Plants

Plants

8

Tecate Cypress: Risky Reproduction

Lauren and Sandra Mardonovich sow Tecate cypress seeds in long pots that provide spacious room for roots.

The Tecate cypress Hesperocyparis forbsiiis a tree found only in Southern California and northern Baja California, Mexico. It has a limited range and is fire dependent, which means the cypress needs fire to reproduce. The cones of this species are serotinous, which means the seeds are released by an ecological trigger (in this case, fire) instead of being released once they reach maturity. When the cones are exposed to heat, the resin that keeps them sealed is melted, the cone opens, and the seed is released. Without fire, the Tecate cypress keeps its seed bank within persistent cones in the tree canopy. When a fire burns a mature stand of Tecate cypress, new seedlings pop up in its place. If this second generation is burned before it reaches maturity, it could wipe out the entire population. There are only four stable populations remaining in California, three of which are in San Diego County. It is because of its limited range and risky reproduction technique that this tree is such a sensitive species.

Tecate cypress cones collected from Otay Mountain await processing.

The Applied Plant Ecology Division at the San Diego Zoo Institute for Conservation Research has partnered with the Nature Conservancy, the Bureau of Land Management, and the California Department of Fish and Game to preserve this unique species. The goal of the project is to provide a safe guard against high-frequency fires wiping out the population.

To do this, we collected enough seed from a mature population to have a portion for safe keeping in the Native Plant Seed Bank at the Safari Park and a portion that could be germinated and planted as a nursery stand. Cones were collected from Otay Mountain and processed at the State of California’s Lewis A. Morgan Reforestation Center. The processed cones resulted in thousands of seeds, and of those, a fraction was planted. From the planted seeds, we are hoping to get 400 to 500 seedlings.

Here's a close-up view of the seeds before being covered with soil.

Once the seedlings have grown to a suitable size, they will be planted at the Rancho Jamul Ecological Reserve. The planted cypress trees will be monitored over the next six months. These trees will be used as a sort of “plantation” where more seeds can be collected as needed in case the other stands burn before reaching sexual maturity.

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, The Desert: Blooms and Hail.

2

The Desert: Blooms and Hail

Grape-soda lupine

San Diego County is the most botanically diverse area in the U.S., with nearly 2,000 species, many of which are endemic (unique to a defined geographic area, so many are found only in San Diego County). There are not many places where you can experience the ocean, the snow, and the desert within a couple hours. The desert transition habitat is found down the east side of the Peninsular Ranges, and this is the site of our recent seed collection trip. The weather forecast looked ominous, but we were optimistic. To get to our site, we had to drive up and over the Cuyamaca Mountains and out into the lower elevations beyond.

Apricot mallow

When we finally reached our site, we saw a mix of cacti, shrubs, and huge granite boulders. It was freezing cold and very windy. At certain points the wind became so strong it was difficult to open the truck doors to get out and identify plants. Despite the rough conditions, it was a beautiful place to explore. We saw desert apricot Prunus fremontii, golden gooseberry Ribes quercetorum, and grape-soda lupine Lupinus excubitus in bloom.

As the day wore on, the weather only got worse. When we tried to collect a sample of apricot mallow Sphaeralcea ambigua, the rain turned to hail, and we decided to admit defeat for the day.

McCain Valley overlook

On the drive back up and over the Cuyamacas, the hail turned to snow! It was so much fun to watch everything turn white throughout the course of our drive. We followed a snowplow most of the way down the mountain; I never would have imagined experiencing something like that in Southern California! As we dropped in elevation, the snow slowly changed back into rain and everything turned green again. It was odd to realize that we had only been a half an hour away from the ocean.

San Diego is truly a remarkable place, and I couldn’t ask for a better area to study plant diversity.

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, Wake Up, Seeds! Germination Testing.

7

Analyzing Bamboo and other Foods

Bai Yun analyzes her nutritious bamboo.

What, if any, analysis is conducted at the San Diego Zoo to check the nutritional value of the different kinds of bamboos given to the pandas? The Nutritional Services departments at the Zoo and San Diego Zoo Safari Park routinely sample our animals’ foods for nutrient analysis. We do not have a complete nutrient laboratory onsite, but we send feed and forage samples to multiple laboratories around the country to get complete nutrient profiles as needed. What our nutrition laboratory can do is prepare samples for analysis through oven- or freeze-drying techniques and grind the samples to 1 millimeter to ensure a representative sample.

