The history of a forest is written in the shape of its trees. The shape of each tree tells not only its life story, but also the story of its neighbors: where they lived, who came and went, when they departed.
Woodland trees have a distinctive shape: deep wide crown, short fat trunk, and thick low branches. They’re great for wildlife and beautiful to behold. So how do you grow a woodland tree? Like good Slow Food, the recipe is simple but can’t be rushed. The key ingredients are space and time: space to spread and time to sag. Without both, a woodland forms a forest.
Step 1 – Provide lots of space to spread
Trees grow toward the light. That’s obvious; big trees don’t grow in caves. To get the maximum amount of light, they need lots of space.
When a young sapling is surrounded by lots of neighbors, most light comes from straight above. Light from the sides is intercepted (and used) by neighboring trees. As a result, closely-spaced trees grow straight up towards the light, not sideways. To do this, they shed the shaded, lower branches and leaves. This leaves a long, bare trunk, and a small upper crown.
By contrast, a sapling with no neighbors receives light from the sides as well as from above. Branches low on the trunk are retained, not shed, as they capture light from the sides of the tree. This creates a wide canopy, with low branches, a short trunk, and a deep canopy with low-hanging foliage.
A picture-book woodland tree wouldn’t be a picture-book woodland tree if it didn’t have a short trunk and thick low branches. To grow these features, it needs space to spread sideways.
Step 2 – Add lots of time to sag
Space alone doesn’t create a majestic old tree. It also needs a liberal dollop of time; time to grow and time to sag. As branches grow older, they get thicker and heavier. It’s hard to hold up all that weight, so just like us, old trees sag. New branches stretch up to the sun while the old boughs bend to the ground.
The bent boughs of an old tree didn’t always bow down low. They started off perky and erect; time did the rest. Look at the upper branches of a young tree. They don’t sag. They head bold upright, and the angle between each branch and the central trunk is narrow (acute). As the tree grows, each branch is over-topped by younger shoots. As you scan a tree from top to bottom, the angle between the trunk and each branch widens. The top branches head upwards while the lower branches head outwards. Every low branch was once at the top of the tree, and they all started off upright, stretching towards the sun.
As a tree grows older still, big old branches bend in the middle and bow down to the ground, weighed down by accumulating wood. Compare a young tree, growing out on its own, against an old veteran tree. The lower limbs of the young tree might spread wide, but they rarely sag down towards the ground; gravity and age does that. For an aging tree, “every asset’s heading south,” as Tim Rogers once sang.
Step 3: Add time again to grow new branches
There’s another reason why old woodland trees look like they do. An old tree is like an old house that’s been added to regularly. Some bits are old and others are new. As time goes on, old boughs sprout new young shoots, not just from the end, but along the length of the branches.
The lower boughs of a mature, actively growing tree are often clean, with few side branches. Why don’t new branches grow along these open boughs? Trees and shrubs don’t want to invest energy to grow leaves in positions that won’t receive much sun. So the foliage at the end of each branch produces hormones that inhibit buds further back along the stem. When the terminal foliage is growing actively, the buds along the branch stay suppressed, and no new side branches can grow.
When old branches die and break, less inhibitory hormones are produced. This lets the buds (that were once suppressed) along the remaining bough spring into life, and new secondary branches grow along the once-bare bough. This second wave of regrowth often creates erect, upright branches on the upper side of the older boughs.
The big upright branches in the center of the tree above didn’t exist when the tree was younger. Instead they formed when the bough they grow on began to die. It takes a long time for a bough to grow wide, to die back, and for another big bough to grow upon it.
As time progresses, these secondary branches may bear another crop of younger branches, when they in turn start to die back. Like a renovated old house, an old tree accumulates successive generations of branches; boughs on boughs, trees in trees.
Step 4: Stand back and admire the handiwork
To grow a picture-book woodland tree – with a deep wide crown, short fat trunk, and thick low branches – you need space, time, and more time again. Like good Slow Food, the recipe is simple but can’t be rushed. You just can’t skimp on space nor time.
