Wood-pasture hypothesis

Free-ranging Longhorn cattle, stands of mature oaks in the distance, Knepp Wildland

According to the hypothesis, open wood-pasture like this one in Denmark comes close to a European virgin vegetation

The wood-pasture hypothesis, also known as the Vera hypothesis and the megaherbivore theory is a scientific hypothesis that proposes that open and semi-open pastures and wood-pastures other than primeval forests would have formed the predominant type of landscape in post-glacial Europe, thus opposing the common belief. As the name Vera-hypothesis implies, it was first proposed by Dutch researcher Frans Vera in his book Grazing Ecology and Forest History in 2000 and translated into English in 2002, although similar ideas had already been developed by others, including Oliver Rackham, but never comprehensively published. Especially in Great Britain Vera's findings have prompted considerable investigation by ecologists.

Although Vera largely focused his research on the European situation, his findings could also be applied to other temperate ecological regions worldwide, especially the broadleaved ones. More so in his book Vera also discusses the decline of ancient oak-hickory-forest communities in Eastern North America, arguing against the widely accepted assumption that those are a product of frequent fires, instead suggesting that herds of American bison that roamed the East coast in the pre-settlement period kept the forests open, thus supporting light-demanding plant communities consisting of oak, hickory and hawthorn species among others.

Vera's ideas have met with both rejection and approval in the scientific community, and continue to lay an important foundation for the rewilding-movement. While his proposals for widespread semi-open savanna as the predominant landscape of temperate Europe in the early to mid-Holocene are at large conceived as non-conforming with interdisciplinary research into vegetational patterns of the period, they do partially agree with the established wisdom about vegetation structure during previous interglacials. Moreover, modern research has shown that, under the current climate, free-roaming large grazers can indeed influence and even temporarily halt vegetation succession. It has also been questioned whether the Holocene prior to the rise of agriculture provides an adequate approximation to a state of "pristine nature" at all, since by that time anatomically modern humans had already been omnipresent in Europe for millennia, with in all likelihood profound effects on the environment. After all, the severe loss of megafauna at the end of the Pleistocene and beginning of the Holocene known as the Quaternary extinction event, which is frequently linked to human activities, did not leave Europe unscathed and brought about a profound change in the European large mammal assemblage and thus ecosystems as a whole, which probably also affected vegetation patterns. The assumption, however, that the pre-neolithic represents pristine conditions is a prerequisite for both the "high forest theory" and the Vera hypothesis in their respective original forms.

Definitions

As defined by Vera the general area his ideas refer to covers western and central Europe between 45°N and 58°N latitude and 5°W and 25°W longitude. This includes most of the British Isles and everything between France and Poland and Southern Scandinavia to the Alps. Furthermore, he confined it to altitudes below 700 m. By extension, the North American east coast is also addressed as a analogy with a comparable climate.

High Forest theory

If the high forest theory holds true, beech forests would naturally dominate temperate Europe

Contrary to Vera's ideas, the established and widely accepted view of the history of vegetation in temperate Europe and by extension the temperate hemisphere is one of more or less dense closed-canopy forest, pioneered by Heinrich Cotta in his work "Anweisungen zum Waldbau" (Directions for Silviculture) in 1817, in which he posits that if humans abandoned his native Germany, in the space of 100 years it would be "covered with wood".

Later, this position was accompanied by Clements' formulation of the theory of linear succession, meaning that under the right conditions bare ground would, over time, invariably become colonized by a succession of plant communities eventually leading to closed stands dominated by the tallest plant species. Because in most of the temperate hemisphere, the potentially tallest plants are trees, the final product would therefore chiefly be forest. Albeit with changes in conceptualisation and some modifications, this concept remains the one favored by most, providing the conceptual framework for many forest-related methods and customs in forestry and conservation, including the Prozessschutz doctrine advocated by German forest-ecologist Knut Sturm, which highlights the importance of non-intervention and space of time for forest protection, as it is implemented in forest reserves such as Białowieża. Although Clements' notion of stable climax communities was later challenged and refined by authorities such as Arthur Tansley, Alexander Watt and Robert Whittaker, who championed the inclusion of dynamic processes, like temporary collapse of canopy cover because of windthrow, fire or calamities, into Clements' framework, this didn't change anything about the status of the "high forest theory" as the commonly accepted view; that without human intervention closed-canopy forest would dominate the global temperate regions as the potential natural vegetation.

