Silverback forestry: reflections on breeding super trees

Foresters Frank Batini and Charlie Kelers admire a Pinus canariensis in the Mundaring pine plantations. It is tall, straight, free of branches, cylindrical, and dominant over its neighbours … the perfect mother to kick off a tree breeding program.

One of the best jobs I had in my young days as a forester was cruising the pine plantations near Mundaring Weir, looking for ‘Plus Trees’. It was 1963 and I was working as a junior Forestry Officer, my first position after graduating from Forestry School. It was not an arduous job. Indeed, it involved not much more than walking around in the forest all day looking at trees, while getting paid to do so. What more could anyone want, let alone a young forester!

At that time the WA Forests Department had a very active and advanced tree breeding program, the aim being to improve the quality of the trees in the State’s pine plantations. For many years the “genetic improvement program” (as tree breeding was called by those who were conducting it), had focused on maritime pine (Pinus pinaster) for which large plantations were being developed on the coastal sandplains north of Perth. Maritime pine was well-adapted to these dry and infertile soils, but initially there had been no access to high quality seed. The pre-War plantations were (to be frank) pretty ugly, the trees being slow-growing, branchy and crooked. The strains that had come from France and Corsica were especially ugly … but this soon changed as the tree breeding program developed. The project involved collecting seed for new plantings only from the best parent trees and also bringing breeding material from elite trees in Portugal (where the finest maritime pine grew). The trees in the new plantations, grown from “improved” seed, were bigger, prettier, faster growing and had higher quality timber.

An elite maritime pine in Portugal, genetic material from which was bought to Western Australia for our breeding program.

The success with breeding superior maritime pine led the department’s research officers to turn their attention to the other pine species being established in WA plantations. This was radiata pine (Pinus radiata) which originated in the Monterey area of California, and was proving an exceptional plantation tree in New Zealand, Australia and South Africa. There were big plans for expansion of the radiata plantations in south-west WA, especially in the Blackwood Valley where the government was purchasing degraded pastures on steep hillsides that no farmer wanted. But the early plantations were all grown from “wild” seed, no attempt having been made to confine seed collection to the finest and fastest growing parent trees.

To initiate the radiata breeding project, the first step was a detailed inspection of all our existing radiata plantations to find the best mother trees from which to collect seed. This First Step could only be done by the department’s foot-soldiers, walking every hectare of every plantation, finding, checking, measuring and surveying the potential champions (known in the tree breeder’s jargon as ‘Plus Trees’). Later, the Plus Trees would be evaluated by the department’s expert in charge of the tree breeding program, namely the outstanding forest scientist Dr Eric Hopkins.  He would winnow down the initial selections to ensure that only The Best of the Best would become the parents of the next generations of fast-growing, straight, and all-round champion radiata pine trees.

Mundaring District at that time had some of the best and oldest radiata pine forests in Western Australia. These were in the Greystones, Helena, Darkin and Beraking plantations. The oldest trees dated back to the 1920s and there were some magnificent specimens. The hardest part of identifying Plus Trees in these areas was that there were so many candidates.

Radiata pine in the Greystones plantation planted in 1922 and photographed here in the late-1950s. That’s Peter Hewett in the picture, my first boss and a fine forester.

The job of Plus Tree selector was pleasant and invigorating. It was autumn, my favourite time of the year, with crisp mornings and mild sunny days. Older pine plantations have a lovely resinous aroma, especially when the mid-morning sun strikes though, and the needlebed is soft and springy underfoot. Unaware that they had been denigrated by some misanthropes as ‘ecological deserts’, the plantations were havens for wildlife, alive with kangaroos and enlivened by flocks of black cockatoos. The air would be full of their screeching, calling and chortling as they tore open the pinecones looking for seeds. All of this was accompanied by the sighing of the wind through the crowns above.

There was even an opportunity for a post-prandial nap after I had demolished my lunchtime crib, or at least for lying back on the soft needles for half an hour or so, watching the cockatoos or listening to the thump-thump of a passing roo. At those times I sometimes remembered the words of 'Doc' Jacobs, the famous Principal of the Australian Forestry School, who once remarked "Any forester who claims he has never had a sleep under the pines after lunch on a hot day is either a fool or a liar".

Once or twice, as late autumn turned to early winter, a rainstorm swept in, and I would hear it coming towards me on a heavy wind in the crowns of the trees. With luck I could find shelter standing with my back to a good-sized tree, or under the skirts of a grass tree in a neighbouring patch of bush, but mostly you expected to be rained upon when you worked as a forester. This was just how it was. I did retreat into my vehicle once, however, when a fierce hailstorm stuck, and I forbore to follow the example of that great bushman Dave Regan (see Endnote 1).

