GEO 200: Physical Geography

GEO 200: Physical Geography Terrestrial Biota (1 of 2)

Geographical questions • What is the range of a species or group of species? • What are species or groups of species distributed as they are? • What is the significance of the distribution pattern? Terrestrial Biota

Natural distributions • Four conditions determine the natural distribution of any species or group of organisms: • Evolutionary development • Migration/dispersal • Reproductive success • Extinction Terrestrial Biota

Evolutionary development • According to the Darwinian theory of natural selection, the origin of any species is a normal process of descent, with modification, from parent forms. • Origin of species or genus can have either: • A very localized beginning • Similar evolutionary development at several scattered localities. Terrestrial Biota

Terrestrial Biota

Migration and dispersal • Movement of organisms can have • Active mechanisms • Passive mechanisms • Passive mechanism particularly influential in seed stage, through wind, water, and animals. • The contemporary distribution pattern of many organisms is often the result of natural migration or dispersal from an original center(s) of development. • Examples are the cattle egret and coconut palm. Terrestrial Biota

Reproductive success • There are a number of reasons can cause poor reproductive success, among them: • Heavy predation • Climatic change • Failure of food supply. • Reproductive success is usually the limiting factor that allows one competing population to flourish while another languishes. Terrestrial Biota

Extinction • No species is likely to be a permanent inhabitant of Earth. • Plant succession is the process whereby one type of vegetation is replaced naturally by another. • Succession is a spatially and temporally variable process; it is not a permanent loss like extinction. Terrestrial Biota

Terrestrial flora • Geographers are interested in natural vegetation of landscape for three reasons: • Plants are likely to dominate a landscape (except where terrain is rugged, climate is harsh, or humans have intervened); • Vegetation is a sensitive indicator of other environmental attributes; • Vegetation is often instrumental to human settlement and activities. Terrestrial Biota

Characteristics of plants, part 1 • Most are very hardy • Plants’ high survival potential is dependent on • Subsurface root system • Reproductive mechanism • Perennials are plants that can live more than a single year despite seasonal climatic variations. • Annuals are plants that perish during times of climatic stress but leaves behind a reservoir of seeds to germinate during the next favorable period. Terrestrial Biota

Characteristics of plants, part 2 • Most are very hardy (continued) • Common characteristics: • Roots (to gather nutrients and moisture and to anchor plant); • Stems and branches (to support and transport nutrients); • Leaves (to collect solar energy, exchange gases, and transpire water); • Reproductive organs. Terrestrial Biota

Adaptations of plants, part 1 • Environmental adaptations • Two prominent adaptation strategies of plants to protect against environmental stress are • Xerophytic adaptations • Xerophytic refers to plants structurally adapting to withstand protracted dry conditions. • Roots, stems, leaves, reproductive cycle can all adapt in various ways. • Succulents are plants that have fleshy stems that store water. • Hygrophytic adaptations • Hygrophytic refers to plants structurally adapting to withstand protracted wet conditions. Terrestrial Biota

Adaptations of plants, part 2 • Hygrophytic adapatation • A hygrophyte is a plant that requires a saturated or semi-saturated environment (frequent soakings with water). • Hygrophytes are likely to have extensive root systems for anchoring in soft ground. • They usually rely on buoyancy of water for support rather than stem. • Many have weak, pliable stems that can withstand currents. • Hydrophytes are often grouped in with this category. • A hydrophyte is a “water-loving” plant that is adapted to live in more or less permanently immersed in water. Terrestrial Biota

Role of competition • Competition is key in which plants grow where. • Even though all conditions (climatic, edaphic, etc.) are favorable, a plant may not take hold in one area because of competition. Terrestrial Biota

Floristic terminology, part 1 • Categorizing by reproduction • Through spores • Those that reproduce by spores are in two major groups: • Bryophytes are spore-bearing plants such as mosses and liverworts; never dominated in history, but can be very important in some localized situations. • Pteridophytes are spore-bearing plants such as ferns, horsetails, and clubmosses; used to dominate continental vegetation, but no more. Terrestrial Biota

Floristic terminology, part 2 • Categorizing by reproduction (continued) • Through seeds • Those that reproduce by seeds are in two major groups: • Gymnosperms are seed-reproducing plants that carry their seeds in cones; also known as conifers. • Gymnosperms were the dominant plant group in the past. • Angiosperms are plants that have seeds encased in some sort of protective body, such as a fruit, a nut, or a seedpod. • Angiosperms have dominated planet vegetation for last 50 million to 60 million years. Terrestrial Biota

Floristic terminology, part 3 • Categorizing by stem or trunk composition • Woody plants have a stem composed of hard fibrous material; refers mostly to trees and shrubs. • Herbaceous plants have soft stems; they are mostly grasses, forbs, and lichens. Terrestrial Biota

Floristic terminology, part 4 • Categorizing by leaf retention • Deciduous trees and shrubs experience an annual period in which all leaves die and usually fall from the tree, due either to a cold or dry season. • Evergreen trees or shrubs sheds their leaves on a sporadic or successive basis, but at any given time they appear to be fully leaved. Terrestrial Biota

