The link between deforestation and soil erosion

With an area the size of Costa Rica being destroyed each year, deforestation to create land which can be used for agriculture is a growing problem, it needs to be addressed soon before it’s too late. Here, I will be looking at the effects of deforestation on soil erosion.

A forest will protect the soil lying beneath it from the immediate effects of rainfall as the canopy and other factors help to lower the rate of erosion in this type of environment. This is because the canopy reduces the fall of raindrops, reducing their velocity and therefore kinetic energy.

The forest is also helped by the presence of humus in its soils (see image). Humus is the term used to describe any organic matter that has reached a point of stability, where it will break down no further and might, if conditions do not change, remain as it is for centuries. Humus helps to absorb the impact of the raindrop and is very permeable therefore allowing the rain to infiltrate its soils and be absorbed by the roots which can then help the plants grow. This humus also helps to bind these soils together, reducing the impacts of wetting and water-drop impact

Another factor that increases the stability of forest soils is the large, deep, tree roots that tend to bind soils together, compacting them and increasing the total strength of the soils.

Therefore, we can expect that with an increase in deforestation; there will be an increase in soil loss and erosion. If the land is left bare, then the effects will be more dramatic than if the land were to be covered with crops, which would have similar (but to a lesser extent) effects as forests. Furthermore, the type of ploughing, time of sewing and type of crop will influence soil erosion rates.

It is evident that the effect of humans upon the soils of the earth has dramatically increased the rate at which soil is eroded and lost. In Colorado, USA, rates of erosion over the past 100 years have been at circa 1.8mm per year, whereas in the 200 years before that, rates were between 0.2 and 0.5mm per year, showing erosion rates have increased at a rate of 5x since 300 years ago. In this specific area, it is because of the number of cattle that now use the fields.

This situation is something that cannot be ignored and has to be dealt with soon before the damage to our environment is irreparable.

Humus in soil. Image courtesy of http://cookingrut.blogspot.co.uk/2011/05/gardening-tips.html#!/2011/05/gardening-tips.html