Healthy roots are vital to plant survival. Woody plants have different types of roots. Under good root growth conditions, typically about 90% of roots grow in the upper 3 feet of soil. Up to about 70% of roots are in the top 1 foot. Because roots need air, even more of a tree's roots are near the surface if soils are compacted or waterlogged. Conversely, drought-adapted species and trees in deep or well-drained soil that receive only rainfall or infrequent deep irrigation have more of their roots growing deeper below ground than shown here. Roots typically extend beyond the tree canopy drip line. Actual root systems can vary greatly, depending in part on cultural practices, soil conditions, and the species of plant. For example, unlike the central taproot of many broadleaf trees and shrubs, plants such as bamboo, palm, and yucca have threadlike or ropelike roots that spread laterally to form a fibrous mat near the soil surface.