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Friday, October 2, 2015

Natural Resource Profile: Rubber Rabbitbrush




Blooming rabbitbrush in the Antelope Valley

Living and working around Tejon Ranch, it is easy for one’s attention to be drawn to all of the things that make this region special. With so many rare/endangered/endemic species and such diverse habitats, it’s easy to overlook some of the more “common” resources that are widespread and happen to also live on Tejon Ranch. In particular, there’s a plant that can be found in arid, high-elevation habitats throughout the West that is easily ignored, but plays an exceptional ecological role. That plant is rubber rabbitbrush. As the Latin name Ericameria nauseosa suggests, this is not a plant that is frequently handled, or highly regarded by humans. In fact, it is common to hear people complain about rabbitbrush-induced allergies during its flowering season in late summer/early fall. 

Rabbitbrush provides habitat for a variety of species
Rubber rabbitbrush is a perennial shrub in the Asteraceae or composite family. It’s well-adapted to dry climates with deep tap roots to access ground water and narrow leaves with hairy trichomes that reduce exposure to sunlight and water loss due to evapotranspiration (Sawyer, Keeler-Wolf, and Evans). In August and September, bright yellow flowers form at the terminus of each stem. This bloom represents a crucial resource for pollinators as late summer in California is when most plants are senescent and flowers can be difficult to find. Of course, where there are pollinators, there are things that eat pollinators, and the rubber rabbitbrush bloom becomes critical for supporting a variety of life during this tenuous period in our Mediterranean climate. During our BioBlitz with the Lorquin Entomological Society at the end of August, the blooming rabbitbrush was one of the best places to seek insects outside of the springs. Orthopterans (grasshoppers, crickets, katydids) were particularly numerous in these plants. Each shrub appeared to have its own fauna enjoying the protection and abundant resources of their host plant.

This northern checkered-skipper was grateful for a flowering perch during the dog days of summer.


Shield-backed katydid hiding in teh interior of a rabbitbrush plant.



 In addition to being an important plant for insects and other pollinators, rubber rabbitbrush is a significant successional species throughout its range. As a native plant that does well in disturbed soils, rabbitbrush is often one of the first colonizers in an area after a flood, fire, heavy grazing, or human activity such as road grading. Its well-developed root system helps to stabilize soils and reduce erosion. Rubber rabbitbrush seeds are dispersed by wind, so they can spread quite a distance, allowing the plant to colonize new territory easily. The seeds likely spread on the fur of animals as well. 

Does the relative lack of other plants blooming during rabbitbrush's flowering season mean a higher instance of rabbitbrush pollination due to less competition?
Anecdotally, it appears that long-term grazing on Tejon Ranch has benefitted rubber rabbitbrush. A   photo taken by AF Weislander during his vegetation mapping surveys in the high-elevation Cottonwood Creek area of Tejon Ranch has this footnote,

 Panorama looking northeast to south of east. Types: Quercus garryana semota and wislizenii chaparral, pinon and Digger pine on south slopes, open woodland of Quercus kelloggii and lobata. Note evidence of over grazing indicated by rabbit brush in grassland.

AF Weislander's photo indicating a relationship between habitat changes favoring rubber rabbitbrush due to grazing.

While this is a far cry from a peer-reviewed scientific conclusion, it does provide some insight about possible changes that have occurred on the landscape. If in fact historical sheep and contemporary cattle grazing have created a more suitable habitat for rabbitbrush in certain locations, it begs the important question of whether land managers like the Conservancy can or should consider “restoring” sites that may have been invaded by rabbitbrush after grazing. Do we even know what the habitat looked like before the rabbitbrush invaded?  After all, rabbitbrush is a native species. Does it make sense to try to replace one native species with another?

One answer to this question might come from examining ecological role of rabbitbrush vis-à-vis other native organisms. In Cottonwood Creek, the Conservancy and our research partners have noticed an incredible number of valley oak (Quercus lobata) seedlings. This is significant because many observers have noted a general lack of oak regeneration past the seedling stage throughout California (McClaran 1986; Griffin 1976; Allen-Diaz and Bartolome 1992). In some cases, it has been observed that overstory “nurse” shrubs may be important for tree seedling survival by protecting the young trees from prolonged grazing and moderating the microclimate (keeping the seedling slightly warmer in winter and slightly cooler in summer). However, Callaway (1992) was unable to draw a correlation between nurse shrubs and valley oak seedling survival. Cottonwood Creek is in the Garlock fault zone, which means there may be high water tables due to trapped or “perched” aquifers resulting from the faulting activity. Is that what is actually encouraging the oak seedling survival in this area? 
Amazing valley oak (Quercus lobata) recruitment in the "Catskins" area of Tejon Ranch. What role if any does rubber rabbitbrush play in the success of these young trees? Photo by Mike White
The Conservancy hopes to spend some time investigating these relationships as we ramp up our work in oak woodlands on Tejon Ranch. One project that is just getting started is an effort to study the oak regeneration and its relationships both grazing pressure and rabbitbrush. If possible, it would be interesting to also find oak seedlings other under potential “nurse” plants such as gooseberry (Ribes sp.), coffeeberry (Frangula californica), and others. 

No matter what the outcome of that investigation, it is clear that rabbitbrush is an integral part of the ecology of Tejon Ranch and beyond. Its presence or absence may have significant management implications that we hope to gain an increased understanding of. As we try to untangle the convoluted web of ecological, historical, and climate future scenarios that surround our landscape, we’ll continue to enjoy the sea of yellow that greets us every fall. We won’t breathe too deeply, though. It gives us allergies.



References: 

Allen-Diaz, Barbara H. and Bartolome, James W, "Survival of Quercus douglasii (Fagaceae)  Seedlings Under the Influence of Fire and Grazing," Madrono 39, no. 1 (1992): 47-53.

Callaway, Ragan M., "Effects of Shrubs on Recruitment of Quercus douglasii and Quercus lobata in California," Ecology 73, no. 6 (1992): 2118-2128

Griffin, James R., "Regeneration in Quercus lobata Savannas, Santa Lucia Mountains, California," The American Midland Naturalist 95, no. 2 (1976): 422-435

McClaran, Mitchel P., "Age Structure of Quercus douglasii in Relation to Livestock Grazing and Fire," (Doctoral Dissertation, UC Berkeley),

Sawyer, John O., Keeler-Wolf Todd, and Evens, Julie M., A Manual of California Vegetation. Sacramento: California Native Plant Society Press. 2008.