Saturday, June 10, 2023

The Good, the Bad, and the Ugly in Vernal Pools

Alopecurus saccatus in margins of vernal pool at Jepson Prairie Reserve, CA

For a detailed look at vernal pools and the endangered species within them, click here.

The cast of characters in and around a vernal pool is quite large, but there is a certain organization to the entire panoply. In fact, it is possible to arrange the types of grasses in an idealized concentric circle, with the star of the entire show at the center (see diagram below).

At the periphery are the species that form the majority of grass cover in California. These are the naturalized exotics such as Lolium multiflorum, Avena barbata, Hordeum spp, and others. The members of this group have dominated the California landscape since their arrival during historical times, pushing the natives into isolated pockets. 

Lolium multiflorum near vernal pool in Sacramento area
Interestingly, the iconic "Golden Hills" of California are a recent phenomenon that is the result of this displacement. But whereas these naturalized exotics have free rein over most of the state, they cannot seem to overcome the vagaries of life in vernal pools. To put it simply, the seedlings drown when the pool fills up with water in the spring.

Aegilops triuncialis (barb goatgrass) near vernal pool in Sacramento area
Among these naturalized exotics are the more recent annual invasives, such as Aegilops triuncialis (barb goatgrass)  and Taeniatherum caput-medusae (medusahead grass). These winter annual grasses outcompete the naturalized exotics to form monocultures, with T. caput-medusae being one of the worst among the new invaders. These are the "baddest of the bad", to put it in colloquial terms.
Taeniatherum caput-medusae (medusahead grass) near vernal pool in Sacramento area
And if there is one species that people might point to as being the "bad AND the ugly" in the group, it would probably be medusahead grass. Masses of still-green T. caput-medusae waving in the wind are undeniably pretty, but once the grasses dry up, the long, wicked looking awns that curve in all directions is something that can only be found in the most extreme alien science fiction movies.  
Taeniatherum caput-medusae (medusahead grass) near vernal pool in Sacramento area
However, just like the naturalized exotics, all these new invasives are just as vulnerable to drowning, and they are seldom found within the vernal pool itself. Instead, I have found masses of T. caput-medusae, A. triuncialis and others such as Bromus diandrus relatively farther away from the pool margins.
The Ugly: What's that crawling up your backpack??!!! T. caput-medusae dried spikelet
Immediately closer to the center of the vernal pool are annual natives such as Alopecurus saccatus (commonly called Pacific Foxtail in the local area), a truly distinctive species that I found sporadically around Olcott Lake in Jepson Prairie Reserve. 

Alopecurus saccatus in margins of vernal pool at Jepson Prairie Reserve, CA
The margins of vernal pools can be flooded at times, and this creates anaerobic conditions in the soil. The lack of oxygen in the soil at these times kills the naturalized exotics and invasives, but some annual natives like A. saccatus have physiological adaptations that allow them to thrive beyond the reach of the usually dominant grasses.

I must admit that when I first discovered this species, I thought at first that they were Orcutt grasses. The specimens were small and compact, the flowerheads rising from the fleshy sheaths like heads poking out of bulky garments. They reminded me most of all, of toy soldiers standing at attention.

Orcuttia viscida
The deepest and most central parts of the pool are where many of the Orcutt specimens make their homes. These areas are inundated for months at a time, which is a prerequisite for this mysterious group of grasses. In addition, the presence of long term water clears the area of potential competitors.

As mentioned in a previous article, the Orcutt grasses have an array of specialized adaptations that allow them to survive the alternating wet and dry conditions of the pool. This includes a fully aquatic growth form at the beginning of its life, as well as numerous glands that produce viscid fluid to help prevent desiccation during the latter parts of its growth.

Orcuttia viscida
It is in this deeper central part that the "good" guys thrive, and it is up to us to make sure that they continue to hold on against the encroaching hordes of naturalized exotics and invasive grasses by continually working to preserve the last remaining vernal pools.

Naturalized exotic Hordeum spp. (?) close to vernal pool in Sacramento area, CA

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