The coastal heathlands of north-western Europe are endangered habitats of great conservation value. Invasion by the bracken Pteridium aquilinum is a major challenge for conservation and restoration of these heathlands, especially in the under-studied northern regions. Today, the herbicide asulam is the most widely applied bracken control measure, but increasing focus on organic farming and nature conservation calls for alternative, preferably mechanical, approaches. In a 7-year replicated restoration effort in western Norway, project researchers investigated efï¬ciencies of the four bracken control measures asulam, Gratil, annual cutting and biannual cutting, for restoring the characteristic heathland vegetation structure and species composition. The project speciï¬cally tested herbicide effects on diversity and composition of non-target species. Effects of treatments over time were evaluated by repeated measures ANOVA, and for multivariate data, Principal Response Curves. Project results show that UK-based control methods are largely applicable to bracken at its northern limit in the European heathland habitat. Asulam resulted in the fastest reduction in cover but cutting proved equally efficient over the long-term. Community compositions progressed toward desired heathland vegetation, but successional trajectories differed. Asulam had unintended effects on a number of heathland species not predictable by species characteristics or functional groups. Gratil failed to have any long-term effects. Overall, cutting is as efficient as herbicide application in reducing bracken, and more so in restoring northern heathland vegetation over time.
Fv614, 6723 Svelgen, Norway, 61.776935944639895, 5.39277412499996
Country or Territory:
University / Academic Institution
Primary Causes of DegradationFragmentation, Invasive Species (native or non-native pests, pathogens or plants), Other
The heathlands are man-made cyclic vegetation systems where secondary succession is manipulated by management, and major threats are abandonment leading to woodland encroachment, development leading to fragmentation, pollution and subsequent loss of diversity and invasion of species such as bracken. The spread of bracken is recognized as a serious threat to the unique qualities of heathlands as it eliminates characteristic ericoid shrubs, graminoids and forbs by the changing successional dynamics of these semi-natural systems, yielding habitats of low conservation, agricultural and recreational value. Bracken is the most widely distributed Pteridophyte on earth and the only terrestrial fern to dominate large areas outside woodlands in temperate climates. Once bracken is established, slowly-decaying litter and potentially toxic compounds may inhibit seed germination, establishment and growth of many characteristic heathland species, including Calluna vulgaris. Changes in climate and land use may favor the spread of bracken. Bracken has increased and by 2004 it had invaded about 30% of the area. The project was carried out in two adjacent areas: A, invaded by bracken and B, no bracken present. In both areas, ericoid shrub species such as C. vulgaris, Vaccinium myrtillus and V. vitis-idaea occurred throughout, in combination with common graminoids, forbs and mosses.
Reference Ecosystem Description
The island is dominated by Calluna/grass heaths with mires/Salix shrubs in wetter areas. Parts of the semi-natural rangelands have been under semi-natural rangeland have been under continuous management (burning, grazing, and turf and heather cutting) up until today, creating a mosaic heathland of different successional stages. The area is grazed by .1 cow/ha in summer and by .8 sheep/ha in winter, which is comparable to stocking levels in other heathland areas.
This project sought to compare the efficiency of different mechanical and herbicide bracken control practices. Our main focus is restoration of the heathland community and potential impacts of herbicides on the species composition and diversity. The project sought answers to several questions: 1) How effective are treatments in reducing bracken? 2) How successful are these different control measures in restoring heathland structure and community composition? 3) Do the herbicides affect structure, diversity, or composition of the non-target community?
The project does not have a monitoring plan.
The lowland heathlands of Europe are endangered habitats of considerable value and are now protected under the EU Habitats directive. Norway has the northern one-third of Europe’s coastal heathlands, which are characterized by long and unbroken histories of management through burning and year-round grazing by sheep of the Old Norse breed. In contrast to their European Union counterparts, which are protected under the Habitats Directive, these northern heathland habitats lack national legislative instruments to ensure their conservation. Bracken is absent from the northernmost heathlands, but it is expanding. Bracken benefits from the reduction of extensive livestock grazing as well as from recent increases in airborne nitrogen deposition and use of artificial fertilizers. Traditionally, bracken was kept in check by grazing and cutting, and fronds used as bedding for livestock. Past practices have shown that biannual cutting is an efficient control measure, but since the 1960s herbicides have been widely used, particularly asulam (which is now the most commonly used herbicide for controlling bracken in Europe). With the rise of organics throughout Europe, all such chemically-based practices have come under increasing scrutiny for their effects.
