Snakes in Paradise

Taeniatherum caput-medusae (medusahead grass)

I visited the  Phoenix Park Vernal Pools in Fair Oaks, California last week.

The park is a designated National Natural Landmark because of its vernal pools, and for those who do not know what these are, vernal pools are a unique type of ephemeral environment which are filled with rain or snow water for part of the year, but which have no inlet or outlet. Vernal pools support an amazing range of plants and animal, some of which are very rare and endangered, and the reason I was there last week was to see whether I could catch a glimpse of the dried remnants of the Sacramento Orcutt grass (Orcuttia viscida) and perhaps Orcuttia tenuis.

Entrance to the Vernal Pool section of the park

If you are wondering why I am so intrigued by these species, then I would strongly suggest reading the article on vernal pool annual grasses from the Winter 2009 edition of the California Native Grasslands Association. You can read the PDF version here. It will go a long way to explaining why  find these rare grasses so fascinating, and why I made a special trip to see them in Sacramento during my West Coast trip.

I arrived in late morning, and there were a few people about. The park environment itself was dominated by the usual mix of golden-hued annual exotic grasses that have reshaped California, with a few trees scattered around. These annual exotics form the iconic golden hills in the state and its neighbors, and were brought over when Europeans arrived a few hundred years ago. 

The typical grasses in the menagerie that I saw included Avena spp (Avena fatua and A. barbata), Bromus spp (B.diandrus, as well as a species that I found quite curious called Briza minima.

In addition to the usual exotic grasses, I also found a colony of the hegemonic invasive grass Taeniatherum caput-medusae (medusahead grass). I have posted about this species before, and how it has been transforming rangeland in vast areas of the West, and it can be recognized by the twisted awns that resemble the snakes in the fabled Medusa's head.

Medusahead with the distinctive twisting awns

The medusahead formed its distinctive dense thatch as it sprawled along a 10 meter section parallel to the trail, pushing aside other grasses. This high-silica thatch prevents other plants species from growing in the midst of the stand of medusahead, and I was alarmed that the infestation might spread further and endanger the vernal pools.

Dense thatch of Taeniatherum caput-medusae (medusahead grass) in Phoenix Park

I took note of its location, then continued to wander the trails for awhile, taking pics but not exactly sure where the actual pools would be. I knew they would be dried up by now, but I had no idea how to distinguish the dried pools from the surrounding grounds. 

Fortunately, I met a local man who was also using the trail, and he kindly pointed out to me those areas which would have been filled with shallow water during earlier in the season. He mentioned that they stood out because wildflowers bloomed from them at one time.

Dark depression that marks the site of the vernal pool

The dry vernal pools were depressions that had a slightly darker color than the surrounding area. One of them was close to where I had been walking, and you can clearly see the outlines of the pool in the image above.

Since we were not allowed to step outside the trail,  I used a drone to view the pool from above, and again the pool was quite obvious from several meters up.

Vernal pool from several meters up.

It was while photographing the pool that I noticed the patch of yellow-white that lay near its center. The patch was quite distinctive, but I could not make out what it was from the trail, so I moved the drone closer to hover over it and took several pics. 

Possible medusahead grass in center of vernal pool

Imagine my surprise when I looked at the image later on my laptop and discovered that the white patch looked to be a thatch of medusahead grass!

A quick survey of the literature mentioned that this species could be found in the vicinity of vernal pools, and sometimes all the way to the high water mark of such pools. But like many other grasses, it did not seem to be able to proliferate in the pools themselves, so I am at a loss as to how this colony could thrive in this case. Perhaps there was a slight mound in that part of the pool that allowed the medusahead seedlings to take hold.

Whatever the reason, the best course of action would be to positively identify the grass, and take measures to remove these particular snakes from the park, and especially from the pools themselves. Without direct and decisive intervention, this hegemonic species might slowly take over the park, turning it into a monotypic stand of medusahead.