求翻译：继续推进天然林保护、京津风沙源治理等生态建设，五年累计退耕还林3191万公顷，退牧还草3460万公顷。是什么意思？

Continue to promote the protection of natural forests, Beijing and Tianjin sandstorm source control (control the factors causing sandstorms in beijing and tianjin) and other ecological construction, and five-year cumulative Grain 31.91 million hectares, 34.6 million hectares of grazing land to grass

Continue to promote natural forest protection, Beijing and Tianjin sand Source Control Management (sandstorms in the factors causing Beijing Tianjin), and ecological building, 5 years, the accumulated forests and grasslands, 31.91 million hectares of pasture and 34.6 million hectares.

Continues to advance the natural forest protection, the Beijing and Tianjin sandstorm source government (control the factors causing sandstorms in Beijing and Tianjin) and so on the ecology constructions, five years accumulation takes back from agriculture also the forest 31,910,000 hectares, draws

Continue to promote the natural forest protection, Jing-Jin sandstorm source control (control the factors causing sandstorms in Beijing and Tianjin), eco-building, five years of returning farmland to forest 31.91 million hectares, 34.6 million hectares of grazing grass.

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