Marian Temple of Wanstead Community Gardeners emailed this appeal on 16 July 2022, shortly before the record heatwave struck Wanstead:
TREE WATERING.
This is really needed. Newly planted trees are very vulnerable in their first couple of years but I can see a tree in my street that’s been there for a good 6 years and it’s suddenly looking very unhappy indeed. They really need a watchful eye in dry spells and I guess a lot of street trees will be lost this summer. They will be replanted at great expense but we’ll be back to square one. If they are not looked after during their first couple of years, they too won’t survive.
PLEASE, PLEASE cast an eye on your local street trees and take action. If they have been planted with a watering tube, usually blue, it’s easy just to pour water down. If they have no tube, then it’s a bit more problematic. Sometimes, as the tree has grown, the ground has risen and so the trunk comes out of a mini hillock. Any water on dry soil will just run off. In this situation, I go to work with my trowel to break up the soil and to try to create a depression where the trunk goes into the earth so that any water sits there and sinks in. It needs watching. When the water has disappeared, more can be added. Not a quick job but worth it if the tree is preserved and we don’t get into a cycle of young trees dying and being replaced ad infinitum. How much to water them??? Well in this situation, I guess it’s not possible to over water.
This is really worth doing for our street trees. We all benefit from having them. They help filter the air, give shade, good for birds etc. etc. you know the rest. The council can’t seem to look after them in their vulnerable period so it’s up to us.
On this matter, one of the first things the Wanstead Society did, when it was first formed over 25 years ago, was to ask for trees to be planted down the Snaresbrook end of the High Street. At that time, it was just all hard surfaces. The trees were planted and they were well watered by members of the Wanstead Society. They have thrived and brought greenery to that hot dry stretch of road. One of the council street tree people visiting a few years after they had been planted, was amazed at how well they had done. None had needed to be replaced. A really good example of community action.
YOUR STREET TREES NEED YOU. Please help them now in preparation to the excessive heat wave to come. Marian.
Comment: Wanstead’s iconic sweet chestnut trees, planted in long avenues around the 18th-century Wanstead House, seem particularly vulnerable to drought and high temperatures. It looks like we’ve lost one on George Green and at least one other on Christchurch Green. The smaller sweet chestnuts (Castanea sativa) flowered as normal in June, but then leaves and catkins alike have shrivelled as if caught in a blast. The same process has affected the top canopy of the ‘Witches’ Tree‘ in Bush Wood which probably dates back to the Tudor Wanstead House or earlier. Some of the medium-sized trees, including four or five near the Temple in Wanstead Park that are about 6 metres tall, seem to be going the same way. Time will tell which will survive (late August update: looks like three have died).
The drought is not what is mainly giving the autumnal colour to the mature horse chestnuts (Aesculus hippocastanum, the web tells me), the leaf of which is the official logo of Redbridge council. The horse chestnuts are suffering as usual from fungal blight, as well as leaf miner moths and maybe bacterial canker, and so dropping their leaves. Sweet chestnuts are immune from most of those afflictions and usually look much healthier. This is a meteorological drought if not a hydrological one, with the lowest July rainfall in records going back over 200 years. The Ornamental Water in the Park has no water north of the Grotto.
However, it’s not just sweet chestnuts suffering. Some silver birches dropped leaves as temperatures rose, presumably to lower their water requirements, and the one on Wanstead High Street outside the picture-framers seems to have died. Cherry trees curled in the heat but seem to have scraped through by losing the outer thirds of their leaves (or more); smaller London Planes have also dropped almost all their leaves if not given extra water. Even small-leaved limes and a mature beech show signs of extreme thirst. While a hosepipe ban is likely in August (from 24 Aug), as many watering cans as you can carry won’t significantly worsen the water shortage and could save years of growth of a local tree. There will be skill in triaging trees: which should cope; which are already too far gone; and which are where a little water will make a difference. Please contact us if you know about ‘tree-age’.
If you concentrate on trees where 90-95% of leaves have turned brown, it seems they could survive, and presumably only need water to support the remaining fraction, so making them realistically manageable to support until the rains come. It might also make sense to prioritise stressed oaks and other slower-growing trees with greater biodiversity. As Marian wrote, it’s theoretically only whips and saplings with a mere year or two of roots that can be killed by a single year’s drought; this year it seems we need to pay equal attention to semi-mature trees that would take so much longer to replace. If they have a crown and root system covering 10 sq m, then 1 mm of light rain equates to 10 litres from a watering can. For larger trees, you can often find a spot against the trunk or between the roots where water is absorbed readily without running off. In other cases, surface tension of dry ground prevents absorption, and using a trowel as suggested near the lowest surrounding point under the crown can access some deeper soil. Sometimes the sandy ground sounds ‘hollow’ and a day or two after first wetting, these watering points become so thirsty that you wonder if there’s a drain running underneath. Presumably it’s actually good root structure. Assuming you weren’t too late and the trees are not dead throughout, sweet chestnuts and limes that were extremely stressed can go back into bud. Forget false autumn, once the rains and cooler weather comes, August can also be false spring.
From a climate adaptation perspective, trees of course provide shade and cooling from transpiration particularly in evenings, as well as supporting hundreds of insect and other species.
In terms of climate mitigation, allowing trees to mature is what will absorb and hopefully retain carbon, which can reduce ocean acidification and, you would hope, global warming. Unfortunately, tree planting is not as simple a solution as is sometimes believed and it is often abused, not only with the wrong trees in the wrong places and inadequate maintenance. The ‘albedo effect’ means trees planted in temperate latitudes like Britain can result in the surface absorbing more solar energy and so have a slight warming effect, according to a 2007 study that led to confusing headlines.
(IPCC AR5 WG2)
More to the point, native species are going to face these weather risks increasingly often, and there is no way our small-scale tree care in Wanstead streets could scale to our surrounding urban area, let alone the hundreds of billions of stressed trees in forests. Some familiar trees are going to find it very hard to reach maturity, and populations may crash together with everything adapted to them; as with Amazon dieback, the main drivers of climate change are capable of reversing tree-planting efforts and the limited CO₂ fertilisation effect. Maintaining our local trees is a necessary palliative for the comfort of humans and other species, and a welcome statement of community values, but will fail in the long run if we keep burning carbon.
Wanstead Climate Action 