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The drought-tolerant trees we should all be planting
Arit Anderson is passionate about trees and what they can offer us: the ecosystem services and benefits, including their ability to provide shelter, improve the soil, sequester carbon and mitigate against excessive heat, flooding and erosion. ‘Trees have all these amazing services on tap for free,’ she explains. ‘But only if they are healthy and have the right environmental conditions. With climate change, we have to look beyond the right plant, and right place mantra to add the right future adaptation. It’s not just about planting a tree, but about establishing it and thinking of trees in a more considered way.’
With the expert tree scientist Henrik Sjöman, Arit has written The Essential Tree Selection Guide, which encourages a complete re-evaluation in our changing climate. ‘For so long, we have assessed trees from a purely aesthetic viewpoint, looking at their height, spread and seasonality,’ says Arit. ‘With the climate changing so rapidly, we urgently need to find a new language to talk about trees, thinking about the capacity of a particular tree to perform in the future climate.’ She urges all of us to spend time evaluating a site and understanding the conditions, ‘We need to think about each tree’s ability to deal with rising temperatures, drought and increased rainfall, and even about intricacies like leaf shape and branch structure, which contribute to the degree of shade cast.’ She also talks about the importance of succession, which is the process of change and species distribution within an ecosystem, and the need to choose both pioneer species (which establish quickly and easily in an empty site) and late-successional species (which require a stable and sheltered environment to thrive).
One of the most crucial elements of selecting trees as the climate changes is to look beyond the tried and tested species and varieties that have thrived in Britain for hundreds of years and to consider lesser-known, non-native species suited to a warmer climate. ‘Look at our beloved birch,’ Arit points out. ‘They are water sensitive and struggle with drought, so they aren’t necessarily the right choice for your garden.’ Periods of drought are perhaps the most damaging climatic challenge, causing more stress to trees than excessive rainfall or short-term flooding. Useful tables in The Essential Tree Selection Guide give you at-a-glance information about the trees that are most likely to cope with the environmental stresses of flooding, wind or drought.
According to Kevin Martin, head of tree collections at Royal Botanic Gardens, Kew, trees in areas of drought evolve to allow them to survive. Researchers at Kew have been studying species distribution and future climate projections with genetic material collected from areas such as the Mediterranean and Caucasus. Using state-of-the-art techniques, they are able to assess the drought tolerance of trees by measuring what is called the turgor pressure (or hydrostatic pressure) of a leaf and the length of time that it can withstand a total lack of water. From this knowledge, they can identify the trees that could shape future treescapes in Britain. These include the Tatar maple, Acer tataricum, and the golden rain tree, Koelreuteria paniculata, which are good for small urban gardens experiencing excessive heat in summer, and the super-resilient Italian elm, Alnus cordata, which can survive periods of extreme wet as well as summer heat. With temperatures rising at an unprecedented rate, there has never been a more crucial time to plant the next generation of climate-resilient trees.
10 climate-resilient trees:
A large tree not widely grown in the UK, the Italian maple has great drought tolerance, so may soon be better known. It is available from Dutch nurseries and there is a magnificent specimen at Kew.
Small and shrubby, the Tatar maple grows wild in central and south eastern Europe up to eight metres tall. It has red-winged seeds, vibrant green leaves in summer and attractive autumn foliage, and it is extremely drought and wind tolerant.
Also known as the Turkish hazel, this medium-sized tree will reach 20 metres. Growing well in most soil conditions, it is drought tolerant once established, producing long, yellow catkins and heart-shaped, bright green leaves. A good alternative to a lime tree.
The golden rain tree is very resilient and will thrive in most conditions apart from excessive wind. Growing to 15 metres, it bears long leaves – bronze in spring and dark green in summer – and yellow flowers.
The slow-growing American hop hornbeam can reach 18 metres, with hop-like flowers in summer. Adapting to a variety of soils, it is drought and wind tolerant.
This medium-sized tree is already widely grown in the UK for its fantastic autumn colour. Also known as the Persian ironwood, it thrives in a warm climate and is drought tolerant once established.
This eastern European form of the wild pear grows in difficult conditions, making it an ideal tree for an urban environment. Reaching up to 25 metres, it offers blossom in spring and edible fruits.
Growing wild in Britain and throughout Europe and the Caucasus, the sweet cherry is vigorous and easy to establish on most soils apart from dense clay. It produces blossom in spring and fruit in summer.
This magnificent, semi-evergreen oak is a hybrid between Quercus robur and Q. ilex and is, as a result, extremely hardy. It shows good drought tolerance.
The Caucasian elm is slow growing, up to 15 metres, with dark green, saw-toothed leaves. Tolerant of hot and dry conditions, it prefers a sheltered site
