The ground in winter can be saturated after many days and weeks of rain and most scientists predict that the extreme weather we tend to experience now in the UK will become ‘normal’. Call it climate change or just prolonged periods of ‘wet’, followed by extended times of ‘dry’, the results can be devastating for people living in low areas or around rivers. And, of course, for those using land for food production and other purposes.
But there are steps that can be taken to help alleviate the damage that results from flooding and even to prevent the events happening in the first place...
Trees are becoming our saviours in the battle against climate change. But the most important aspect of this whole tree thing is to choose the right variety. There is absolutely no point in planting trees that like dry, free-draining soil, in ground that is likely to flood. Some trees drown very easily – in as little as 96 hours (four days) standing in water - because of the lack of oxygen to the roots.
There are, however, some great trees that can help to deal with flood water. Their roots will stabilise the soil which will minimise soil erosion. They will also uptake a surprising amount of water and prevent more rain from even reaching the ground in the first place. You can use trees as a form of ‘sump pump’ which draw water from the soil, up the trunk, to be excreted gently through the leaves as vapour. A tree can take up 100 gallons of water per day, thus effectively slowing down the deluge of water during heavy rainfall. If flood water passes through a plantation, it not only slows the flow but each tree is responsible for taking up some of the water.
Five trees that will thrive in in UK, in seasonally wet positions
A watery planting site represents heaven to several trees and you only need to look along a riverbank to see what grows happily there.
- Willows (Salix): there are more than 400 species of willow. Some are little more than a large shrub, whilst others eventually form huge trees measuring more than 20m tall. One of the best for a watery location is Salix alba ‘Tristis’, the instantly recognisable weeping willow. They have an extensive root system which helps to stabilise them on wet sites and on riverbanks. This also anchors the soil rather nicely and prevents landslips. Once they have established, which takes around three years, these grow quickly – maybe up to three metres per year. They are not fussy about the type of soil and can even withstand some drought. Their roots will attempt to seek out water across a wide area.
- Alder (Alnus glutinosa) also like it wet and these trouble-free trees are at their happiest in swampy ground and by rivers. Alder wood is soft and porous but is extremely durable when wet. It is able to withstand rotting in water. For this reason is has traditionally been used for boat construction, also sluice gates. Alder roots are able to ‘fix’ nitrogen in nodules and this conditions the soil, thus improving ground fertility. Another bonus is that the female woodworm apparently likes to lay her eggs in alder and many people still cut some branches and place them in cupboards. Any woodworm would choose to lay eggs on the alder wood rather than the cupboard timber itself.
- Then there’s poplar (Populus tremula), often known as aspen trees (above). These gain the name (tremula) due to the rounded leaves which tremble in a breeze, giving a shimmering appearance. The stalks of the leaves are flattened and they are flexible, hence the reason why they flutter. This large tree thrives in damp soil. It has a broad-headed shape, unlike the tall, slim poplar that were traditionally planted as wind breaks around apple orchards. The leaves turn a buttery yellow colour in autumn.
- Next, there’s the aptly named river or red birch, Betula nigra (above). It’s a great tree for those positions where visual impact is required. The bark of this stunning large tree (up to 17m tall) is cinnamon coloured and it continually sheds papery layers, thus forming a shaggy and flaking appearance. It’s a bit like peeling skin! Similar to other birch trees, the leaves are diamond shaped. It is very happy in boggy ground but can even be used for street planting too. A highly ornamental tree that looks even better when planted in groups in order to accentuate the visual effect of the bark.
- The swamp cypress is another well-named, big beauty. Taxodium distichum is an unusual, deciduous conifer that loves very wet or seasonally flooded ground. It is native to the Florida Everglades and was first introduced into the UK in 1640. The tree has been given the Award of Garden Merit by the RHS. This lovely tree has needle-like foliage that turns bright orange in autumn.
Choose your site carefully and don't be tempted to plant any of the Prunus family in sites that flood regularly. Some trees will tolerate very brief flooding but the favourite five, mentioned above, will be as happy as Larry!