Another measure of ‘ecological’ might involve the degree to which ‘non-natural’ approaches are used to manage vegetation. Hence, the Organic Movement see cultivated vegetation which is hand weeded or mulched with decomposing organic debris, and with pests controlled by plant synthesised pesticides, such as pyrethrum, as more ecological than that in which pests and weeds are managed by factory synthesised organic (i. e. carbon based) chemicals. The underlying rationale for this view is the value judgement that, irrespective of actual toxicity, the latter are intrinsically bad and must have a greater negative effect on non-target fauna. Again, this perspective is problematic: does native vegetation in a National Nature Research managed by English Nature become less ecological because herbicides are used to control some problem weed species, despite the fact that on all other counts it is a model of ‘ecological-ness’? Conversely, do exotic species planted in a conventional garden become more ecological when managed by organic husbandry?
Sustainability has also been subject to highly selective interpretation from within the environmental movement. For example, some would argue that it is unsustainable to use any sort of organic chemical in vegetation management because such materials are synthesised in a factory. As the lives of most people in industrial and post-industrial cultures are, and will continue to be, heavily dependent on anthropogenic organic molecules, is this a sensible measure of sustainability? A more useful measure might be to contrast how much fossil-fuel derived energy is required for synthesis in comparison with alternative means of undertaking the task. The situation becomes even more complex when toxicological concepts are considered. It has been put to the authors that it is better to use rhubarb leaves (a potent source of oxalic acid) to control weeds than a herbicide such as glyphosate because, despite similar toxicity, the former is naturally occurring. Putting weed-control efficacy to one side for a moment, no fossil-fuel energy has been used by the rhubarb in producing the oxalic acid, but are natural toxins more sustainable than anthropogenic toxins? Is it better to control weeds by burning propane gas in a flame gun or to use a far less energy intensive herbicide, or an even less energy intensive person with a trowel who may have to be transported regularly to the site in a diesel-fuelled vehicle? The latter may be very energy intensive but valuable in terms of social and economic sustainability, if funds are available to pay the wages. In North
America, spring burning is a standard technique for managing prairie vegetation, and is seen as good because it is a ‘natural’ and highly effective form of management with a long history of use by aboriginal Americans. Yet, in terms of current environmental dialogues, it is undesirable in terms of CO2 emissions?
In highly urbanised societies, discussion of sustainability in relation to vegetation management is never too far away from romantic sepia images of contented agricultural – horticultural workers cultivating the earth, in perfect harmony with the land. Surely all one has to do to be sustainable is to reconnect with this halcyon past. Many urban people enjoy cultivating plants as a recreation, however relatively few seem to want to hand – weed urban plantings all day as a full-time job for low wages. Even if these people existed, there are not the funds to pay them. Hein Koningen discusses the implications of changes in the aspirations of staff for the management of naturalistic vegetation in Chapter 10. In some situations, however, with the increasing involvement of local communities in urban green space management, and given some initial training and ongoing support where required, it may be possible for volunteers to successfully direct the development of naturalistic landscape plantings through occasional intensive maintenance days. In many naturalistic plantings, for example, woodland edges or prairie type vegetation, annual maintenance can be compressed into a couple of days in spring, cutting down the previous year’s growth and manually removing undesirable colonists (Figures 1.11 and 1.12). Access to sufficient skilled labour would largely negate the need to use herbicides and other techniques that may be seen as undesirable.
We all want to be as sustainable as possible, but the problem is in agreeing what are the limits to what is sustainable and what is not? Can you be not very sustainable on one aspect and then very sustainable in another and come out overall with an acceptable sustainability ‘score’, or does one transgression place you outside the sustainability project? We are sure all of the authors in this book have struggled with these ideas, although given that they come from a variety of disciplines and traditions they will no doubt have come to different positions.
Most nature-like vegetation is potentially highly sustainable biologically in that it is intended to persist and regenerate in situ given appropriate management, and is expected to grow without additional inputs of water and nutrients, pest and disease control. Its complex structure and taxonomical diversity provides habitat opportunities for many other organisms, and if it is attractive and appropriate to its context it may be embraced by local people, thus fostering its social and economic sustainability. The sustainability score for nature-like vegetation will, however, fluctuate across time, as more or less management is required. Economic and biological sustainability is likely to be lowest during establishment and at critical points in long-term management, due to the need to manage to temporarily eliminate or reduce populations of weeds and some herbivores that may compete with, and lead to the decline of, the vegetation. To put this into perspective, these inputs are far greater with vegetation based on traditional horticultural principles of comparable taxonomic diversity. The only vegetation that is free of these sorts of inputs is that which spontaneously occurs and is in the process of turning into something else, plus monocultures of densely leafy long-lived evergreen shrubs. Whilst of value in specific situations, neither of these types of plant community can meet the needs of twenty-first-century green space, referred to at the beginning of this chapter.
North American prairie vegetation created through sowing in a trial plot in Sheffield. Creating colourful herbaceous vegetation through seeding is both cost-effective and promotes a spontaneous visual effect
Management will generally be most sustainable where plant communities are designed from the outset to be managed primarily by simple non-selective techniques that are applied to all the plants in a community, as discussed by James Hitchmough in Chapter 6. This has often been the philosophy behind the creative conservation landscape style, but has been conspicuously absent from many continental European examples of anthropogenic plant communities. These have been maintained by the traditional horticultural technique of intensive hand-weeding; they look but do not necessarily function ecologically. In the absence of clear information to the contrary, people seem to perceive that plants arranged to mimic the structural and spatial arrangements found in naturally occurring vegetation are more ‘ecological’ than those that are not. From these spatial arrangements the concept of ‘nature-like’ or ‘naturalistic’ vegetation is born. In most cases, of course, a more nature-like structure is likely to support a wider range of species and be more open to dynamic processes. However, Noel Kingsbury, in Chapter 3, raises the possibility that more formal planting styles can also have ecological characteristics.