三北防護林

Green Wall of China, a massive afforestation program on the eastern margin of the Gobi Desert aimed at stopping the desert's expansion, started in 1978 and planned to be completed by 2050

three / 3

China's three northern regions, 東北|东北[Dong1 bei3], 華北|华北[Hua2 bei3] and 西北[Xi1 bei3]

north / (classical) to be defeated

to protect / to defend / to guard against / to prevent

to defend / to protect

to protect

woods / forest / CL:片[pian4] / circle(s) (i.e. specific group of people) / a collection (of similar things)