Bracken Control Treatments Research Articles

Factors Affecting the Restoration of Heathland and Acid Grassland onPteridium aquilinum–Infested Land across the United Kingdom: A Multisite Study

AbstractThe variability in the success ofPteridium aquilinum(bracken) control and vegetation restoration has been highlighted as a major issue in the United Kingdom. Experiments were set up at four different regional locations to assess bracken control at the national scale and the impact of restoration practices at the local scale. Bracken control treatments (cutting once or twice per year, a combination of cutting and asulam spraying, and asulam in year 1) were combined with site‐specific treatments designed to restore appropriate heathland or acid grassland vegetation. This article considers the effects on the developing understorey vegetation, testing the following hypotheses: (1) local differences between sites would affect community change; (2) treatments applied to controlPt. aquilinum(same at all sites) influences community change; and (3) treatments applied at the individual site level to restore vegetation influences community change toward the target vegetation. There were a considerable number of spatial effects. It is, therefore, difficult to develop a one‐size‐fits‐all policy for vegetation restoration within a nationalPt. aquilinumcontrol strategy. Few bracken control treatment effects were found, and, where they were detected, it was only at single sites. Thus, the development of target vegetation requires a combination of control and restoration treatments that take into consideration the aspects of that site. Only three species,Deschampsia flexuosa,Galium saxatile, andCampylopus introflexus, increased as a direct effect of the control treatments. Vegetation restoration was most successful in the cutting‐twice‐per‐year plots, the treatment with the greatest reduction inPt. aquilinumcover.

A multi‐site assessment of the effectiveness ofPteridium aquilinumcontrol in Great Britain

AbstractQuestions:The objectives of this study were to assess the effect ofPteridium aquilinum(bracken) control treatments, at the national scale, and the impact of restoration practices, at the local scale, onP. aquilinumperformance.Hypotheses:1. Geographical location (locally between and within sites) affects the control ofP. aquilinumthrough time. 2. Are theP. aquilinumcontrol treatments successful at all sites, and if so which ones? 3. The treatments applied at the individual site level to restore vegetation influences the performance ofP. aquilinumthrough time.Location:Four geographically distinct acid grassland and heathland sites infested withP. aquilinumacross Great Britain.Methods:Six main‐plot, bracken control treatments were applied to all sites with site‐specific vegetation restoration treatments. Response variables (P. aquilinumcover, frond length and density) were monitored twice yearly, in June and August between 1993 and 2003.Results:Between‐ and within‐site spatial variation was found, although impact is perhaps less than suggested from shorter‐term data. Despite local variation all sites responded similarly to bracken control treatments; asulam treatment resulted in a rapid reduction in frond performance followed by a continued recovery taking approximately ten years to return to untreated values. Cutting treatments tended to have a slower impact at the start but an increasing one over time, especially cutting twice per year. Restoration treatments had a limited impact; the only significant effect in August was grass seeding on frond length at Sourhope. In June only, the plots where sheep were fenced out showed a significant reduction inP. aquilinumcover at Peak.Conclusions:Long‐term control ofPteridium aquilinumat all sites and on all measures was best achieved using a continuous cutting treatment, preferably twice per year.

Competing conservation goals, biodiversity or ecosystem services: Element losses and species recruitment in a managed moorland–bracken model system

