8 minute read
Growing Our ‘‘Ex Situ’’ Conservation Plan, One Grove at a Time
By Christina Varnava, Living Collections Curator
It’s very easy to appreciate a tree. They make shade (which is very cool — and cooling — of them), and they even create their own microclimates that help buffer temperature extremes. Trees also provide habitat and shelter for creatures of many sizes, from the tiniest insect to larger beasts like bobcats and red-tailed hawks. They provide food for so many animals, including us humans. Trees really do a lot for us, and it’s important for us to return the favor. That is one of the goals of botanic gardens in general and Santa Barbara Botanic Garden specifically. Our Living Collection is intended to conserve and protect tree species from across California. The trees in the living collections of botanic gardens and arboreta are becoming increasingly valuable, not just for their beauty but their immense “ex situ” conservation value.
Helping Outside a Habitat
What is ex situ conservation? Essentially, the best strategies for conserving threatened wild plants take a two-pronged approach: protect plants and the wild habitats where they grow (aka “in situ” conservation), and safeguard plants outside their habitat (aka ex situ conservation). Ex situ conservation can help protect plant species from going extinct in the wild on unprotected land or from stochastic (i.e., random) events like wildfire, novel diseases and pests, or severe storms. Threatened plant species may have very limited geographic ranges, making them even more vulnerable to these types of habitat-destroying events.
Ex situ conservation includes both systematic seed banking efforts and the living plant collections in botanic gardens. Plants that are protected outside of their habitat in seed banks or living collections can then be cultivated, used to bulk up seed reserves, and reintroduced as part of restoration efforts. Botanic gardens and arboreta are increasingly recognizing the power of their living collections to do this type of work, since these collections are backed by provenance information, essentially cataloguing location and other details each time seeds or plants are gathered for propagation. There are now global networks and conservation strategies in place that allow institutions to collaborate to protect rare and threatened plant species by sharing information about their plant collections, and the Garden is an active participant in these groups. There are also coordinated efforts to collect new material for threatened species that are underrepresented in these collections.
There are a variety of reasons to grow tree species in living collections as part of a larger conservation strategy. Trees generally have much longer generation times than herbaceous or annual plant species, so growing mature trees is a more expedient way to collect and generate seed for restoration efforts. In contrast to their long generation times and lifespans, tree populations in the wild can be destroyed quite quickly, in the event of a wildfire or an invasive insect pest, making it even more important for land managers and conservationists to act nimbly. Additionally, the seeds of tree species are generally not easy to store long term. Trees tend to have larger seeds with much higher fat content than herbaceous or annual plants, and that means they cannot be stored in a freezer. This is especially true of acorns, which have a very short life in storage as the high fat content means they can become rancid quickly (making oak trees [Quercus spp.] great candidates for ex situ conservation in living collections). Finally, trees in living collections can also be advocates for their own conservation, simply because people connect with trees instinctually. We can stand in their shade, we can appreciate their beauty, we can bird watch, and more. All of these experiences make it more likely that we will speak up and take action when trees are at risk.
Growing Groves for Good
As part of enhancing our living tree collections, the Garden will install two new tree-focused gardens on the grounds this winter: one for the Santa Catalina Island ironwood (Lyonothamnus floribundus ssp. floribundus) and one for the Santa Rosa Island Torrey pine (Pinus torreyana ssp. insularis).
Meet the Catalina Ironwood
The Catalina ironwood is a small tree species in the rose family (Rosaceae) endemic to Catalina Island. They are close relatives to the Santa Cruz Island ironwood (Lyonothamnus floribundus ssp. aspleniifolius), which is a bit more widespread and found on the three northern Channel Islands (and likely the subspecies you may have seen in a nursery). Catalina ironwoods are unusual, resilient trees, seldom found available for purchase in the nursery trade. They are a small-statured tree, often developing multiple trunks with beautiful peeling reddish-brown bark and lovely sprays of white flowers in late spring. They grow in groves consisting of identical clones. Some of these groves can have over 100 individual trunks and span over large areas. Catalina ironwoods are highly threatened in the wild because the island still has populations of deer and other large herbivores, which graze and trample young trees. Garden staff visited in 2018 and collected seed from nearly 30 groves all over Santa Catalina Island. The seeds from these groves have been grown into trees in our Living Collection Nursery, and this winter it will be time to plant the grove. That will be located on slopes to the east of the Pritzlaff Conservation Center (PCC).
Meet the Torrey Pine
Torrey pines (Pinus torreyana) are the rarest pine species in North America. They are only found in two places on Earth: on the northeastern edge of Santa Rosa Island, where you’ll find the Santa Rosa Island Torrey pine and in coastal northern San Diego, where you’ll see a different Torrey pine (Pinus torreyana ssp. torreyana). Each of these populations represent their own subspecies with distinct appearances. However, both subspecies grow on steep coastal terraces where they can benefit from coastal fog. Torrey pines have large cones and seeds that must be distributed by animals, especially the Island Scrub Jay (Aphelocoma insularis). Both subspecies have endured massive declines in their wild habitats. The Santa Rosa Island population was heavily impacted by cattle ranching operations, and the San Diego population is still struggling under pressure from drought and bark beetle (Family Scolytidae) infestations.
Staff from the Garden visited Santa Rosa Island in 2022 and collected seeds from 45 individual trees across the population there. We also collaborated with San Diego Botanic Garden in 2023 to help collect seeds from 40 trees in Torrey Pines State Natural Reserve, which have been distributed to botanic gardens across California. Our planned grove of Santa Rosa Island Torrey pines will feature trees from each of the 45 maternal lines collected on Santa Rosa Island. We’ve been growing these from the seeds we collected, and the trees are ready to be planted this winter on the slope to the west of the PCC.
These new Santa Catalina Island ironwood and Santa Rosa Island Torrey pine groves will continue to enhance our ex situ tree conservation efforts here at Santa Barbara Botanic Garden. We are very excited that visitors will also be able to stroll through groves of these incredible, rare tree species someday. Funding from two Tree Gene Conservation Partnership grants provided by the American Public Gardens Association and the U.S. Forest Service, as well as support from the Alice Tweed Tuohy Foundation, has made this possible. Through continued support from innovative partnerships and members like you, the Garden plans to continue to advance tree conservation projects for more shelter, more shade, and more beauty across the central coast.
