The ecological changes of Breckland grass heaths and the consequences of management

Published source details Dolman P.M. & Sutherland W.J. (1992) The ecological changes of Breckland grass heaths and the consequences of management. Journal of Applied Ecology, 29, 402-413.
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Summary

The Brecklands of East Anglia are characterised by sandy soils and a semi-continental climate. In addition to heather Calluna vulgaris-dominated heaths, there are areas unusual amongst British lowland heaths, dominated by calcareous and acidic grass heath communities. A number of plots within grass heaths have been rotovated in the past in order to benefit characteristic plant communities of these heathland habitats. In particular management is aimed at perpetuating disturbed conditions in light of reduced sheep and rabbit grazing at many sites which formerly fulfilled this role. This management is aimed in particular at benefiting less competitive, often early successional, plant species.

The study summarized here examined long-term effects on plant communites of soil disturbance management of two plots last rotovated 9 years previously.

Study site: The study was undertaken in 1989 on Weeting Heath National Nature Reserve (National Grid ref: TL 761899), in Norfolk, eastern England. Two c. 0.4 ha plot had been rotovated annually in spring 1960-72 (not in 1967, twice in 1970), and once in 1980) (rotovated 14 times in total). Prior to this survey the plots had last been rotovated 9 years previously. The average soil pH was 7.2 in one plot and 6.4 in the second (at 0-4.8 cm depth).

Grazing history: The site had been rabbit Oryctolagus cuniculus grazed from the late 1960s until the mid 1980s

Vegetation sampling: Vegetation in each plot was recorded within 10 paired, 0.25 m² quadrats (20 quadrats in total) laid in a stratified random manner, with10 quadrats in and 10 (adjacent to these) out side, the plot boundary. In each quadrat the percentage cover of each species was estimated visually. Species recorded were placed in the appropriate Raunkiaer plant group (see Table 1, attached). Sward height was measured in March and May by random stratified sampling (within each plot and along a single transect parallel to the perimeter 5 m outside the plot) using a sward stick (disc diameter 90 mm, weight 250 g, rod diameter 17 mm). Vegetation assessment was undertaken by the same observer.

Rabbit faecal pellet production: Rabbit faecal pellet production (as a measure of rabbit abundance) was determined by pellet counts within 1 m² quadrats placed at sward measurement points. The number of pellets estimated by eye to be less than 8 days old or less (by comparison with a reference collection of known age) were counted. Pellet production rate was undertaken by the same observer.

Soil analysis Ten pairs of soil samples were taken (15 cm diameter, 10 cm deep cores). Samples were air dried, passed through a 2 mm sieve and stored at 4ºC until analysed. Ph (two subsamples from each sample) and percentage loss-on-ignition (375 ºC for 16 h) was recorded in and outside the plot. (Due to methodological problems, samples from one of the plots were not analysed).

The results are summarised in Table 1. The rabbit index (pellets/m²/day) was more than 2-fold higher in the treated plot (9.26) compared to the control, i.e. outside the rotovated area (3.97). This rabbit activity was responsible for the much higher amount of bareground in the rotovated plots (9.2%) compared with outside them (0.8%).

Conclusions: The rotovated plots had 9-fold more bare ground and much shorter grass (one third the height) of that outside the plots, presumably due to the much higher rabbit activity recorded in the rotovated areas. The rotovated plots also had a higher abundance of lichens, cushion-forming mosses and annual plants, and slightly less organic matter (in the one plot where this was analysed) than control plots. Thus over 9 years since last rotovated, beneficial effects of rotovation management on the flora were still evident. The authors consider that encouraging rabbits and disturbing the soil are essential to maintain these heathlands plant communities.

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