Tag Archives: dawn redwood

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June 12, 2015

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Climate change, Garden trees, Gardening, natural history, Plants and what I know about them, Seasons

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Autumn in terminal decline?

Red wattlebird in our Japanese maple

In amongst the nasty consequences of global warming – sea-level-rise-ocean-acidification-violent-storms-heat-waves-large-scale-extinctions (if you say it quickly and rock back and forth at the same time it doesn’t seem quite so bad) – a decline in the intensity of autumn leaf colour really doesn’t draw the eye.  Bar a few unusual plants like the red-fruited kurrajong and the Antarctic beech, most deciduous plants around here aren’t even natives.  So who cares, eh?

But as I huddle in my chilly house on its shady south-facing hillside, waiting for the leaves on the neighbour’s looming liquidambar to fall, the impact of climate change on deciduous trees seems like a tremendously pressing question.

I’m not the only one gripped by this crucial topic.  The latest  Trends in Ecology and Evolution has roundly denounced the scandalous neglect of autumn. Spring gets its own live feed on BBC TV, but even scientists get depressed by extended discussions of leaf senescence, it seems.   Garnering less than half as many articles as its greener sibling, autumn, according to the indignant authors, is a “neglected season in climate change research”.

Well, neglected no longer!  Not here in the backyards of Berowra.  Right here, right now we bring you…. in the prophetic words of Gallinat and her outraged colleagues… “the future of autumn research”.

Rainbow lorikeets in the bare liquidambar
Liquidambar leaf pattern
Red liquidamba leaves

As we march boldly into fall’s future, I’m cling to the hope that photoperiod (that’s the day-length to you and me) will rescue me from climate change, sending that winter-sun-blocking foliage promptly into the compost bin regardless of how roasting hot it is. And it’s not a vain hope – the amount of light a deciduous plant receives does seem to help many decide whether it’s time to shed their leaves or not.

In the case of liquidambar, long days or lots of light delay dormancy, as you can see from these nifty pictures of a specimen down the street, well illuminated day and night so as to minimise deaths on a local pedestrian crossing, clinging to its leaves long after its neighbours have shrugged their own.

Illuminated liquidambar leaves
The leafy and the leafless
Liquidambar experiencing artificial lighting “long days”

Depressingly, it does seem that sweetgums need cooler weather to finally ditch their leaves, even in the short days of midwinter.   Photoperiod matters most near the poles – but for trees at the lower latitudes (like Sydney, curse it) temperature is the clincher.

This raises interesting questions about the future of the veggie garden. Around the winter solstice it lurks in the shade of our dawn redwood, a living fossil that grew across the temperate Arctic when dinosaurs stomped the earth, and was dramatically rediscovered in the 1940s in a single isolated valley in China.  Will its gorgeous copper needles still fall in time to give my broadbeans a decent run-up to spring when we’re wearing shorts all winter?

Fall leaves of dawn redwood

In the words of a Facebook status update, “it’s complicated”.  Could this be why climate scientists, like nervous singles, are staying well clear?

For instance, warmer springs lead to earlier bud burst, which can sometimes mean earlier leaf-fall.  And deciduous trees in general tend to lose their leaves more readily in dry weather.  “On average”, according to Estiarte and Peñuelas (2015) “climatic warming will delay and drought will advance leaf senescence”.  Work that one out.

And that’s not even throwing nutrient availability into the mix.  For instance, what if trees start going ballistic with all that carbon dioxide in the atmosphere?  This vision of a greenhouse planet jungle awash with joyful plants growing at breakneck speed sounds like something out of a climate denialist fantasy, doesn’t it?  “More open cut mines, pretty please!” beg the earth’s desperate forests “my future is coal!”

Sadly for the wind-farm haters, it mostly doesn’t work like that.  Carbon dioxide can give trees a flying start but eventually the nitrogen supply conks out, or drought and too much CO2 do the leaves in.  Even with the help of globe-trotting survivors like sweet gums and dawn redwoods, coal (and copious quantities of greenhouse gases) won’t make the world greener.  Let’s just hope, even gardening in our bikinis, we can still find gold.

