8.1 Climates and Biomes

Explain the relationship between climate and vegetation structure.

The type of native vegetation found in any given area mainly reflects three physical limiting factors: temperature, water, and light. At a local level, other factors may be important too, such as soil types and biological limiting factors like herbivory and nutrient supplies. In mountain ranges, slope steepness, slope aspect (the direction the slope is facing), and microclimates (the distinct climates of restricted areas) also determine the types of plants that will grow.

When viewed from a small-scale perspective, Earth’s land surface is covered by biomes. A biome is an extensive geographic region with relatively uniform vegetation structure. Vegetation structure refers to the type of vegetation that dominates a region, such as closed forest or open grassland. Biomes are the second-largest units in the ecological hierarchy; Only the biosphere is larger (see Section 7.5). Biome classifications are based on vegetation structure, which is determined mostly by climate. Table 8.1 summarizes the terms describing vegetation structure that will be used in this chapter.

biome

An extensive geographic region with relatively uniform vegetation structure.

Table : TABLE 8.1 AT A GLANCE: Vegetation Structure

STRUCTURE

DESCRIPTION

Forest

Dominated by trees with a closed canopy

Woodland

Widely spaced trees with a grass understory

Shrubland

Continuous cover of shrubs

Grassland

Continuous cover of grasses

Scrubland

Widely spaced, drought-adapted shrubs

Desert

Sparse plant cover

Within each biome, plants take on a variety of growth forms, detailed from largest to smallest in Table 8.2. In addition to the names of these plant growth forms, this chapter will use a number of botanical (plant-related) terms that describe characteristics of plant growth and plant adaptations (Table 8.3).

Table : TABLE 8.2 AT A GLANCE: Plant Growth Forms

GROWTH FORM

DESCRIPTION

Tree

Tall, upright woody growth

Liana

Woody, climbing vine

Shrub

Many woody stems

Forb

Low, nonwoody plant other than grass

Epiphyte

Grows on surfaces of trees, not parasitic

Bryophyte

Member of the division that includes mosses
Table : TABLE 8.3 AT A GLANCE: Botanical Terms

TERM

DESCRIPTION

Broad-leaved

Has wide, flat leaves; usually deciduous

Coniferous

Bears cones; usually needle-leaved and evergreen

Deciduous

Loses all leaves in one season, usually winter

Evergreen

Loses leaves gradually so it always has leaves

Herbaceous

Lacking woody tissue

Needle-leaved

Has narrow, needle-like leaves; usually evergreen

Sclerophyllous

Has hard, leathery, and waxy leaves

Woody

Grows rigid trunks and stems

Because of the spatial correspondence between climates and biomes, classifying and categorizing climate types is fundamental to this discussion of biomes. One of the most widely used climate classification systems is the Köppen climate classification system, first published by Wladimir Köppen in 1884. The Köppen system categorizes climates based on the temperature and precipitation characteristics of a region. (Appendix 6 provides further detail on the Köppen climate classification system.)

Köppen climate classification system

(pronounced KUHR-pen) A system used to classify climate types by temperature and precipitation.

Because of the strong correspondence between vegetation structure and climate, the Köppen climate categories were originally based on the type of natural vegetation growing in an area. There are six major Köppen climate groups containing 25 climate zones. The climate zones and Earth’s biomes are mapped in Figure 8.2.

Figure 8.2

GEO-GRAPHIC: Climate zone and biome maps. A comparison of the spatial distributions of (A) Köppen climate zones and (B) biomes shows that the two correspond roughly in space. Extreme events such as droughts and disturbances such as fire can also determine the spatial distribution of vegetation. For this reason, biomes and Köppen climate zones do not overlap precisely.

Biomes can be portrayed graphically by plotting temperature and precipitation. As shown in Figure 8.3, each biome occupies a different climatological space on the graph.

Figure 8.3

Biome and climate diagram. This modified Whittaker diagram portrays the relationship between biomes and climates graphically. Tropical rainforests occupy the climates with the highest precipitation and temperature, represented by the space at the top left. Tundra occupies the climates with the lowest precipitation and temperature, at the lower right, and subtropical desert occupies warm and dry climates, at the lower left.

Animation

Biome and climate diagram

http://qrs.ly/fw44otx

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