Sunday, July 15, 2007

BBNP Photo Report ~ the Sotol Grasslands

Between 3500 and 5000 feet in Big Bend is a grassland ecosystem. The grassland is somewhat ecotonal between the lower desert and higher woodlands. It may be the most diverse ecosystem in the park, and species composition in any one place is highly variable.

Sotol (Dasilyrion wheeleri) is the primary indicator species and give the grassland it's name.

Sotol is a plant in either Liliaceae or Agavaceae, depending on if one is a lumper or a splitter. Thier flowers may be up to three meters tall.

The 'wood' of the flowering stalk is often used to make excellent walking sticks.

Apparently animals like thier tough serrated leaves as well.

Here is a close-up ofa Sotol flower. There were many insects crawling around each cluster of anthers.

Also common in the grassland is Indian Basket Grass (Nolina erumpens).

The Sotol Grasslands are the lowest elevation in the park where we see one of the deserts most infamous characters, Agave havardiana. Also called Big Bend Century Plant, this agave is the primary contributo to tequila. At various sundry times many, including myself, have both blessed and cursed this plant.

I failed to take a photo of an entire flowering stalk and rosette. But the stalks can be over six meters tall. They have great leaves.

The panicles can be 30 cm in diameter. They attract many insects,bats, and birds.

There are cacti in these grasslands as well. This is Opuntia macrocentra or Purple-Padded Prickly Pear.

Koeberlina spinosa or Allthorn. The thorns were all grean and pliable when we were in Big Bend because of the high amount of rain recently. The Spanish name for this plant is "Corona del Cristo".

Bee Bush (Aloysia grattisima) with Bee

I don't know what this shrub is. It sure has great flowers though.

Rain Lily (Cooperia drummondii)

I don't know what this is either. I do know that I took a photo of the same flower our way to Austin a few months back, so it must be a generalist and common to more than just the Sotol.

I've since forgotten the name of the obvious hummingbird pollinated plant. I took several pictures in several locations, but could not capture the flowers clearly. It is a great little shrub.

I actually saw more lagomorphs in the Sotol than in the desert. This is a Black-Tailed Jackrabbit (Lepus californicus).

Several grasses are common in the Sotol. Bouteloua brevista, or Chino grass has great sessile flowers with red anthers.

I saw several bluestems (Schizachrium spp.). I've had the privilage to get to know this species very well. My friend Marnie did her master's thesis working with this plant and we harvested individuals to plant part. One can learn a lot by tearing plants apart.

This grass was common near our camp. It looks to me like a Poa or Bluegrass; I'm not certain though. The above mentioned lagomorphs like it though, I do know that.

When the Big Bend became a park, the ranchers who had run cows there were displaced. As part of the agreement, they were given five more years to grow cows in the Sotol grasslands. Usually ranchers are a logical lot; they knew how many cows could be put on a particular piece of ground. They normally would have practiced discretion and stewardship, however, when they knew that the land would be reverted to federal control after five years, they grazed the hell out of it. Thus, much of the Sotol grassland is shrubby. Since 1950, the grasses are slowly returning, but shrubs remain a very important component of this ecosystem. This common shrub is White-Thorn Acacia (Acacia constricta).

And it's fellow legume, Catclaw Mimosa (Mimosa aculeaticarpa)

And, Catclaw Acacia (Acacia roemeriana).

And Mesquite (Prosopis glandulosa), with obvious red beans.

The fly on this Mesquite has a great looking head.

I don't really have anything poignant to say about the Sotol grassland. In many ways the Sotol is ecotonal between the low desert and the higher woodland. Species come into and out of the assemblages with elevation. This grassland is a Gleason/Clements type of place, I'm reminded. Questions come to mind. Do individual species matter? Are there really ecosystems at all, or are they simple constructs of n-dimensional space in our own minds overlaid on real space and time? Of course there are real answers to these questions, but the Sotol seems grassland, desert and woodland at different times in different places. One could spend a career describing and understanding the Sotol.