Little wattlebird doing something mysterious with a maple leaf
Sulphur crested enjoying liquidambar seeds
Mooned by a red wattlebird

References

  1. Estiarte, M and Peñuelas, J (2015) “Alteration of the phenology of leaf senescence and fall in winter deciduous species by climate change: effects on nutrient proficiency” from Global Change Biology 21(2) 1005-17
  2. Flexas, J, Loreto, F and Medrano, H. (2012) Terrestrial photosynthesis in a changing environment: a molecular, physiological and ecological approach, Cambridge, Cambridge University Press
  3. Gallinat, AS, Primack, RB, Wagner, DL (2015) “Autumn, the neglected season in climate change research” from Trends in ecology and evolution 30(3)
  4. Warren JM, Jensen AM, Medlyn BE, Norby RJ, Tissue DT, (2015) ‘Carbon dioxide stimulation of photosynthesis in Liquidambar styraciflua is not sustained during a 12-year field experiment’, AOB Plants, vol.7, Article no.plu074
  5. Warren, JM, Norby, RJ, Wullschleger SD (2011) ‘Elevated CO2 enhances leaf senescence during extreme drought in a temperate forest”.  Tree Physiology 31, 117-30
  6. Worrall, J (1993) “Temperature effects on bud-burst and leaf-fall in subalpine larch” Journal of Sustainable Forestry 1(2)
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September 16, 2014

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Death, Garden trees, Gardening, History, natural history, Ornamental gardens, Plants and what I know about them, Seasons

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A fossil in the garden

Gardens are time-capsules.  I don’t just mean the odd, poignant occasion when you dig up a bone carefully buried, long ago, by a dog you never met. I mean the fashions in plants that date gardens just as surely as winklepickers, blue eyeshadow or shoulderpads date photographs.  As you walk round the suburbs you’ll see  jacarandas arching over Californian bungalows, rows of red cordylines hemming eaveless McMansions, 70s brick veneer hidden behind shaggy bottlebrushes and rambling grevilleas.  Social history has roots in the backyard.

Our place was built in the late 1950s, and I reckon a few of the bigger trees date from about that time.  The largest hibiscus I’ve ever seen, entwined with an ancient honeysuckle as weighty as a strangler fig, reaching up above the roof of our neighbour’s two-story house to catch the light, speaks to me of post-war dreams of expansive America, a Hawaiian fantasy.  The liquidambar and the Japanese maple – a yearning for colour in the fall.

A fossil in the garden

Until today, I put the tallest tree in the yard in the same category – I figured it was a swamp cypress, native of the Everglades, happy knee-deep in water (and, with enough water, they do grow knees!).  Like a larch, it’s a deciduous conifer, needles turning copper in the autumn, then returning, fresh and feathery green in the spring.

But I was wrong.  It’s not an imposing American, though it is a cousin of the great sequoias.  It’s Metasequoia glyptostroboides, a dawn redwood: living fossil from the “dawn of time”.  It’s the Wollemi Pine of the 1940s.   An expedition to a remote village in Szechuan province in 1946 discovered a giant living Metasequoia, a species known from fossil evidence to have existed for 100 million years, thought to have been extinct for at least two million more.

Metasequoia (“sort of Sequoia”, “Sequoia-ish”) was something of a sensation in the late 1940s. In 1948 Sydney’s Royal Botanical Gardens, along with arboreta all over the world, received seeds and commercial nurseries in Australia began growing them for sale the same year. With seeds both easy to collect and propagate, the dawn redwood, George Seddon says, was a big money spinner and the trees are are now common in parks and gardens all over the world, from the subtropics to Alaska.  It’s proudly grown as a street tree in China, though it is critically endangered in its only location in the wild, Metasequoia Valley, not far from the staggeringly huge Three Gorges Dam, a hydro scheme so big filling it slowed the rotation of the earth.

Now of course, I want more lazarus taxa – more trees returned from the dead.  Gingko with its maiden-hair leaves, a clear yellow in the fall.  Okay, it has fruits that smell of vomit and its edible nut is toxic.  Who cares! It’s a dinosaur tree, over a hundred million years old!  As is the Wollemi Pine – three clumps of genetically identical trees discovered in a deep, remote canyon in 1994 – weird looking, self-coppicing, lusted over by others in possession of dawn redwood, it seems.  Although John Benson of the Royal Botanical Gardens in Sydney advises against hoarding this fossil: “people who put them in their backyard will soon have no backyard” (Seddon, 2005, 100).

A fossil in the garden

My neighbours say every winter they look out their window and think, hearts sinking, that the redwood tree we share has gone and died.  Perhaps I should reassure them that it will live for more than a hundred years; that it is Lazarus, come back from the dead; that it has been around for a hundred million years.