The pie chart demonstrates the main reasons that cause land degradation all over the world. The most serious problem is over-grazing, which causes 35 percent of worldwide land degration. Deforestation does less harm but it also acount for 30 percent, followed by over-cultivation, which takes up 28 percent.

The table above tells us the particular data about how these causes influenced North America, Europe and Oceania during the 1990s. It is obvious that land degradation was most severe in Europe,which almost took up a quarter. Although all three problems played important roles in Europe， deforestation and over cultivation were also more critical, comparing to other two regions.

As for Oceania, over-grazing became the most noticeable problem, which caused almot double land degradation than it did in Europe, let along North America. In North America, land degradation was not that serious. However, it can't be ignored that over-cultivation still causes 3.3 percent of land degradation.

To summarize, land degradation is relevant to human's activities and the natural condition. We should take these two elements into account.