Passage: Minnesota has four ecological provinces: Prairie Parkland, in the southwestern and western parts of the state; the Eastern Broadleaf Forest (Big Woods) in the southeast, extending in a narrowing strip to the state's northwestern part, where it transitions into Tallgrass Aspen Parkland; and the northern Laurentian Mixed Forest, a transitional forest between the northern boreal forest and the broadleaf forests to the south. These northern forests are a vast wilderness of pine and spruce trees mixed with patchy stands of birch and poplar.

Question: What single word describes how large or wide these forests are?
vast