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Plant Focus

Quercus macdougallii
A rare oak endemic to the Sierra Juárez in Oaxaca

Importing Endangered Engelmann Oaks into Australia

Lying in trays of seed raising mix in the Royal Botanic Gardens Victoria Melbourne Gardens (RBGV) nursery are 99 unassuming Quercus engelmannii acorns. They are special, however, because they are from an endangered species and it has taken five months of collaboration with the Los Angeles County Arboretum and Botanic Gardens (LACABG) and the Australian Department of Agriculture, Fisheries and Forestry (DAFF) to get them here. More excitingly, some have survived transit and prescribed biosecurity treatments and are starting to germinate. All going well, they will be ready to plant in our Oak and North American Drylands Collections in May.

Quercus engelmannii radicle
Quercus engelmannii radicle © Jo Brennan, RGBV

Importation Challenges

The Oak Collection within the RBGV dates to around 1862 and features numerous old and venerable specimens, many of which would have been brought into Australia as acorns stowed in the pockets or suitcases of avid collectors. Since the passing of the Quarantine Act in 1908, Australia has maintained a national approach to the prevention and eradication of imported pests. In recent times, Australia has transitioned to the Biosecurity Act 2015, which maintains and strengthens Australia’s stringent biosecurity laws. Australia has strict controls on the importation of oak acorns and with good reason—no one wants to accidentally introduce an exotic weevil or khapra beetle (Trogoderma granarium). However, this can make obtaining wild-collected material from overseas complicated and time consuming. Importing acorns is even more complex—they are desiccation-sensitive, so minimizing storage and transit time is crucial. To manage the biosecurity risk of exotic weevil larvae, known to internally infest acorns, they must be fumigated with phosphine or undergo cold treatment at -18 ˚C, both of which can add another ten days to three weeks to their journey. Given that Quercus are recalcitrant species and generally do not survive freezing below -10 ˚C, cold treatment is a high-risk option. The effect of phosphine gas on acorns is not well-documented but has also raised concerns. Add in potential disruptions to freight services, staff absences due to COVID-19, and the busy holiday season and you would be forgiven for wondering why anyone would attempt to bring in acorns during a pandemic!

An Opportunity to Conserve Rare Oaks: An Intersection of Projects

For the last three years, my colleagues and I have been working with San Diego Botanic Garden (SDBG) to import wild-collected seed for our North American Drylands Collection, in exchange for rare and interesting Victorian species. Last year, staff from SDBG collected seed from 11 species on our target list. This "wish list" comprises southern Californian plants identified by climate modeling as likely to survive Melbourne’s projected increase of 3 ˚C in mean annual temperature over the next 50 years. They are also on the DAFF’s Permitted Seeds list—those not on the list are subject to even more stringent import conditions and biosecurity measures.

Among the seed collected by SDBG were acorns from two rare and endangered shrub oaks. Around the same time, the curator of our Oak Collection, Peter Berbee, was offered several other endangered species through his engagement with the Global Conservation Consortium for Oak, of which SDBG is a member. Given that plant conservation is a priority for the RBGV, we jumped at the opportunity to import them all. SDBG kindly volunteered to gather and forward the acorns from the various donor institutions, along with their own. However, LACABG had Quercus engelmannii acorns ready and waiting to go before the rest. Keen to expand the ex-situ conservation of this endangered species, a remnant population of which features in the arboretum, curator of Living Collections Jim Henrich generously proposed that he ship them separately. So began our collaboration with LACABG and DAFF.

The Perils Facing Quercus engelmannii 

Quercus engelmannii is a fascinating species. It belongs to an ancient lineage of Mexican oaks and has persisted from a time when northern Mexico’s and southern California’s climates were subtropical and experienced monsoonal summer rains. Its range has since contracted due to various pressures, not least the increasingly long, dry summers characteristic of this region’s Mediterranean climate. As climate change intensifies, the range of Q. engelmannii is expected to decline further. Urban development, livestock grazing, altered fire regimes, and pest incursions are also responsible for Q. engelmannii death and low recruitment levels, resulting in its designation as an endangered species by the International Union for Conservation of Nature (IUCN). Ninety-five percent of the remnant trees are found in San Diego County, while small populations remain dotted around Los Angeles and Baja California. Luckily, its plight is now well recognized and various organizations, including LACABG and SDBG, are directing their efforts towards both in-situ and ex-situ conservation.

