A walk through the garden

We took a turn around Cambridge University Botanic Garden's climate change and plants trail...
25 August 2020

Interview with 

Chantal Helm, Cambridge University Botanic Garden


photo of a lavendar plant


Back to the Cambridge University Botanic Garden where they’re exploring the collision between gardens, plants and climate change. Katie Haylor went for a walk with Chantal Helm...

Chantal - We're having summer high temperatures, I suppose, as part of climate change predictions that are becoming reality. And here in Cambridge being probably the driest part of the UK and probably the driest area in Western Europe, we deal with high temperatures and low rainfall quite often. I think with these increased temperatures, the moisture deficit within the soils is becoming more and more of a problem to deal with.

Katie - You've got a new trail in the garden?

Chantal - All about plants and climate change, yes. Comes out of hope to try and encourage our visitors to appreciate plants for their diversity in terms of their adaptations to climate change. Also to, I suppose, encourage our visitors to understand why we are going certain ways with certain plantings and also to really talk about how plants can help in mitigating climate change. There is a lot of climate modelling that is trying to group plants into the winners and the losers and plants that are already adapted to dry, hotter conditions, potentially going to be the winners. And then those plants with much more specialist requirements are probably going to be the losers. So we're talking about plants that are probably adapted to very high altitudes.

Katie - But we're here in the Mediterranean garden, these plants are designed to be in hot dry conditions, right?

Chantal - Yep. So the Mediterranean - hot dry summers is the key thing. And I suppose more rainy, wet winters is what they're able to survive. Very sandy soils is the other sort of thing, so that there's a sort of drainage in the summertime. So reduction in leaf surface area is a big key one for many plants, lavender and rosemary we're familiar with, they will have very small leaves.

Katie - So what's going on there is that because you've then got less area for the water to evaporate?

Chantal - Exactly. Some plants have gone to the extreme where they've lost their leaves entirely. There are a lot of succulent plants, for example, even maybe cactuses and stuff like that, you'll have no leaves. And the only thing you're seeing there, the leaves, are actually the thorns and that is an adaptation for a dry environment. So those can do quite well if they're able to deal with the winter temperatures that we have in the UK. So with a Mediterranean planting and a garden, you've got to think about the whole year, the whole season, even though it may have some good adaptations to summer drought, is it able to survive frost? Many of the plants have got hairs and maybe are grey, so that's all about reflecting light, making sure that the heat doesn't impact on the photosynthetic capability of the plant. But also the hairs will track moisture close to the leaf surface.

Katie - So what about the losers?

Chantal - If we come back to the issue with high altitude plants, especially Alpine plants, for example, many of them have adapted to an extreme environment in growing which is rapidly disappearing. So obviously as temperatures rise, we are going to have increasing temperatures that's going to move up a mountain environment. They're going to lose space. Depending on where they are in the mountain and the sort of micro climate, the topography of that mountain, there may be opportunities for them to hide out, but there's also this competition with other species that are also moving up the mountain. They may be faster, better competitors, may grow faster. Alpine plants tend to grow very slowly because of the extreme environment and extreme conditions they're having to survive in. So there is sort of those losers. The physiology depends on the mountain itself and whether they're going to be able to survive or not. So we've got a giant Redwood. They've been here for 150 years. Some of the largest plants in the world, they don't obviously grow to their natural size here in the garden, even though they are 150 years old, because of various constraints. But this plant is useful in the climate change trail because it can show how much carbon a large tree like this can lock away. I think it came up to 50 tonnes of carbon dioxide, the same as eight return flights from London to Sydney

Katie - On the one hand, that sounds pretty impressive. But on the other hand, that's a lot of trees, right?

Chantal - Yes. And if you think how many flights there are, obviously every day, all the time, to different locations, the idea of planting trees to offset all of our carbon emissions is probably not going to be a very sustainable thing. It's just not enough land. And I think that's what we're trying to sort of bring home with this point in the trail.

Katie - But it's not just individual plants that can mitigate against some of the impacts of climate change, is it, I'm pretty sure you've got a landscape or a type of environment on this trail somewhere as well?

Chantal - Yes. So the other point in the trail is the Fen display being a carbon sink.

Katie - Very fitting for Cambridgeshire! Can we go and have a look?

Chantal - Yes, definitely.

Katie - Just to describe where we are, we've come into an area - it's waterlogged. What classic plants would you find in this kind of Fen environment?

Chantal - You got a lot of sedges, and a lot of reeds. If you have the water logging taking place over an extended period of time, you will then have the buildup of the peat, which then provides that substrate in which all the plants are then growing.

Katie - And what exactly is peat?

Chantal - So peat is an organic material that is formed over time through very slow to no decomposition of organic material, dead plants, pretty much. In terms of a very low oxygen environment, the decomposition is very much slowed. So the organic matter is built up, maintained within that environment, so it becomes the substrate. It has got a very wonderful structure that in terms of water holding capacity and other features that make it very good for composting and providing structure to your soils and gardens, and hence has become very popular in horticulture for many, many years. Though, in recent decades, we realise that peat is actually locking away carbon. The extraction of peat, the whole industry is releasing huge amounts of CO2 into the atmosphere, which would have been locked away. Not only that it's also this rare habitat that's sort of been destroyed for that peat to be extracted for our gardens. Most of our natural Fen habitat has actually been lost in the UK. It would have been extensive in this East Anglian region because of water log conditions, very low lying land areas. That was all drained a while back for agriculture. Agriculture was working very well for a long time in the environment because the soils, once you've drained them, they have very high nutrients, but the loss of this habitat has resulted in the loss and extinction of a large number of different species. So the whole Fen land area, in terms of agriculture, is sinking for one in that as the peat degrades, it's no longer waterlogged. The carbon is being broken down. It's released as carbon dioxide, and that is then increasing the amount of carbon dioxide that's coming up. So now the whole area is actually a carbon source where it used to be a carbon sink. So it's a very rare and protected habitat and we're trying to recreate it here.


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