2017 Anslinger, Sophia: Comparison of Different Conservation Approaches for Oligotrophic Acidic Grassland and Dwarf-Shrub Heath in the Black Forest National Park, Germany

Heathland in the Black Forest National Park, commonly referred to as “Grinden” was created under the influence of anthropogenic fires, intensive grazing and hay-making, combined with environmental factors, such as high precipitation and acidic soils. Heathland abandonment resulted in overgrowth of the grass Molinia caerulea, and loss in species diversity. Restoration of heathland started with re-introduction of sheep-grazing and cattle-grazing in the 1990s. Most studies focused on the implications of cattle-grazing, while no systematic repeated sampling of permanent plots for sheep-grazing was conducted, and no other management approaches apart from grazing were recorded. In this study, heathland management by sheep grazing, burning and mulching in the Black Forest National Park is compared. Objectives focused on differences between treatments in terms of vegetation diversity, performance of influential species and whether influential species can represent a proxy for management success. Further, management success by sheep-grazing is evaluated individually by re-sampling of permanent grazing plots and by comparison with permanent control plots. Objectives focus on differences in vegetation between grazing and control plots, differences in vegetation between initial and repeated sampling and differences in vegetation between initial and repeated sampling regarding influential species.
The study shows differences between treatments in terms of plant diversity, thereby supporting the first objective. Species richness in the herb layer is highest for the mulching and lowest for the grazing treatment, while species richness in the moss layer is highest for the burning treatment. High herbaceous species richness in the mulching treatment is biased partly by the management itself, which shows slope-related differences in efficiency, and partly by local variability due to trenches and close proximity to forest. Species richness in burning treatment is biased by proximity to roads and seed dispersal via car lanes. High species richness in the moss layer for the burning treatment is a result of specialized, fire susceptible moss flora, which could colonize open soil patches created by burning treatment. Shannon evenness shows no specific trend for the herb layer due to high variability within the treatments themselves, while Shannon evenness in moss layer is biased by high differences in terms of data amount between treatments. Species richness in the herb layer is the only parameter to shows significance between treatments. Beta-diversity shows significant differences between treatments, but hierarchical clustering reveals that the mulching and burning treatments show much higher similarity compared to the grazing treatment. Furthermore, the mulching treatment shows a unique group including forest species and species of oligotrophic acidic grassland. The uniqueness of this group is probably related to mulching efficiency, as they are located at the bottom of the slope. Ellenberg indicator values for moss layer are not reliable due to high differences in terms of data volumes between treatments. However, the Ellenberg indicator values for herb layer are very similar between mulching and burning treatment as well. This similarity can be explained by the fact that treatments are adjacent to each other, which results in very similar local site conditions and, in turn, in similar vegetation composition. Furthermore, burning and mulching treatment underwent the same management for a long time. Ordination shows significance for elevation and exposition regression parameters, thereby highlighting site related differences between mulching and burning treatments compared to grazing treatment. Comparison of mean
environmental parameters shows an increase of 25 m in elevation for the grazing treatment. Differences in expositions probably play a minor role as west-east exposition is not recorded to have a strong influence on vegetation. However, considering that higher elevation is related to an increase in humidity and light intensity, this factor is more relevant. Implications of elevation difference are reflected by vegetation as Ellenberg indicator values show highest humidity and light value for the grazing treatment. Furthermore, ISA results show the highest indicator value for the species Trichophorum germanicum and Pleurozium schreberi. Both species are typical for blanket bog vegetation. Thus, elevation differences, in combination with dominance of the blanket bog species Trichophorum germanicum, imply that grazing treatment shows site conditions that favor blanket bog vegetation. Historical land-use included drainage of blanket bogs in order to create pasture land, and while no such record exists for Schweinkopf, it can be hypothesized that this management was applied there, as well. Consequently, Schweinkopf area can be categorized as deteriorated blanket bog vegetation. In contrast to that, mulching and burning treatment resemble dry, montane heathland, which is closely linked to oligotrophic acidic heathland. Previous studies (Vollmer, 2008; Wacker 1989) did not differentiate different heathland type for evaluation of management success, and as grazing treatment plots represent repeated sampling, no obstacles were apparent when vegetation assessment was conducted. However, as