Description of Project Activities:
Experimental square plots of 25 sq m were established in two areas: A, invaded by bracken and B, no bracken present. The latter area was included to enable us to test for herbicide effects on the heathland community, independent of the effect of removing bracken. Plots were placed at least 10 m apart, creating a buffer zone to avoid effects of airborne herbicides. Three 0.5 m x 0.5 m permanent quadrats were randomly placed within each plot. In mid June of year T0 quadrates were analysed for % cover of all species of vascular plants, bryophytes and lichens, functional groups (graminoids, forbs, ericoid shrubs and mosses), and environmental parameters (topography, slope, and aspect). Treatments applications were started in T0 and the quadrats were reanalyzed yearly in July/August of T1 - T6. Treatments were randomly allocated to plots within each area. The experimental design was expanded successively over the ï¬rst three years, yielding a balanced design of four replicate plots by ï¬ve treatments in area A and four replicate plots by three treatments in area B. In all cutting treatments bracken stems were cut app. 20 - 30 cm above ground, not affecting the non-target vegetation, and newly cut bracken fronds removed. After initial testing of different cutting techniques (motorised vs. scythes) a long handled scythe was selected as the most efï¬cient tool for our area. In area A, follow-up cutting of emerging bracken fronds in the chemically-treated plots was performed yearly in late July following the methods of Lowday and Marrs.
Ecological Outcomes Achieved
Eliminate existing threats to the ecosystem:
Results of the project showed that all treatments reduced bracken signiï¬cantly during the course of the test period, but that the response rates differed considerably. Biannual cuttings or spraying with asulam followed by annual cutting were the most effective means of reducing bracken cover long-term, conï¬rming that previously reported high efï¬ciency of these measures holds true for northern heathlands. Yearly cutting took longer to take effect, as one might expect, but once it did it was as effective as cutting biannually. As asulam is not legal in Norway, and as Gratil has been recommended as an alternative to asulam based on one short-term (2-year) experiment, it was of interest to include Gratil into the experimental protocol. In doing so, the project highlighted the importance of long-term monitoring in researching vegetational change, as called for by Stewart et al. (2005). However, the results showed Gratil sprayed bracken to regain dense cover the third year after treatment and can not be recommended as a bracken control tool. This recovery, in spite of follow-up cutting, is difï¬cult to explain and should be addressed in further investigations. All bracken control treatments affected species composition, inducing a shift towards more open and species-rich communities dominated by ericoid shrubs, graminoids, and forbs. Research found more species beneï¬ting from the removal of bracken than suffering from the treatments, such as Hypericum pulchrum, C. pilulifera, V. ofï¬cinalis, Conopodium majus, L. corniculatus, Festuca vivipara and Vaccinium vitis-idaea. Some previous attempts at restoring Calluna heathlands by bracken control in the UK have resulted in grass-dominated communities, and simply controlling bracken by herbicides may not result in conservation or restoration of Calluna heathlands.This seems not to be the case at our site. The grazing regime at the site (sheep and cattle) is one possible explanation as Williams (1980) found bracken regrowth after asulam application to be considerably slowed by grazing sheep and cattle compared to sites grazed by sheep alone. Hence, trampling by cattle can be an important factor in bracken control, at least in areas where bracken stands are not too dense. The use of follow-up annual cutting treatments may also have increased the rate of success in re-establishing desirable heathland vegetation.
