Wild Things 3 of 6 - London

This week the gang are London bound and begin with a really interesting subject. Sally introduces us to something that we’ve seen on our pavements for years, but probably misidentified as chewing gum. However, this interesting species is a lichen commonly called the chewing gum lichen (Lecanora muralis). To explain how this lichen can survive – and perhaps even thrive – being on the pavement pounded by constant footfall Sally excavates a slab laden with this lichen treasure. We see that the lichen gets deep in the holes of the concrete by sending out microscopic threads providing an anchor. Observing the outer surface of the lichen Sally notes that it is made of thousands of tightly packed filaments, which collect moisture and nutrients from the air and protects it from our trampling. Interestingly it can even use our footwear to spread probably one of the reasons that from being a rarity 50 years ago it is now prevalent throughout the country.

Chris investigates how the Loquat tree (Eriobotrya japonica), a member of the rosaceae family and native to China has begun to make London its home. The reason being two-fold: Firstly the temperature in London is much higher than it normally would be due to the extensive construction that uses large amounts of concrete, which collects heat during the day and radiates it back out during the night. Making London up to 10 degrees centigrade warmer than surrounding rural areas. Secondly, evidence shows that after people have eating the juicy part of the plum and then discard of the stone by spitting it or throwing it into the grass or other planted areas - an ideal environment to germinate.

Chris and Trevor set up an experiment to test the greenhouse effect in London by using two glass cabinets. One filled with plants and the other concrete. After some hours in the sun we find that the air around the concrete is at 26 degrees centigrade. The air around the plants in the cabinets is at 22 degrees centigrade. Trevor explains that it is the large amounts of oxygen released by the plants that not only refreshes the air, but also has a cooling effect due to the water vapour leaving the leaves. I was very happy to see Chris and Trevor explaining the stomata which allows gaseous exchange between the atmosphere and the plant. A very interesting fact Chris gives us is that one large beech tree can supply the oxygen requirements for 10 people.

Trevor goes off exploring and shows us the gorgeous passionflower (Passiflora sp.), of warm climate areas such as Brazil’s Amazon rainforest, growing in the wild around London. While some have been found growing wild elsewhere in the country, it has only survived in London due to the extra heat there. It’s a rambling sort of plant that grabs onto other plants with its tendrils for support. While being difficult to eliminate, I wonder why we would – the flower is a wonder of nature and interestingly Trevor shows us that its fruit is edible (which to me at least is a new find!). But I can see that it can smother other plants and may decrease diversity and even be partly responsible for us losing some native species. But along with the heat of concrete, we have the current global warming, so we may have to lose a few species along the way and embrace what nature provides.

Finally we get to visit a sky high wild place in the form of a rooftop garden on the Barclays building; 500 foot up. This gravel bed on the rooftop was initially planted with grasses, mosses and shrubs 2006 to encourage other plants to grow. It has certainly been a success. It’s a low maintenance, perhaps even no maintenance wild place that is sustaining itself.

Update: Here's Trevor's blog post for this episode.