In recent years, years, South Korea[5][6] a an nd China have participated in reforestation reforestation e efforts fforts in the source region .[citationneeded ] This has not affected the problem in a significant way, however. In April 2006, South Korean meteorologists reported the worst yellow dust storm in four year s.[7] China a China also lso has taken steps, with international support, to plant trees in desert areas, and has claimed to have planted 12 billion trees. But the winds are so strong in certain places that the trees simply topple or get buried in sand. In 2007, 2007, South Korea sent several thousand trees to help block the migration of the yellow dust. These trees, however, were planted only by highways, becaus e China China t tol old d South Korea t Korea that hat the former would decide where the trees would be planted.