It has been a number of years since bamboo has been analyzed for the giant pandas. Joyce Nickley, a former keeper at the San Diego Zoo Safari Park, completed her masters of science research by looking at the nutrient content of bamboo, with the results published in her thesis as well as in a chapter in Giant Pandas: Biology, Veterinary Medicine, and Management (2006, edited by D.E. Wildt, et al.). Additional browse plant analysis has been completed on multiple primate browse species, four of the many species of eucalyptus grown for koalas, four species of acacia browse, and pennisetum used for the elephants. Every load of hay (Bermuda grass, Sudan grass, and alfalfa) is sampled for nutrient analysis, and our custom feeds, commercial feeds, and prey items (insects, fish, rodents) are routinely analyzed.

Our typical analysis includes moisture, protein, fiber (neutral detergent fiber, acid detergent fiber), and minerals (calcium, phosphorus, magnesium, potassium, sodium, iron, zinc, copper, manganese, molybdenum, sulfur chloride, and cobalt). In addition to these basic analyses, we often have lignin, sugar, starch, and fat analyzed. Due to the increased cost, we only analyze vitamins (A, D, E, C, and B vitamins), fatty acids, amino acids, selenium, and iodine for specific projects or clinical cases.

Routine nutrient analysis of the feeds we use at the Zoo and Park has allowed us to build a database of feed nutrient profiles that help us formulate diets for all of our animals, including our popular pandas, to keep them healthy and satisfied.

Michael Schlegel is the director of nutritional services for San Diego Zoo Global.

1

Elephant Odyssey through Horticulturist Eyes

Golden barrel cactus

Zoo InternQuest is a seven-week career exploration program for San Diego County high school juniors and seniors. Students have the unique opportunity to meet professionals working for the San Diego Zoo, Safari Park, and Institute for Conservation Research, learn about their jobs, and then blog about their experience online. Follow their adventures here!

Today at the San Diego Zoo we met with horticulture expert Mike Letzring, who took us on a tour through Elephant Odyssey. Mr. Letzring, who is the collections manager, pointed out the diverse collection of plant life found in Elephant Odyssey. He shared his perspective on plants, which goes much deeper than looking at a plant’s surface. He sees a rare and unique live organism that has a super capability to survive with little to no water!

Mr. Letzring shared with us how he and his team of landscapers are not only in charge of the plants outside of the exhibits but also for the plants that go inside. In this rattlesnake exhibit at Elephant Odyssey, the Horticulture Department chose plants that are native to San Diego because they are relatively drought tolerant like the plants rattlesnakes are used to being around in their natural home, the desert.

In Elephant Odyssey, we stopped at a very interesting tree. This tree is sometimes referred to as an “upside-down tree” because its branches look like a root system. Mr. Letzring, explained to us that this tree is very rare and indigenous to Madagascar. Make sure the next time you are in Elephant Odyssey, you take a moment to look at this amazing tree!

This brilliant orange and yellow flower is indigenous to San Diego. Mr. Letzring tells us that this unique-looking flower is called “the monkey flower” because its petals resemble the shape of a monkey’s face. Can you see it?

Along this particular walkway in Elephant Odyssey, do you notice a theme among the plants? When designing this area, Mr. Letzring and his team wanted to go with a theme that included plants with spines (thorns). The plants were received from a generous donor, a local San Diegan!

One of the plants we stop to look at was the African Erythrina latissima. This plant’s biggest threat is the gall wasp. Mr. Letzring showed us how the gall wasp penetrates the plant, which ultimately destroys it.

One of the last plants we came across on our tour was the golden barrel cactus. To our surprise, it’s actually possible to pull out the flower of the cactus to reveal a good source of moisture inside it. We learned that this cactus is very valuable to animals that come across it in the hot desert.

 

At the end of the tour, the interns had the rare opportunity to sample these delicious exotic fruits! What a treat to sample dragonfruit! It is clear that Mr. Letzring and his team work hard to spice up the Zoo with a variety of plants to not only diversify the landscape but for us to learn about the amazing world of horticulture.

