Lynne Torvell

Rehabilitation of degraded dry heather [Calluna vulgaris (L.) Hull] moorland by controlled sheep grazing

Many areas of heathland in Europe have seen a decline in the area and condition of Calluna vulgaris (heather)-dominated vegetation, with subsequent declines in the associated faunal interest. Grazing, alongside burning, is still the predominant means of managing heathland vegetation, and, therefore, it is by manipulating this management that cost-effective improvements in vegetation condition can be made. This paper investigates the suitability of different grazing treatments for rehabilitating degraded ‘dry heath’. Treatments varied in the intensity (0–1.9 sheep ha−1 year−1) and timing (summer vs. winter) of sheep grazing. These treatments were compared with the behaviour of vegetation outside the fenced area kept under the previous management (open access all year round). As rabbits were common on the site, fences were erected to prevent access to the sheep grazed plots. Vegetation composition remained stable outside the fenced area, whilst all the fenced treatments showed a decrease in heather utilisation and an increase in the relative frequency of heather over the 5 years of the experiment. The increase was in proportion to the reduction in stocking rate, with only slow increases in relative frequency observed in the high grazing treatments (winter and summer). Other species that benefited from reducing grazing included Empetrum nigrum and Vaccinium myrtillus, whilst declines were observed for Agrostis capillaris and total monocotyledonous species. Only small overall differences were observed between the winter low, summer low and no sheep grazing treatments. However, a difference in response was present between the sheep exclosures and the sheep+rabbit exclosures, indicating that rabbits were having a noticeable effect on heather recovery at this site. On this degraded ‘dry heath’ system, imposing a reduction in stocking density improved the condition of the dwarf shrubs present and reduced the grass component of the vegetation. There was little effect of the timing of grazing, such that a reduction in sheep numbers to 0.8/0.9 sheep ha−1 year−1, to give utilisation levels of below 20%, can achieve the desired result of improving vegetation condition whilst still achieving some economic return from grazing. However, the wide range of ‘sustainable’ stocking densities for different heathland systems highlights the need to base effective management on measured utilisation rather than on stock numbers.

Controlled grazing studies on Molinia grassland : effects of different seasonal patterns and levels of defoliation on Molinia growth and responses of swards to controlled grazing by cattle

Experiments were carried out at three sites in southern Scotland to determine the suitability of Molina grassland for sustained use in providing summer grazing for cattle, and to investigate grazing control as a tool to manipulate the species composition of hill pastures in Britain. Cutting experiments showed that frequency and severity of defoliation were more important than timing in their effects on Molinia. Weights of clippings declined in successive years only in response to treatments that involved repeated within-season cutting. Three years of repeated light defoliation (33% lamina length removed each June, July and August), compared with uncut controls, reduced leaf production in a fourth uninterrupted growing season by 40%, while repeated heavy defoliation (66% lamina removal) reduced it by 78%. Reductions in both the numbers and the size of tillers contributed to this result. Single annual cuts only reduced leaf production at 66% lamina removal when they took place late in the season. Plots grazed by cattle at two sites for 6 years compared treatments where 66% rather than 33% of the herbage was removed by grazing. The rates of leaf extension in Molinia were reduced at the higher level of use. In comparison with areas protected from grazing during the final year of treatment only, the biomass of Molinia and other grasses in areas open to grazing showed that the taller Molinia was utilized to a much greater extent than the other grasses. After 6 years of grazing, the biomass of Molinia at 33% utilization was reduced by 46-65% compared with ungrazed exclosures, while at 66% utilization it was reduced by 86%. Basal internode size was greatly reduced in the grazed plots compared with the ungrazed exclosures, with effects on tiller base size being more important than variation in concentrations in determining amounts of starch, total water soluble carbohydrates, N, P and K on a per tiller basis. Site x management interactions for concentrations could be interpreted in terms of variations in stage of maturity, potential for growth and plant/animal nutrient cycling pathways. Floristic diversity was increased on grazed compared with ungrazed areas. The cover of Molinia was decreased and that of other broad-leaved grasses increased by grazing. At 33% utilization, the cover of Molinia appeared to be levelling off (at around 60-65% after 3-5 years) while at 66% utilization a continued downward trend was evident. Species trends were also influenced by site factors, with exclusion of grazing leading to a reduced cover of Festuca ovina only where conditions were favourable for high yields of taller grasses. The responses of Molina to defoliation are discussed in relation to its pattern of growth and low rate of leaf and tiller turnover and to its responses to soil and climatic factors. The effects of grazing on nutrient cycling and sward canopy structure, in influencing competitive relationships with other species, are considered and the wider issues relevant to management protocols are outlined.

