Heilongjiang province shares a 1,865-mile border with Russia. Oil and timber riches have not prevented a long decline of the province's industrial base. Cross-border trade with Russia has been thwarted by Russia's economic decline. About half of the land area is mountainous and includes large forests that contain one-third of China's timber resources. Heilongjiang is the nation's biggest producer of soybeans, milk and beetroot. Grain, beef, corn, and wool production rank in the countries top five. Japan occupied in 1932 and held it until 1945, when the Russians returned to occupy it. After removing much of the industrial plant, the Russians handed it back to China in 1946.