deteriorated blanket bog vegetation strongly differs from deteriorated montane heathland vegetation, this study suggests that these vegetation types are not fit for comparison. Consequently, comparative evaluation between treatments is viable between mulching and burning treatment only, while grazing treatment is evaluated separately by means of repeated sampling. Species richness in the herb layer is higher for the mulching treatment than for the burning treatment, while species richness in the moss layer is higher for the burning treatment. ISA results for the mulching treatment shows the highest indicator value for species typical of montane heathland and oligotrophic acidic grassland, while the burning treatment shows highest indicator values for woody species and the dwarf-shrub Vaccinium myrtillus. While burning treatment is more favorable in terms of moss flora diversity and promotion of the dwarf shrub Vaccinium myrtillus, which is recorded to be fire susceptible, the treatment shows major drawbacks. It promotes undesirable species with subterraneous organs, such as Molinia caerulea and Pteridium aquilinum, and invasion of woody species. However, promotion of these species is probably related to secondary succession processes, but to what extent remains unclear. Comparison between the mulching and burning treatments revealed that, in terms of herbaceous species richness, promotion of typical vegetation of montane heathland and oligotrophic acidic grassland, and repression of undesirable species, mulching treatment is more favorable than burning treatment. Thus, the objective that influential species can act as a proxy for management success is partly supported, as this is true for the mulching and burning treatments only. Contrary to the impression of poor management success compared to the other treatments, repeated vegetation assessment at Schweinkopf reveals an overall positive trend for management success by grazing treatment. Comparison between initial and sampled vegetation shows an increase for all dwarf shrubs except for Vaccinium uliginosum, which is probably based on observer bias, and a small increase in woody species. Further, an increase in the species Deschampsia flexuosa and decrease in the species Molinia caerulea is apparent. Comparison of environmental parameters reveals a decline of mean litter cover and a slight increase in moss cover for grazing management. Increase in herb layer height reflects the change from a Molinia caerulea dominated vegetation to co-dominance of Molinia caerulea and Trichophorum germanicum. The Majority of control plots show increase in Molinia caerulea and decrease in dwarf-shrubs, and mosses. However, some control plots show an increase for the species
Calluna vulgaris and Sphagnum capillifolium as well. Similarly, environmental parameters show increase for mean litter cover and moss cover. This discrepancy is caused by differences between control plots. Increase in Calluna vulgaris and Sphagnum capillifolium is only apparent for very wet plots (S1 and S2), as Molinia caerulea is outcompeted by Calluna vulgaris in wet areas and Sphagnum capillifolium, which grows underneath the latter, can thrive. Analysis of browsing and trampling effects show high browsing preference for Molina caerulea and high trampling of Trichophorum germanicum. As Trichophorum germanicum shows high increase compared to initial sampling and high trampling intensity, trampling susceptibility of the species is supported. Repeated sampling was limited due to observer bias, inconsistent grazing intensities and simultaneous usage of several sheep breeds. Furthermore, no measure for exclusion of roe deer- and red deer-grazing was present. While observer bias is always present, future studies should attempt to control these limitations for grazing treatment. Similarly, roe deer- and red deer-grazing were not controlled for the mulching and burning treatments either. As mentioned above, the mulching treatment shows differences in management efficiency related to slope, and the burning treatment is biased by seed dispersal via car lanes. Due to a lack of data regarding faunal presence, management recommendations focus on vegetation implications and give general information on entomofauna management response. Management recommendation on montane heathland include that mulching treatment is more favorable than burning treatment on vegetation in most aspects. Furthermore, burning treatment is not a viable option for future management due to increased risks involved with adjacent blanket bog areas. Mulching treatment can have severe impact on Entomofauna but one-year management in late season diminishes this effect. As soil compaction by large browsers should be smaller compared to that from a mulching machine, grazing management by heck cattle in Muceknloch area seems appropriate and is probably more favorable on Entomofauna. In contrast, Schweinkopf seems to be highly susceptible to trampling disturbance, which is probably related to increased soil humidity. Here, grazing by lighter animals, such as sheep and goats, is preferable. In order to evaluate restoration potential of seed banks, seed bank analysis should be conducted. Further, management implications on important animal species should be studied, as this represents an important factor for management evaluation, as well. As this study emphasizes that, future heathland management should be applied and evaluated based on different heathland types.