Management of roadside vegetation: the long-term effects of cutting

Summary

Some roadside verges in the UK provide a valuable habitat for wildlife, and a few, due mainly to their floristic interest, have been afforded a degree of protection having been classified as Sites of Special Scientific Interest (SSSIs) and/or given nature reserve status. To maintain such sites, appropriate management, usually entailing regular cutting, needs to be applied. However, long-term effects of roadside verge cutting regimes and changes in cutting regimes are difficult to assess because of the absence of adequately controlled experiments. To help redress this, results from an 18-year experiment which compared, among other things, measurements of the effect of a range of cutting treatments on the vegetation of roadside verges, including cutting frequency, cutting date, method of cutting and the effect of removing or leaving cuttings.

Study areas: The experiment was set up in 1965 on road verges at Ickleton (south-east Cambridgeshire) on chalk soils, and at Keyston (west Cambridgeshire) on Oxford clay, in south-east England.

Cutting treatments: There were two unmanaged control and 18 treatment plots (each 1.8 x 18.3 m, replicated four times in a randomized block each site). There were 11 cutting treatments (Table 1). The treatments continued unaltered until 1978. In 1979 each plot was divided in half, with one half left uncut to study reversion of vegetation. The plots were managed in this way until 1982 (18 years of management).

Comparisons were made of cutting date (single cuts in June or July), cutting frequency (0, 1, 2 or 5 times per annum), cutting machine (hay mower, flail mower or rotary mower), and of leaving cuttings or removing them by hand raking. All cutting was undertaken in the third week of each month.

Machines used for cutting were tractor-mounted reciprocating cutter-bar haymowers, tractor-mounted flail mowers, and a self-propelled hand-held 61 cm (24 inch) 'Hayter' rotary mower (as used for mowing road verges and amenity areas). Stubble height after cutting was 2-8 cm.

Vegetation sampling: In July/August of most years between 1965 and 1982, species composition was determined by presence/absence in 40 quadrats each 225 cm², placed at random in each plot: the total number of species per plot and the average number of species per quadrat were estimated.

Vegetation height was measured at two positions in the central areas of the plots during the week of but before treatment (six occasions each year between 1966 and 1976, from April to September at monthly intervals).

Soil analyses: To examine the effect of removing cuttings on soil nutrients, five replicate samples of the 0-10 cm soil horizon were taken from each plot of treatments 6,7,10 and 11 (Table 1) in May 1976 and 1982. The samples were air dried and passed through a 2 mm sieve, then analysed for pH, % loss-on-ignition, sodium, potassium, calcium, magnesium, manganese, phosphorus and total nitrogen.

Thirty-three vascular plant species at Ickleton and 24 at Keyston had a mean frequency over 2%. The effects of the treatments on species-richness and the frequencies of individual species were very similar at both sites.

Effect of cutting date and machinery: Species-richness was unaffected by altering the date of a single cut from June to July or by cutting with different types of machine. It was lowest in the uncut plots and highest in plots cut twice per annum.

Effect of cutting frequency: Increased cutting frequency significantly decreased the frequency of 10 common, mainly coarse growing highly competative species, including common couch Elymus (Elytrigia) repens, false oat-grass Arrhenatherum elatius and cow parsley Anthriscus sylvestris. Eleven finer species (mostly grasses) increased in frequency and two herbs (creeping buttercup Ranunculus repens and ribwort plantain Plantago lanceolata) reached a maximum at two cuts per annum.

Effect of cutting removal: Removing cuttings led to an increase in species-richness, mainly due to increases in herbs. Removal led to a decrease in extractable potassium in the soil but most other soil nutrients, including total and available nitrogen, were unaffected, as were other soil variables measured.

Conclusions: With the exception of very nutrient-poor habitats, there is considerable evidence that species-richness of grasslands is negatively correlated with nutrient richness and plant productivity. However in this long-term study, other than a reduction in potassium, there was little or no effect of removal of cuttings on soil nutrients. It is therefore of interest that the removal of cuttings at Ickleton and Keyston over 18 years led to an increase in plant species-richness. The authors suggest that this observed increase in species-richness was not due to reduced levels of soil nutrients, but in fact was probably associated with disturbance and scarification which accompanied the removal of cuttings by hand raking, and the absence of smothering caused by leaving cut vegetation on the verges which would otherwise inhibit the growth of less robust species.


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