 

Kayla, Photo Team
Week Two, Winter Session 2012

0

Focusing on Plants

Zoo InternQuest is a seven-week career exploration program for San Diego County high school juniors and seniors. Students have the unique opportunity to meet professionals working for the San Diego Zoo, Safari Park, and Institute for Conservation Research, learn about their jobs, and then blog about their experience online. Follow their adventures here!

When you go to the Zoo, the first attraction you head toward may not be the landscape. You may head straight through Elephant Odyssey to check out the lions or massive Asian elephants. But if you go straight to the animals, you could miss some of the elaborate ficus plants, olive trees, or sunflowers that spot the trails. Though the animals are the main attraction at the Zoo, the plants are pretty important, too.

Michael Letzring is the plant collections manager at the Zoo, and last week he spent a few hours with InternQuest, teaching us about the Zoo’s landscape and why it’s so amazing. Mr. Letzring has a degree in landscape and horticulture from Mesa College and 31 years of experience working in his field. He started his own landscape company, has worked in a nursery, and has been at the Zoo for 15 years. Although he loves animals, he is even more passionate about plants and where they come from. Mr. Letzring has been very invested in the Zoo’s conservation efforts over the past decade and a half.

As we wound through Elephant Odyssey, Mr. Letzring pointed out the diversity of the trees, flowers, bushes, and cacti that line the pathways. He talked about everything from the African thorny acacia to the stout bottle tree and why these specific trees were planted by certain enclosures (i.e., African thorny acacia would typically be by the giraffes or elephants since it would occur in their natural habitats). Yet the most impressive part of the tour, one might argue, was Mr. Letzring’s incredible memory. He knew each plant’s name, almost all of their Latin names, and lots of facts about them.

As our group walked along, passing the animals’ enclosures and instead focusing on the unique flora, Mr. Letzring described some of the most rewarding aspects of his job. He focused the first part of his answer on conservation. As the plant collections manager at the San Diego Zoo, he really enjoys being able to show visitors all of the different kinds of plants that grow in the world, especially the endangered ones. In fact, Mr. Letzring was excited to show us the Zoo’s Madagascar Forest, where some very unique trees, specific to the island nation, grow. He explained that most of the plants in Madagascar, including the triangle palm that can be seen at the Zoo, are endangered due to deforestation for local farmland. Not only does Mr. Letzring get involved with conservation here at the Zoo, he also supports the Zoo’s conservation mission in other places. Every year or so, Mr. Letzring travels to Molokai to remove exotic weeds and plant native flora, helping to preserve some of Hawaii’s unique, endangered plants.

At the Zoo, Mr. Letzring maintains a very busy schedule. His typical day of work includes briefing the Horticulture Department and then attending to each plant-related project that the Zoo is working on. For example, Mr. Letzring is responsible for heading the relocation of plants during construction of new exhibits. This includes moving plants from enclosures to other parts of the Zoo—a massive project, especially when it includes large trees. He also determines how and where to use plant donations, which can be quite large and extensive. On top of that, he oversees the Zoo’s quarantine station, which isolates exotic plants before they enter the country or the Zoo. Mr. Letzring is currently busy with the Zoo’s koala project, which requires the relocation of many different plant species. In all, Mr. Letzring’s multi-faceted job does not have a typical day of work.

Mr. Letzring explained to us what challenges him most in his career. Instead of answering, “relocating the trees with 12-foot circumferences,” he said that his biggest challenge is being successful in planting exotic plants that wouldn’t normally grow in our climate. He strives to prove that nonnative species can thrive here so that he can present their uniqueness to guests. Hopefully, that will inspire people to preserve these plants and learn how to take care of them.

As our tour came to a close and we neared the end of Elephant Odyssey’s wild, plant-lined path, Mr. Letzring gave us some advice for anyone interested in horticulture: first, go to school and get a degree in horticulture or landscaping; then, work at a nursery. And with that, he gave us each exotic fruit from plants around the Zoo, which included obtuse bananas, dragonfruit, and custard apple fruit. The refreshing, juicy fruit was nice after a long trek, and quite a new experience since the custard apple had light green spikes everywhere (which you can see in the above picture). It was very cool to learn about the landscape at the Zoo, and next time I come here I will definitely reconsider the importance of the windy, spiny cacti growing on the side of the path!

