See the context of this sign.

Nurses of the Desert

Shrubs account for most of the greenery in the
Sonoran Desert and, while sometimes unnoticed
among the larger cacti, act as vital nurse plants to
young seedlings and provide safe havens from
predators for smaller animals.

Several creosote bushes along the trail shelter
nestlings in their leafy foliage and provide seeds
for ground squirrels, quail and rabbits; kangaroo
rats nest in their root systems. The wolfberry's
small red fruits feed cactus wrens. The abundant
triangle bursage protects saguaro seedlings from
rodents and birds, and shades hedgehog and
fishhook cacti from summer heat and winter frosts.

Notice the spacing of shrubs; the competition for
moisture and nutrients is constant. These plants
protect their space by keeping rivals for food or
water away. The creosote bush roots, for instance,
secrete a growth inhibiting toxin into the ground to
discourage encroaching plants.

Don't miss the rest of our virtual tour of Saguaro National Park in 687 images.