I just returned from the UK, where I made lots of presentations to a bunch of great folks about trees, stormwater and minimum soil volumes for trees, and what those things mean for London and other UK cities.
Besides the Royal Wedding, to which I wasn’t invited, the great Clash song “London Calling,” rang in my head throughout the trip. This was all while looking at London’s green infrastructure — its great parks, trees, and the mighty Thames. You’re probably wondering why this brought the Clash to mind.
Well, one part of the chorus to the anthemic “London Calling” includes these warning phrases:
“The ice age is coming,
the sun is zooming in,
. . .
London is drowning —
and I live by the river.”
Although this song was written about a nuclear attack, London is suffering from another attack — CO2 and more sudden, erratic rain storms. The consequences of this on London specifically and the UK generally is striking.
On this trip, I could definitely feel climate change in London. It was much warmer there than in Minneapolis, Minnesota, where I live. I noticed this same warming phenomena when I was last in London in April 2008.
I grew up in Ireland, which is 8 degrees latitude further north than the Twin Cities. London is 7 degrees further north, about level with Hudson Bay in Canada. The 45th meridian north runs right through the Twin Cities — in European terms that’s the same as Rome, but we are much colder than Rome. Despite that geographic reality, London is, well warmer, and drier.
Drizzle seems to have gone away — replaced by cloudbursts. I went on the web to examine this further, and the data bears it out. London is getting warmer. It was shocking to feel the difference.
Our British colleagues are not yet requiring minimum soil volumes for street trees. In the past, typical London “drizzle” covered a multitude of transplanting sins by creating perfect conditions for newly moved trees.
Today, young urban trees in London are failing much more frequently than decades ago. Most London Planes in London are now over 150 years old. At some point in the near future, however, that population will crash. London now has a 1.5 million tree planting program — a visionary thing. Those hundreds of thousands of new trees will have large soil volumes to fill.
Along the Thames, in the London Plane tree pits, it was possible for me to expose the rich silty loam deposits of the Thames floodplain. These gigantic London Planes on the Thames Embankment are now showing signs of decline. To me these trees are iconic, as much a signature part of London as Big Ben and the Houses of Parliament. Those huge trees swaying in the breeze have a very civilizing effect on London, and for me, are part of what makes it a world city.
These huge trees are also providing a great many ecological services to London. An i-Tree model could quantify that number exactly (that’s something we hope to work on in the future). When those trees were planted, development happened in a much different fashion than today. Buildings had their foundations dug by hand. To limit hauling of material, most of this soil was scattered by the street or became the garden. Typically, food scraps and other organic matter made its way to the soil pits. It was loose and well aerated — in horticultural parlance, it was double dug. As those young London Planes grew bigger their roots moved into this voluminous oxygen rich loams.
Today’s young, newly planted trees do not have such an advantage. Construction today is about compaction — extreme compaction. Also, narrow sidewalks have forced tree planting pits to become smaller and smaller. Truly, these newer trees have no chance of success to grow to maturity under these growing in these conditions. I don’t expect that any of them will achieve the size of the current heritage London Planes.
It doesn’t have to be this way. If London were to adopt a minimum soil volume standard for each of the new 1,500,000 trees to be planted, these trees would easily meet the challenge. I’m proposing a loam volume standard of 30 cubic meters per tree when trees are planted in their own individual tree pit OR 15 cubic meters when they are in connected tree pits. Let’s try and get that accomplished so we can all enjoy this great city long into the future.