Apart from theoretical considerations, this concept has relied and continues to rely heavily on both field observations and, more recently, on findings from pollen analysis, which allow inferences about the vegetation structure of past epochs based on the ratio of for instance tree pollen to pollen associated with grassland and is the most widely used means of generating historic vegetation data. The analysis of pollen data has provided a solid database from which a predominance of forest throughout the Holocene of temperate Europe is generally inferred, although the possibility of regional differences remains open.

Theory

In how far African savannas are adequate to draw comparisons to the primeval European landscape remains debated

The hypothesis states, that although the warming climate of the onsetting Holocene in Europe provided conditions that would allow for the formation of a closed canopy forest, this process was interrupted and altered by herbivores such as aurochs, European bison, red deer and tarpan, historically, with the addition of many other megafaunal mammals prehistorically, who shaped more open landscapes instead by grazing and browsing and likewise also did so in previous warm interglacial periods. It further states, that lowland forest did not emerge on a large scale before the onset of the Neolithic period and subsequent local extinctions of herbivores, which in turn allowed forests to thrive more unhindered. Indeed, investigations point to at least locally open circumstances, for example in floodplains, on infertile soils, chalklands and in submediterranean and continental areas, but maintain that forest largely dominated.

However, the wood-pasture hypothesis is to some degree based on the Quaternary extinction event, around the Pleistocene-Holocene boundary, which started around 130,000 years ago but reached a maximum extinction rate from 13,000 to 8000 years ago, when a large amount of the world's megafauna and almost all megafaunal animals above 1000 kg on the northern hemisphere, in Latin America, Australasia and the Pacific islands as well as in Madagascar and the Caribbean died out in a relatively short period of time, with the most popular example probably being the woolly mammoth.

As it stands, the wood-pasture hypothesis builds in part on the overkill-hypothesis, which holds that human predation was the dominant factor for the Quaternary extinction event and was coined by Paul S. Martin in 1966, and the second-order-predation hypothesis, respectively, which states that the pressure of climate change on the Pleistocene ecosystems was exaggerated by human actions, as opposed to the climate change hypothesis which attributes the extinctions solely or mostly to the changes in climate. Thus, the theory says, human predation led to the extinction of the northern megafauna, leaving ecological niches previously occupied by megafaunal animals vacant and leading to forest vegetation ultimately.

Paleoecological evidence drawn from Coleoptera deposits has also shown that, albeit rare, beetle species associated with grasslands and other open landscapes were present throughout the Holocene in Western Europe, which points to open habitats being present, but restricted. However, insect assemblages from previous interglacials when the larger megafauna was still present indicate widespread warm temperate savannah, pointing to the possibility that elephants and rhinos were more effective creators of open landscapes than the herbivores left after the Quaternary extinction event. On the other hand, traditional animal husbandry might have mitigated the effects of possibly human-induced megafaunal die-off, and thus enabled the survival of an array of species associated or dependent on landscapes created and maintained by megafauna.

The baseline: Quaternary glacial cycles and the Quaternary extinction event

Main articles: Quaternary glaciation, Pleistocene Megafauna, Quaternary extinction and Holocene Extinction

Some megafauna of the Late Pleistocene of Spain

Important for the hypothesis is the fact, that during the Pleistocene warm periods alternated periodically with colder glacial periods, globally. In Europe, this had the effect that two very different faunal and floral assemblages took turns in central Europe. On the one hand, the warm-temperate Paleoloxodon-faunal assemblage, consisting of the straight-tusked elephant, Merck's rhinoceros, the narrow-nosed rhinoceros, European water buffalo, aurochs and several species of deer among others had its core area in the Mediterranean and periodically expanded from there into the rest of Europe during warm interglacials, and receded during glacial periods back into refugia in the Mediterranean. On the other hand, the cold-temperate faunal assemblage of the mammoth steppe, consisting of the woolly mammoth, woolly rhinoceros, reindeer, saiga, muskox, steppe bison, arctic fox and lemming among others was spread across vast areas of northern Eurasia as well as North America and during cold glacials periodically advanced deep into Europe. Other animals like horses, steppe lions, the scimitar cat, the Ice Age spotted hyena, wolves, wild boar and red deer among others were part of both faunal assemblages.

