Vernal Pools and Islands of Vegetation

I already described how Vernal Pools support Fairy Shrimp on Enchanted Rock.  Another result of the Vernal Pools are islands of vegetation that form up on the bare rock.

Vernal Pools are shallow depressions that temporarily hold water after rain. Algae grows in the water, and organic matter also get trapped.  In addition, blowing sand and stone fragments are also trapped in these pools. In the image below a Vernal Pool is drying out.  You can see the algae and other material left on the bottom.

Drying Vernal Pool

Over many years enough sediment and organic matter might collect in a pool to support plant life.  Grass seed blowing across the rock will find its way into the pool and sprout. In the middle pool below you can see grass sprouting on the left side of the pool.

Vernal Pool with Vegetation

Once grass starts to grow the depression catches even more sediment and organic matter, and larger plants gain a toehold.  Cactus and Yucca seem to be the next plants to sprout.

Prickly Pear and Grass

Yucca and Grass filling Vernal Pool

With enough time the soil and vegetation will deepen, and may eventually support small trees. Unfortunately the tree in the image below seems to have succumbed to the drought. 

Vernal Pool with (dead) Tree

Who knew that these shallow depressions in rock could eventually support an entire plant community?

Mark