A Place for the Heathlands

The ambiguity surrounding the management and conservation of anthropogenic heathlands is, in my opinion, evident. On the one hand, heathlands in Denmark are valued and conserved as historic monuments and scenic landscapes. On the other, they are designated as habitats crucial for biodiversity conservation, requiring protection and management through the Natura 2000 network. This dual emphasis on his­tory and biodiversity creates a tension in how these landscapes are understood and managed.

Defining heathlands can be complex. They are often described as "ecosystems dominated by dwarf shrubs," but this definition has its shortcomings. For instance, some dry heathlands may transition into grass-dominated systems over time, while other habitat types, such as bogs and sandy forests, can also support a high cover of dwarf shrubs. Adding criteria like "sparse cover of woody plants or occurring on both dry and moist ground" may seem logical, yet the risk of narrowing definitions is that it fails to capture the dynamic nature of wild ecosystems. The strict boundaries between the woodland and open semi-natural habitats often seen in conservation are, in fact, results of historical human intervention – specifically, the Forest Protection Act, implemented in Denmark in 1805. This act excluded grazing animals from woodlands with the aim of promoting high-quality timber production, and contributed to the sharp lines drawn between forests and open land.

In contrast to human-created landscapes composed of rectangular habitat types, a natural Danish landscape would be composed of a chaotic mosaic of trees, shrubs, dwarf shrubs, and herbs. It would also show considerable variation in soil moisture, giving rise to a diverse mix of mires, fens, forest swamps, ponds, meadows, grasslands, and heathlands, changing over relatively short distances. Natural disturbances – flooding, wildfires, wind throws, erosion, and sand drift – would all play crucial roles in maintaining this dynamic landscape. The grazing, browsing, and trampling of large herbivores would be integral to and decisive for the system. Unfortunately, this natural baseline is often overlooked. Instead, rare and declining features of the landscapes are being idealized for their beauty and for mysterious hints of ancient times. I would argue that we are living under what has become known as the "shifting baseline syndrome," whereby the understanding of nature becomes progressively disconnected from its wild potential. I remember attending a restoration conference in Belgium, where Paul Keddy, an American ecology professor, opened his keynote with the following statement. "I so enjoy coming to Europe," he said, before delivering his punchline: "the only continent on Earth where nature is a garden." This remark, though humorous, underscores a painful truth: the detailed management of habitats, aiming for poorly defined baselines, can deliver neither biodiversity nor wild ecosystems.

From a biological perspective, it is unfortunate that historical landscapes are valued over wild ecosystems, as the former are poor representatives of the evolutionary cradle of plants, animals, and fungi. It has been discussed how human actions often disturb ecosystems, and how general human management strategies have not sufficiently accounted for the full scope of biodiversity that pre-dated human influence. The idea that human-driven landscapes contribute to biodiversity is increasingly being challenged in ecological research.^{1 ( 1 )}
Van Meerbeek et al. 2019, 997–1007.

The large tracts of heathland found in central Jutland are largely the result of the clear-cutting of forests followed by overexploitation of the sandy soils, which led to nutrient depletion, leaching, acidification, and sand drift. As such these heaths are depleted ecosystems in soil fertility, biodiversity, and structural complexity. Heather (Calluna vulgaris), the central component of these inland heaths, relies heavily on recurrent and intensive disturbances – otherwise it is replaced by grasses, shrubs, and trees. These disturbances were historically driven by traditional heathland farming, involving a mix of prescribed burning, livestock grazing, and sod cutting. The natural counterpart to these inland heaths is the coastal dune heaths, which emerge as late stages in a dune succession once the sand has been sufficiently leached, allowing dwarf shrubs to replace the herbs of the grey-green dunes.

Today, inland heaths occupy only a tiny fraction of their historical extent. In my view, the most coherent approach to their conservation would be to focus either on cultural heritage or on natural ecosystems, as these should be considered mutually exclusive, or at least potentially conflicting. Cultural heritage heathland could be managed according to traditional practices, and there is ample evidence that this would result in a lush cover of heather over large tracts of land. This would serve as a habitat for some characteristic plants, animals, and fungi, thus providing ecological value. However, from a biological conservation perspective, this approach bears similarities to traditional farming: a prescribed sequence of actions leads to the desired outcome, and the outcome would be a rather monot­o­nous and not very species-rich ecosystem.