Conservation management in Europe is often geared towards restoring semi-natural ecosystems, where the objective is to reverse succession and re-establish early-successional communities, to comply with national and international conservation targets. At the same time, it is increasingly recognised that ecosystems provide services that contribute to other, possibly conflicting policy requirements. Few attempts have been made to define these conflicts. Here, we assess some potential conflicts using a Calluna vulgaris-dominated moorland invaded by bracken ( Pteridium aquilinum) as a model system, where the current policy is to reverse this process and restore moorland. We examined impacts of bracken control treatments on services (stocks and losses of C and mineral nutrients), litter turnover and biodiversity within a designed experiment over 7 years. Bracken litter was >2000 g m −2 in untreated plots, and treatments reduced this quantity, and its element content, to varying degrees. Cutting twice per year was the most successful treatment in reducing bracken litter and its element content, increasing litter turnover, and increasing both mass and diversity of non-bracken vegetation. Diversity was greatest where bracken litter had been reduced, but species composition was also influenced by light sheep grazing. There was a significant loss of some chemical elements from bracken that could not be accounted for in other pools, and hence potentially lost from the system. In absolute terms large amounts of C and N were lost, but when expressed as a percentage of the total amount in the system, Mg was potentially more important with losses of almost a third of the Mg in the surface soil-vegetation system. There is, therefore, a potential dilemma between controlling a mid-successional invasive species for conservation policy objectives, especially when that species has evolved to sequester nutrients, and the negative effect of increasing environmental costs in terms of carbon accounting required, the potential input of nutrients to aquatic systems, and long-term nutrient loss. There is, therefore, a need to balance conservation goals against potential damage to biogeochemical structure and function.

Changes in the rhizome system of bracken subjected to long‐term experimental treatment

Summary Bracken Pteridium aquilinum is a serious weed of upland and marginal land. Its extensive rhizome system and large carbohydrate reserves make control difficult. This paper reports the results of seven long‐term experiments, established in four diverse UK locations, to test control and vegetation restoration treatments. Samples were obtained from 580 rhizome pits between 1998 and 2000. Total dry mass per unit area (M, a measure of performance) and ratio of frond‐bearing to total rhizome dry mass (R, a relative measure of investment in frond production) were measured. The range of means for M in untreated bracken was 1·8–5·1 kg m−2, greater than that reported by others (1·2–3·0 kg m−2). Measured values for R were 0·24–0·42, again differing from other reports (0·10–0·38), probably due to our policy of avoiding advancing bracken fronts. Randomization tests were used to check for non‐independence of sampling units. They confirmed the general adequacy of the anova results; there was little detectable interference between plots. Two regions contained matching pairs of experiments, thus variation within region was tested and differences were found in one region. Five bracken control treatments (cutting, herbicide application and combinations) were employed at all but one experiment. Cutting once or twice per year generally gave the best results, reducing M by c. 60% after ≤ 5 years. Some subtreatments designed mainly for vegetation restoration, notably surface disturbance, also affected M. R was reduced by herbicide treatment, for example from 0·30 to 0·16. Such low values of R are typical of invading bracken and are thought to represent rejuvenated and invasive rhizomes. Follow‐up treatments are needed in such situations. Despite large differences between untreated M at matching experiments on Cannock Chase (Staffordshire), treatment effects were similar at both sites (cutting twice per year or cutting together with herbicide application were best). At Sourhope (Cheviot Hills) a different pattern of response was obtained, with cutting alone giving better results than treatments involving herbicide. The ratio of rhizome to frond dry mass per unit area was 10 : 1 in good conditions for growth, but the proportionate size of rhizomes could be reduced in poor growing conditions such as wet summers. Synthesis and applications. In order to develop a national control strategy the following must be considered: rhizome mass differs between sites and in response to control treatments; cutting twice per year is generally most effective; where cutting is impossible, herbicide treatment should be applied. Weather may affect rhizome mass, with wet years being detrimental. This raises the possibility that bracken may increase under the drier conditions that may occur with global warming.

Control of bracken and restoration of heathland. VII. The response of bracken rhizomes to 18 years of continued bracken control or 6 years of control followed by recovery