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Thanks, Ian, for another wise and engaging post. When I compare your words and handsome photos to our midwestern U.S. oak woodlands, I notice interesting differences. Our open oaks often grow squat with horizontal branches from the beginning. But the deer eat them off as long as they can reach them. Fire burns them off as well. We don’t have open oaks except where there is frequent fire. As a result, our most open and “picturesque” trees are often those that grew in pastures that didn’t burn. Our more “natural” trees are sometimes vase shaped, as a result of lower limbs burning off. I’d be interested in your thoughts on the role of herbivores and fire in the architecture of Australian woodland trees – perhaps in another post when you get lots of free time?
Hi Stephen, thanks for an informative comparison, I hadn’t thought about those options. The old growth trees in the photos have probably remained unburnt, or rarely burnt, since European settlement. The top photo is in a cleared pasture (which fits your observations) and the others are in an or beside an intermittent wetland, which would be flammable in some seasons and not others.
One reason I wrote the post is because I’ve become increasingly interested in how stand structures (density, gaps etc) affect the shape of trees, and how tree shapes then influence further changes in stand structures, especially gaps. There’s very little written in Australia on this topic, and tree shape has been somewhat neglected as an indicator of ecosystem processes here. I’ve been busy reading US silvicultural texts recently, which deal with shape from a foresters perspective (ie how it affects timber) but these don’t really discuss shape per se.
Your comments remind me of pictures from South African savannas (I think by William Bond), which probably share a similar fire patterns to your prairie woodland sites. Any chance you could share some photos of these contrasting growth habits in one of your great blogs at Vestal Grove? http://vestalgrove.blogspot.com.au Would make a great comparison. Thanks again and best wishes for a great year in your prairies in 2013, Ian
Love how you use the beautiful shapes of old trees to sneak in a lovely plant phys lesson. Hope you submit to Berry Go Round – I think this post would add a lot to next month’s carnival!
Hello Susannah, thanks very much for your kind comment. That’s a good idea, I look forward to reading next month’s Berry Go Round once again, best wishes Ian
Thank-you for this fascinating post, which reminded me of the extraordinary shapes of the Huangshan pine tree (Pinus hwangshanensis) I observed on a visit to the Huangshan (Yellow Mountain) World Heritage area here in China in 2009 – see the last five images of the gallery at http://discoverchina.info/galleries/henan-anhui-zhejiang-2009/yellow_mountain_huangshan/
Hi Bruce, thanks for your comment, there are some beautiful trees throughout the world, aren’t there. Best wishes Ian
Thank you Ian for an elegant explanation of veteran paddock tree morphology. I have shared your blog on our Veteran Tree Group FB page
Looking forward to more of your research and observations of veteran trees. Please continue sharing.
Hello Jan, thanks very much for exchanging links. I’m glad you enjoyed the blog and hope readers enjoy your great Facebook site. There’s more to come on big old trees in the next few blog posts. Best wishes Ian
what a fabulous set of pictures -they are inspirational – so I will be using them as a basis for some art and will try to capture the grandeur
Hi Kath, thank you for your generous comment. I hope the art they inspire is even more inspirational. Best wishes Ian
Thanks for sharing this info on tree shapes and how we can interpret what we may see in the landscape.
If anyone wants to explore this more, there is a book “The Biggest Estate on Earth” by Gammage (2011) that puts landscape history into a context by looking at various bits of evidence (see chapter 2 – Canvas of a continent for more tree interpretations).
Keep up the good info!
Hello Rus, thanks very much for your comment, I’m glad you enjoyed the blog. As you’ve may have seen in another of my blogs from earlier this year – https://ianluntresearch.wordpress.com/2013/02/17/location-location-location-the-future-of-environmental-history/ – I disagree with some of Bill’s interpretations of landscape history. Nevertheless, I really do like the way that he interpreted landscape dynamics from the shape of trees in that chapter, it’s really, really well done. It’s a great education for field naturalists everywhere. Thanks for suggesting it to other readers, best wishes, Ian