The vulnerability of this ecosystem refers to its ability or lack of ability to return to its dynamic equilibrium state after change. Thus this rainforest can be said to be very resilient with little natural vulnerability as it has existed for many millennia in such a state. This is partly due to its position on the Guyana shield which experiences very little dramatic tectonic activity and partly due to its location in the equatorial climatic zone. In this zone near permanent annual rainfall and high temperatures give rise to a highly productive ecosystem with plenty of available energy to support the greatest level of biodiversity in the world. This biodiversity means that niches for species are small and specialised and thus the loss of any one species will be very unlikely to have a permanent effect on the forest.
However the fact that the Amazon like many other tropical rainforest ecosystems is found within an LEDC means that its vulnerability in human terms is very high. Pressure on the forest to be cleared to stimulate economic development and to provide land for subsistence agriculture for a growing population mean that much of this ecosystem has been permanently changed to agricultural ecosystems and its ability to recover will be severely hindered in the short term.
Traditionally human inhabitants of the ecosystem have cleared the forest through 'slash and burn' agriculture. But the forest system has been able to recover from this localised shocks because the scale of the clearance has been small enough for regeneration to take place from trees left standing. Also hunting has been at a subsistence level only and small populations of indigenous tribes have not lead to a significant threat to the species equilibrium. Vulnerability has only increased because of the larger scale clearance of forest for commercial ranching and Soya production. Removal of the trees and burning of the timber disrupt the nutrient cycle so that leaf littler cannot now decompose to provide the nutrients for regrowth. Cattle grazing can then lead to the dominance of invasive grass and weed species suppressing natural regeneration of the forest, while in Soya production nutrients are removed at harvest again limiting recovery. Large scale clearance and burning have also threatened top predators like the Jaguar that require very large areas of continuous forest to hunt. Furthermore fragmented areas of forest are far more vulnerable as their separation from other areas restricts the essential migration of species and reduces the opportunity for seed dispersal to aid regeneration
However protected areas in the Amazon such as the newly expanded areas in Para state in Northern Brazil have reduced this vulnerability to human activity. The creation of a corridor of protected areas (where only limited human activity is allowed) along the River Amazon aids species migration and helps to protect the clean water that the Ecosystem depends on by maintaining the 'ecosystem service' that the trees provide in recycling water to the atmosphere and filtering its flow to the river. The increased size of the total protected areas now adjacent to other reserves in neighbouring countries such as Guyana mean that loss of flagship species such as the Jaguar is far less likely.
In conclusion it can be seen that as ecosystems tropical rainforests with their high biodiversity are naturally resilient. Their longliveity is ample evidence of that. The Amazon forest on an ancient shield is especially so. Thus vulnerability seems entirely dependent on human factors. Brazil's Amazon forests have been perceived as a vast area with the potential for clearance for development and this clearance on a now massive scale has made the remaining forest less able to adapt to change unless it is carefully protected on a large scale. Its fate remains very much in human hands. |
