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10.3 - Soils and vegetation - content
10.3 - Soils and vegetation - content
Vegetation: biomass productivity (biodiversity, limited nutrient cycling, fragility), adaptation of plants to extreme temperatures, physical and physiological drought.
Soils processes: upward capillary movement of water and minerals (salinisation).
The process of desertification (both natural and human factors) leading to the degradation of soils and vegetation in semi-arid environments.
Desert Biome & Biomass
Desert Biome & Biomass
Biomass describes the total mass of living matter in a defined area. The concept helps scientists categorise different ecosystems by biological productivity. Zones with high biomass, like a rainforest, are high in productivity. On the other extreme, desert ecosystems have the lowest biomass on Earth, but that does not mean that deserts have zero biomass. On the contrary, desert biomass includes unique organisms often found nowhere else on earth.
Soils
Soils
Desert soils are grey in colour. They are thin and have little organic matter. Because water is evaporated so quickly, salt builds up on the surface of the soil. Desert soils are not very fertile. Solis in desert regions are called aridisols. In order to survive in the very arid conditions found in deserts plants and animals have evolves specific adaptions.
Soils in desert environments are particularly fragile, and despite their apparent stasis are complex and vulnerable to change. One particular concern is salinisation, which may cause physiological drought.
Slow-Growing Plants
Slow-Growing Plants
The largest proportion of the desert's biomass consists of plants. Because of the desert's limited water, only plants that require little water can survive. Most commonly, these take the form of succulents such as cacti. Cacti are adapted to the desert environment because they retain water for long periods of time. Unlike non-desert plants, cacti grow extremely slowly, and lack true leaves. Instead, they have hard protective spines and, frequently, protruding thorns. This is an evolutionary adaptation meant to discourage herbivorous predators. Succulents tend to be fairly fat fleshy plants that are able to store water in their leaves, trunks and roots. Desert plants typically have very long roots so that they are able to absorb the maximum amount of rainfall during periods of rainfall. It also makes them more stable in very loose soil. In addition, succulents protect themselves from both predation and water loss with waxy surfaces, making them less palatable, this trait is frequently combined with poisonous or foul-tasting sap which further reduces the likelihood of them being eaten.
Herbivorous Rodents and Reptiles
Herbivorous Rodents and Reptiles
The second-largest proportion of the desert's biomass comes in the form of small rodents and reptiles. Like their desert plant counterparts, these animals are well-suited to dry and sunny environments. They rely on plants -- including cacti -- for food, though they generally eat very little. The desert kangaroo rat does not drink. Its only source of water comes water produced by its own metabolism of food. Reptiles are cold-blooded, which allows them to eat little but remain warm in the desert's hot sun. The chuckwalla is an example of a herbivorous desert reptile.
Carnivorous Reptiles and Arachnids
Carnivorous Reptiles and Arachnids
The third-largest proportion of the desert's biomass are meat-eating reptiles and spiders. In the driest deserts, this level of life will be the highest on the food chain. It includes animals such as venomous snakes, tarantulas and insect-eating lizards. Like the prey it consumes, these animals tend to be cold-blooded and eat relatively small amounts. The zebra-tailed lizard, for example, eats insects and smaller lizards. It regulates its body temperature by efficiently absorbing the Sun's heat.
Carnivorous Mammals and Birds
Carnivorous Mammals and Birds
Not all deserts in the world will include meat-eating mammals and birds in their biomass. Deserts that are extremely dry - like the Atacama Desert - have too little vegetation and herbivorous life to provide enough food to these carnivorous predators. Other deserts with more vegetation, however, can support life as complex as hawks and coyotes. In general, these parts of the biomass will be scavengers who eat carrion and already dead animals. Because there is so little food for them to utilise, these complex animals form only a very tiny fraction of the total biomass of the desert. Frequently they are nocturnal or crepuscular, a behavioural adaptation to the high daytime temperatures.
Whittaker's Climograph
Whittaker's Climograph
Pyramids of Energy Comparison
Pyramids of Energy Comparison
Standard and Desert Specific Gersmehl Diagrams
Standard and Desert Specific Gersmehl Diagrams
The inter-relationships between nutrient stores and flows are affected by climatic factors (e.g. temperature and rainfall), as such Gersmehl diagrams differ between biomes (e.g. tropical rainforest, taiga and desert).
Gersmehl diagrams show the differences in nutrient flow and storage between different types of ecosystems
Nutrients are stored in one of three nutrient sinks – either as biomass, litter or soil
Biomass is the total mass of living organisms (mainly plant tissue) in a given area
Litter is any organic matter in and on the soil – it includes humus and leaf litter (defoliation). Litter can additionally gain nutrients via precipitation (rainfall) and lose nutrients in surface runoff
Soil is the top layer of the earth that is composed of disintegrated rock particles. It can gain nutrients from the erosion of rocks via weathering, but will lose nutrients via leaching
Nutrients can be transferred between nutrient sinks and may also be cycled via environmental inputs and outputs. Nutrients can be transferred from biomass to litter (fallout), litter to soil (decay) or soil to biomass (uptake)
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