Caroline, Careers Team
Week Two, Winter Session 2012

0

Stopping to Smell Flowers with Zoo Horticulture

Zoo InternQuest is a seven-week career exploration program for San Diego County high school juniors and seniors. Students have the unique opportunity to meet professionals working for the San Diego Zoo, Safari Park, and Institute for Conservation Research, learn about their jobs, and then blog about their experience online. Follow their adventures here!

The San Diego Zoo is a world-famous organization. Its impressive collection is one of the most diverse among the world’s zoos. Each year millions of visitors from around the globe come to the Zoo for a chance to see animals like the giant panda, California condor, and Queensland koala that make the Zoo so particularly unique. What is less well-known about the Zoo is that its plant collection is actually even larger than its animal one. The diverse horticulture (the science of plant cultivation) around the Zoo is one of the most remarkable dimensions of the Zoo experience.

This week, the InternQuest team had the opportunity to experience this aspect of the Zoo firsthand. Mike Letzring, the Zoo’s plant collections manager, lead us on a tour through Elephant Odyssey with not elephants but plants as our sole focus. Having walked around Elephant Odyssey many times since it opened in 2009, I was surprised at all of the new things I discovered throughout the day.

Mr. Letzring is an ideal guide—with 31 years of experience in horticulture, his knowledge is extensive, and his passion is clear. He describes himself as “sort of a fanatic with plants,” and tells us, “I wanted to know everything [about plants] I possibly could.” From our point of view, it really seems like he’s been successful. As we walk through Elephant Odyssey, he points out everything from the extremely drought-tolerant Texas “zig-zag tree” to the African “sausage tree” that relies on bats for pollination, providing detailed presentations on both species.

Elephant Odyssey features elephants, jaguars, lions, camels, pronghorn, and countless other animals to compare them to their prehistoric counterparts that once lived in Southern California. So what’s the point behind the extensive plant collection, featuring species from all over the world? I ask Mr. Letzring what he wants guests to take away from the vegetation element of Elephant Odyssey. He tells us, “I want to show everyone the uniqueness of plants and where they come from… I want to broaden everybody’s education of what’s out there so they take care of it.” In this way, Elephant Odyssey can expose the everyday individual to some plant life they would be hard-pressed to find anywhere else. The Zoo is, quite literally, a plant museum. Each year it goes through an extensive effort to catalog its collection to gain official accreditation through the AAM, the American Association of Museums. As Mr. Letzring said, the idea behind showcasing the world’s foliage to Zoo guests—globe-trotters and average citizens alike—is to increase appreciation for plant diversity.

The truth is, many plants need this support from regular people like us, because many of the plants we see are as rare as they are beautiful. Take the flowering Erythrina trees, for example. Our intern team comes across one of these so-called “coral trees,” and Mr. Letzring informs us that 30 to 40 species of Erythrina are on the “Red List,” which means they are in danger of becoming extinct. Mr. Letzring himself has been to Hawaii to help with the coral tree conservation effort during a collaboration project between San Diego Zoo Global and several botanical gardens in Hawaii. Clearly, the plants’ own displays at the Zoo aren’t simply there to create an eye-pleasing environment—they are there to give everybody a rare look at conservation in action.

The plants of Elephant Odyssey are many things: some are rare, some are common; some are old and some are new; some are native and some are exotic. One thing nearly all of them are is drought-tolerant. A primary goal of creating Elephant Odyssey was to build a section of the Zoo that demonstrated exemplary water-conservation through its selection of greenery. The best part is, there’s a lot we can apply to our own backyard. Aloe, for example, is a plant exhibited all throughout Elephant Odyssey (we even find a section specifically devoted to aloes from across the world). For Southern California gardeners, this plant is a great option. It flowers November through March and is a hummingbird favorite. Overall, Elephant Odyssey is a great source of inspiration for beautiful, drought-tolerant landscaping.

When it comes to plant diversity, as Mr. Letzring puts it, “inside the Zoo… the sky could be the limit.” So next time you visit the Zoo, or even simply go outside, appreciate the plant diversity that surrounds you, and stop to smell the flowers.