Each morning, I would drive out from HQ to the plantations in my black-and-orange departmental Land Rover and then spend the day walking a predetermined system of survey lines, compartment by compartment. I marked my progress on a map and kept records of discoveries in a field book which I carried, with other items of equipment, in a leather field bag slung over one shoulder. In the older plantations, the potential Plus Trees were always easy to spot – they stood out from their neighbours like Gulliver among the Lilliputians. In these stands, of course, my work had largely been done before me, as generations of field staff had treemarked the plantations for thinning, progressively removing the weakest and poorest trees. Nevertheless, there were still many thousands of trees to inspect and then to choose from.

I marked my champions by tying coloured plastic tape around the trunk. Then, each tree would be given an identity number, and I would enter key data about it in a field notebook. I measured the tree's height and diameter and recorded a general description. The location would be marked on the 40-chain to the Inch map. I always selected more trees than I needed, allowing me eventually to narrow them down to the three or four best and biggest before I moved to the next compartment.

The characteristics I looked for were those familiar to all foresters: height and diameter growth compared with neighbouring trees (known as ‘dominance’), trunk straightness, branch size and angle, freedom from forks or other blemish – in short, superiority. The aim was to identify the four or five tallest, straightest and meatiest trees in each plantation. When I settled on the final candidates, I painted a ring of white paint around each tree's trunk and a big letter ‘P’ (I didn't want some treemarker to come through and mark it for felling). Finally, I prepared a report and map and sent it off to Dr Hopkins down in Perth. He would make the final evaluation and selection.

It was the sort of job I wouldn’t have minded lasting a couple of months, but as I remember it, I had it all done in three or four weeks.

Mature radiata pine at Helena, one of the plantations I assessed at that time.

Not long after I completed this work, I was transferred south, so I never did hear whether any of the trees I selected made it into the final list of first-round mothers for the radiata breeding program. I have no doubt some of them would have, as they were very superior trees.  And I also saw the end-product many years later, the radiata tree breeding program coming to fruition under the direction of my colleague Trevor Butcher – another unsung hero of Western Australian forest science – and resulting in thousands of hectares of beautiful trees.

Reflections on tree breeding.

My days in tree breeding were brief and my contribution trivial, but I rubbed shoulders with the experts, did my homework and learned something about the business in the process. It was always interesting, and the outcomes were nearly always rewarding. Mostly, I learned, it is a lengthy process requiring patience and corporate commitment. There are variations around the theme, but in general (and greatly simplified) it works like this: After selection of the superior mother trees comes the collection of seed from these trees and raising and then planting out of their progeny in special trial areas. As they grow into young trees, the “half-sibs”, as the “children” of a known mother and unknown father are called, are constantly assessed and re-assessed, the best identified and nurtured, and the worst winnowed out.  A second-generation “best of the best’ is then raised and planted out in special little plantations called ‘seed orchards’. Sometimes there is another step, with controlled pollination of the best mother trees in the seed orchard with pollen from the best father trees, and the progeny from these crosses are again planted out and assessed and nurtured and winnowed, each generation being an improvement on its predecessor. I was always surprised about how large was the improvement simply by using seed from the original Plus Trees. We also learned that seedlings grown from big fat seeds grew into big fat trees, while those from little, shrivelled seed became little shrivelled trees (actually I think nurserymen in Roman times knew this).

A tree breeding program with pine might take twenty or thirty years, but was always worth the effort, resulting in plantations of very superior trees. The duration of a program might be off-putting to some, but as foresters we were used to long timelines and looking well to the future. [I once discussed this with my father, an agricultural scientist, and drew attention to how lucky he and his colleagues were, since with cereal crops like wheat, or pasture species like clover, an entire breeding program can be completed in one year. Dad sympathised, but not convincingly.]

I should have mentioned that during the early phase of the breeding program, use is also made of cuttings. These would be taken from the Plus Tree mother and grafted onto root stock in the same way that horticulturalists propagate roses and fruit trees, and this could short-circuit the program slightly.

Another innovation has been the use of clonal material - slices of tissue from the superior tree are grown as laboratory cultures into seedlings, producing in the offspring an exact genetic copy of the parent.  I have gasped, almost with disbelief, at the vigour and beauty of clonal flooded gum (Eucalyptus grandis) plantations in South America, where they seem to be further advanced with genetic improvement of Australian eucalypts than are we in Australia.

