Engelmann oak finding a home in Melbourne

(From left) me, Governor Linda Dessau, Engelmann oak, Tony Howard and Penny Fowler (current Chair of Royal Botanic Gardens Melbourne Board), Royal Botanic Gardens Melbourne, 9 June 2023

Last year, Linda Dessau and Tony Howard planted one near the new City Gate in Royal Botanic Gardens Melbourne (on 9 June 2023), to mark the end of the Linda's eight-year term as 29th Governor of Victoria. 

A month or so later, I planted one in Oak Lawn (on 14 July 2023) to mark the end of my ten-year term as the thirteenth Director (and Chief Executive) of Royal Botanic Gardens Victoria. I included a picture of me at the planting last week but here I am 'watering it in' (with Peter Berbee talking to fellow arborist Charlie Carroll at centre behind me, and Jo Brennan at the far top left talking a guide with red hat) 

Let me tell you what I know about Engelmann's oak (Quercus engelmannii) and how it got to Royal Botanic Gardens Melbourne. 

First to Mr Engelmann. George was a nineteenth century, German-born, American (USA) botanist, physician and meteorologist, with a particular interest in cacti and dodders from the west of North Amercia. His interest in the flora of California presumably led to his recognition in the name of this oak described in 1889.

The oak itself is a small 'sub'-evergreen (probably evergreen in Melbourne) tree, to about ten metres high. What it lacks in height it makes up for with gnarly ('large twisted) limbs - maybe competing with the English and Daimyo oaks on Oak Lawn I mentioned last week.

The leaves are tough and papery, and typically grey-green in colour. The margins can vary from strongly toothed, as in this close up from my planting, or almost entire. All perhaps surprising for another (in addition to the Daimyo oak last week) relative of the English oak - again in the same subgenus and section of Quercus.

Other common names include Pasadena Oak and Mesa oak, referring to where it comes from, a 'narrow band that stretches along the foothills of Southern California, from Pasadena down through Orange and Sand Diego County into Baja California'. Its evolutionary origins are in Mexico, home to more than a hundred oak species.

These days the oak is listed as an Endangered Species, due to the cumulative effects of climate change (including different fire frequency and intensity), land clearing (for housing), introduced pests, and over grazing by livestock. All human induced. The bulk of the remaining trees are in San Diego County with only a few near LA and in Baja California (Mexico).

Royal Botanic Gardens Victoria managed to import 99 acorns from colleagues at the Los Angeles County Arboretum and Botanic Gardens, collected from a remnant Engelmann oak habitat within their arboretum. The acorns came from more than one tree to increase genetic diversity. 

This was part of a broader exchange program with San Diego Botanic Garden, started by Jo Brennan, horticulturist and curator of the California Collection (soon to expanded into the North American Drylands collection and landscape). Royal Botanic Gardens Victoria will provide similarly rare species from Victoria. 

Plant exchange contributes to the conservation efforts of botanic gardens worldwide, and with climate modelling showing that Melbourne will become even more suitable for growing Engelmann oak over coming decades, it is the perfect place for an ex situ conservation collection. The city may also find it has a new ornamental tree to replace those unable to cope with warmer summers and less rainfall.  

Surprisingly perhaps, acorns are only viable for about six months, and it took some wrangling, and support from the Australian Commonwealth Government, to expedite the importation process to five months. Which wasn't easy, with delays in freighting, staff away during holiday season at both ends, and all this was at tale end of the COVID-19 pandemic in February 2022.

On top of this, to reduce the risk of introducing pests such as exotic weevils into Australia, the acorns had to be either frozen or fumigated with a largely untested chemical phosphine. As Jo explained in a piece written for the International Oak Society, freezing had to be at -18 degrees C (a few degrees above the temperatures in Iowa at the time of the fateful Republican caucuses two weeks ago but below the -10 degrees that acorns can generally tolerate). 

The decision was to fumigate fifty and freeze the rest. From those treated with phosphine, 24 were germinated by Jo and Peter Berbee (arborist and curator of the Oak Collection in Melbourne) within a few weeks of arrival at the Gardens. None of the frozen batch survived. Of the 24, 21 continued growing and are now ready for planting out or are already in the ground. 

Murphy Westwood, Abby Meyer, and Peter Berbee after planting an Engelmann oak in the Grey Garden at Royal Botanic Gardens Melbourne, October 2022. Photo by Peter Symes; from International Oak Society webstory)

Apart from the Governor's and my own tree, there was another ceremonial planting during the Global Botanic Gardens Congress in October, 2022, with colleagues from the USA (above). Since then, a couple of other Englemann oaks (from different trees in LA to increase diversity) have joined this specimen in the Grey Garden, and there is at least one near the new Tecoma Gate on Anderson Street.

Other seedlings will be donated to botanic gardens in Sydney, Blue Mountains, Orange, Warrnambool and Castlemaine, in part to test out the tolerance of this species to different climates and conditions.

Meanwhile, I'll be watching to see if my tree mimics the nearby beautifully languid oaks of Oak Lawn, and on the lookout for more rare oaks from western USA (Jo and Peter are germinating some newly imported acorns as I type!).