Thursday, November 21, 2013

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?



  1. I'm glad you took the time to point these facts out to us about vernal pools. I will look at them differently now. :)

  2. Looks like a cool place to visit. I am paid up at this campground until Dec 8th and then I plan to travel around to several Texas State Parks.

    1. This is a beautiful place, but there is no RV camping here. Plenty of campsites nearby though, so you can still visit!!

  3. Looks like a great topic for a nature talk. -Rick