Urban & Peri-Urban Soils, destroyed beyond the point of repair?

The continued disproportionate rise in our urban / peri-urban or suburban population against a rural population and the infrastructure that it requires equals the largest threat to present & future sustainability due to the continuing heavy abuse of soils.

We are now in a situation where urban soils can no longer be subject to any standardised text or media output with regards gardening, landscaping or land management.

The disgraceful trade in soil is one of the worst legacies we are leaving for our children, but it is very conveniently ignored, due to an ignorance of its importance.

Sustainable land management, (SLM), depends on soil and despite some massive progression in terms of the realisation of threats to our environment and the consequences we as a species will suffer as a result of allowing such threats to enter our urban community through the vector of soil.

Taking a transect from the centre of large population, (>250,000), will display a range of soil characteristics which alter so frequently towards the start as to render the exercise useless, the paper to illustrate the changes would have to be as long as the actual transect line itself. In one plot of a syndicate garden in the centre of Paris (1400m2) there were 14 changes so dramatic as to render any existing planting plan useless and certainly condemning what many gardeners believe to be The Soil Test, (Ph Values), to the dustbin. 9 of the soil types now present were the direct result of practitioner methods albeit unwittingly.

The sheer complexities of soil combined with the unattractiveness of its study have allowed this situation to develop. I always enjoy watching landscapers or gardeners sniffing, (sometimes even tasting) soil; it is truly the mark of the professional. However their control of soil is limited to the price a client is prepared to pay, which given the ignorance involved and exasperated by a garden media who continue to uphold the myth that a ‘a healthy dose of good mulch or compost’ will cure all ills, leads to the current situation where any mention of increased costs due to soil state will have them quickly replaced by another £10 an hour ‘jobbing’ gardener.

The quantity of nitrate rich soil ‘additives’ used within the urban environment exceeds dangerous levels, without even discounting for non permeable surface area. The trade in such products has increased despite a new resurgence in composting. The urban soils of a country as small as England are often as rich in nutrients as to be equivalent to the complete needs of a country three times its size. Yet in my own experience around 60% of urban soils I work with are nutrient deficient.

Given the shallow consolidation found in most urban sites, in some cases actual underlying infrastructure in larger cities, you will find reservoirs of nutrient sludge, stagnant and not only dangerous to human health but containing a rich seam of maladies which can affect the most resilient of out trees, both indigenous or introduced and certainly a highway for potential new threats to enter our ecosystem.

The peat argument is raging high at the moment and there is one argument which is rarely mentioned; peat is an excellent plant medium, it provides a safe solution for nurseries and subsequently for some practitioners in guaranteeing a plant short term. It is in the long term very damaging to urban soils. Containerised plants will outgrow their potted medium in varying times, but when the roots enter the inherent soil the potting medium becomes a menace. This is the point where many introduced containerised plants die. The trace elements of peat remain in the soil; this is often wrongly assumed to be beneficial. It is in reality very damaging to the soil matrix and causes immense harm and fragmentation to the soil organism ecosystem in that particular spot. There is a heightened risk of mortality to any plant that replaces the previous dead plant, which is assumed to be the fault of a disease in the medium of the previous plant. It is usually the complete collapse of the complex symbiotic relationships contained within soil, which most plant roots require for any chance of long term survival. This is no small problem in garden obsessed England.

The above problems are from a sector which many deem to be good custodianship of soils, so now add the threats from actions clearly defined as bad:

1)      The overlay of infrastructure; paving, tarmac, concrete. A recent and continuing trend to provide more hard standing for parking and also to diminish any need for weeding and maintenance should be subject to SUDS regulations, yet planning controls seem unable to enforce these measures.

2)      Contamination; there is a huge rise in the dumping of materials hazardous to the environment. The rising costs of transporting to recycling centres, has led to fly tipping in locations which are deemed unattractive. Paints, solvents and petrochemical traces are now so frequent as to register as a common attribute in tree and plant mortality within the urban zone.

3)      Dog and cat excrement and urine; a much ignored problem causing an average 50% rise in nitrates as well as causing mortality to a wide range of soil organisms. In some areas the problem is so great as to have caused an artificial new soil profile changing vegetation patterns irreversibly.

4)      Development consolidation; the use of machinery, particularly in peri urban environments have created artificial soil pans, top soil is simply spread over the top causing erosion problems on a par with those seen following the removal of primary growth in developing countries. In many post 1960’s gardens the quantity of builders waste and the consolidation have created gardens where plants simply do not have the required depth of soil to develop.

Thus problems are further exasperated and any notion of mapping and then controlling soil damage is simply a cost that is too great even when not considering industrial waste traces which have left many brown field sites far too costly an option to remediate for development, thus placing further pressure on green field sites, which due to ‘planning gains’ are made an attractive and financially rewarding option to local planners.

Technology to aid quick remediation, through enzymes, microbial and mychorrizal supplementation is still in its infancy. I am a huge advocate of mychorrizal treatments having witnessed the remarkable positive changes to soil and to tree health, but it is very much a product for specific urban areas, those which are not linked to natural soils. Research to further the use of mychorrizal treatments is thwarted by the desire to utilise mychorrizal for future agricultural purposes and the required research needed is great, together with its potential damage to the existing rich and powerful chemical fertiliser industry. In the rush to ‘green our cities’ I fear we are facing a future problem where although the trees are planted and maintained after 12 years, the damage to our soils will become clearly evident above ground .

The potential longevity of a tree will be reduced to such an extent that any ecological or environmental values the tree could have attained are rendered null and void.

In the rush to dominate offsetting and to ensure grant flow, quoted prices do not reflect the required costs of planting and maintaining a tree in the long term let alone provide for soil study to ensure longevity of the trees. Through our ignorance of soils we are on the brink of becoming guilty of actually creating more harm for the next generation to deal with in the effort to reduce costs to ensure philanthropic money flow.

We are also guilty of ignoring the fact that soils are the second largest carbon store on our planet after oceans. The obsession by many to ensure that ‘green’ really is ‘green’, could perversely prove to be ‘greenwash’ itself.

And why are we so opposed to allowing natures detritus, the food for healthy soils to settle and rest on our soils? The obsession with clearing grass cuttings, removing dead wood and even using products to kill earth worms is sheer madness. The earthworm fascinated Darwin and others and is one of the most important species for human survival.

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