Primary productivity in the region is very high, and is the most biologically diverse region in the world. Intense competition ensures that very few species dominate; the species diversity, which leads to this intense competition, is a result of several factors including:
The rainforest has developed over a long period of time, which has encouraged complex food webs do develop.
The constant warm temperatures permit reproduction throughout the year, meaning natural selection and evolution take place at a relatively rapid rate.
Growth is not restricted by water supply
Forrest stratification creates variations in temperature, humidity, sunlight and soil conditions, producing a variety of balanced ecological niches.
The variations in the biodiversity of the region also reflect differences in regional climates, soils, geology, drainage and past ecological histories (Primary or secondary succession) Examples of variation as a result of varying abiotic factors include:
In the western Amazon, which doesn’t experience a dry season, there is higher species diversity and more epiphytes than forests in the dryer south and east. The trees are also thinner and have smoother bark than those found in the south and east.
Towards the Andes there are cloud and montane forests, the trees are smaller and more spread due to the fact they are more prone to tree falls because of the topography of the area.
These distinct variations in characteristics due to geographical location and abiotic factors are evidence that the current state of the rainforest is a result of natural responses to the climate of the areas.
Due to its equatorial location, the Amazon receives high levels of sunlight throughout the year, resulting in high levels of photosynthesis and lots of biomass; together with the warm, wet climate creates an environment that encourages growth. This results in intense competition for sunlight, which has lead to the development of a vertically stratified forest, just another example of how characteristics of the biome are a result of natural processes. It is also important to note that individual plant species characteristics are the result of adaptations to environmental factors such as:
Leaves in the canopy are large in order to maximize photosynthesis as light levels are lower whereas emergent trees have smaller leaves to minimize the water loss through transpiration.
Leaves in the understorey have extended apical ends or ‘drip tips’ in order to reduce water build up on the leaf which hinders transpiration. This is especially important in the understorey layer as lack of wind and high humidity reduces transpiration rates.
But climate isn’t the only factor that can effect the biome.
Up until the 1960’s, shifting sustenance farming had little effect on the biome, but during the late 1960’s the Brazilian government encouraged colonization and sponsored large-scale projects to exploit resources in an attempt to grow the economy and accelerate infrastructure development. The construction of roads opened up previously inaccessible areas to activities such as logging and as much as 17% of the original forest is estimated to have been lost since the 1960’s. It is important to note that as the country develops further economically the levels of human activity increases up until the point that the economy of the region has developed sufficiently so that they no longer need to exploit the natural resource.
Timber isn’t the only resource the rainforest had to offer, oil and gas are extracted in the western side of the amazon, and gold mining (a highly invasive process involving the washing away of large quantities of soil, effecting not only the immediate area but also areas downstream) is rife, both legal and illegal in the Brazilian state of Para.
The main cause of deforestation is cattle ranching (which accounts for upwards of 80% of all deforestation in Brazil) Improvements of infrastructure, eradication of foot and mouth disease and the devaluation of the Brazilian currency against the dollar have all encouraged growth in this sector. Brazil is also making the transition from non-renewable energy sources to renewable and supposedly greener energy sources, and in order to meet targets they have constructed hydroelectric dams on rivers such as Rio Tocantins, consequently flooding large areas of rainforest.
Human activity can also have an indirect effect on the biome as well as direct effects, as more countries make the transition from LEDC to MEDC, economic growth fuelled by the burning of cheap fossil fuels such as coal, CO2 levels rise effecting the growth of plants, the increasing temperatures caused by the release of greenhouse gasses also decrease the efficiency of photosynthesis as enzymes vital to the process become denatured, hindering the efficiency of the process, causing the CO2 levels to rise further. The increasing temperatures also upset the balance of the water cycle in the rainforest, resulting in a net water loss in the biome, an impact who’s consequences are not been fully understood yet.
This essay intended to assess the extent to which these influences have shaped the present day characteristics of the tropical biome, using the Amazon as an example. From discussion and assessment of the features it has become evident that the present day characteristics of the biome are a result of a natural response to the climate, this is shown through the variations in biodiversity depending on the region and their varying climate. Although mans impact is not to be forgotten about, its effect is minimal when compared to natural effects at present. Although as mans influence grows so to will the impact, and the full consequences of the rising CO2 levels and global temperatures are still not fully understood.
by
liam-galvin (student)
