Mixed forests are a temperate and humid biome. The typical structure of these forests includes four layers. The uppermost layer is the canopy composed of tall mature trees ranging from high. Below the canopy is the three-layered, shade-tolerant understory that is roughly shorter than the canopy. The top layer of the understory is the sub-canopy composed of smaller mature trees, saplings, and suppressed juvenile canopy layer trees awaiting an opening in the canopy. Below the sub-canopy is the shrub layer, composed of low growing woody plants. Typically the lowest growing (and most diverse) layer is the ground cover or herbaceous layer.