The data given indicates the main reasons of land degradation and the differences between their effects on three different regions in the 1990s.
It is clear from the pie chart that decrease in land productivity was triggered mostly by over-grazing of animals which accounted for 35% of the total worldwide land degradation. Tree clearance and over crops cultivation also contributed to the land degradation, at 30% and 28% respectively.
As can be seen from the table, Europe is the region which had the largest amount of degraded farmland (23% of total farmland). This was caused mostly by deforestation (at 9,8%) and over-cultivation (at 7,7%). Oceania had 13% of land degraded, which stood at the second place. Unlike the Europe, the major reason for land degradation in this area was over-grazing, which constituted 11,3%. North America is the least affected by land degradation. The total land degraded was nearly a quarter of Europe's amount and half of Oceania's one. The main reason for this was over-cultivation of crops(at 3.3%).
In conclusion, over-grazing was the major cause of land degradation and Europe is the mostly affected region.