Floristic terminology, part 5 • Categorizing by leaf shape • Broadleaf trees have flat and expansive leaves. • Majority are deciduous. • In rainy tropics, everything is evergreen. • Needleleaf trees are adorned with thin slivers of tough, leathery, waxy needles rather than typical leaves. • Almost all are evergreen. Terrestrial Biota

Floristic terminology, part 6 • Categorizing by supposed structure (this works for foresters, but not geographers) • Hardwoods are angiosperm trees that are usually broad-leaved and deciduous. • The wood has a relatively complicated structure, but is not always hard. • Softwood are gymnosperm trees. • Nearly all such trees are needle-leaved evergreens with wood of simple cellular structure but not always soft. Terrestrial Biota

Spatial groupings, part 1 • Geographers are usually more concerned with spatial groupings than individual plants. • Groups are based on dominant members, dominant appearance, or both. • The floristic pattern of Earth is impermanent. • Change can be slow and orderly, as in lake infilling. • Change can be abrupt and chaotic, as in wildfire. Terrestrial Biota

Spatial groupings, part 2 • Floristic pattern of Earth (continued) • Climax vegetation is a stable plant association of relatively constant composition that develops at the end of a long succession of changes. • Is an association in equilibrium with prevailing environmental conditions. • Should persist until environmental disturbance/change occurs. • Seral associations are various stages leading up to climax vegetation. Terrestrial Biota

Spatial groupings, part 3 • Geographers can face significant difficulties in recognizing spatial groupings. • As one tries to identify patterns and recognize relationships, must make generalizations. • When associations are portrayed on maps, boundaries usually represent approximations. • Human interference plays a major role. • Because of human impact, climax vegetation is now the exception rather than rule. • Maps often ignore human interference, so are actually maps of theoretical natural vegetation. Terrestrial Biota

Spatial groupings, part 4 • Spatial groupings of plants (continued) • There are many ways to classify plant associations. • Geographers usually place emphasis on structure and appearance of dominant plants. • Major associations include forests, woodlands, shrublands, grasslands, deserts, tundra, and wetlands. Terrestrial Biota

Spatial groupings, part 5 • Classification of plant associations (continued) • Major associations (continued) • A forest is an assemblage of trees growing closely together so that their individual leaf canopies generally overlap. • Forests are likely to become the climax association in any area where moisture is adequate and the growing season is not very short. • A woodland is a tree-dominated association in which the trees are spaced more widely apart than those of forests and do not have interlacing canopies. Terrestrial Biota

Spatial groupings, part 6 • Classification of plant associations (continued) • Major associations (continued) • A shrubland is a plant association dominated by relatively short woody plants. • Shrublands have a wide latitudinal range but usually are restricted to semiarid or arid areas. • A grassland is a plant association dominated by grasses and forbs. • Prominent grassland types include savanna, prairie, and steppe. • Grasslands are associated with semiarid and subhumid climates. • A desert is actually a climate type, not an association per se, but is typified by plants widely scattered on bare ground. Terrestrial Biota

Spatial groupings, part 7 • Classification of plant associations (continued) • Major associations (continued) • Tundra is a complex mix of very low-growing plants, including grasses, forbs, dwarf shrubs, mosses, and lichens, but no trees. • Tundra only occurs in the perennially cold climates of high latitudes or high altitudes. • A wetland is a landscape characterized by shallow, standing water all or most of the year, with vegetation rising above the water level. • Wetlands have a much more limited geographic extent than any other above associations. Terrestrial Biota

Spatial groupings, part 8 • Various plant associations will exist in relatively narrow zones when mountain slopes have significant elevational changes in short horizontal distances. • Vertical zonation is the horizontal layering of different plant associations on a mountainside or hillside. • Elevation changes mirror latitude changes. • Treeline elevation vary with latitude. Terrestrial Biota

Spatial groupings, part 8 • Elevational changes (continued) • Vertical zonation (continued) • Southern and Northern hemispheres experience different elevation-latitude relationship, with the Southern Hemisphere having lower treelines. • The reason for the discrepancy is not understood yet. Terrestrial Biota

Spatial groupings, part 10 • Can have significant local variations caused by a variety of local environmental conditions. • Exposure to sunlight is often a critical determinant of vegetation composition. • An adret slope is a Sun slope; a slope where the Sun’s rays arrive at a relatively direct angle. • An adret slope is relatively hot and dry, and its vegetation is sparser and smaller than that on adjacent slopes with different exposures. • Adret slopes are likely to have a species composition different from adjacent slopes. Terrestrial Biota

Spatial groupings, part 11 • Local variations (continued) • Exposure to sunlight (continued) • A ubac slope is a slope where sunlight strikes at a low angle and hence is much less effective in heating and evaporating than on the adret slope, thus producing more luxuriant vegetation of a richer diversity. • The differences between adret and ubac decreases with increasing latitude. Terrestrial Biota

Spatial groupings, part 12 • Local variations (continued) • Valley-bottom locations can have vegetation composition significantly different from slopes running to it. • Riparian vegetation is streamside growth, particularly prominent in relatively dry regions, where stream courses may be lined with trees, although no other trees are to be found in the landscape. Terrestrial Biota

GEO 200: Physical Geography