By Rhian Campbell, Nursery Manager
Have you ever felt challenged by growing a certain plant in your garden? At NTBG’s conservation nursery on Kauaʻi, we can relate! Our nursery is tasked with the propagation and care of some of the world’s most endangered plants. Every day we see the challenges plants face from habitat loss and invasive predators to attacks from opportunistic pathogens. Our job is to preserve and propagate these rare species with the goal of outplanting them into protected reserves or back into the wild where they can fulfill their ecological roles, supporting native birds and insects and contributing to healthy ecosystems in a myriad of ways.
Our nursery team strongly believes that people and plants are both products of our environment. It is the community that surrounds us that keeps us alive while the close connections we forge with others allow us to thrive. In forest communities, all plants have relationships with the species that surround them. Some of the most important connections take place out of sight and underground where vast networks of mycorrhizae transfer nutrients between plants. These mycorrhizae can even mine nutrients from rocks and exchange them for the sugars that plants produce through photosynthesis.
Other microorganisms contribute to this process by breaking down dead leaves and detritus to recycle the nutrients plants need to become strong and healthy. Because plants can’t escape when they’re being attacked, many rely on intricate forms of chemical defenses such as the production of scents or toxins. Strategies vary widely but if plants can’t obtain the nutrients they need, they become much more susceptible to attack.
Cyanea kuhihewa in it’s native habitat, surrounded by leaf litter and detritus. Photo by Ken Wood.
To understand why certain plants struggle in the wild, we need to understand their habitat. At NTBG’s conservation nursery, we examine the challenges plants face from multiple angles. Our botanists help us understand current field conditions and we can study notes on historical habitat conditions that are maintained in our herbarium.
Furthermore, we can go into the field to directly observe factors such as exposure to sun, soil type, and topography. This information not only helps us grow these plants better in the nursery, it can also guide decisions we make as we take the next generation of plants back into protected restoration sites, increasing the odds of long-term conservation success.
One example has been the study of nutrient cycling between the ocean and the land. Consider Kauaʻi’s seabird population which was much larger before humans arrived. The guano and food scraps the birds once left behind would have helped distribute marine nutrients onto the land.
Armed with this concept, our horticulturalist, Hayley Walcher, researched different fertilizers and soil amendments to find a viable pathway that would allow us to transition from the synthetic fertilizers we had been relying on to a mixture based mostly on seabird guano, composted invasive seaweed, bone meal, and other organic fertilizers. Additionally, vermicompost — a form of soil enhancement — was added to boost microbial activity in our sterile growing media. Regular applications of fish fertilizer are given to provide a supply of readily available nutrients.
Left: Horticulture assistant Haley Walcher caring for plants in NTBG’s conservation nursery on Kauaʻi. Photo by Erica Taniguchi. Right: Cyanea kuhihewa in its native habitat. Photo by Ken Wood.
Perhaps most importantly, we began inoculating our potting mix with a small amount of soil from certain plant species’ native habitat. Doing so introduces them to the microbial community members they are likely to need to help sustain them as they transition to a more natural environment. We believe the use of synthetic fertilizers in plants destined for restoration projects may have been creating an unsustainable dependence. Without fungal and microbial partners, once that supply of easily digestible food was exhausted, it became difficult for nursery-grown plants to adapt to natural conditions.
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One species benefitting from these new methodologies is Cyanea kuhihewa, a Critically Endangered plant previously believed to be extinct. For several years, we struggled to propagate these plants and return them to their native habitat. Seedlings wilted and died before they could be transplanted into pots, so we enlisted the help of the University of Hawaiʻi’s Lyon Arboretum in producing plants using tissue culture.
Unfortunately, our success rate remained low until we tried growing the plants in our temperature-controlled fern lab. Because they were accustomed to higher elevations than our nursery could provide, we focused on protecting them from excessive heat. C. kuhihewa was also one of the first species where we tried amending potting media with native soil and organic amendments. The plants responded very well, demonstrating that we could plant seeds in the fern lab with native soil and get good results without the expense and complexity of tissue culture propagation.
Left: Nursery manager Rhian Campbell watering Cyanea kuhihewa in NTBG’s fern lab. Photo by Chastity Hada. Right: Cyanea kuhihewa detail. Photo by Rhian Campbell
Within two years, we had plants that were large enough to handle being transplanted into the Upper Limahuli Preserve. Our success rate increased from no more than five plants produced in 2020-2021 to a dozen in 2022 and approximately 50 in 2023. Field observations support our hypothesis that these new practices are enabling us to grow plants that are adapting better and surviving longer than those sent in our first few years.
Introducing these practices has expanded the number of species we are able to successfully care for in our nursery, increased the number of seeds we are producing from plants that might have otherwise died prematurely, and gradually raised the number of species and survival rate of plants we grow for restoration sites. We believe that if our ultimate goal is to create sanctuaries in which rare plants can thrive, our conservation nursery has a kuleana (responsibility) to learn as much as we can about the surrounding ecology of native plants and to foster a supportive environment from the moment they leave the forest as cuttings or seeds until the day they are returned to protected sites as healthy, well-adapted plants.