For some years past, the society’s trees and wildlife committees have been trying to persuade local schools to “set aside” green areas for nature and wildlife. So it was gratifying to see the recent decision by Alleyn’s School to plant a belt of trees and a mixed-species hedgerow around the perimeter of its playing fields. Elsewhere, however, the news has gone down less well.

The tree-planting has produced a chorus of protests from residents living around the playing fields, on both sides of Townley Road. Objections included the “mess” created by the honeydew from lime trees, plus worries about the density of planting and the potential loss of light to gardens. Some young trees from a previous planting have meanwhile mysteriously disappeared; others have been gouged in what may have been an attempt to kill them off. The school is now believed to be rethinking its planting plans.

At the same time, fuelled by the recent growth in environmental awareness, a new fashion for food-growing has swept through Dulwich. Householders are turning parts of their gardens into vegetable patches, or re-colonising derelict allotments. There is a scheme for a “model allotment”, with Dulwich Park earmarked as a potential site.

All well and good, one might think, except that all too often, the allotments or veggie patches entail the loss of existing green space. The model allotment may be sited in one of the park’s few remaining wild corners - which will not only mean the wildness being tidied away but will almost certainly generate pressure for removal of trees, again for reasons of shading. Resident non-human life-forms will suffer, too - biodiversity and horticulture are uneasy bedfellows. More food for humans will mean less food (and habitat) for wildlife. There will be a further, less tangible, much less quantifiable, but equally serious penalty - the loss of that ingredient we struggle to capture when we talk about wildness or natural beauty. Whatever that ingredient is, life, especially in cities, would be inestimably poorer without it.

Local food growing is, of course, said to be green. And clearly it is - up to a point. But how do you measure the green gains of food cultivation against the green losses of nature and habitat? Which is more truly green? For example, what could be greener than cycling, and bike paths? The bike charity Sustrans has won environmental awards galore for its national bike routes initiatives. Yet what may suit cyclists doesn’t always suit practitioners of that other green transport mode - walking. Sustrans has angered parts of the Ramblers’ Association because its plans have involved a high-tech, hard-surfacing approach on previously “natural” paths. Similarly, in Dulwich, there has been talk of linking up hard-surfaced cycle routes across local parks.

Against a background of international food crisis, to argue that preserving greenery may be more important than growing food - or to challenge the assumption that food-growing is a paramount environmental desideratum - may sound perverse, even “anti-human”. After all, which is more important - feeding homo sapiens or leaving space for nature? Yet if the environmental crisis we face is fundamentally about human impact on the planet, then true greenness surely lies not in increasing that impact, but in reducing it wherever possible, so that other life-forms - not to mention nature itself - have room left to live and breathe and regenerate.

Humans can do this by reducing their numbers or by reducing their activities and consumption, or by a combination of the two. They key concept these days is footprint - the overall impact we make on the planet - and ours (that is, Homo sapiens’) needs to be smaller. In practice that may mean a bigger stress on the planetary value of trees - as opposed, say, to bedding plants - and a rethink of our enthusiasm for food-growing where it involves the loss of greenery. Maybe, instead of cannibalising existing green space, some small part of the human footprint could be reclaimed for our veggie patch or allotment, for example. Maybe we could remember that bees (vital for food growing but currently in steep decline) are partial to lime blossom and we could learn to tolerate larger trees in, or at least near, our gardens. On both counts currently, it seems, Dulwich has a long way to go.

David Nicholson-Lord is an environmental author and journalist and a member of the trees and wildlife committees. He is policy director of the Optimum Population Trust -

by David Nicholson-Lord