1. The effects of six bracken control treatments applied in combination with a Calluna* seeding treatment on the rhizome system of bracken Pteridium aquilinum at Cavenham Heath in Breckland was assessed after 18 years. Bracken control included cutting once and twice yearly between 1978 and 1996; spraying the herbicide asulam at the recommended rate (4·4 kg a.i. ha−1) in two treatments (1978 and 1978 plus 1979), each followed by repeat doses in 1984 and 1990, and spraying asulam followed by cutting once yearly. After 6 years the experiment was split and bracken control was continued/reapplied on half the plots and stopped on the remainder. The effects of treatment on the numbers of active and dormant buds and the length and biomass on both frond‐bearing and storage rhizomes were measured. 2. When applied continuously over the 18 years, all treatments reduced all rhizome measures, but treatments that included cutting were more effective than ones that just used asulam. The best treatment after 10–12 years was cutting twice yearly, but after 18 years this treatment had apparently reached an equilibrium and the cutting‐once‐yearly treatment was superior. No treatment eradicated the bracken in 18 years of continuous treatment. 3. When bracken control treatments were stopped after 6 years rhizome recovery started within 4 years and there was significant recovery thereafter. After 12 years the least effective treatment, cut once yearly, although still showing a significant reduction in rhizome biomass, had recovered to 88% of the untreated plots. The most effective treatment was cutting twice yearly for 6 years, where most measures of rhizome performance remained at approximately 50% of untreated plots 12 years after cutting stopped. 4. Regression analysis was used to investigate the relationship between frond production and rhizome characteristics. Rhizome biomass, especially of the storage rhizome component, was consistently the most important variable; frond bud numbers were less important. 5. Simple models, developed making assumptions that the response of the rhizome to treatment is linear through time, have been shown to be invalid over the longer time period. This is because the impacts of the treatments reduce through time. 6. These results are discussed in relation to long‐term bracken control and the assessment of bracken stocks. If bracken is to be suppressed on a long‐term basis a continuous control strategy is needed. It is unlikely that complete eradication will be possible with current control technology. The long time scale found for the total recovery of the bracken from only 6 years of treatment (>12 years) means that the large areas of bracken that have been treated in the past will take some time to recover to pretreatment levels. This recovery is an unknown factor in bracken stock assessments.

Control of bracken and restoration of heathland. VI. The response of bracken fronds to 18 years of continued bracken control or 6 years of control followed by recovery

Summary This paper examines the effectiveness of a range of bracken control and heathland restoration treatments on bracken performance over an 18‐year period on a Calluna health in Breckland, UK. Initial treatments were a combination of cutting and spraying with asulam, with and without sowing Calluna seeds. After 6 years a further treatment was added, with the bracken treatments being either continued/reapplied or discontinued. Seeding with Calluna had no long‐term effect on bracken levels recorded under any bracken control treatment. No treatment eradicated bracken completely, although all achieved some control. Asulam was the most effective treatment in the 2 years after application, but bracken recovered rapidly thereafter. Bracken frond biomass was reduced to c. 6% of untreated levels after 18 years by cutting once yearly, irrespective of whether combined with an initial asulam application or not, but to 3% by cutting twice yearly. Re‐applications of asulam produced similar responses to the initial application, with a rapid decrease followed by recovery. Where bracken control was stopped after 6 years there was an increase in bracken in all treatments compared to where control was continued/reapplied. However, even after 12 years of remission, frond biomass was lower than that of untreated bracken in most treatments. Where cutting was applied twice yearly for 6 years and then allowed to recover for 12 years, the frond biomass was still less than 40% of untreated values. The response of bracken to asulam was compared to predictions from published models and a reasonable fit was obtained, although the sensitivity of one such model to the efficacy of the initial bracken reduction was noted. The implications of these results for both long‐term bracken control and the monitoring of bracken stocks are discussed.

Restoration of Calluna heathland on a bracken Pteridium-infested site in north west England

Heathlands tend to occur on low fertility soils, but where heathland has been invaded by bracken Pteridium soil nutrient concentrations may be increased. In order to reestablish Calluna-dominated heathland these elevated soil nutrient concentrations may have to be reduced. This paper describes an attempt to re-create an area of Calluna-dominated heath on land which had been invaded by bracken. Several management techniques were implemented in a hierarchical manner to control a dense bracken stand, including: litter stripping, ploughing and traditional bracken control methods such as cutting and herbicide treatment. Finally a heathland propagule source, which was rich in Calluna seeds, was added. The effects of these treatments on both nutrient budgets and soil chemical properties were also investigated. Litter stripping removed a large amount of nutrients, ranging between 19 and 98 years' worth of rainfall inputs depending on the element. Ploughing caused an initial reduction in frond density and biomass but effects were not significant thereafter. Cutting twice yearly was the most effective treatment in reducing frond biomass. The establishment of Calluna seedlings was directly related to the success of the bracken control treatments.

