Describe the characteristic features of a biome of one tropical region that you have studied [10]

by ccsimsemanuelorguk (student)

The tropical rainforest biome occupies the area 100 North and South of the equator, where the yearly insolation and precipitation is abundantly high. These conditions provide optimum growing conditions for the flora that thrive in this region. Precipitation is the chief determinant of the overall type of vegetation and thus ecosystem development, however soil nutrients is the main limiting factor to the growth for such tropical vegetation.

The climate of this biome is characteristically hot and humid, with an unwavering constant yearly temperature of 270C that rarely exceeds 320C. Despite this, the diurnal temperature can vary as much as 10-150C due to the waxing and waning cloud cover throughout the day. Furthermore the annual precipitation is between 2000-3000mm coupled with a high humidity ranging from 80-100%. Due to the proximity to the equator most areas experience an equal split of day-time and darkness. Although the flora of this biome experience a constant growing season, dry seasons can emerge as the ITCZ migrates after the equinox, resulting in lower rainfall and a subsequent increase in average daily temperatures.

The vegetation in this area is thought to be the classic climatic climax vegetation of the planet and due to the biomes long term stability over millions of years, competition for sunlight among the plant species is such that every species occupies its own niche, often symbiotically with other neighbouring plant species. This allows a large variety of species to coexist without excessive competition for resources, a process of resource portioning. For example Lianas, a climbing vine, shares a symbiotic relationship with the forest trees. Because forest trees reach towering heights with a shallow rooting system, they can easily be uprooted, however the Liana grows up the trunk of a tree and once it reaches the canopy layer it grows onto adjacent trees, thus anchoring the host against its neighbours as well as giving the Liana better light exposure to photosynthesise. However, it should not be noted that no single species of vegetation dominates the forest nor are there clustered areas of only one type of tree species.
Most of the forest trees share similar adaptations, predominantly a thin layer of bark, as insulation in cold weather is unnecessary, and broad waxy leaves. The leaves cover to encourage transpiration, they are also able to rotate on their stem, maximising the exposure to direct sunlight as the sun moves throughout the day – increasing its ability to photosynthesise. The presence of the waxy cuticle is two-fold. Firstly to prevent the leaves burning in the intense sunlight and secondly to prevent the colonisation of algae and mosses that would otherwise block the stomata and thus hinder the leaf’s ability to photosynthesise. This is due to the fact that the cuticle and drip-tips easily dispel water off the leaf allowing it to quickly dry, preventing the moist conditions necessary for microorganism growth. The pollination of the trees is achieved via insect, bird or bat as the winds are too light for the trees to disperse their pollen independently. Thus forest trees have evolved very colourful and scented flowers to attract pollinators.
Little vegetation exists at ground level, with exceptions along river channels and clearings in the forest where light can penetrate towards the surface and foster growth. More commonly the floor is dominated in decaying detritus.
As shown the flora species have evolved to occupy many different niches but are also highly dependent on each other, thus these combinations of specialisation and interdependence increases the overall fragility and vulnerability of this biome. Furthermore due to the constant abiotic conditions, specialisation has occurred to such a degree that even the slightest ecological or environmental disruption cannot be accommodated, meaning individual habitats and ecosystems can be easily destroyed.

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In regard to the soil type of this biome, there is no one archetypal soil that covers the entire tropical region. Due to millenniums of stable conditions that surpass the global soil disruptions caused by the Pleistocene glaciations, rainforest soils have been subjected to long and intense periods of weathering and can be as deep as 30m in some places. Most equatorial soils have poorly distinguished horizons due to heavy leaching from intense precipitation, thus resulting in ferrallitic soils. These soils are low in silica but have a high content of iron and aluminium sesquioxides. This is because in the hot and humid conditions organic acids in the topsoil are rapidly decomposed and replaced by carbonic acid (H2CO3) a weaker, non-complexing (non-separating) acid which raises the soil pH to 5. Clays in the soils are broken down into silicates which at this pH have the highest solubility in water, whereas iron and aluminium are comparatively insoluble and as a result are not hydrated. Therefore the silicates and removed from the system, leading to the residual accumulation of iron and aluminium oxides. The ferrallitic soils are known as latosols, where the abundance of iron oxides gives the soil its characteristic red colour.
The constant growing season of the aseasonal deciduous trees ensure a plentiful and constant supply of leaf litter deposition on the forest floor. The leaves are rapidly decomposed in the humid conditions facilitating rapid nutrient recycling from the leaf litter store, thus counteracting some of the effects of leaching due to the constant release of by-product bases into the soil – recuing the soils acidity. However there is a relatively very low nutrient sore in the soil due to the mycorrhizal association, a symbiotic relationship between the forest tree root system and the species of fungi that live in the soil. This is a novel adaptation of the rainforest’s nutrient cycle. Whereby the nutrients pass directly from the leaf litter store to the root system of the trees via the decomposing action of the fungi, thus removing the need for a soil storage of nutrients. Thus the nutrient cycle for a tropical rainforest can be thought as a closed system as very few nutrients are lost by leaching as there is a very small amount of nutrients in the soil originally.

The characteristic features for the animal life that exist in a tropical rainforest biome are somewhat similar to that of the flora, in that there is high specialisation of small niches within the environment. Most animals only operate on one stratified layer of the forest and some have adaptations specific to feed on one food type, thus meaning that all animals to an extent (with the exception of birds) are endemic to a very small part of the forest. The large majority of the fauna, particularly the mammals, are arboreal and seek the rich source of shelter and food in the canopy layer. Few animal occupy the emergence zone due to turbulent winds, moreover few animal have also adapted to live on the forest floor, with exception of; tigers and other big cats, elephants, and other animals such as Tapirs. However it should be noted that there is a vast abundance of insects, ants and termites that operate on the forest floor and in the soil layer.

Describe the characteristic features of a biome of one tropical region that you have studied [10]

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