At the end of the Pleistocene however, at the end of the last glaciation, the mammoth steppe faunal-assemblage receded with the warmer temperatures, but was not replaced by the Paleoloxodon-faunal assemblage whose most prominent members, straight-tusked elephants and the two species of rhinoceros, had already gone extinct. Similarly, the mammoth steppe faunal assemblage also collapsed not long after, although regionally small woolly mammoth populations held out well into the Holocene, and the Irish elk was present in the southern Ural region into historical times. Both have been attributed to either climate change or human impact, or a combination of the two.

These extinctions were not limited to Europe or the Palearctic, but rather represent a global phenomenon, which occurred on all continents except for Antarctica, albeit with varying severity. Together, these extinctions are commonly known as the Quaternary extinction event. Whereas today megafaunal Proboscideans, Rhinocerotidae and Hippopotamidae significantly above 1000 kg exclusively exist in the global south, notably Sub-Saharan Africa and South Asia, land mammals of comparable or greater size used to roam the northern hemisphere and South America until relatively recently, dying out around 10,000 BC or being geographically restricted nowadays, respectively. Notable examples include the taxa Palaeoloxodon, mammoth, mastodon, Stegodon, Cuvieronius, Notiomastodon, Stephanorhinus, woolly rhinoceros, Elasmotherium, Toxodon, Mixotoxodon, Eremotherium, Megatherium, Glyptodon and all Diprotodontids.

Late Pleistocene distribution of the woolly mammoth, marking the extension of the mammoth steppe

Furthermore, other megafauna above 45 kg, including various species of Cervids, Bovids, Antilocaprids, Meridiungulata, Marsupials, Camelids, Tayassuids, Equids, Felids and Ursids that were spread across all continents except for Antarctica prior to the Quaternary extinction event, have since declined across their range, or become extinct, respectively. More so, many big mammal species have since become locally extinct and survive only in fractures of their once greater distribution, examples of which include the Eurasian saiga, wapiti-deer, the Asian black bear, the yak, bison, the dhole, lions, the leopard, the jaguar and the giant anteater. While the exact cause of these events remains debated among scientists, it seems clear that this left ecological niches in Europe, the Middle East, big parts of Asia and the Americas unoccupied, since upon the extinctions of these species, unlike the entire Cenozoic, they did not see any ecological replacements and their ecological niches remain largely unoccupied to this day.

File:Hunting Woolly Mammoth.jpg

A woolly mammoth hunt. Although early human weaponry consisted of more primitive tools, research has shown that they could kill even the largest animals of their time

Similar to how big herds of herbivores like wildebeest, zebra and buffalo as well as elephants manage to drive vegetation patterns in the African savanna, and not vice versa the vegetation dictating the activities of these herbivores, it is argued that herds of similar-sized animals with similar ecological niches could have employed these ecosystem functions in the temperate regions as well until they largely vanished as part of the Quaternary extinction at the Pleistocene-Holocene boundary.

An illustration of this almost global phenomenon is the situation in Europe, where the only remaining large wild herbivores and omnivores widely distributed across the continent are red deer, fallow deer, roe deer, elk, reindeer, wild boar, beaver and the brown bear, and the largest remaining wild animal is the wisent. On the other hand, the Aurochs, the straight-tusked elephant, two species of Stephanorhinus as well as several native hippopotamuses, the Irish elk, wild horse and Haploidoceros mediterraneus among many others were lost. Other continents like South America and Australia have witnessed even more drastic changes and lost almost all of their native megafauna. Thus, it is argued that the remaining herbivores do not manage to adequately replace the extinct ones, and, since their extinction is often attributed to human activity, that these extinctions were not natural, i. e. that the modern ecosystems of Europe miss the megafauna's services as ecosystem engineers. Alternatively, it is argued that since the Quaternary extinction herbivore numbers have never fully recovered in Europe, and that the remaining fauna could have maintained semi-open landscapes if humans had not actively limited their numbers and restricted their ranges.

