Biosphere 2 CenterExercise 1: The Terrestrial Biomes: Identification of Major Controls over Structure and Distribution
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Your Questions
BackgroundCharacterization of Climate ControlsThe distribution of vegetation is controlled by several factors (regional climate, topography, soil parent material, time, and organisms). However, at the broadest scale, the scale of biomes, global climate patterns are the primary factor determining the structure and distribution of vegetation. We will discuss the role of the other 4 factors in subsequent modules on the local biome (Module Two) and abiotic factors (Section C). Aspects of climate that exert strong control over vegetation are temperature, precipitation, humidity, solar radiation, and wind. Each of these affect plant physiology directly (through effects on photosynthesis and respiration) or indirectly (through effects on nutrient availability via decomposition, and soil development). The simplest schemes relating biome distribution to climate evaluate annual or monthly mean temperature and precipitation. In this exercise, we will use a system devised by Henrick Walter to plot monthly mean temperature and precipitation on the same graph in a way that illustrates both (1) seasonality of thermal regime and (2) seasonality of moisture availability. In this way, these climate diagrams depict key (but not all) features of climate that control the structure and distribution of biomes. Information on the features of a Walter diagram is in the Lieth et al. CD, or will available as a handout. Characterization of Vegetation StructureAt the local scale, the structure of vegetation is usually described in terms of dominant plant species that are commonly found together as a plant community or association. At the biome level, however, this approach is problematic because species that characterize a biome on one continent are generally not those that typify the biome on another continent (or even in different regions of the same continent). Rather, we find that species of similar lifeform or plant functional type describe a biome. For example, the mid-latitude forests of eastern US, eastern China, and western Europe are primarily dominated by Winter-Deciduous Broadleafed Trees. At the simplest level, biomes are first distinguished by the dominance and density of trees, shrubs, vs. grasses:
Then, functional aspects of vegetation are included in the definition:
And finally, zonal (latitudinal/climatic) distinctions are made to imply other lifeform features:
Hence,
Often, these names are shortened because certain aspects are implied: e.g., Temperate Deciduous Forest and Subtropical Desert. However, be careful with what is implied are all Boreal Conifer Forests evergreen? Are all Subtropical Deserts shrublands? Your AssignmentYour assignment is to build Walter climate diagrams for the major biomes (Task A) and to evaluate these to understand why each biome typically has a given vegetation structure and distribution (Task B). Task A Climate Diagrams:
Task B Climatic Controls over Biome-level Vegetation Structure:
Evaluation:
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