Vegetation zones are large geographic areas defined by the distinct plant communities that grow there. These zones, often called biomes, represent a grouping of plants and ecosystems that share adaptations to specific environmental conditions. The types of plants that survive in a zone reflect adjustment to the available resources, particularly climate. Understanding these zones provides insight into how the physical environment shapes life on Earth.
The Primary Factors That Shape Zones
The most influential determinant of a vegetation zone is climate, primarily the interaction between temperature and moisture availability. Plants have specific tolerances for heat and cold, and their growth is directly tied to the amount of water they can access annually. High temperatures combined with high annual precipitation, such as near the equator, support dense, continuous plant cover like tropical rainforests. Conversely, areas with extremely low precipitation, regardless of temperature, give rise to desert vegetation adapted to water scarcity.
Temperature and moisture distribution are closely linked to latitude, but other factors modify these climatic effects on a local scale. Altitude significantly affects temperature, causing it to drop about 6.5 degrees Celsius for every 1,000 meters of elevation gained, leading to distinct vegetation belts on mountainsides. Topography, the physical shape of the land, influences microclimates; for example, sun-facing slopes receive more heat and can be drier than shaded slopes. Edaphic factors, or soil characteristics, also play a direct role, as nutrient-rich, well-drained soil supports more luxuriant plant growth than thin, rocky, or waterlogged soil.
How Vegetation Zones Are Classified
Scientists categorize vegetation zones primarily by the visible characteristics, or physiognomy, of the dominant plant life rather than by the specific species present. This classification focuses on the structure and life-form of the plants, such as whether the area is dominated by trees, shrubs, or grasses. Key characteristics include the density of the plant cover, like a closed-canopy forest versus a sparse savanna, and the foliage type, such as broadleaf, needleleaf, or sclerophyllous (hard-leaved) plants.
This structural approach allows for the grouping of geographically distant regions that share similar plant forms because they have adapted to similar environmental pressures. For instance, classification distinguishes between a closed forest, where canopies overlap, and an open woodland, where trees are scattered. It is also important to distinguish between natural vegetation, which develops without human interference, and cultural vegetation, which has been modified by human activities like agriculture or logging.
Major Global Examples
Forest zones represent regions with sufficient moisture to support a continuous cover of trees, subdivided based on temperature regimes. Tropical forests, located near the equator, receive high temperatures and rainfall year-round, resulting in the greatest biodiversity and layered canopy structure. Temperate forests, found in mid-latitudes, experience four distinct seasons and are characterized by deciduous trees that shed their broad leaves in the cooler months. Further north, or at high elevations, Boreal forests (taiga) are dominated by cold-tolerant, evergreen needleleaf trees adapted to long, cold winters and short growing seasons.
Grasslands, such as the prairies of North America or the steppes of Eurasia, are found in areas with moderate rainfall, insufficient to support forest growth but too high for a desert environment. These zones are characterized by deep-rooted grasses and herbaceous plants that survive seasonal droughts and grazing pressure.
Deserts form where precipitation is extremely low, typically less than 25 centimeters per year. This leads to sparse vegetation like succulents and xerophytic shrubs that have evolved specialized water-storing or conserving mechanisms.
The Tundra, located in the high latitudes of the Northern Hemisphere, is defined by permanently frozen subsoil, or permafrost. This restricts plant growth to shallow-rooted mosses, lichens, and dwarf shrubs that survive the harsh, cold conditions.