Changes caused by agriculture and overgrazing
Agriculture is the world’s oldest and largest industry; more than half of all the people in the world still live on farms. But, because of production, processing and distribution of food — and that took on a large scale larger effects on the environment are unavoidable.
Agriculture has both primary and secondary environmental effects. A primary effect is an effect on the area where the agriculture takes place i.e. on-site effect. A secondary effect, also called an off-site effect, is an effect on an environment away from the agricultural site.
The effects of agriculture on the environment can be broadly classified into three groups, viz. global, regional and local:
(1) Global Effects:
These include climate changes as well as potentially extensive changes in chemical cycles.
(2) Regional Effects:
These generally result from the combined effects of farming practices in the same large region. Regional effects include deforestation, desertification, large scale pollution, increase in sedimentation in major rivers and in the estuaries at the mouths of the rivers and changes in the chemical fertility of soils over large areas. In tropical waters, sediments entering the ocean can destroy coral reefs.
(3) Local Effects:
These occur at or near the site of farming. These changes / effects include soil erosion and increase in sedimentation downstream in local rivers. Fertilizers carried by sediments can also transport toxins and destroy local fisheries.
Changes caused by Overgrazing:
The carrying capacity of land for cattle depends on the fertility of the soil and the rainfall. When the carrying capacity is exceeded, the land is overgrazed.
The changes that result from overgrazing include:
(a) Reduction in the growth of vegetation.
(b) Reduction in the diversity of plant species.
(c) Increased soil erosion as the plant cover is reduced.
(d) Damage from the cattle trampling on the land, like paths made by cattle develop into gullies, which erode rapidly in the rain.
(e) Dominance of plant species that are relatively undesirable to the cattle.