Oak regeneration failure

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Oak regeneration failure is a woodland phenomenon whereby insufficient oak ( Quercus ) seedlings and saplings are recruited into the canopy to replace dead mature oaks. The result is a local decline in oak numbers while other more shade-tolerant trees such as maple, lime, and ash may become more prominent. Oak regeneration failure has been observed across Eastern and Midwestern forests in the United States as well as in Europe. [1] [2]

Contents

History

The failure of oak regeneration has been recognised for centuries. Early evidence of challenges to oak regeneration can be found in French ordinances from the 13th century which mandated the planting of oak seedlings to ensure that harvesting did not exceed production, due to oak's high timber value and versatility. [3] Great Britain imported oak from colonial America to make up for the shortage in Britain. [3] One of the first government-sponsored pieces of forestry research in America was to promote the growth of live oak ( Quercus virginiana ), which was used for shipbuilding. [3]

Oak remained a significant source of lumber even after wooden ships were no longer in use. Concerns about its regeneration persisted as forestry developed. In the early 1900s, researchers studied forests in the American Midwest and South. They found that oaks could maintain their dominance in the next generation after clearcutting a forest lot if there was significant advance regeneration or disturbance from fire. However, they declined in many other cases. [3]

Oak appeared to regenerate more freely in the distant past than in modern times, which may in part be due to obsolete or declining woodland management practices as well as local site ecology. [4]

Causes

Oak regeneration failure may be caused by various factors at different stages of the oak's lifecycle. Among these, seedling growth and survival are critical stages that determine the success or failure of oak regeneration. This is especially true during a seedling’s first summer after germination. [5] Oak is a light-demanding genus, so the survivorship of seedlings recruited into the canopy is mainly determined by incident light levels on the woodland floor. These light levels are, in turn, governed by gaps in the woodland canopy.

As well as limiting the levels of incident light onto the woodland floor, mature oaks can also impede growth of seedlings by dropping on them leaf-eating caterpillars. The caterpillars can proceed to defoliate the seedlings, depriving them of their energy reserves and inhibiting survival. [5]

In unmanaged stands and under historical indigenous management in America, fire was a primary agent of creating sizable canopy gaps, enabling the recruitment of oaks into the mature canopy. [6] However, modern forest management often entails fire exclusion, leading to smaller canopy gaps and less capacity for oaks to access the needed light. [7] The decline of coppicing and other traditional woodland management practices have resulted in a similar situation in Britain and Europe. [4]

Successful regeneration relies on the production and dispersal of sufficient acorns for regeneration. [6] In the wake of extensive logging, many forests in the United States have more simplified and homogeneous stand compositions compared to natural stands. Because acorn production declines with age, [6] this may lead to a decrease in acorn dispersal, endangering the next generation of oaks.

Oaks are also under threat from pests, pathogens, and animal browsing, all of which damage the vulnerable understory trees that replace older oaks. For example, the arrival of a non-native powdery mildew pathogen in European woodlands and forests in the early 1900s gave rise to concerns about the regenerative failure of the widespread native pedunculate oak ( Quercus robur ).

Powdery mildew is a prominent example of a pathogen hampering oak regeneration. In affected pedunculate oaks, research shows that powdery mildew makes them more light-demanding, reducing their competitiveness with other tree species (known as the pathogen mildew hypothesis), [7] and making them succumb to even a small degree of shade which they may otherwise have survived. [4]

Predation of oaklings by browsing herbivores such as deer can also have a deleterious effect on oak regeneration. Moreover, because fencing and other exclusion methods are cost-prohibitive, deer are also able to browse freely on many managed forests, which reduces oak competitiveness because they are a favored species of the herbivores. [8]

Oaks are generally tolerant of browsing under sufficient light conditions, and in Europe can still regenerate in transitional habitats such as forest edges, fallows and abandoned grassland, [9] habitats where Eurasian jays, the most important disperser of European oaks, prefer to deposit acorns. [10] Nonetheless, studies on oak regeneration commonly focus on closed-canopy forest. Therefore, it has been suggested that the main reason for oak regeneration failure in Europe is land-use changes since the early modern period, with the abandonment of wood-pastures, pannage and forest grazing and the more homogenous landscapes this brought about. Overall, oaks appear to be specialized colonizers of formerly grazed grassland or areas recently burned, which would render the search for oak regeneration inside forests futile from the outset. [10] According to the Vera hypothesis it has consequently been suggested that oaks are originally adapted to regenerate in savanna-like habitats shaped by large herbivores. Indeed, extensive grazing followed by temporary abandonment can result in almost closed stands of oak. [11]

