The notion of using fire to ‘care for’ a vegetation is counter intuitive in the urban psyche, but fire is a very useful device when it can be adequately controlled. In Britain, many dry agricultural meadows were traditionally managed by fire (Wells and Barling 1971) but this practice has now passed out of the public consciousness. In Central and Eastern Europe however, it is still common to see dry meadows managed by spring burning.
Green (1996) provides an excellent review of burning rural grasslands to promote conservation values, and laments the negative attitude to this. Clearly, fire is potentially dangerous and can generate nuisance, but these problems are resolvable. In North America, the burning of restored prairies in urban areas is becoming commonplace, and there are many information sources on how to do this safely (Pauly 1997). Burning has additional benefits to cutting in that it darkens the soil’s surface and clears away leaf litter and other debris, and it facilitates the germination of many species (including weeds). It also kills some invertebrates and, in particular, molluscs, some seed on the soil surface, young seedlings and annual weeds. Most of the nitrogen in organic debris is volatised at 200°C (Wright and Bailey 1982), so in the absence of legumes, regular burning will tend to decrease soil nitrogen levels, generally to the detriment of weed species. Burning is normally undertaken in spring to combust dead overwintering foliage and to defoliate winter-growing weeds. In the author’s prairie research, we generally use propane gas – fired triple burners from the tool-hire industry that are designed to soften tarmac in road – repair works. These devices have a work rate of approximately 3 min/m2 where used to ‘ash’ all foliage present. Burning is very effective against annual weeds, but defoliates rather than kills many perennial herbaceous plants. It is very effective against some short lived but problem perennial weeds, for example the Epilobium species of nursery container plant production. It will also check, but not eliminate, creeping buttercup Ranunculus repens. Burning greatly reduces the scale of weed-management problems and allows managers to focus better on the selective management of the weeds that remain.
Most of the author’s use of fire as a management tool has been in conjunction with prairie plant communities, for which burning is the standard management treatment in North America (Figure 6.21). We normally burn between mid-March and mid-April. The later the burn the greater the amount of foliage of weeds and desired species destroyed. This takes great courage but we have not observed any obvious lasting damage to the prairie species. All of the species listed in Table 6.5 other than the vernal Dodecatheon, tolerate spring burning, including the semi-evergreen, surface rooting Rudbeckia fulgida var. deamii. The advantage of burning later in spring is that you are likely to kill or check a wider range of weeds than will be encountered earlier. When burning, no attempt is made to avoid sown or planted species unless these are known to be sensitive. With North American prairie grasses and forbs, the blackened soil warms up more quickly, allowing these species to grow away more rapidly, shading the ground and
Use of burning to manage North American prairie grasses. The dead overwintering foliage is burnt in early April to defoliate invading weeds on an experiment involving small discrete blocks. For safety, we normally cut down the dead foliage and remove, prior to burning with a propane-fuelled burner
eliminating later germinating weed cohorts.
Burning can also be used on steppe-like and dry meadow communities, although there is little or no research as to the response of individual species. In Europe and Eurasia, many of these communities have traditionally been managed in this way as a means of encouraging fresh grass growth for domestic stock. Many species should therefore tolerate this practice. Linum narbonense and Origanum vulgare, and presumably many other evergreen perennials, recover rapidly even when burnt in late March in full leaf.