DROUGHT, TREES and the Urban Environment
DAVID GREEN, MD of Terrain Aeration, ponders the plight of our trees in times of climate change
TREES are constantly under stress in our increasingly urban environment. This stress springs from a multitude of causes; vandal- inflicted damage, pollution and now, more urgently, our swiftly changing climate. Trees that originally evolved in cool, moist woodland, surrounded by many thousands of other plants, now grow alone or in small isolated clusters surrounded by our man made structures of glass, stone and concrete. The differences between their original growing conditions and those they are exposed to now - higher temperatures, an increase in reflected heat, increased exposure to drying winds and direct sunshine and the much lower relative humidity between the new and old environment, will stress any tree. Add drought to all this, and the result, (at least in most of southern England) is many trees that need help. Newly planted semi-mature
trees, important features of many landscaping projects, are particularly at risk. The
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methods used to uproot and transport these specimens leave less than 50% of the roots intact and so the tree, when planted in its new position, has much less access to any available water. Flooding the tree pit helps in the short term but long-term waterlogging is as harmful as long-term drought, so care must be exercised. To make life easier we could select the tree species that tolerate hot dry conditions in the first place, but these are not always entirely at home in the UK and suffer from our cool, dank, dark winters. By their very presence they would also change the character of our urban green spaces. After all, I can think of no one who is in favour of replanting the parks in our major cities with date palms!
Given that we want to conserve our ancient trees, and continue to plant semi- mature natural species, what are we to do? We can no longer simply pour on extra water. We are entering a new era when water is becoming precious and must be
conserved, so minimising water loss is the only way to go.
Strategies such as
minimising the amount of water escaping from the root zone are possible, but such systems must be capable of storing water without impeding drainage and causing water-logging at wet times of the year. Limited efficient irrigation is also possible, but inherently expensive.
How can we ensure that the
tree’s root zone carries water in times of drought but is free draining during wet weather? Well, just imagine that it is possible to create a series of small pockets of water beneath each tree, somewhere water was always available on the driest hottest day. These reservoirs, when filled to capacity, do not block any substantial amount of the natural drainage in the soil, and refill by themselves when water is available. Using our Airforce Terralift machines, (which were invented for the aeration of trees in the first place), we can inject up to a litre of
product, carried on the final air blast of our routine aeration treatment. Our seaweed and synthetic polymer mix can be blown into the root zone of stressed trees and, once injected, the polymer absorbs excess water (following a downpour or irrigation) and releases it only when conditions are dry and the tree roots require it. The seaweed is present as a carrier and also to keep the airways/drainage channels open so that surface water can sink rapidly down to the root zone where it is captured in the polymer.
I do not think for one minute we have ‘the’ answer to the welfare of all our urban trees, but what we do have is a system, which will help both establishment of new plantings, and continued growth of mature ancient specimens. In times of stress they need all the help they can get.
Terrain Aeration Services. Tel: 01449 673783
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