Controlled grazing studies on Nardus grassland: effects of between-tussock sward height and species of grazer on Nardus utilization and floristic composition in two fields in Scotland

1. The utilization of the tussock-forming grass Nardus stricta was investigated in controlled grazing experiments in which various sward heights of between-tussock grasses were maintained thoughout the growing season using either sheep, cattle or goats. 2. The utilization of Nardus increased as the height maintained for the between-tussock grasses was reduced. The relationship between sward height and level of utilization of Nardus, however, differed greatly among herbivore species. 3. Under similar sward conditions, cattle and goats utilized more Nardus than did sheep. Utilization of Nardus declined over successive seasons under grazing by sheep but was sustained under grazing by cattle or goats. 4. The severity of defoliation of Nardus achieved by cattle or goats when between-tussock grasses were maintained at 4.5 cm (mean sward surface height above ground) resulted in disappearance of tussocks from the sward and in reduced size, leaf extension growth and nutrient reserves of Nardus tillers. Under cattle grazing, the cover achieved by Nardus decreased from 55.4% to 30.0% over 5 years. 5. Under sheep grazing, both the biomass of individual Nardus tussocks and the cover of Nardus increased. Cover increased from 58% to over 86% at a between-tussock height of 4.5 cm, while at a height of 3.5 cm, after initially declining, it increased to reach 72%. 6. The broad-leaved grasses showed a trend towards increase in cover when between-tussock sward height was maintained at 4.5 cm whether grazing was by cattle or by sheep; the trend was not evident at 3.5 cm (sheep grazing only). 7. Changes in the floristic composition of the sward are discussed in relation to the roles of the inherent growth characteristics of the species present, to selective defoliation and uprooting of the shoots, to altered nutrient cycling pathways under grazing and to the nutrient status of sites.

Rehabilitation of degraded Calluna vulgaris (L.) hull-dominated wet heath by controlled sheep grazing

Abstract Many upland areas of the British Isles have seen declines in the area and condition of heather ( Calluna vulgaris )-dominated heathland vegetation. To reverse this decline, management regimes must be designed to rehabilitate areas that have seen this decline. As most of this heathland vegetation is primarily managed by grazing, such management has to determine what stocking levels can maintain the vegetation in a desired state. This paper describes how to reverse this decline through suitable grazing management. A degraded ‘wet-heath’ system, previously grazed at 2.1 sheep ha −1 , was subject to a range of grazing treatments over a 5-year period. Treatments varied in intensity (0–1.4 sheep ha −1 ) and timing (summer only, winter only, or year round) of grazing. Grazing levels were maintained at 2.1 sheep ha −1 outside the fenced areas. Vegetation composition remained stable outside the fenced treatments. All the fenced treatments showed an increase in the relative frequency of the evergreen Calluna vulgaris , with the greatest increase being in the ungrazed treatment, and the least in the year round 1.4 sheep ha −1 treatment. This increase was in line with a reduction in heather utilisation to relatively low and sustainable levels. Other species that benefited from reduced grazing included Carex nigra , Deschampsia flexuosa and to a lesser extent Galium saxatile and Erica tetralix , whereas a range of moss species including Hypnum jutlandicum and Rhytidiadelphus loreus were more frequent at higher grazing levels. Though the recovery of heather was similar in the two seasonally grazed treatments, the vegetation showed different overall trajectories. Winter only grazed allowed a substantial increase in the cover of the deciduous Molinia caerulea , whereas this species was kept in check by summer only grazing. A stocking level of between 0.7 and 1.4 sheep ha −1 appears to be appropriate to maintain and even enhance the cover of heather on degraded wet heath. Complete removal is not necessary. Grazing restricted to the winter period is inappropriate in areas where M. caerulea occurs. Setting appropriate stocking levels to maintain the condition of the vegetation must take into account site conditions, especially the presence of species that can affect the utilisation of heather.