Main arguments

Oak and hazel

Oak sapling (left) growing in direct vicinity to a young blackthorn shrub.

Being relatively hardy to browsing, (e. g. by roe deer) oaks (shrub in the corner) are generally able to establish under moderate grazing pressure, depending on the conditions

Over time, such "shrub-oaks" enlarge in width, being eventually able to shoot up in the centre, where the developing tree becomes inaccessible to herbivores

One of the most elementary arguments often put forward to substantiate the hypothesis is the widespread lack of successful regeneration of light-demanding tree species in modern forests, especially the lack of regeneration of pedunculate oak, sessile oak and common hazel in Europe. This reality is starkly contrasted by European pollen deposits from previous ages, with oak and hazel often forming a dominant amount of pollen, making a dominance of these species in previous ages conceivable. Especially in regard to hazel, sufficient flowering is only achieved when enough sunlight is available i. e. the plant grows outside of a closed canopy. Thus it is argued, that the high abundance of pollen of the two taxa Quercus and Corylus in previous ages can only be explained by the primeval landscape having been of a more open nature, and this contrast forms the principal theorem of Vera's hypothesis. Further, It has been suggested that oak requires disturbances for successful establishment.

However, pollen records from islands that lacked many of the large grazers and browsers that, according to Vera, were essential for the maintenance of landscapes with an open character in temperate Europe show almost no differences in comparison to mainland Europe. More specifically pollen records from Holocene Ireland, which during the early Holocene was apparently, owing to a lack of fossils, devoid of any big herbivores except for abundant wild boar and rare red deer, show almost equally high percentages of pollen of the two taxa. Thus, one could conclude, that large herbivores were not a required factor for the degree of openness in a landscape, and the abundance of pollen from species unable to reproduce and regenerate sufficiently under a closed canopy, e. g. hazel and oak could only be explained by other factors like windthrow and natural fires. Observations over the course of 20 years forest regeneration in forest gaps created by windthrow, however, showed that hornbeam and beech dominate the emerging stands and largely displace oaks, rendering the formation of oak-dominated forests on nutrient-rich soils without further disturbance unlikely at best. On the other hand, substantial natural oak-regeneration often takes place outside of forests in fringe and transitional habitats, suggesting that a focus on regeneration in forests in an attempt to explain oak regeneration failure might be insufficient in regard to the ecology of central European oak species. Rather, an underestimated reason for widespread failure of oak regeneration may be found in the direct effects of land-use changes since the early modern period, which has led to a more simplisitc, homogenous landscape, as spontaneous regeneration of both oak and hazel does frequently occur in margins, thickets, low grazing intensity and abandoned pasture and arable land.

Furthermore, new species of oak mildew (Erysiphe alphitoides) observed on European oaks for the first time at the beginning of the 20th century have been cited as a possible reason for these differences, since they affect the shade tolerance, particularly of young pedunculate and sessile oaks. Although the origin of these new oak pathogens remains obscure, studies point to it being an invasive species from the tropics, possibly being conspecific with a pathogen found on mangos

Other European light-demanding woody species

Another prominent argument mentioned by Vera in his book and subsequent publications is the existence of other light-demanding and often thorny woody species in Europe, species such as common hawthorn, midland hawthorn, Crataegus rhipidophylla, blackthorn, wild pear and crab apple. He argues that their ecology can only be explained under the influence of large herbivores, and that in the absence of these they represent an anachronism.

Underrepresentation of grasses and insect-pollinated plants in pollen deposits

Ultimately they may form large, old solitaires, such as these oaks in Breite Nature Reserve near Sighișoara in Transylvania. In rural landscapes, these old solitary trees are often signs of ancient silvopasture regimes.

