Phoenix trees

As we are again beset by storms and high winds, which will bring another bout of tree loss, it seems a good time to think about the reaction of trees, once they are wind thrown. We assume that’s it; end game, but the tree knows better and will regenerate if it can – and if we leave it alone. We call these trees recumbent, or phoenix trees, as they appear to arise from the (metaphorical) ashes.

Trees that get uprooted don’t always die. Unless there was almost total internal decay in all the anchor roots, then when a tree falls, the roots on the underside remain in the soil and continue to function. If the tree remains in this position (i.e., not cleared away by tidy-minded humans) then the tree will often carry on growing. Not every tree will do this, some are better than others, but you might be surprised at how many can and will, given the opportunity.

When a tree blows over, provided it has the energy (reserves and some connected roots) it begins the task or re-orientating it’s crown. Adventitious and epicormic buds will break from various points along the trunk and branches, forming a mass of dense foliage which will initially help replace lost photosynthetic ability. From these growths, a new branch structure will form, with the less vigorous growth dying off as it is crowded out. Eventually, it will form a new crown and may grow as big as any tree of its species. Often, the effect can be more of a multi-stem copse than an individual tree, with trucks spaced out along the old framework. Like pollarding, this can give an old tree new life. There are emerging terms that describe the various forms these processes can take, which we will explore here.

Such trees develop where they are not perceived as dangerous to leave, blocking access or field use. Those factors probably account for the removal of most fallen trees, leaving only those in out of the way places. It’s a shame, because a mature tree is the most biologically diverse one and if it becomes a phoenix, it will rapidly become a veteran tree in a phase of secondary canopy formation.

As to which trees will do this, it is probably any that respond to wounding via adventitious/epicormic bud growth. Those trees prone to suckering, or which coppice well are the strongest candidates; I have no doubt there will be many examples of less obvious species becoming phoenix trees. After all, for them it is do or die. Conifers are less likely to respond, though Scot’s pine and larch do, as will redwoods.

Where trunks have touched the ground, many trees will have formed new roots; there would be limited opportunity for the old roots to expand to accommodate the new growth, plus the new trunks will bring new wind loadings as they grow. New roots are therefore essential to ensure long-term endurance. The exception are oak trees, which appear to only rarely make adventitious roots, despite being one of the most common phoenix trees. Where these do not form, or are insufficient, the tree may fall again as it puts on top growth; downy birch does this a lot. Such trees have been known to respond again, becoming a double phoenix.

There is not much literature on phoenix trees, but I found an excellent publication by Richard Worrell from 2019 called the “Ecology of Scotland’s Recumbent or ‘Phoenix’ Trees”, which I’ll put a link to at the end. In this he describes various methods of failure and of response, which are worth understanding. A brief summary is below:

Manner of failure:

• Lifted rootplate – the most common failure, tree falls and lifts rootplate by 90 degrees
• Gradual root failure – tree slowly falls without lifting rootplate (rare)
• Stem failure – stem or large branch fractures close to the ground
• half-trees – trunk splits vertically and falls
• Collapsed coppice – coppiced branches split out and fall

Position of stem:

• Grounded – trunk touches the ground
• Propped – trunk held aloft by own branches
• Suspended – trunk held aloft by other tree or rocks

Structure of new crown:

• Hedge phoenix – lots of linear small growth along trunk
• New-tree phoenix – one or more new main trunks emerge
• Crown phoenix – existing crown reorientates
• Double phoenix – falls , re-establishes, falls again, re-establishes
• Complex – multiple combinations of above

For more detail on these categories, read the document referenced.

The pictures below are from two sites I surveyed in Abu Dhabi, UAE. There, moisture is always the limiting factor but I saw plenty of native ghaf (Prosopis cineraria) blown over and resprouting. Where these are in parks or palace grounds – in out of the way corners – they are left, but maintenance teams insist on pruning off the epicormic response, thinking they are tidying up. Sidr (Ziziphus spina-christi) responds in a similar way, as do various Vachellia (Acacias). In such climates, leaving this ecological niche is essential.

This process happens everywhere there are trees, from temperate forests, tropical rainforest and in arid desert climates (see pics above); even the boreal forests, which are conifer-dominated, will have (at least) pine and larch phoenix trees. Another conifer known for it’s phoenix regeneration are redwoods. The pictures below, kindly supplied by Rob McBride, show some amazing coast redwoods, Sequoia sempervirens, at the Charles Acker’s redwood grove, Leighton, near Offa’s Dyke in Wales, part of a large, early plantation of the species.

So as we clear up from the latest storm (or the next, or the next…) where possible, let’s leave the trees lie and see what happens – a phoenix may arise from disaster. Such trees, to be sure, are fantastic to behold, ecologically enriching and a haven for our beleaguered wildlife. Leaving them to veteranise in this way, helps to plug the looming age gap between our mature and ancient trees.

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Rob Mcbride, the tree hunter: https://www.instagram.com/thetreehunter/

Ecology of Scotland’s Recumbent or ‘Phoenix’ Trees, Richard Wirrall, published by the Scottish Forestry Trust, available as a PDF here: https://www.scottishforestrytrust.org.uk/userfiles/file/projects/p16_264_phoenix_trees/the-ecology-of-phoenix-trees-in-scotland.pdf

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