Soil Erosion In Northern Mexico Worsens Under Intensive Overgrazing - AFP

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These original measurements suggest that, in this northern area of Mexico, it is the soils of all the drainage slopes that lose several millimetres every year. In this part of the country, with its steep slopes, this process was found to be the consequence of livestock"s trampling of vegetation combined with the sheer intensity of rainfall events.

The intense grazing pressure exerted by cattle, which eat mainly grassy and herbaceous plants, means that the unpalatable species that the livestock leave alone no longer have any competition and eventually take over the whole of the space. This overgrazing therefore causes the grassland ecosystem to be replaced by thorn scrub and pine, less effective for holding in place the fine layer of fertile soil.

In the space of around ten years, pressure from ever-growing herds and tree-felling for timber have contributed greatly to changes in the landscape. In the western Sierra Madre, practically all the pasture land located at 500 to 2500 m altitude are already degraded. Yet paradoxically it was in the valley bottoms where there was least rainfall that sheet erosion was most intense. These zones were also the site of the most degraded pastures and where runoff was strongest.

These observations provide scientists with a better understanding of the functioning of soil and the erosion processes in regions like northern Mexico where it is becoming especially intense. This type of approach offers a better way of assessing soil degradation. It should in the long term offer easier identification of the places most vulnerable to erosion and runoff, a capability useful for devising control measures to limit certain detrimental practices such as tree clearance or over-intense grazing practices.

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http://www.terradaily.com/reports/Overgrazing_Accelerating_Soil_Erosion_In_Northern_Mexico_999.html