Vera further contests that pollen diagrams can adequately display past species occurrences, since, inherently, pollen deposits tend to overrepresent species that are wind-pollinated and notoriously underrepresent species that are pollinated by insects. Furthermore, he proposed that an absence of grass pollen in pollen diagrams can be explained by high grazing pressure, which would prevent the grasses from flowering, and claims that under such conditions, open environments with scattered mature trees may appear as closed forests in pollen deposits. He consequently proposes that the conspicuous scarcity of grass pollen in pollen deposits dating from the pre-neolithic Holocene might not necessarily speak against the existence of open environments dominated by grasses. However, it is generally considered that over 60% tree pollen in pollen deposits indicates a closed forest canopy, which is true for the vast majority of European early to mid-Holocene deposits. Sites with less than 50% arboreal pollen, on the other hand, are consistently associated with human activities.

Eventually, through disease, lightning strike or old age, they begin to decay and die, leaving precious habitat for a variety of species.

Large herbivores as overlooked drivers of vegetation patterns

Vera stresses that the prevailing "high-forest theory" was born out of observations of spontaneous regeneration in the absence of grazing animals. He argues, that the presupposition that these animals do not exert a significant influence on natural regeneration and thus on the vegetation structure as a whole was assumed without comparative confirmation, and as such is a circular argument. Indeed, modern forestry and modern forest theory arose largely in the modern era and went hand in hand with the ongoing inclosure of common land throughout Europe. A consequence thereof was in many cases a ban of livestock from the forests, which had previously been largely open woodland pastures, often dominated by oaks, which were multifunctional and used for a range of purposes ranging from pannage and livestock grazing to the production of tree hay, coppice, charcoal and timber as well as crop and fruit production. This former usage of forests is often still revealed by a big age gap between tree generations, particularly if the oldest trees are mainly oaks, and many central European forest reserves originated as common wood-pastures.

Associational resistance and cyclic succession

Associational resistance

The term associational resistance was proposed to describe a phenomenon occurring in grazed ecosystems, where trees and other palatable woody species establish within thorny shrubs and subsequently benefit from their thorn protection, ultimately replacing the light-demanding mother bush or living alongside it, respectively. According to Vera, associational resistance is a key process in grazed environments, ensuring natural succession and the establishment of trees under such conditions. The consequent hypothesis is known as the associational resistance and aggregational resistance theory.

In temperate Europe, shrubs providing thorn protection include blackthorn, roses, hawthorn, juniper, bramble and barberry, which presumably can establish themselves under moderate grazing pressure, where they grow bigger over time and subsequently allow other, less resilient species to establish in their thorn protection. Species such as yew, buckthorn, alder buckthorn, wayfarer, guelderrose, wild privet, dogwood, cornel, checker tree, rowan and whitebeam, which are distributed by fruit-eating birds through their faeces, would frequently be placed within these shrubs, through resting birds leaving their droppings.

On the other hand, nut-bearing species such as hazel, beech, chestnut and especially pedunculate and sessile oak would become "planted" somewhat deliberately in the vicinity of those shrubs by rodents such as red squirrel and wood mouse and corvids such as crows, magpies, ravens and especially jays, which store them for winter supply. In Europe, the Eurasian jay represents the most important seed disperser of oak, burying acorns individually or in small groups. It does not only bury acorns in depths favoured by oak saplings but seemingly also prefers spots with sufficient light availability, i. e. open grassland and transitions between grassland and shrubland, seeking for vertical structures such as shrubs in the near surroundings. Since oak is relatively light-demanding while not having the ability to regenerate on its own under high browsing pressure, these habits of the jay presumably benefit oak, since they provide the conditions oak requires for optimal growth and health.

In addition, species such as wild pear, crab apple and sorb tree, which bear relatively large fruit, would find propagators in herbivores such as roe deer, red deer and cattle, or in omnivores such as the wild boar, red fox, the European badger and the raccoon, while wind-dispersed species such as maple, elm, lime or ash would only land within these shrubs by chance.

Since many of these species are analogously replaced by either closely related or ecologically similar species across the temperate northern hemisphere, a comparable scheme could probably apply to these regions as well.

Shifting mosaics and cyclic succession

Young hawthorn shrub, heavily browsed upon by cattle and therefore shaped. A young dogwood bush inside benefits from the hawthorn's thorn protection.

