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.
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.
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.