The trees in this clonal plantation of Australian eucalyptus in Uruguay are only 20-years old. This photo was sent to me by Evan Shield, a contemporary at Forestry School, who has devoted his career to the development of tree wonders like these in South America.

I love to walk around in a plantation of superior trees arising from a tree breeding program.  I think the finest I ever saw was a plantation of Hoop Pine at Imbil in Queensland. Hoop pine is a beautiful tree at any time, but here every tree was an outstanding beauty and each a spitting image of its neighbour, a credit to the art and science of the tree-breeder, in this case Dr Garth Nikles, the doyen of Australian tree breeders.

The problem of ‘genetic homogeneity’.

A plantation of ‘genetically-improved’ trees has a marked visual uniformity … the trees all look exactly alike. This dismays aesthetes and artists. But these trees are being grown to produce a valuable commercial product, not as ornamentals … although many ornamental trees these days are also the product of tree-breeding, the end-product being a tree with, for example especially beautiful or unusually coloured blossom. Similarly, there are programs to breed salt-tolerant or disease resistant trees where appearance or growth rate is immaterial. But when you boil it all down, a plantation of identical trees is no different aesthetically to a herd of Friesian dairy cows or a flock of prime merino sheep, in which the animals all look identical (to my eyes), the product of intensive breeding programs over a century or more.

A plantation of genetically improved Southern Pine in Queensland, each tree a carbon-copy of its mate. (Photo by Ian Bevege)

Having said that, uniformity, or “genetic homogeneity” as the geneticists describe it, carries some risks, as I will discuss in a moment. But first I must digress and make a quick comment on my favourite tree breeding program.

Breeding sandalwood silverbacks

Over the years I was involved (marginally) or observed many tree breeding programs around Australia, mostly involving pines or eucalypts. However, the one I found most intriguing was the Indian sandalwood breeding program. This was under the direction of that great tropical forest scientist Ken Robson, and because it was brilliantly done and Ken is a good mate, I found it doubly interesting.

The early (pre-2005) plantations of sandal trees (Santalum album) in the Kimberley and Northern Territory were established using ‘wild seed’ collected from any old tree in India. The form and growth rate of individual trees in the early plantations varied enormously but was mostly poor. However, it was easy to spot rare superior trees among them; they were dramatically outstanding.  Ken dubbed these beauties “Silverbacks”, and the trees grown from silverback seed promised to be spectacular.

An Indian sandalwood “silverback”, still a young tree, but towering over its fellows, and with a fine, straight, clean trunk. Seed from this tree went straight into the breeding program to raise seedlings for new plantations. (Photo courtesy of Ken Robson)

The term “silverback”, as everyone knows, is derived from the sobriquet applied to the alpha male of a troop of mountain gorillas, an animal of abnormal size and dominance. When I first heard Ken calling his champion sandalwood trees silverbacks, I was not sure if it was appropriate … but I came to love the term, and to use it for champion trees whatever their species or provenance.

Tree breeding has its risks.       

Can tree-breeding be taken too far? We know already that this point has been reached with the genetic improvement of, for example, racehorses and some breeds of dog, where individuals are so highly bred they can hardly survive without daily medication, constant attention by vets, and pampering by their owners. It is even worse in horticulture where the taste of many fruits and vegetables has been bred out, an unintended consequence of breeding for appearance and supermarket shelf-life.  How well I sympathise with the American writer who lamented:

Apples, apples everywhere and hardly a one to eat. The big red and yellow plastic spheres, waiting in the market for the unsuspecting, are so suspiciously, so blatantly thick-skinned and shiny it is easy to pass them by. What we must live on is the memory of what a good apple used to taste like {Endnote 2].

Maintaining genetic diversity is critical with trees. There will always be trouble if they are bred too fine. This is because trees, unlike for example hot-house tomatoes, live for a long time out in the natural environment, subject to the vagaries of climate and the slings and arrows of outrageous fortune in the form of fire, frost, storm, drought, flood, disease and insect plague. I can think of one instance where this was not fully considered: a tree was bred with rapid growth, lovely form and superb timber, but all of these were at the expense of wind resistance, and the whole lot blew over in a cyclonic gale.

I recall another good example of unintended consequences. The maritime pine breeding program in WA produced a tree with a long straight trunk with few branches, ideal for the future production of beams and sawn timber. However, maritime pine was also the tree grown specifically for Christmas trees for the Perth market, and seed from the genetically superior pines made terrible Christmas Trees, having no branches on which to hang the decorations. The problem was easily solved, however, Christmas Tree growers going back to early ‘pre-breeding’ maritime pine trees for the seed for their annual plantings.

