Arizona-Sonora Desert Museum Digital Library

Thornscrub is intermediate between the desert and tropical forest biomes. The vegetation consists largely of short trees, ten to twenty feet (3-6 m) tall, and shrubs, with cacti also being common in the “New World” communities. It is generally more dense and taller than desert vegetation, and many species are thorny. Annuals and herbaceous perennials are abundant, and vines — a primarily tropical life form — are well represented. During the dry season most perennial plants are drought-deciduous (as opposed to plants of more temperate regions which are cold-deciduous). In contrast, the rainy season, though short, is moderate and dependable and the vegetation grows lush. The climate is nearly frost-free, so temperature is not limiting; the vegetation is determined by the alternating dry and wet seasons.