Aiming for natural heathland would imply a restoration of natural disturbances, particularly the grazing and browsing of large herbivores and the re-establishment of natural hydrology. In the coastal zone, restoration of natural dynamics such as erosion, sedimentation, flooding, and sand drift would be pivotal.^{2 ( 2 )}
Brunbjerg et al. 2014, 101–10. Once ecological restoration has taken place, heathlands should be left for natural succession. The future of these ecosystems, following ecological restoration, would be less predictable than if the heathlands were managed as cultural heritage sites. This approach, known as "open-ended management," emphasizes non-intervention, in which no predetermined outcome is defined or guaranteed. As seen from the paleoecological rec­ord, particularly through the analysis of prehistoric pollen and macrofossil remains from the last interglacial, we could likely expect a mosaic of open heathland and grassland patches, interspersed with light forests of oak, hazel, and pine, along with abundant dwarf shrubs. Furthermore, we should anticipate a diverse fauna of large herbivores at densities far higher than those seen in today's unfenced landscapes, echoing studies on the historical importance of large herbivores grazing in shaping landscapes.^{3 ( 3 )}
Fløjgaard et al. 2022, 18–24.

The habitat-oriented conservation approach of the Nature Protection Act and the EU Habitats Directive tends to treat the loss of classic heathland habitat as a breach of law, thus taking a conservative position. This could potentially obstruct the restoration of original ecosystems that would operate without frequent human interventions as seen in traditional management. Luckily, experience from mapping and managing dune-habitat mosaics has taught us that the habitats directive comes with sufficient flexibility to embrace the inherent chaos of natural dynamics.

I fear that a narrow focus on heathland as cultural heritage could decrease the contribution to halting the biodiversity loss. Inland heaths are often monot­o­nous and species-poor; unlike natural forests, mires, and grasslands, very few species – if any – are known to be exclusive to traditionally managed inland heaths. To elaborate this further, let us consider the black grouse (Lyurus tetrix), which is an illustrative example. Despite concerted efforts to recreate traditional heathland management practices, this charismatic bird went extinct in Denmark, with the last sightings in Randbøl Hede (1992), Vind Hede (1996) and Kongenshus Hede (1998). Evidence from its preferred habitat in Scandinavia suggests that a more natural heathland with mosaics of scrub, woodland, and wetland would likely have been more conducive to the grouse's survival. This aligns with current research that indicates that biodiversity thrives when landscapes are managed in a way that more closely mimics natural processes.

Similarly, consider the case of the marsh fritillary butterfly (Euphydryas aurinia), which was once widespread throughout Denmark but has seen a massive decline in the twentieth century. Today, it is confined to a few small populations in northern Jutland. The host plant for the marsh fritillary, devil's-bit scabious (Succisa pratensis), is primarily found in heathland, meadow, and grassland habitats. The butterfly's decline has been driven in part by the conversion of semi-natural habitat into intensive farmland, but the acidification of poor sandy soils has also been a significant factor. Succisa is sensitive to ammonium toxicity in acidic soils, and the acidification of inland heaths is, in part, a consequence of traditional management practices. Yet it has also been exacerbated by the deposition of acid rain from fossil fuel combustion. Although acid rain has decreased in recent decades, the restoration of a higher pH in many inland heaths remains necessary. According to current research, restoration of natural hydrology and the spread of deep-rooted shrubs and trees that bring minerals back to the soil could help reverse some of this acidification. Large herbivores also play a role in this process, by increasing the decomposition of organic matter, which in turn would increase soil fertility. With the restoration of more favourable conditions for the host plants, there is hope that the marsh fritillary could regain some of its former range.^{4 ( 4 )}
Brunbjerg et al., 2017, 117–24.

Perhaps the strongest argument for allowing encroachment by shrubs and trees in heathlands is that a significant portion of the wild invertebrates and fungi are intimately connected with these plants,^{5 ( 5 )}
Bruun et al., 2022, e08823. thriving particularly in warm and sunny environments. In this way, the development of a more natural, dynamic landscape can foster biodiversity across multiple trophic levels.

Some conservation managers, particularly those advocating active human interventions, express concern that the loss of control associated with open-ended management would lead to a decline of biodiversity. In response, I would point out that the monitoring of ecosystems subjected to goal-oriented management reveals a troubling pattern of unmet objectives. A substantial proportion of protected habitats and species across Europe remain in an unfavourable conservation status, while biodiversity continues to decline. Human simulation of natural processes appears both costly and ineffective.

The future of European heathlands will inevitably be shaped by the decisions of managers and politicians, guided by the expertise of scientists. Based on my experience as a community ecologist, I would recommend that ecosystem restoration and rewilding of heathlands should be prioritized over cultural heritage management, except for sites serving as museums of our recent his­tory. This approach would allow for the restoration of more dynamic, self-sustaining ecosystems, and would contribute to the long-term conservation of biodiversity.

The future of heathlands is defined by the choices we make today. As cultural heritage, these landscapes offer a window into the intertwined his­tory of humans and their environment, reflecting centuries of land-use practices. However, their potential as wild and biodiverse ecosystems is compromised by agricultural practices such as burning, cutting, and logging. Species like the black grouse and the marsh fritillary exemplify how natural dynamics, such as the grazing of large herbivores, hydrological restoration, and natural succession, can promote habitats for a wider range of species. Deliberate physical planning should determine where we prioritize cultural heritage, and where we target the restoration of natural ecosystems.