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Friday, July 11, 2014

Managing Grasslands on Tejon Ranch: The Ecological Site Concept, by Dr. Mike White, Conservation Science Director



One of the Conservancy’s priority resources for management at Tejon Ranch is our grasslands.  Tejon Ranch supports over 100,000 acres of grasslands, which in-turn support many native plants and animals for which we would like to enhance conditions.  Under the Tejon Ranch Conservation and Land Use Agreement, conservation of the Ranch is via conservation easement and under these conservation easements the Tejon Ranch Company retains the right to run livestock in conserved lands.  Therefore, developing a better understanding of our grasslands and identifying ways to better manage them has been a high priority for the Conservancy since its inception.  To gain this knowledge, we embarked on what is now a 5-year research partnership with the UC Berkeley Range Ecology Laboratory directed by Dr. James Bartolome.  The research briefly discussed below will ultimately serve as the PhD project of Sheri Spiegal, who is expecting to finish her degree at the end of the year.  You can find more details on our grassland research at our website: http://www.tejonconservancy.org/research.htm

The focus of the Tejon Ranch grasslands research has been to document how the composition of plant species in our grasslands changes from one location to another on the Ranch and from year to year (primarily due to changes in weather).  One of the findings of Sheri’s research is that geographic locations that support grasslands on Tejon Ranch can be usefully organized into ecological sites.  An ecological site is a set of land units with a common climate, similar topographic and soil characteristics that support similar potential vegetation, and respond similarly to management.  The idea is that a site with a particular combination of soil, topography, and climate will support a specific set of plant species, while another site with different soil, topography and climate will support a different set of plant species.  For example, Sheri has found that sandy soils at flatter, low elevation locations in the San Joaquin Valley support a different set of plant species than do silty soils, on steeper sloped locations at higher elevations in the foothills of the Tehachapi Mountains. 

Ecological sites can change over short distances. In the Tejon Hills, soils change quickly making room for a variety of rare plants. In the northwest (green) portion of this area, plants such as Comanche Point Layia (Layia leucopappa) can grow due to sandy soils. In the eastern, higher portion of the hills (red), clay soils support more geophytes, like striped adobe lily (Fritillaria striata).

To-date eleven ecological sites supporting grasslands have been identified at Tejon Ranch.  Furthermore, Sheri has also found that plant species in our grasslands vary in their species composition from year to year depending on weather, but that the changes in species composition within ecological sites are more similar than the changes seen between different ecological sites.  So the ecological site concept does appear to be a useful way to describe grassland plant communities and their changes over time.  The use of ecological sites in range management is being promoted by agencies such as the USDA Natural Resources Conservation Service (https://esis.sc.egov.usda.gov/About.aspx), and the Conservancy is using this ecological site framework to organize our grassland and grazing management planning.


"An ecological site is a set of land units with a common climate, similar topographic and soil characteristics that support similar potential vegetation, and respond similarly to management."

 


One of the interesting and relevant findings of this research is that some ecological sites tend to support higher abundance of native plant species, while other ecological sites are always dominated by nonnative plant species, but the abundance of natives can vary dramatically from year to year based on weather.  Look at the photos below, which show two different ecological sites (Sandy Alluvial Flats and Sloping Loamy Sands) in two different years (2010, 2011).  In general, the colorful wildflowers are native species while the green grass is predominately nonnative.  You can see that the Sandy Alluvial Flats ecological site supported good native wildflowers in 2010, whereas the Sloping Loamy Sands ecological site was dominated by nonnative grass.  However, in 2011 both sites were dominated by nonnative annual grass.
The Conservancy’s challenge is to identify grazing management regimes that can enhance the native species that we care about.  Based on this body of grasslands research, we believe that some ecological sites, like the Sandy Alluvial Flats site, have a greater potential to support native plants than do other sites (like the Sloping Loamy Sands site).  Understanding ecological sites provides us information to consider where we prioritize our scarce management resources within the large area of Tejon Ranch to get biggest native grassland biodiversity bang for our buck. This research also gives us information on how to manage grassland biodiversity.  We believe that in some cases the high abundance of nonnative grasses depresses habitat quality for not only native plants but some native animals as well.  We are currently working with the grazing lessees at Tejon to utilize livestock as a management tool to help remove dense nonnative grasses in those ecological sites that support high native plant potential to improve grassland habitat quality.

Keep in mind that these are management experiments – we must document whether the proposed managed grazing regime achieves our conservation objectives or not.  However, we feel that 5 years of grassland research has provided us with a strong science foundation rationalizing these experiments, and we’ll learn about their efficacy from our long-term monitoring.  Stay tuned as we continue to learn more about our grasslands and how to manage them!!