Control of Bracken and the Restoration of Heathland. V. Effects of Bracken Control Treatments on the Rhizome and its Relationship with Frond Performance

The effect of three bracken control treatments on the rhizome system of bracken (Pteridium aquilinum (L.) Kuhn) at Cavenham and Weeting Heaths in Breckland was assessed. Control treatments included cutting once and twice yearly between 1978 and 1990, and spraying the herbicide asulam at the recommended rate (4-4 kg a.i. ha −1 ) in 1978 and 1985. In addition, the effect of continuous treatment was compared with plots in which bracken control ceased after 6 years. The effects on rhizome biomass and length, numbers of active and dormant buds, and starch and solubIe carbohydrate concentrations were measured. Cutting twice yearly was the most effective treatment, but rhizomes persisted even after 12 years of continous treatment. Cutting once yearly and applying asulam gave intermediate reductions in all rhizome variables (...)

Control of Bracken and the Restoration of Heathland. I. Control of Bracken

1. This paper examines the effectiveness of a range of bracken control and heathland restoration treatments on bracken performance and the redevelopment of heath vegetation over a 10-year period on a Callunaand a grass-heath in Breckland. Initial treatments were a combination of cutting and spraying with asulam, with and without sowing seeds of heathland species. After 6 years a further two treatments were added, with the bracken control treatments being either continued/reapplied or discontinued. 2. No treatment eradicated bracken completely, although all had some control. Asulam was the most effective treatment in the 2 years after treatment, but bracken recovered rapidly thereafter. Yearly cutting reduced bracken fronds by 70%, and cutting twice yearly by >90%. 3. After cutting was stopped, bracken recovered rapidly on plots cut yearly, but more slowly where it was cut twice-yearly. Reapplication of asulam produced a similar response to the initial application, with a rapid decrease followed by recovery. 4. Heathland at the Calluna site took 6 years to reach maximum biomass levels, and seeding had no effect on biomass. On the grass heath, vegetation developed much faster on the seeded plots where bracken was also controlled. At both sites cutting appeared to accelerate vegetation establishment probably because of litter disturbance. 5. At the grass heath, vegetation development suppressed bracken recovery 5-6 years after treatment started, when there was a maximum difference in grass biomass between unseeded and seeded plots. 6. The relevance of these results to both conservation management and the assessment of bracken distribution and encroachment are discussed.

Control of Bracken and the Restoration of Heathland. IV. Effects of Bracken Control and Heathland Restoration Treatments on Nutrient Distribution and Soil Chemistry

1. The effects of treatments to control bracken and to restore either Calluna heath or grassland on the amounts of bracken rhizomes, the distribution of nutrients in the vegetation, and selected aspects of soil chemistry, were studied. 2. The effects of the bracken control treatments on bracken rhizomes were similar to those reported earlier for midsummer bracken-frond yields. The most successful treatment was cutting bracken twice yearly for at least 10 years, which reduced frond-bearing rhizomes to 2-4% and storage rhizomes to 8-11% of untreated levels. 3. There were differences in the amounts of nutrients found in the bracken rhizomes and litter in the untreated plots at the two study sites. The maximum potential flux of nutrients to the soil was lower for some elements in plots with maximum heath development or bracken recovery, but for other elements no significant effects were found. 4. There were a few significant differences in soil chemical properties between the different management treatments, but they were difficult to interpret. There was no evidence of any reduction in soil chemical properties in these experiments where Calluna heath and grassland have re-established. If soil fertility is to be reduced during such restoration schemes this problem needs to be addressed further.