Impact

Oak regeneration failure can have a significant economic impact since oak is a crucial tree genus in many American and European forests. Moreover, it has been estimated that as few as 4% of oak-dominated forests in the Eastern U.S. have sufficient oaks to replace the current canopy. [12]

Oak forests comprise 51% (78.5 million ha) of U.S. forestland. [13] As such, they have high economic value and ecological importance. Many animal species, especially among insects, prefer the composition and structure of oak forest types over others, and regional-scale declines in oak forest are shown to have deleterious impacts on animal populations. [6]

Modern efforts are focused on sustaining pre-modern conditions through such tactics as reintroducing fire to forests that were previously under natural or indigenous fire regimes and creating deer exclusion zones to reduce the intensity of browsing. [12] Scientists are also studying how climate change will impact the regeneration of oaks. Some models suggest that oaks will rise in prominence as warming temperatures favour their proliferation in certain habitats over other species, [14] but changes in temperature and precipitation patterns are also likely to have adverse effects on oaks, particularly young trees. [6]

Related Research Articles

<span class="mw-page-title-main">Oak</span> Tree or shrub in the genus Quercus

An oak is a hardwood tree or shrub in the genus Quercus of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisphere; it includes some 500 species, both deciduous and evergreen. Fossil oaks date back to the Middle Eocene. Molecular phylogeny shows that the genus is divided into Old World and New World clades, but many oak species hybridise freely, making the genus's history difficult to resolve.

<i>Quercus kelloggii</i> Species of oak tree

Quercus kelloggii, the California black oak or Kellogg oak, is an oak in the red oak section native to western North America. Although genetically separated from them for more than 20 million years, its leaves are remarkably similar in appearance to several other members of the red oak section including the red oak and the black oak found in eastern and central North America.

<i>Quercus rubra</i> Species of flowering plant in the beech and oak family Fagaceae

Quercus rubra, the northern red oak, is an oak tree in the red oak group. It is a native of North America, in the eastern and central United States and southeast and south-central Canada. It has been introduced to small areas in Western Europe, where it can frequently be seen cultivated in gardens and parks. It prefers good soil that is slightly acidic. Often simply called red oak, northern red oak is so named to distinguish it from southern red oak (Q. falcata), also known as the Spanish oak. Northern red oak is sometimes called champion oak.

<span class="mw-page-title-main">Coppicing</span> Method of woodland management

Coppicing is the traditional method in woodland management of cutting down a tree to a stump, which in many species encourages new shoots to grow from the stump or roots, thus ultimately regrowing the tree. A forest or grove that has been subject to coppicing is called a copse or coppice, in which young tree stems are repeatedly cut down to near ground level. The resulting living stumps are called stools. New growth emerges, and after a number of years, the coppiced trees are harvested, and the cycle begins anew. Pollarding is a similar process carried out at a higher level on the tree in order to prevent grazing animals from eating new shoots. Daisugi, is a similar Japanese technique.

<i>Quercus velutina</i> Species of oak tree

Quercus velutina, the black oak, is a species of oak in the red oak group, native and widespread in eastern and central North America. It is sometimes called the eastern black oak.

<i>Quercus robur</i> Species of flowering plant in the beech and oak family Fagaceae

Quercus robur, the pedunculate oak, is a species of flowering plant in the beech and oak family, Fagaceae. It is a large tree, native to most of Europe and western Asia, and is widely cultivated in other temperate regions. It grows on soils of near neutral acidity in the lowlands and is notable for its value to natural ecosystems, supporting a very wide diversity of herbivorous insects and other pests, predators and pathogens.

<i>Quercus garryana</i> Species of oak tree

Quercus garryana is an oak tree species of the Pacific Northwest, with a range stretching from southern California to southwestern British Columbia. It is commonly known as the Garry Oak, Oregon white oak or Oregon oak. It grows from sea level to an altitude of 690 feet in the northern part of its range, and from 980 to 5,900 ft in the south of the range in California. The eponymous Nicholas Garry was deputy governor of the Hudson's Bay Company.

