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  Relationship between Vegetation and Climate, Biology tutorial

Introduction:

Usually, the climate of place or region influences the kind of vegetation to be found in such region. Moisture content, availability of nutrient in soil depends on climatic conditions of the area. These in turn find out kind of vegetation which can be found in given place .

On a global average, of 100 units of energy entering global climate system, 46 are absorbed by surface and 31 are exchanged in form of sensible and latent heat. Vegetation influences absorption of energy by surface using modification of surface albedo and via alteration of energy partitioning between sensible and latent heat. In addition, vegetation alters surface roughness length. These procedures are accounted for by soil-vegetation-atmosphere transfer schemes (SVAT) that serve as land surface modules inside atmospheric general circulation models (GCMs).

In regions with strong zonal atmospheric circulation, like northern middle latitudes, effect of local vegetation changes on regional climate may be smaller than effects because of such changes in remote regions. At the same time, changes in vegetation cover influence not only region with modified vegetation, but also neighboring regions. Local effect is most pronounced for temperature, as vegetation changes directly influence local radiative budget.

Changes in vegetation also alter evaporation. Though, changes in air moisture content may result in quite remote effects because of long distance transport of moisture. For instance, in Europe there is general reduction in precipitation towards continent's interior as transport of moisture from Atlantic Ocean declines with distance to the ocean.

Climate-vegetation Interaction in Sahara/Sahel Region:

Dependence of vegetation on climate in subtropical deserts and semi deserts can in a first approximation be stated in terms of precipitation as vegetation productivity is severely restricted by low water availability. Vegetation doesn't entirely cover land surface. Drier the climate is, the scarcer is the vegetation and the greater is fraction of bare soil. Physical features of bare soil (albedo, roughness, and water conductivity) vary from those of vegetation cover. That, in turn, creates the basis for influence of vegetation on climate.

Low precipitation results in little vegetation cover, and surface albedo is determined by bare ground with high albedo. This positive feedback supports the desert which self-sustaining. On the other hand, if there is more precipitation, there is more vegetation; this is darker than sand so albedo is lower, surface temperature is higher, and gradient in temperature between land and ocean increases, amplifying monsoon circulation and upward motion over desert.

Nigerian Vegetation: Case Study of Relationship between

Vegetation and Climate:

Nigeria has the tropical climate with sharp regional variances depending on rainfall. Nigerian seasons are governed by movement of intertropical discontinuity, zone where warm, moist air from Atlantic converge with hot, dry, and frequently dust-laden air from Sahara called locally as harmattan. In the summer, zone of intertropical discontinuity follows sun northward. As a result, more and more of the country comes under influence of moisture-laden tropical maritime air. As summer wanes, zone shifts southward, bringing an end to rainy season. Temperatures are high during the year, averaging from 25° to 28°C (77° to 82°F). In higher elevations of Jos Plateau, temperatures average 22°C (72°F).

Northern Nigeria usually experiences greater temperature extremes than south. Rainfall differs extensively over short distances and from year to year. Parts of coast along the Niger Delta, where rainy season is year-round, receive more than 4,000 mm (160 in) of rain each year. Region along Nigeria's northeastern border receives less than 500 mm (20 in) of rain per year, and rainy season lasts barely three months.

Climate (particularly rainfall) has the significant influence on distribution of vegetation in Nigeria. There are 10 major vegetation zones: Sahel, Sudan and Northern Guinea zones, Jos Plateau, Montane forest and grassland, Rain forest, Oil palm bush, Southern Guinea zone, Swamp and Mangrove forest. These main zones have different vegetation kinds that can be further subdivided in coastal forest and mangrove, deltaic swamp forest, swamp forest and wooded savanna.

Vegetation also differs dramatically at both national and local level in relation to climate, soil, elevation, and human impact on environment. Southern margins of Guinea savanna-that has been so modified by humans that it is also known as derived savanna-were created by repeated burning of forest until only open forest and grassland were left. Burnings decimated significant fire-sensitive plant species and contributed to erosion by eradicating ground cover. Tropical forest is giving way to Guinea savanna at such a rate that only forests expected to survive next generation are in reserves. Beyond the Guinea savanna lies drier Sudan savanna, a region of shorter grasses and more scattered, drought-resistant trees like the baobab, tamarind, and acacia. In Nigeria's very dry northeastern corner, semi desert Sahel savanna persists.

Influence of Vegetation on Soil Type:

A close relationship between soil type and vegetation tends to grow as soils start to form. Vegetation plays the significant part in formation of soils from solid rock. Acids released by roots of some plants act to breakdown rock on which soil is forming. Vegetation on soil is mainly significant in supplying soil with precious organic matter. There is frequently close relationship between vegetation and soil, vegetation supplying its dying remains to soil and soil converting them in nutrients so vegetation can carry on to survive and grow in years ahead. Different kinds of vegetation give rise to different forms of organic matter in soils.

Growth of plants and activities of plants also depend on nature of soils. Soil kinds with high sandy particles have low water retention ability with high porosity. With high porosity, such soils have little retention of nutrients therefore support little vegetation. In case soils with high level of fine particles, water retention is very high and pore spaces are simply filled with water. This decreases gaseous exchange between atmosphere and soil making soil to be more or less in aerobic in nature. Plants generally exchange hydrogen ions for such nutrients. Though, as clay particles don't generally retain negatively charged ions like nitrates, soil types with high clay contents have low nitrogen contents and don't support plants with high nitrogen demands. Loam soil kinds adequately retain water and nutrients while still permitting for enough drainage to provide air spaces in soil. Such soil type permits for growth of plants. Humus content of soils also influences growth of plants. Humus has capacity to absorb and swell with water and shrink as water is slowly released from it. These alternating swelling and shrinking aerate soil. Also as decomposers work on humus, nutrients are released to soil which is taken up by plants. Usually, soil types with10-20% are favorable to plant growth whereas soil types with less than 10% or more than 90% humus are not good for plant growth.

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