Navigating the Acorn Importation Process

While navigating plant importation requirements is no doubt straightforward for a seasoned importer, it presented a steep learning curve for me. Ensuring both state and federal biosecurity conditions were met, and that the air freight company selected would process our precious cargo as quickly as possible, involved a great deal of research and countless phone calls. Slotting this into my core work as a horticulturist was more of a challenge than expected given the time-sensitive nature of the task. Thankfully the Plant Division of DAFF arranged a meeting with me to explain the importation process, which included a discussion of the treatment options for oak seed, as listed in DAFF’s biosecurity import conditions database (BICON). Furthermore, they kindly offered to facilitate the acorns’ treatment and transit on arrival, in recognition of the important role that botanic gardens play in species conservation. A lack of commercial operators set up to cold treat small parcels meant a special arrangement was devised with the DAFF Mickleham Post Entry Quarantine Facility in Victoria. Meanwhile, in Los Angeles, Jim Henrich diligently navigated the phytosanitary certification process and Australia’s documentary requirements, a first for him also.

Peter Berbee and Jo Brennan with newly arrived acorns
Peter Berbee (Oak Collection curator) and Jo Brennan (North American Drylands curator) with newly arrived acorns at Royal Botanic Gardens Victoria Melbourne © Tessa Kum, RBGV

Surviving Shipping and Biosecurity Treatments

In early February, Jim Henrich packaged up the acorns and sent them on their way, with fingers crossed that they wouldn’t end up sweltering in a warehouse while awaiting customs clearance and transit. Given the extended drought in Los Angeles, we also feared that a number would contain larvae that were undetectable to the eye but would render the acorn unviable: fewer acorns are produced in dry years, meaning they are more likely to host larvae. This underscores the importance of biosecurity treatments. In the spirit of experimentation, we opted to fumigate half with phosphine and cold treat the rest. Interestingly, a few acorns had begun to germinate on arrival at Mickleham: they were alive but were yet to be frozen. Once collected and potted into trays, we held our breath. Five months had passed since collection and some of the acorns rattled when sown, suggesting desiccation. After two excruciating weeks, we discovered bright, healthy radicles emerging from several acorns. We have now potted up 23 and hope that a few more will germinate in the coming weeks. All were treated with phosphine. The frozen acorns show no sign of germinating.

Quercus engelmannii seedling
Quercus engelmannii seedling © Jo Brennan, RGBV

From Little Things Big Things Grow

Enhancing the climate-change resilience of our collections and increasing our holdings of wild-collected material, for scientific and conservation benefit, are stated goals of both our Living Collections Plan and Landscape Succession Strategy. Quercus engelmannii ticks all the plant-selection criteria for our Oak and North American Drylands Collections—conservation, education, climate suitability, and aesthetic value. Research suggests that Q. engelmannii will flourish with our summer storms and higher rainfall. As always, we will need to monitor for any adverse effects of cooler temperatures, greater water availability, and interactions with other critters in their new homes. To ensure against failure and promote their conservation more broadly, we intend to share any excess seedlings with other well-suited botanic gardens. Quercus engelmannii is just the beginning—now that we have a greater understanding of the importation process and time commitment involved, we hope to continue bringing in rare and threatened species, starting with the other endangered oaks already on offer.

Jo Brennan is a Horticulturist at Royal Botanic Gardens Victoria Melbourne Gardens.

Further reading

Carrero, C., D. Jerome, E. Beckman, A. Byrne, A.J. Coombes, M. Deng, A. González- Rodríguez, H. Van Sam, E. Khoo, N. Nguyen, I. Robiansyab, H. Rodríguez, J. Sang, Y.-G. Song, J. Strijk, J. Sugau, W. Sun, S. Valencia-Ávalos, and M. Westwood. 2020. The Red List of Oaks 2020. The Morton Arboretum. Lisle, IL. https://www.researchgate.net/publication/346934290_The_ Red_List_of_Oaks_2020 Accessed August 9, 2022.

Henrich, J. (n.d.). The Most Majestic California Oak. Pacific Horticulture website https://www.pacifichorticulture.org/articles/the-most-majestic-southern-california-oak/ Accessed August 9, 2022.

Meyer, E., N, Jensen, and N. Fraga. 2014. Seed banking California’s rare plants. California Fish and Game 100(1): 79–85. https://www.caplantrescue.org/uploads/1/0/2/7/102741700/meyer_etal_2014.pdf Accessed August 9, 2022.