<i>Quercus suber</i> Species of plant

Quercus suber, commonly called the cork oak, is a medium-sized, evergreen oak tree in the section Quercus sect. Cerris. It is the primary source of cork for wine bottle stoppers and other uses, such as cork flooring and as the cores of cricket balls. It is native to southwest Europe and northwest Africa. In the Mediterranean basin the tree is an ancient species with fossil remnants dating back to the Tertiary period.

<i>Quercus petraea</i> Species of flowering plant in the beech and oak family Fagaceae

Quercus petraea, commonly known as the sessile oak, Cornish oak, Irish Oak or durmast oak, is a species of oak tree native to most of Europe and into Anatolia and Iran. The sessile oak is the national tree of Ireland, and an unofficial emblem in Wales and Cornwall.

<i>Quercus stellata</i> Species of oak tree

Quercus stellata, the post oak or iron oak, is a North American species of oak in the white oak section. It is a slow-growing oak that lives in dry areas on the edges of fields, tops of ridges, and also grows in poor soils, and is resistant to rot, fire, and drought. Interbreeding occurs among white oaks, thus many hybrid species combinations occur. It is identifiable by the rounded cross-like shape formed by the leaf lobes and hairy underside of the leaves.

<i>Quercus douglasii</i> Species of oak tree

Quercus douglasii, known as blue oak, is a species of oak endemic to California, common in the Coast Ranges and the foothills of the Sierra Nevada. It is California's most drought-tolerant deciduous oak, and is a dominant species in the blue oak woodland ecosystem. It is occasionally known as mountain oak and iron oak.

<span class="mw-page-title-main">Oak savanna</span> Lightly forested grassland where oak trees are dominant

An oak savanna is a type of savanna—or lightly forested grassland—where oaks are the dominant trees. The terms "oakery" or "woodlands" are also used commonly, though the former is more prevalent when referencing the Mediterranean area. These savannas were maintained historically through wildfires set by lightning, humans, grazing, low precipitation, and/or poor soil.

<span class="mw-page-title-main">Killarney National Park</span> National park in County Kerry, Ireland

Killarney National Park, near the town of Killarney, County Kerry, was the first national park in Ireland, created when the Muckross Estate was donated to the Irish Free State in 1932. The park has since been substantially expanded and encompasses over 102.89 km2 of diverse ecology, including the Lakes of Killarney, oak and yew woodlands of international importance, and mountain peaks. It has the only red deer herd on mainland Ireland and the most extensive covering of native forest remaining in Ireland. The park is of high ecological value because of the quality, diversity, and extensiveness of many of its habitats and the wide variety of species that they accommodate, some of which are rare. The park was designated a UNESCO Biosphere Reserve in 1981. The park forms part of a Special Area of Conservation and a Special Protection Area.

<span class="mw-page-title-main">Silvopasture</span> Agricultural practice of grazing animals in woodland

Silvopasture is the practice of integrating trees, forage, and the grazing of domesticated animals in a mutually beneficial way. It utilizes the principles of managed grazing, and it is one of several distinct forms of agroforestry.

<i>Dehesa</i> Multifunctional agro-sylvo-pastoral system

A dehesa is a multifunctional, agrosylvopastoral system and cultural landscape of southern and central Spain and southern Portugal; in Portugal, it is known as a montado. Its name comes from the Latin defensa (fenced), referring to land that was fenced and usually destined for pasture. Dehesas may be private or communal property. Used primarily for grazing, they produce a variety of products, including non-timber forest products such as wild game, mushrooms, honey, cork, and firewood. They are also used to raise the Spanish fighting bull and the source of jamón ibérico, the Iberian pig. The main tree component is oaks, usually holm and cork. Other oaks, including melojo and quejigo, may be used to form dehesa, the species utilized depending on geographical location and elevation. Dehesa is an anthropogenic system that provides not only a variety of foods, but also wildlife habitat for endangered species such as the Spanish imperial eagle.

<span class="mw-page-title-main">Browsing (herbivory)</span> Type of herbivory

Browsing is a type of herbivory in which a herbivore feeds on leaves, soft shoots, or fruits of high-growing, generally woody plants such as shrubs. This is contrasted with grazing, usually associated with animals feeding on grass or other lower vegetations. Alternatively, grazers are animals eating mainly grass, and browsers are animals eating mainly non-grasses, which include both woody and herbaceous dicots. In either case, an example of this dichotomy are goats and sheep.

