Lauren processes native yucca seeds.
When I tell people I collect seeds for seed banking, the first question I’m asked is if the collections are stored in the Svalbard Global Seed Vault, which is located on the Norwegian island of Spitsbergen. While it’s awesome that so many people know about that bank, please know that it is used primarily for agricultural species. Native plant species, especially those that are not threatened or endangered, receive much less attention. There are very few native seed banks around the world, and San Diego County happens to have one of them.
Seedlots await processing. Note the cut out in the wall, showing the building is made of straw bales.
The seed bank here at the San Diego Zoo Safari Park houses more than 500 different plant populations. It is a straw-bale, solar-powered structure that has all sorts of interesting contraptions used for seed processing. The seed bank is located at the back of the Safari Park and is the first permitted straw-bale building in San Diego County. Cleaning and storing seeds is time consuming and often tricky, but it can also be very rewarding. Our goal is to collect multiple populations of the same species, as each population may have adaptations unique to its location. San Diego County is home to over 1,500 different native plant species, so that adds up to a lot of seed collections!
When we first find a population that we want to collect, we take clippings of the plant and press them to preserve the specimens as herbarium vouchers. It is best to take a sample that has both flowers and leaves so that a specialist can verify the species. Our herbarium vouchers are sent to the San Diego Natural History Museum for verification. Data on the location, soil color, slope, habitat, and associated species are also collected. After theses initial steps are taken, we monitor the population until enough of the seeds ripen for a collection. We often have to compete with herbivores and rough weather to collect the seeds before they are lost.
Lauren at work conserving seeds native to San Diego County.
Once the collection is made, it is taken back to the seed bank and processed. The steps involved in processing the collections generally depend on each particular species. The seed and plant material is often rubbed over screens of various sizes until the seed is separated from its various shells, pods, leaves, pappi, and stems. Once separated, it is run through air separators so that lighter material is blown off and/or the seeds are lifted away from the heavier debris. Even after all of these techniques are used, we are often left with seed that is still mixed with extra plant material. When this happens, our only option left is to clean the seed by hand. With larger seeds this can be fairly easy, but with the small seeds it often involves a microscope, tweezers, and a lot of patience!
Clean seed lots are placed in the drying room to lower their moisture level. Once the seeds reach a moisture content of five to nine percent, they can be placed in long-term storage in a hefty freezer. Five hundred of the seeds are counted out into groups of 100 and then weighed. We then weigh the entire collection of seed in order to estimate the total number of seeds. At least 10,000 seeds are placed in storage at a time. If there are extra, they are set aside for future restoration and research. The seed is sealed in double-layered foil bags and frozen. It has been proven through germination testing that frozen seeds remain viable for decades.
Lauren Anderson is an intern at the San Diego Zoo Institute for Conservation Research through the Bureau of Land Management’s Seeds of Success Program. Read her previous post, Exploring Anza-Borrego Desert.
Wow, leave it to SDZ to even collect and save for future use the native plants of the area!! Kudos!!
After reading this article I have the utmost respect for SDZSP. This article about the native plants at your doorstep being as valued as any fuzzy Panda, convicts me that you have your priorities straight when it comes to the value of life forms. Most life forms are only a generation away from extinction, no matter how common they may be at this time. I would like to know what seed gathering modifications you make when dealing with rare and endangered plants in San Diego County?
Hi Paula,
We do occasionally take contracts to collect rare or endangered species, but for the most part we only collect common native plants. Our goal is to make multiple collections of the same species in different geographic locations. By doing this, we are able to capture intraspecific variation found throughout the county.
One rare plant collection that we have made is the Torrey pine, one of the rarest pine species in the world with only about 4,000 left in the wild. The seed collection of this tree was made through the collaborative efforts of the Applied Plant Ecology Division, the City of San Diego, and horticulturists/arborists from both the San Diego Zoo and the Safari Park. The cones were sent to the State of California’s Lewis A. Morgan Reforestation Center for processing and drying. We do not have the facilities to handle such a large quantity of pine cones at the Safari Park’s Seed Bank.
To answer your question, the collection techniques are dependent on the species. For all our collections we are careful not to take too much seed, but we are especially careful when dealing with rare or endangered species.
A collection of a rare species like the Torrey pine will be left in cold storage in case disaster strikes what’s left of their population. The seeds will not be used for germination testing or any other research.
-Lauren