Factors limiting recovery of the ecosystem:
In the bracken-dominated area the majority of non-target species were positively affected by asulam, suggesting the herbicide to have little detrimental effect on biodiversity. However, this effect confounds two causal factors: the herbicide per se and its effect through the removal of bracken fronds. Treatments in the area lacking bracken were included in the experimental setup to tease apart these two effects. Here, a majority of species were negatively affected, suggesting asulam to have negative effects on the biodiversity of non-target communities. A dense cover of bracken fronds will act as an umbrella, somewhat protecting the underlying vegetation from the full effects of the chemicals. However, the topography, vegetation cover and bracken density of northern heaths are very heterogeneous and herbicide application will unavoidably result in non-target species being sprayed directly. This calls for caution in herbicide application in heterogeneous heathlands, as found in northern regions, where non-target communities are intermingled with bracken-invaded heath. The negatively affected species belonged to different taxonomic and functional groups, and include the graminoids A. capillaris, Anthoxanthum odoratum, J. squarrosus and H. lanatus, the forbs V. ofï¬cinalis, G. saxatile, L. corniculatus, V. palustris, T. europaea and P. erecta, the ericaceous dwarf-shrub V. myrtillus, and the mosses H. splendens and Psuedoscleropodium purum. A number of additional species showed negative trends but occurred too sparsely to prove statistical signiï¬cance. V. myrtillus and P. purum were negatively affected in both areas and might be particularly sensitive to asulam. Other species found to be asulam sensitive are Digitalis purpurea, Prunella vulgaris, Lychnis ï¬‚os-cuculi and Centaurea nigra. A particularly interesting group of species are those unaffected or showing a positive response in area A, yet negatively affected in area B, such as V. ofï¬cinalis and L. corniculatus. This apparent shift can be accounted for by the "˜dual effect' of asulam in the bracken-dominated area where the positive effect of its removal cancels out the negative effect of the herbicide per se. By including this "˜double control-method' in the experimental setup, researchers were able to identify this group of bracken-suppressed, yet herbicide-sensitive species. Such species may be particularly difï¬cult to restore by chemical control, especially if repeated spraying is part of the protocol. This project was carried out on a small scale in vegetation dominated by common species. Species negatively affected by the herbicides belonged to different taxonomic and functional groups, making generalizations of potential responses of other (groups of) species very difï¬cult and need further investigation. In particular, many ferns are sensitive to asulam, and particular care should be taken in areas with a diverse and/or threatened fern ï¬‚ora.
Socio-Economic & Community Outcomes Achieved
Economic vitality and local livelihoods:
As most studies of herbicides are conducted in the ï¬elds of agriculture, forestry or by the manufacturers, they yield little information on the effects of these herbicides on semi-natural vegetation for conservation or restoration purposes. While much is known about the effects on target species, there is less information regarding their effects on non-target vegetation dynamics and on endangered or vulnerable non-target species likely to be found in heathlands. For successful conservation management these effects should be of most important consideration. For organic farming, which preclude the use of chemical control, alternative control methods need to be formulated. Our work shows that biannual cutting retards regrowth sufï¬ciently for effective control. Annual cutting was nearly as efï¬cient as biannual cutting after ï¬ve years, and may be a more economic option long-term. It is not possible to eradicate the species permanently, as other researchers did not succeed in this even after 18 years of continued bracken control, but the population can be kept at a level acceptable for keeping grazing livestock and conserving the threatened habitat of coastal heathlands. All bracken control measures were more efï¬cient in reducing bracken cover and had longer-lasting effects in this study compared to studies further south in Europe. This could be due to climatic and environmental constraints at the northern brink of bracken's distribution in the heathland habitat, suggesting that bracken control may be easier and less labour intensive here. On the other hand, bracken shows strong plastic responses to yearly climate variability. In northern areas, where temperature is the main limiting factor for growth, future increases in temperature and growing season duration could imply range expansion, increasing rates of bracken invasions and denser bracken stands in already-invaded areas. Future climate change could therefore result in a greater need for bracken control measures in the management of northern heathlands.
Overall the project noted that selection of bracken control measures for heathland conservation, restoration or management needs to take into account regional location and topography, the desirable future vegetation after control as well as any special needs of particular land-uses such as organic farming, habitat conservation or conservation of rare/endangered species. Mechanical control can be relatively efï¬cient, especially in northern areas when combined with grazing. These are important issues as it is likely that the use of bracken control measures will have to increase if the heathlands of Northern Europe are to be conserved for the future.
Sources and Amounts of Funding
The project was funded by the Agricultural board of Hordaland, the University of Bergen, Grolles legat and Bergen Myrdyrkningsforeningsfond.
Inger, Elisabeth Maren, Vigdis Vandvik, and Kristine Ekelund. 2008. Restoration of bracken-invaded Calluna vulgaris heathlands: Effects on vegetation dynamics and non-target species. Biological Conservation 141: 1032-1042.