Starting from an extensively grazed pasture, one could thus figure the natural development of succession, according to the hypothesis, as follows: First unpalatable species would gradually establish, either perennial plants like nettles, thistles, teasels and restharrows or woody plants like junipers, brooms, roses and sloes. Second, these would start to form thickets avoided by herbivores, thus enabling larger, palatable shrubs and trees respectively to grow in their protection. Over time these would then outshadow the unpalatable but light-demanding thickets and emerge as big solitary trees or groups of trees. Because of the browsing pressure, even shade-tolerant tree saplings would not be able to grow under the established trees, which means that there would virtually be no vegetation beneath them. Finally, the established trees would start to decay, either due to old age or other factors like pathogens, illness, lightning strike or windbreak, eventually leaving open, bare land for grasses and unpalatable species to colonise, thus closing the cycle. On a large scale, different successional stages would thus contribute an ecosystem where open grassland, scrubland, emerging tree growth, groves of trees and solitary trees exist next to each other, and the alternation between these various successional stages would create dynamic shifting mosaics of vegetation. This in turn stimulates high biodiversity. Consequently, Vera's counter-proposal to the linear succession of closed-canopy forest is a model of successional cycles known as the shifting mosaics model.

Ecology of wood-pastures

Grazed woodlands, wood-pastures and pastures in many regions of the world harbour high biodiversity and are important for many species. Rare perennial plant species commonly or exclusively associated with these ecosystems in Europe include hellebores, peonies, asphodels, dittany, black false hellebore and Melittis melissophyllum. The tree layer is often dominated by a number of oak species and many rare, local and threatened species such as Malus florentina, Malus (Eriolobus) trilobata, medlar, sorb tree, Macedonian oak, Lusitanian oak, pears and wild plums like Prunus cocomila, Prunus webbii and Prunus cerasifera are more often found in European silvopastoral systems than in commercial forest. Rare or declining bird species such as the European roller, hoopoe, several species of shrike, owls (scops owl, little owl) as well as wrynecks, middle spotted woodpeckers and the Spanish imperial eagle are attracted by wood-pastures in particular, for various reasons, while Iberian lynx depend on dehesas.

Rewilding and practical implementation of the hypothesis

Wisent herd in Milovice Nature Reserve, Czech Republic

Although the validity of Vera's hypothesis remains debated among ecologists and conservationists, it is often considered a fruitful approach for environment protection and conservation, and thus has been widely implemented in daily practice.

Examples of such projects include the Dutch conservation area Oostvaardersplassen, which was initiated by Vera, as well as the Knepp estate in Sussex. Isabella Tree, co-owner of the latter, has named Vera and his ideas as important reasons for her and her husband to consider rewilding their private estate with fallow deer, red deer, English Longhorn cattle (as ecological proxies for the extinct aurochs) and Tamworth pigs (as proxies for the wild boar).

Furthermore, in the shape of Rewilding Europe, a pan-European organization that aims for creating wild spaces in Europe by re-establishing food chains and reintroducing formally missing species, has identified Vera's proposals as key to complex ecosystems and, taking them into account, works to establish big herds of European bison, aurochs-proxies (e. g. Taurus-cattle), proxies for the wild tarpan (e. g. Konik, Exmoor pony) as well as water buffalo and kulan, which were present in Europe until the early Holocene, to create dynamic ecosystems maintained by the grazing and browsing activity of these herbivores.

Implications for environment protection and conservation practise

Taurus cattle in the Lippeaue, serving as proxies for the aurochs

Historically, environment protection in Europe and around the northern hemisphere, in the temperate, broadleaved regions was often focused on the protection of old forests, since it was perceived that these old-growth forests represent the closest modern analogy to the original European vegetation prior to the likewise assumed clearing of these forests on the advent of agriculture, by humans. More so it was mostly believed, that open and semi-open landscapes like heathland, wood pastures, pastures and in general any kind of landscape apart from more or less dense forest can be solely seen as a substitutional habitat for the original woodland, and that open habitats, if there, in fact, were any, would have been restricted to places uninhabitable for trees. Only in areas too dry, wet, rocky or sandy for trees to colonise, or where vegetation periods were too short to support trees, would these forests be replaced by other vegetation types, most notably steppe ecosystems. The dominating natural virgin vegetation of the broadleaved regions was assumed to be a climax community that over time develops into a steady state dominated by a few shade-tolerant, competitive species such as beech and maple. Although this theory is mostly abandoned in favour of theories that account for dynamic processes in ecosystems, e. g. temporal collapses of forest cover and disturbances through fire, storm or browsing, the prevalent conception of European virgin vegetation remains to be forest. Examples of this include Białowiża on the Polish-Belarusian border as well as the Hainich in central Germany.

