Sunday, 27 July 2014

Old Man Ivy

Heronry Wood at Earlham is a mature wood, filled with tall trees casting a deep shade. My eye reaches up into the sunlit canopy where tiny birds are twittering and foraging, and from where unripe beech mast is dropping sporadically to earth through solid space. At ground level,  ivy is crawling everywhere like a lustrous, dark green fog, masking the tree trunks and blanketing the woodland floor; it has had over 160 years to put down roots here.




The wood is now part of the grounds of the University of East Anglia. I shall be leading a group of young students around the campus next Tuesday, as part of the Art & Nature Summer School at the Sainsbury Centre. I am looking for things to fire their imaginations.

I could start with ivy (Hedera helix). It is scrambling over the ground and scaling the trees with its hairy limbs. The contrast between its five-pointed, palmate leaves at ground level and its lance-shaped leaves on the vertical plane is striking. There's a story here. 

The plant ramps across the forest floor in a dark green, immature state, before finding an opportunity to reach for the light. It then starts climbing, bushing out and questing for reproductive maturity: its leaves become lance-shaped and lighter in colour, and its flowers develop and so disperse their pollen at a suitable height from the ground [1]. There's also a story in its thick, bristly stems which look more like roots. They embrace the trunks and climb upwards in a basket-work of ramifying arms. Recent research has shown that these adventitious roots are able to climb because they secrete a glue made of polysaccharide and miniscule nanoparticles. Scientists believe that synthesised ivy nanoparticles will have important technological applications [2].



Ivy is our only native representative of the Araliaceae, a complex family of plants, originally of palaeotropical origin over 50 million years ago, which includes Panax (ginseng), Tetrapanax, Fatsia and Fatshedera. The oldest fossil examples of the genus Hedera date from Oligocene times in Korea, perhaps 30 million years ago [3], and Hedera helix probably evolved in the Mediterranean area in Miocene times, perhaps 10 million years ago. It is now a native of the warmer parts of Europe and western Asia. 

Ivy looks exotic and behaves strangely - there's something rather unBritish about the way it thrives in shady places and shamelessly exploits other plants to meet its needs. It has a whiff of the jungle about it. Its mode of life is that of a liana, one of those long, tropical vines beloved of Tarzan which use other trees for support in order to reach the light. It flowers later than most other plants, in October and November, which may be evidence that the plant is not fully adjusted to our present climate [4], but a fact that is convenient for insects who struggle to get late-year food. Its pollen gets plenty of attention then. Foresters are not so enamoured: they cut it off at ground level, in the belief that it strangles growing timber. Ivy is an alien tree in America which has invaded deciduous forests and created an 'ivy desert', stifling understorey and ground cover plants [5]. It has a reputation as a poisonous food plant for humans [6], although my neighbour's sheep eat its leaves with gusto in winter time, and rabbits often gnaw its bark when deprived of their usual food by a snowfall; their depredations are evident in Heronry Wood. Ivy  may be palatable to rhinoceroses too: fossil ivy pollen has been found in sediment embedded in the tooth of an extinct species of rhinoceros found in river deposits of Hoxnian age at Clacton, Essex; as much as 37% of the pollen was ivy, suggesting that the animal died in autumn time [7]. A cynic would blame the ivy.

Ivy limbs scarred by browsing rabbits.

Ivy ramps around in my imagination. Its Will to Life is uncompromising. While some people may find it sinister, I like to follow its deep, Aralian genetic roots back to the time of our remote ancestors, to the immense forests of the Palaeocene, which were home to the monkeys, lemurs or tree shrews which gave rise to our Miocene forefathers, the apes. Hedera helix is far older than human kind. It was was thriving in the forests which Adam and Eve entered when they first came out of Africa; it lives alongside us today in our technological civilisation, and will no doubt embroider our bones when the last of us eventually becomes extinct. 

With its unscrupulous vertical ambition, ivy may be a good plant metaphor for human invasiveness and hubris. Perhaps we recognise a kindred spirit when we see one. 

I wonder what my students will make of it.




References

[1] - Okerman, A (2000): Combating the 'Ivy Desert': The Invasion of Hedera helix (English Ivy) in the Pacific Northwest United States; Restoration & Reclamation Review, 6.4 - Online at http://conservancy.umn.edu/bitstream/59738/1/6.4.Okerman.pdf [accessed July 2014]
[2] - Burris, N et al (2012): Nanoparticle biofabrication using English ivy (Hedera helix); Journal of Nanobiotechnology 10, 2012
[3] - Metcalfe, D (2005): Hedera helix L.; Journal of Ecology, 93.3 - Online at http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2005.01021.x/full [accessed July 2014]
[4] - Godwin, H (1975): The History of the British Flora. A factual basis for phytogeography; 2nd edition, Cambridge University Press.
[5] - Okerman, ibid.
[6] - Hyde, M (1976): Hedgerow Plants; Shire Publications Ltd.
[7] - Godwin, ibid.


1 comment:

Jenny said...

A beautiful piece. I love all the ivy information woven into writing prompted by a wander round a bit of everyday secondary woodland. "... there's something rather un-British about the way it thrives in shady places and shamelessly exploits other plants..." I love the idea of a plant being un-British...