An argument over the use of ‘leaf blowers’ has been raging in the US for a few years now, the primary objection to them being the noise level, which at 90 – 100 dB is damaging to hearing for the operative- but they are amongst all other machinery particularly annoying. In the UK there have been some restrictions on usage during summer months, close to schools etc. But asides these anti blower arguments there are a host of others, including risk to human health, particularly the operative themselves by way of inhaling the disturbed particles. The emissions from these machines are too high and partly destroy justifying the environmental or sustainable attributes of the landscaping, horticultural or green keeping industries where leaf blowers are now a standard tool in their arsenal.
The threat from existing pathogens and non native invasive species, the threat from climate change factors and the stresses placed upon trees, particularly urban trees by way of human detritus, including domestic pet excrement or urine is compounded by the use of these machines.
They spread fungal spores, excrement, urine saturated top layers, insects and a host of other nasties, (including inherent toxins occurring in the soils) about, particularly unto stems, getting trapped in bark and lower branches. We know on average that some trees in Paris have as much as 25litres per week of urine onto their basal area, the root systems are just about able to cope, but with extended dry periods lower stems are suffering badly. The cost of removing an urban tree is huge against the cost of fencing the tree off, a suggested answer in restricting day by day stresses to trees, but one that does not account for leaf blowers.
This year I inspected two sites and saw many more, where hedges had their bases scorched. The most striking was a beautiful mature Hornbeam hedge. Up to around 50cm in height had been exposed to extreme scorching, with the only option to remove the bottom branches, which destroyed the look and purpose of the hedge. The culprit was assuredly the leaf blower as many hedges suffer from being used as a store for the blown leaves, (this was witnessed at one site, where a municipal employee used the machine weekly, even during spring and summer). As with the movement of trees by vehicles there is a common disregard for the fact that scorching by winds, particularly during dry periods, (when perversely leaf drop occurs out of season and the machines are put into action), or cold periods can have a dramatic affect on foliage and ultimately kill trees or lead to their removal due to aesthetics.
The other problem is the disproportionate amount of leaf litter onto soil in urban and peri urban areas. The soil organisms struggle to cope with the sheer quantity of leaves and the rich partial compost levels and the host of fungi this attracts are regularly above the basal area of trees resulting in a weakening of the tree stem. The argument put forward by some that worms will quickly process the leaves leading to a much healthier soil is simply not true, even a very healthy population of worms are not that hungry!
In some parts of the Paris Banlieue the amount of trees is equal to or exceeds the stems / ha of a woodland, yet the available exposed soil is less than 10% of the surface area.
The French were slow to pick up on the removal of Horse Chestnut leaves to reduce the damage by leaf miner (Cameraria ohridella) and the leaves are still regularly blown about, lodging themselves under nearby hedges or fences, before the annual clear up and utterly destroying the worth of the efforts to contain leaf miner which has had such a dramatic effect on the landscape of Paris.
This is of course not just a problem confined to France and the problems of effective leaf management in the suburban garden landscape of the UK are not being realised. The overall disregard of the true costs of landscape maintenance are leading to much greater costs not that far into the future and threaten the survival of all new tree planting in the urban environment.
Leaves have little value at present asides their use in enrichening soil biodiversity for horticultural gain. But I watched one old boy in St Germain en Laye collecting up sackloads of leaves and after a difficult questioning, (he thought I was an official condemning his action), he explained his purpose. He had a little crushing gadget used for squashing the plethora of publicity leaflets the French are subjected to for burning in a conventional wood burning stove. He only used it for leaves and collected enough for 20 – 25 days of heating a year. He preferred this system because it reduced the resulting ash quantity considerably.
But certainly one solution is to accept the fact that we need to pay those charged with the maintenance of our landscapes more in order to ensure the landscape remains in the future.