This is commonly associated with meadow management. These are mostly mown in spring and are cut as hay with a strimmer in summer or early autumn. The principle behind this is that by mowing in spring, as grasses (and other species) are beginning to grow vigorously, they will be temporarily checked, thereby favouring slower-growing species. Complete defoliation associated with the summer hay cut imposes a further check on grasses and forbs. Hay cutting is, however, a very blunt instrument, and the author’s work on establishing native and exotic forbs in sown meadows shows that the vigour of many forbs is also severely reduced by this practice and is leading to the elimination of some species. This is particularly marked with early cutting, i. e. in July. In a 10-year study of the effect of management on vegetation change in upland native hay meadows, Smith et al. (2002) found no significant difference in the numbers of different species present in plots cut in June, July and September. The cutting date did, however, have a significant effect on the percentage cover of some species.
Forbs that most obviously benefit from early cutting are low-growing rosette formers, such as Plantago, and species that either rapidly replace lost foliage or are winter green, and are able to make use of the additional sunlight at ground level post-cutting. For some forbs it seems very likely that the benefits of cutting in summer, which are derived from temporarily reduced grass competition, are outweighed by the disadvantages of the loss of photosynthetic productivity. In an urban context, the simple mantra of cutting in summer, based on traditional agricultural, native hay meadows warrants reassessment. Research is needed to identify grass-based plant communities and species that, on balance, are best cut in summer and those that are best cut in autumn or winter. To do this, one needs to target key species that one may wish to promote, rather than just looking to see what maximises overall species diversity. As of yet, information of this type is not available.
Cutting can also be used in non-meadow vegetation. In North America, mowing in spring is considered to be a reasonable substitute for burning in the management of restored prairie vegetation (Prairie Nursery, 2002b). In applying this to Britain, the author has only looked at the mowing of prairie vegetation in early spring. By itself this is not very effective, as few tall invasive native species are defoliatated at this time and grasses rapidly regrow before most of the prairie species emerge. Cutting in early May when weeds and prairie plants are more advanced would probably be more effective, but we have not yet attempted this (Figure 6.20).