Seasonal pattern of leaf growth and senescence of Nardus stricta and responses of tussocks to differing severity, timing and frequency of defoliation

1. A field study of the seasonal growth of Nardus stricta showed that leaf turnover was slow, averaging 2.5 leaves per tiller over the growing season. Periods of lamina extension growth and senescence were generally separated in time; fastest growth, at 4-5 mm per tiller per day, occurred in June July and the senescence rate was low until early autumn when it rose to 6 mm per tiller per day. Sheathing tiller bases, already well developed in May, increased in weight by 27% between May and October; total water-soluble carbohydrate (TWSC) concentration increased by 150% (from 75 to over 165 g per kg dry weight) while N, P and K concentrations declined over this period. 2. A pot study showed that the age class of inter-connected tillers on rhizome tips greatly influenced growth; mean rates of lamina extension and production of daughter tillers were higher in younger tillers while the likelihood of flowering was greater for older (3-4 leaf) tillers. The pattern of growth provided evidence for acropetal movement of assimilate. 3. Field cutting experiments showed that Nardus was relatively insensitive to defoliation in the short term. Removal of 50% or 100% of the length of the leaf lamina in June only, July only or in both June and July resulted in a temporary reduction in lamina extension rate per tiller but did not significantly affect the weight of leaf produced in the first season. There was a non-significant trend for the size of tiller base to be reduced as the severity of cutting was increased. Concentrations of TWSC and N,P, and K in tiller bases showed no variation attributable to cutting. 4. In a long-term cutting experiment lasting 4 years, Nardus was cut so as to leave 1, 4 or 8 cm of lamina in June only, July only, or in June and July. Two seasons elapsed before lamina extension was reduced on cut plants. The weights of clippings were greatly reduced over successive years when tillers were cut to leave only 1 cm oflamina but were little affected when 8 cm of lamina remained, with the 4-cm treatment intermediate; the reduction was greatest with plants cut in both June and July and least with plants cut in June only with those cut only in July being intermediate. 5. Tussock biomass, assessed after 4 years of cutting and a season of uninterrupted growth, was decreased as the height of cut was reduced and by repeated cutting; timing (June compared with July) was unimportant. Both tiller numbers and mean weight per tiller were reduced. Flowering vigour was increased by cutting. Timing was important, with plants cut in July only or in both June and July having more flowers than those cut in June only. The amounts of TWSC and N, P and K reserves were reduced by cutting with reduction in tiller base size being more important than effects on concentration. 6. In a comparative field study, the rate of lamina extension in Nardus averaged less than half that of Agrostis capillaris or A. canina growing in the same sward. This underlines the importance of selective grazing as an influence on species balance in acid grasslands.

Identifying suitable restoration sites for a scarce subarctic willow (Salix arbuscula) using different information sources and methods

Background: Subarctic willow scrub is an extremely restricted habitat within the UK. Restoration efforts are now targeted at expanding current populations and establishing new stands. Aim: Selecting suitable target sites for restoration has to be cost-effective. Efficacy can be ensured through the development of habitat suitability models with high predictive ability but these have to be efficient in using only a small part of the resources of a restoration project. Location: The study was concentrated on the Lochan na Lairige catchment at Ben Lawers National Nature Reserve, Perthshire, Scotland. Additional data were collected from three other sites in the Southern Highlands; Fireach na Moine, Meall Ghaordie and Meall na Samhna. Methods: This research compared the merits of using vegetation or environmental parameters, and a combination of both, to build habitat suitability models for a scarce species of upland Britain, Salix arbuscula. In addition, models derived from three different statistical methods (generalised linear models, linear discriminant analysis and classification and regression trees) were compared. Results: Models based on either vegetation and environmental parameters were very similar in predictive ability, though there was only moderate agreement on which sites were suitable for restoration. The combination of both sets did not improve predictive ability, and hence only one set of parameters is necessary to develop a cost-effective method of identifying suitable replanting sites for S. arbuscula. The models developed by generalised linear modelling were consistently and significantly higher in predictive ability than those developed using the other methods, but there were considerable differences in which sites were highlighted as suitable for restoration between the different methods. Conclusions: Predictive models for suitable restoration sites for S. arbuscula could be assembled cost-effectively from just one parameter set, with a GLM approach providing the most effective statistical approach. However, as there was only moderate consistency between modelling approaches a model averaging approach could be profitably employed in site selection.