Sierra, Real World Team
Week Two, Winter 2012

1

Conserving Threatened Palms

The threatened palm Brahea aculeata

The descriptor “tropical forests” usually conjures images of lush green forests with high canopies brimming with life—or at least for me it did. But as I look across the lands of the Sierra de Alamos-Rio Cuchujaqui Protected Area in Sonora, Mexico, I see large, columnar cacti peeking out from the fading green and pale brown of surrounding trees. Yet this, too, is considered a tropical forest—a tropical deciduous forest. Here the lush green foliage bursts forth with the summer monsoons and extends through mid-fall and hurricane season. As winter approaches, the trees drop their leaves, though not because of the cold temperatures, as with temperate forests, but due to the dry climate. By March, there is nary a leaf in sight, and the hillsides have taken on a red-brown-gray referred to locally as mojino. Many of the adaptations we associate with desert plants developed here to survive the harsh, dry season. The green that remains is found along the arroyos and in the stems of the tall cacti. That’s not to say there is no color, for during the dry season there is always something flowering. Blooming amapas Tabebuia impetiginosa add a splash of color to the fading greens and brown as we drive to the protected area.

A hawk perches on an amapas tree. Click on the photo to enlarge.

But the image of a forest brimming with life still fits, even if the first view doesn’t confirm it. Thousands of plant species live here, many are found only here. The Sierra’s tropical deciduous forest supports a rich array of fauna as well. With over 450 resident and migratory bird species, and many recognized as threatened or endangered, Birdlife International has designated the Sierra de Alamos as an Important Bird Area. The area also provides essential habitat and corridors for charismatic megafauna such as jaguars, ocelots, and margays. Many tropical amphibian and reptile species reach their northern range limits here, while desert species, such as the Gila monster, also extend into the region.

The protected area where we are working represents the northernmost stretch of tropical deciduous forest in the Americas, and possibly the most intact. Once extending from here in southern Sonora to Panama, and usually with only a width of around 30 miles, only 15 percent of the tropical deciduous forest in North America remains. And only about 1 percent of that is in protected areas. Though rather unusual for a protected area, the majority of lands in the Sierra de Alamos-Rio Cuchujaqui Protected Area remain in private hands; the reserve limits activities such as mining and land clearing, but cattle ranching still dominates the land, and overgrazing prevents a large risk. As part of the Applied Plant Ecology Division of the San Diego Zoo Institute for Conservation Research, I’m here as part of a research team focusing on a threatened palm, Brahea aculeata, and how various management practices (i.e. cattle grazing) affect the palm population.

Nature and Culture International (NCI), a nongovernmental organization partnering with San Diego Zoo Global in several locations in Latin America, represents an important resource for our project. They own land, have staff who serve as excellent field assistants and guides, and have strong relationships with ranchers in the area. Seeing the importance in conserving this little-known corner of the tropics, NCI has taken on the task of adding more stringent protection by purchasing the ranches along the main watershed. With just a few years’ break from cattle, it is easy to distinguish NCI lands from neighboring ranches; willows and other riparian vegetation really do flourish without the constant munch of cows. Hoping to widen its impact beyond the landholdings, NCI is working with us on some land-management issues in the area. We hope to base management practices in science and share them with the neighboring ranches. Building on this partnership, we hope to conserve this special part of Mexico, the tropical deciduous forest and the wonderful wildlife it contains.

Christa Horn is a senior research technician in the Applied Plant Ecology Division of the San Diego Zoo Institute for Conservation Research. Read her previous post, Observing Nature as a Child.

For more information on NCI and San Diego Zoo Global’s partnership…

For more information on the tropical deciduous forest of Sonora and NCI…

4

Wake Up, Seeds! Germination Testing

Germinating seeds

Germination testing is used to determine the correct method for bringing seeds out of dormancy. A seed typically consists of the embryonic plant with its food reserve wrapped in a seed coat, which acts as a protective layer between the embryo and outside elements. Some scientists define germination as the emergence of the radical (the first root), but at the Native Seed Bank here at the San Diego Zoo Safari Park, we define it as the emergence of the radical and the emergence of at least one cotyledon (first leaf). This is because some seeds may have enough energy to produce the tip of a root but then lack the ability to develop further.

Most seeds enter a dormant stage in nature, and we can extend this state for decades by lowering their moisture content and storing them at cold temperatures for our Native Seed Bank. However, when seeds enter this phase in their life cycle, it can be very difficult to get them to “wake up” again. In nature, seed germination is triggered by factors such as fire, water, and temperature changes. To test the germination ability of seeds placed in storage, we try different dormancy-breaking mechanisms to determine which protocol is effective. Scientists look at things like the species’ natural habitat and what triggers have worked with closely related species. The process is further complicated by the fact that species require different combinations depending on how long they have been in storage. For example, a trigger that works for seeds stored for 10 years may not work for seeds stored for 50 years. Another complicating variable is that even within the same species, different populations may have been reproductively isolated enough so that their seeds have different requirements.

