Rare Plant Reintroduction: Dudleya brevifolia – Part 2

It’s been five months since we planted our Dudleya brevifoliacorms into sandstone bluffs along the San Diego coastline. We’ve had some success and some disappointment, and we’ve gleaned valuable insight along the way. (Read Part 1 of this blog here.) 

It can be difficult to define success and failure when analyzing the results of an experiment like this, and when introducing plants or animals into the wild, we must be prepared for both. While success should be celebrated, failure is also an important facet of experimentation, it teaches us what doesn’t work, and why. 

In January 2019, 46 corms that we grew from wild seeds were reintroduced into habitat near one small and imperiled wild population. This reintroduction would effectively double the population of corms at this location. You can think of corms as bulbs, which grow aboveground in ideal conditions, and go dormant underground in adverse conditions. 

The exact location of each introduction was carefully chosen, recorded, and marked with an underground pit tag. We monitored the corms using a tag reader, allowing us to find the exact location of the reintroduced plant when we returned to monitor. 

Transplanting Dudleya brevifoliacorms had never been attempted before, and we weren’t sure how they would respond. Many of the factors that could contribute to their success or failure were unpredictable. 

While we tend to think of animals as rather independent life forms, able to seek out food and water, defend themselves, and reproduce, plant survival is often conditional upon factors out of their control. In contrast to animals, plants are rather dependent on whatever is around them. Many plant species have symbiotic relationships with fungi in soils that are necessary for nutrient uptake. Many are completely reliant upon pollinators to reproduce. All plants are stationary and unable to escape from herbivory, human impacts, and abiotic factors like weather or poor soil conditions.

Because this was our first reintroduction of Dudleya, we used an experiment to test factors that could help us learn the best methods. Would large corms be more successful than short?  Would any corms survive, or should we consider using seeds? Even if the experiment failed, we would learn from it.

We first noticed the emergence of some tiny Dudleya leaves after about a month. Over the course of the next few weeks we observed the aboveground growth of nine reintroduced individuals, but we also began to notice some potential problems. 

At one point, an introduced individual growing aboveground completely disappeared. We were able to find its planting location using the tag reader, but all visible growth was gone. We suspect herbivory, but don’t know if this will lead to the death of the corm. We won’t know how it responds until next growing season.

On another visit, we noticed a large amount of disturbance in the soil around some of the introduced plants. Shoe prints were visible and some of the wild adult Dudleya nearby had been smashed. Someone had crossed the barrier, likely to take a panoramic photo, and had stepped on some of the inconspicuous plants, destroying any hope that they would reproduce this season. 

In one section of the introduction, small nails marking our planting locations were kicked up and removed. Was this done by vandals, or “good Samaritans” just trying to pick up trash? Either way, several of our introduced corms were damaged.

We noticed signs of human impact on every visit. Large, wild plants are inadvertently kicked or stepped on, delicate sandstone bluffs are damaged, trash is often left behind, marring the pristine habitat. Even at a well-patrolled preserve, in an affluent neighborhood, with signage and barriers in place, the impacts are substantial.

There are many potential hurdles plants must overcome to survive reintroduction, but it’s become apparent that the biggest threat and the highest hurdle for our Dudleya plants is humans.

Despite all the discouraging things we’ve seen over the course of five months, we’ve also observed some remarkable things.

We’ve seen numerous tiny Dudleya brevifolia sprout from a barren landscape that was devoid of other life. We’ve met many enthusiastic citizens interested in saving this resource. We even had one of our introduced Dudleya brevifolia produce flowers! 

Here’s what we’ve learned so far:

  • Around 20% of our corms appear to have survived the reintroduction. This number could increase if some are established underground but not displaying aboveground. It could decrease if some corms do not survive the hot dry summer. We’ll have a better idea next growing season.
  • In order to increase and stabilize this wild population, we’ll need to grow and introduce more corms! Corms aren’t particularly difficult to grow ex-situ. We can collect more wild seeds and continue to reintroduce, on a larger scale.
  • Larger corms are likely more successful than smaller corms in reintroductions based on our initial observations, but we need more data and we’ll understand this relationship better after next year’s growing season.
  • We must continue to work with land managers to educate the public about the perils of this tiny plant, and to better protect this habitat. 

I think this was a very successful first step, and we’re now better prepared to make significant strides in ensuring this species never goes extinct.

If anything, these tiny plants have proven how resilient they can be, and if we continue to actively contribute to their conservation, I believe we can ensure that they will be growing in this beautiful locale for generations to come.

Comments

Seed production

These are questions instead of a comment. You indicated that the seed were easy to germinate. Did you have to perform any treatments with temperature, moisture or abrasion in order for them to germinate? Did you conduct any experiments on pollination to determine if the plants are self compatible or require outcrossing? If so, what were the results? If not, how did the pollination take place to generate the seed for seed bulking, manually or with natural pollinators? When you say that the plants reached maturity in 5 or 6 months, did you keep them on track with the seasons or did you force them to continue and flower and generate seed at a faster pace than once a year in spring time?

Thanks very much.
Tom Oberbauer

Questions

Hi Tom,
Thanks for your interest! I'll do my best to succinctly answer your questions, but feel free to email me for more details - jdavitt@sandiegozoo.org
We did not perform any pretreatments to trigger germination because it wasn't necessary. Our baseline germination protocol calls for a quick seed coat sterilization and a 24 hour imbibe in water. Germination is between 90-100% on agar plates, and equally high directly into soil. Initial germination tests were performed on wild collected seeds, from parent plants which are definitely visited by pollinators and likely outcrossed, but I believe they are self-compatible to some extent as well - just a hunch. Our ex-situ population naturally produces second generation seed for the bulking project, and they are viable and easily germinated. These plants are in a screen house and pollinators are not excluded, but I have not seen insect visitors and we do not hand pollinate. The viability of the seeds produced is the basis for my hunch RE: self-compatibility, but it's possible they are being crossed by random bees, small beetles, flies, or even wind and we just aren't seeing it. We've found it works best to germinate indoors under grow lights. We like to do it in winter, allow seedlings to establish roots and some leaves, then move them outdoors in the spring and slowly introduce them to full sun. We've also found that it's important to allow the plants to naturally enter dormancy. We do not supplementally water past June or July. Our plants senesce and die on the surface until winter rains trigger natural reemergence. I don't think it's possible to supplementally water and force them to continue their growing season. The spring growths basically act as annuals, and begin fading as soon as flower spikes emerge and seeds start to develop. You could probably artificially shorten the dormancy period and produce seed more quickly if necessary. We haven't tried. Feel free to email me for more details or if you have any other questions!

Joe Davitt

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