I hear similar concerns from gardeners, who prefer the old-fashioned garden varieties, especially the roses that were so wonderfully scented before the breeders managed to produce pretty roses with no perfume. As cottage garden expert Dr Judyth McLeod writes in one of her articles:

So many of the [traditional cottage garden] annuals are the more charming the less the plant breeders have interfered with them. 

The Cherry Ingram story

All of this came to mind when I was reading the book (and salutary story) by the Japanese writer Naoko Abe called Cherry Ingram – the man who saved Japan’s blossoms. This is one of the most beautiful and interesting books I have come across in many years.

"Cherry” Ingram with his beloved cherry blossom

Abe tells a classic story about the inattention to preservation of genetic diversity, this time relating to the famous Japanese flowering cherry tree. Deriving from only ten native ‘wild’ species, Japan once boasted perhaps more than 200 different varieties of flowering cherry, each with different characteristics, including the colour and beauty of the blossom and foliage. These varieties were the product of hundreds of years of crossbreeding, growing seedlings, taking cuttings, making grafts, winnowing and selecting, and careful husbandry.  Over those centuries, the flowering cherry tree, in all its multiple forms, became an object of love and almost of worship, deeply immersed in Japanese culture, traditions and religion.

However, in the years after the first World War, under the influence of fierce nationalistic/militaristic governments, a single variety was chosen as the Japanese cherry. Under government edict, this variety was favoured and prescribed. It swept the country, but at the same time, numerous non-favoured varieties began to disappear or die out, including some varieties famous for their wonderful and beautiful blossom.

Cherries (like apples) do not breed true from seed, and a flowering cherry tree only lives for about 25 years, so unless a particular variety is perpetuated by taking and grafting cuttings, it will become extinct – which is what happened to many of the finest cherry varieties in Japan in the years leading up to and including World War 2.

Luckily an eccentric Englishman, Collingwood “Cherry” Ingram had visited Japan (twice) in the 1920s and on his second expedition he saw with dismay what he described as “frightening changes to the country’s cherry populations”. He collected scions (cuttings) of as many different Japanese cherry varieties he could get his hands on, and these he took back to The Grange, his estate in England, where he propagated and cared for them. His cherry tree arboretum even included his favourite, the beautiful Taihaku variety, which by the late 1940s had become extinct in Japan. To cut short a long and fascinating story, it was from Ingram’s collection that the most beautiful of the Japanese cherries were “saved”. From about 1950, Japanese horticulturalists again turned to propagating the full range of cherry varieties, and to do so they first imported cuttings from Ingram’s gardens.  

This is a very sketchy account of a beautifully written book. I could go on about it for hours … but have already said too much in what is a mere aside to another story altogether.

“Cherry” Ingram’s painting of the blossom of the Taihaku flowering cherry. Ingram was a painter and illustrator, and an ornithologist as well as a botanist, excelling in all fields.

Tree breeding: a final reflection

From what I saw, back in the day when I was involved in this business, today’s forestry tree breeders are mostly well-aware of risk of breeding a tree whose genetic diversity is too narrow (although I retain some reservations about the clonal plantations in which every tree has pretty-much the same DNA), and of the need to preserve wild populations and varieties. The horticulturalists, on the other hand, who have succeeded in breeding apricots, nectarines, apples, plums and tomatoes with all the flavour of distilled water, know no shame.

Today, whenever I walk through or admire a photograph of super trees, indubitably a plantation of silverbacks, I take a special pleasure in knowing how the process started … a few young foresters (as I once was), striding through the forest on fine autumn days, with nothing better to do than look at trees and select the best of them.

For many of us it was one of the most enjoyable interludes in our early professional lives.

Endnotes

1.      Dave Regan

Dave Regan was a hero of many of Henry Lawson’s wonderful short stories about bushmen and the bush.  In one story an itinerant swagman is caught in the bush in a huge downpour and is soaked to the skin. But just as the skies clear up rode Dave Regan, his hair damp but his clothes bone dry. Dave’s trick, Dave explained, was, when seeing an approaching rainstorm, to dismount and undress, put all his clothes and the horse’s saddle blanket into in a hollow log, and then dry himself and dress again in dry clothes once the storm had passed.

2.      Apples

 To give apple breeders some credit, I admit that among the varieties on display in my local supermarket there are two that are quite tasty: the Kanzi and the Pink Lady. But even the best of these cannot hold a candle to the flavour of the apples I ate as a boy, especially the Jonathan and the Cleo, both of which are completely unattainable anymore (at least in Western Australia).