Some of the Native Seed Banks many seeds awaiting study

At the Safari Park, all seed lots placed into the Seed Bank are testable once they have been stored for at least one month. Twenty or so seed lots that have been placed in storage around the same time period are then removed and soaked in water overnight before different triggers are tested on them. For some seed lots, this initial soaking is the only stimulus they need, but others have additional requirements.

Some of the other tests we perform include:

Cold Stratification:
Here we expose seeds to changes in temperature by placing them in moist, cold conditions that alter them in physiological ways so that they are able to germinate when warmer conditions follow. This simulates winter followed by spring. The same is true for warm stratification, which allows seeds to germinate in response to cooling temperatures similar to what they would naturally encounter in the fall.

Smoke Water:
In nature, one environmental condition that triggers germination is fire. Either heat, the chemicals released by burned plant matter, or a combination of the two causes seeds to come out of dormancy. To mimic the chemicals released by burned plants, we collect samples of different chaparral species and turn them into charcoal, which is then mixed in water along with the actual smoke, to give us “smoke water.” In some cases, when this water is absorbed through the seed coat, it triggers the seed to grow.

Hot Water Soak and Boiling Water Dip:

There are some species that need to have their seed coat damaged before they can absorb enough water to germinate. One way this occurs in nature is by the high acidity found in animal stomachs (to which seeds are exposed when they are ingested). Instead of soaking seeds in acid, (which can damage the seeds in the wrong concentrations), we use a hot water bath or a boiling water dip. This allows the seed coat to become permeable without damaging the embryo within.

Discovering the correct combinations is like working a time-consuming, yet fascinating, puzzle. Despite all the details that have to be taken into account, germination testing is an extremely important area of study. After all, what’s the point of seed banks if we are unable to germinate the seeds?

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, Native Seed Bank.

0

Seeds Make the World Go Round

There is a whole world of wonder inside a fig most people know little of, from fig wasps to seeds.

Every day I get blown away by certain characteristics of plants. There is no lack of drama or intrigue here. From succulents that look like rocks to flowers that smell like carrion to attract pollinators, the botanical world never seems to disappoint. It would be nice to think that plants do this for the pure pleasure of us humans. But this is, of course, not the case. Their reason is simple: survival. I thought it would be fun to look at some of the various ways plants distribute their seeds. Seed development and dispersal methods take high priority and have had a timeless trial-and-error process resulting in ingenious systems for prolonging the species, something us humans could learn a thing or two from!

We all have memories as kids blowing dandelions into the wind. What we were doing was spreading their seeds. Many primitive and early plants used the wind to spread pollen and seeds, and some still do. As more and more creatures roamed the Earth, plants exploited animals to help pollinate their flowers and distribute seeds. (Plant pollination is another fascinating topic that can be explored in a future blog; for now we will stick with the seeds.) With the help of the increasing numbers of fauna, the floral world really began to blossom.

As with most members of the bean family (fabaceae), Scotia brachypetala's seeds are hard and typical looking. However, many can be very colorful!

If you want something to go somewhere, wrap it in a delicious package. That is exactly what fruit does. The fruit attracts animals to take it off to another part of the forest with the seeds inside where they can be tossed aside to germinate. That is the tastiest method of seed dispersal, but many others exist. Take, for example, seeds that have barbs or hooks. They attach to a passing animal and get a free ride for a distance and fall off. Nuts are often collected by squirrels and buried, later to be forgotten about and so become trees. Winged seeds use propeller-like motion to glide away from their parent plant. And even some seed pods explode when touched by raindrops, sending their seeds a good distance away!

The bottom line is that plants need their seeds to be put in a good position to germinate and carry on the species. By these clever techniques, they achieve this. It is an area in the natural world often overlooked but should not be forgotten.

Seth Menser is a senior horticulturist at the San Diego Zoo. Read his previous post, Biomimicry: Nature Deals with Fire.

3

Native Seed Bank

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.