The transition from forest to treeless tundra on a mountain slope is often a dramatic one.
从森林到山坡上没有树木的苔原的过渡通常会十分突然和明显。
The Canadian Arctic is a vast, treeless polar desert that's covered with snow for most of the year.
加拿大的北极是一个广阔的、没有树木的极地沙漠，一年中大部分时间都被雪覆盖着。
Black bear cubs use trees for defense, whereas brown bears and polar bears, which regularly inhabit treeless environments, rely on aggression to protect their cubs.