Since the megaherbivore theory implies that these closed forests are largely man-made, either through active support of forests or the passive enablement through the suppression of herbivore numbers, i. e. browsing pressure, this would also mean that a large part of modern conservation practice is misguided and fails to create truly natural ecosystems.

Cultural Significance

A young oak utilizes an established juniper bush as protection against browsing in a historical wood-pasture

Many aspects of Vera's theory resonate well with traditional pastoral systems and agricultural practices across Europe and other parts of the world. This is especially true for regions where the pasturing of grazing animals has been carried out for hundreds and thousands of years, and phrases such as the old English saying "The thorn is the mother of the oak", referring to the recruitment of oaks inside thorny shrubs, attest to the knowledge about processes such as associational resistance as part of old traditional farming knowledge that was present in rural communities well before the theory itself was proposed in its current form. Furthermore, following Vera's argumentation, wood-pastures and related farming systems as ancient land-use systems could be viewed as essentially mimicking the primaeval European wilderness. This goes hand-in-hand with the fact that for instance 63 of the ecosystems listed in Annex I of the Habitats Directive of the European Union strictly depend on low-intensity use and maintenance work, mostly in the form of grazing and mowing. These habitats are labelled as high nature value farmland (HNV farmland), and the fact that traditional farming, in particular, can potentially harbour exceptional biodiversity values might in part be due to such mimicking effects some forms of human use such as grazing, pollarding, coppicing and hedgelaying might exercise as analogies to ecosystem services formerly exercised by the megafauna.

Sergey Zimov's megaherbivore decline model

Main article: Pleistocene Park

While Vera's hypothesis focuses on temperate regions and especially temperate Europe, an argumentatively related model has more recently been proposed for high latitude regions of modern taiga and tundra biomes, where formerly mammoth steppe predominated. It essentially challenges the widespread view that the Pleistocene megafauna of the northern steppe vanished as a consequence of the warming climate at the advent of the Holocene and the consequent turnover of cold-adapted grassland and herb ecosystems into expanding forests and tundra dominated by mosses, lichens and dwarf trees. Instead, it argues that vice versa the declining megafauna was the precondition for the vegetational turnover, and that healthy megafauna populations could have maintained their preferred environment, the mammoth steppe, even under the stresses of the warming climate if human-induced extinctions had not occurred. Consequently, Sergey Zimov, one of the main supporters of the latter thesis, proposes that ecosystems functionally similar to the mammoth steppe of the Pleistocene could function under modern circumstances as well, and seeks to prove this in the form of Pleistocene park by reintroducing species extinct in Yakutia today, respectively species that are ecologically similar to species that were present in the region during the Pleistocene but have since become globally extinct, including wild species like reindeer, muskox, bison and wisent, and hardy domestic breeds like Bactrian camels, Kalmyk cattle, domestic yaks and Orenburg goats. With these, the project hopes to revive the mammoth steppe, at least in fractions of its former expanse.

See also

• Quaternary extinction
• Holocene extinction
• Evolutionary anachronism
• Pleistocene park
• Rewilding
• Pleistocene rewilding
• Wood pasture
• Breeding back
• Oostvaardersplassen
• Knepp wildland
• Breite Oak Tree Reserve

External links

• Die natürliche Verjüngung der laubabwerfenden Eichen-arten Stieleiche (Quercus robur L.) und Traubeneiche (Quercus petraea Liebl.) - eine Literaturstudie mit besonderer Berücksichtigung der Waldweide
• Youtube Video "Frans Vera: The search for wilderness needs wildness in mind"