of Argentina and Uruguay and the veldt region of South Africa. Grasslands are found in midlatitude and subtropical zones with pronounced winter and summer seasons.

Terrestrial Ecosystems – The Biomes Desert Biome The desert biome accounts for about one-third of the Earth’s land surface. This vast region includes several formation classes that are transitional between grassland and savanna biomes and the arid desert. Desert climates are characterized by the scarce and variable nature of their precipitation.

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Terrestrial Ecosystems – The Biomes Desert Biome In hot regions, effective precipitation can be further reduced by high evaporation rates, and some classifications recognize extremely arid arid, arid arid, or semi semi-arid arid deserts on this basis. In extreme deserts, precipitation is so low that only the hardiest plants and animals can survive, but even in semiarid regions, moisture surplus is small and available for only a brief part of the year.

Terrestrial Ecosystems – The Biomes Tundra Biome In the Arctic tundra, plants grow during the long days of the brief summer and then endure the long (or continuous) darkness of winter. In the summer months months, air temperature rises above freezing freezing, and a shallow layer of ground ice thaws at the surface. Across much of the tundra climate region, the mean temperature of the warmest month is generally about 10 °C, but winters are long and cold with temperatures commonly falling to between -30 and -40 °C. The summer warmth is not sufficient to thaw the permafrost below a general depth of about 1 m, and the frozen subsoil restricts meltwater drainage.

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Terrestrial Ecosystems – The Biomes Climatic Gradients and Vegetation Types Climate is an important control of vegetation, especially at the global scale represented by the major formation classes. general classification schemes have been devised on this Several g basis. In most cases, global vegetation patterns are examined in terms of temperature and precipitation gradients, with the dominant growth forms, such as trees, shrubs, and grasses, shown in relation to these changing climatic parameters. As vegetation adjusts to climate changes with latitude or longitude, corresponding transformations also occur in soils.

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Terrestrial Ecosystems – The Biomes Altitude Zones of Vegetation Temperature decreases and precipitation increases with y change g in the elevation, and this is reflected in a systematic vegetation cover. The changes that occur with altitude are similar to those related to latitude, and many of the vegetation forms seen in the major biomes recur in the bands of vegetation associated with mountain areas.

Terrestrial Ecosystems – The Biomes Altitude Zones of Vegetation Because corresponding trends were noted between plants p of life zones was p proposed. p and animals, the concept The life zones that occur along geographically restricted elevational gradients are therefore analogous to the biomes that have developed in response to environmental gradients determined by latitude and longitude.

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Terrestrial Ecosystems – The Biomes Ecozones The term ecozone has recently come into use, which similarly is differentiated on the basis of distinctive plants and animals in association with a general land form type associated with specific climate conditions. The National Ecological Framework for Canada (Ecological Stratification Working Group 1996) distinguishes 15 terrestrial and five marine ecozones. Ecozones are part of a hierarchical classification with progressively finer details incorporated at the ecoregion and ecodistrict levels; over 200 ecoregions are listed in Canada.

Terrestrial Ecosystems – The Biomes Ecozones of Canada Arctic Cordillera Ecozone Northern Arctic Ecozone Southern Arctic Ecozone Atlantic Maritime Ecozone Boreal Cordillera Ecozone Boreal Plains Ecozone Boreal Shield Ecozone

Hudson Plains Ecozone Prairie Ecozone Mixed-wood Mixed wood Plains Ecozone Montane Cordillera Ecozone Pacific Maritime Ecozone Taiga Cordillera Ecozone Taiga Plains Ecozone Taiga Shield Ecozone

Terrestrial Ecozones of Canada

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