。
The tree was blown down.
Literal
Tree [topic-は] was-blown-down.
吹き倒される is the passive of the compound verb 吹き倒す ('blow + knock down'). The compound captures 'blown to the point of toppling' in one word — a precision typical of Japanese 複合動詞 (compound verbs). In the passive, the tree is the receiver of the action, with the wind as an unstated agent.