In this lesson we are going to discuss Introduction to Vegetation and Factors Influencing Typesand Distribution of Vegetation
Vegetation- Plant cover on the earth’ssurface.Types of Vegetation1. Natural Vegetation-Which grows by naturalmeans of seed dispersalwithout interference andmodification by man.2. Semi- Natural/DerivedVegetation-Natural vegetation which isin the process of recoveringfrom interference by man.3. Planted/CultivatedVegetation-Vegetation planted by peoplee.g. forests of exotic trees,trees in Agroforestry andplants used as hedges e.g.cypress.Factors Influencing Typesand Distribution ofVegetationTopographical Factors1. Altitude• Coniferous trees are found athigh altitudes because they areadapted to cool conditions.• There is no vegetation onmountain tops because thereare very low temperatureswhich inhibit plant growth.2. Terrain• Gentle slopes which havedeep and well drained soilsare best suited for plantgrowth than steep slopeswhich have thin soils due tosevere erosion and less soilwater to sustain plant growthdue to high runoff.• Flat areas have poordrainage hence are swampyand can only support swampplants.3. AspectThere are a wide range ofplants on the slope facing thesun and in the direction of rainbearing winds as they arewarm and wetter.Grass lands are dominant onthe leeward side because theyare drier.4. DrainageThere is a large variety ofplants on well drained soilswhile water logged soils haveswamp plants such as reedsand papyrus.Climatic Factors1. Temperature• Plants in warm areas arelarge in number and growfaster e.g. in the tropicallands. Also there aredeciduous trees which shedleaves to reduce the rate oftranspiration.• In areas with lowtemperatures there is slowgrowth of plants andconiferous forests are foundthere.2. Precipitation• There are a large number ofplants in areas with highprecipitation and these areasare dominated by forestswhich are broad leaved toincrease the rate oftranspiration.• Areas with moderate rainfallare dominated by grasslandsand those with little rainfallhave scanty vegetation ofscrub and desert types.3. Sunlight• There is large number ofplants in areas experiencinglong sunshine duration.• There is little undergrowth intropical rain forests becausethe canopy prevents sunlightfrom reaching the ground.4. Wind• There is heavy rainfall inareas where warm moist airblow to and hence a largenumber of plants which maybe broad leaved to increasethe surface area fortranspiration.Edaphic/Soil Factors• Fertile soils have a largernumber of plants whileinfertile soils have scantyvegetation.• Soil pollution e.g. oilspillage cause drying up ofplants.• Deep soils have deep rootedplants such as trees whileshallow rooted soils haveshallow rooted plants such asgrasses and shrubs.Biotic/Biological Factors1. Living Organisms• Bacteria, earth warms andburrowing animals improvesoil fertility resulting intomore vegetation growth.• Insect and birds pollinateplants enhancing theirpropagation.• Bacteria and insects causeplant diseases of plantsresulting in death of some e.g.aphids which affected cypressin late 80s.• Large herds of wild animalscan destroy vegetation throughovergrazing and can turngrasslands into deserts.2. Human Activities• Clearing of naturalvegetation for settlement,agriculture etc. can lead todesertification.• Bush fires such as burninggrasslands for the grass tosprout can cause extinction ofsome plant species.• Overstocking can lead toovergrazing turning grasslandsinto deserts.• Rehabilitation of deforestedareas can stop the spread ofdeserts.