<span class="mw-page-title-main">Oak forest</span> Forest with tree canopy dominated by oaks

An oak forest is a plant community with a tree canopy dominated by oaks. In terms of canopy closure, oak forests contain the most closed canopy, compared to oak savannas and oak woodlands.

<i>Erysiphe alphitoides</i> Species of fungus

Erysiphe alphitoides is a species of fungus which causes powdery mildew on oak trees.

<i>Quercus rotundifolia</i> Species of flowering plant in the family Fagaceae

Quercus rotundifolia, the holm oak or ballota oak, is an evergreen oak native to the western Mediterranean region, with the majority on the Iberian Peninsula and minor populations in Northwest Africa. The species was first described by Jean-Baptiste Lamarck in 1785. It is the typical species of the Iberian dehesa or montado, where its sweet-astringent acorns are a source of food for livestock, particularly the Iberian pig. Its acorns have been used for human nourishment since the Neolithic era. It is placed in section Ilex. Some authors described it as a subspecies of Quercus ilex.

<span class="mw-page-title-main">Wood-pasture hypothesis</span> Ecological theory

The wood-pasture hypothesis is a scientific hypothesis positing that open and semi-open pastures and wood-pastures formed the predominant type of landscape in post-glacial temperate Europe, rather than the common belief of primeval forests. The hypothesis proposes that such a landscape would be formed and maintained by large wild herbivores. Although others, including landscape ecologist Oliver Rackham, had previously expressed similar ideas, it was the Dutch researcher Frans Vera, who, in his 2000 book Grazing Ecology and Forest History, first developed a comprehensive framework for such ideas and formulated them into a theorem. Vera's proposals, although highly controversial, came at a time when the role grazers played in woodlands was increasingly being reconsidered, and are credited for ushering in a period of increased reassessment and interdisciplinary research in European conservation theory and practice. 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.

References

  1. ↑ Rucker, William. "The Failure of Oak Regeneration across Eastern Deciduous Forests".{{cite journal}}: Cite journal requires |journal= (help)
  2. ↑ Watt, A. S. (1919). "On the Causes of Failure of Natural Regeneration in British Oakwoods". Journal of Ecology. 7 (3/4): 173–203. doi:10.2307/2255275. ISSN   0022-0477.
  3. 1 2 3 4 Clark, F. Bryan (September 1992). "A Historical Perspective of Oak Regeneration". Southeastern Forest Experiment Station Oak Regeneration Symposium Proceedings: 3–13.
  4. 1 2 3 Rackham O. 2003. Ancient Woodland. Second Edition. Castlepoint Press. ISBN   1-89-760427-0 Pg. 295 – 296.
  5. 1 2 Shaw MW. 1974. The reproductive characteristics of oak. In: Morris MG, Perring F. 1974. The British Oak: its history and natural history. BSBI EW Classey Ltd.
  6. 1 2 3 4 5 Dey, Daniel C. (2014-10-23). "Sustaining Oak Forests in Eastern North America: Regeneration and Recruitment, the Pillars of Sustainability". Forest Science. 60 (5): 926–942. doi: 10.5849/forsci.13-114 . ISSN   0015-749X.
  7. 1 2 Demeter, László; Molnár, Ábel Péter; Öllerer, Kinga; Csóka, György; Kiš, Alen; Vadász, Csaba; Horváth, Ferenc; Molnár, Zsolt (2021-01-01). "Rethinking the natural regeneration failure of pedunculate oak: The pathogen mildew hypothesis". Biological Conservation. 253: 108928. doi:10.1016/j.biocon.2020.108928. ISSN  0006-3207.
  8. ↑ "Scouting for deer this fall? Scout for deer browse, too". Department of Ecosystem Science and Management. Retrieved 2022-11-29.
  9. ↑ Kuiters, A. T; Slim, P. A (2003-08-03). "Tree colonisation of abandoned arable land after 27 years of horse-grazing: the role of bramble as a facilitator of oak wood regeneration". Forest Ecology and Management. Forest Dynamics and Ungulate Herbivory : From Leaf to Landscape. 181 (1): 239–251. doi:10.1016/S0378-1127(03)00136-1. ISSN   0378-1127.
  10. 1 2 Bobiec, Andrzej; Reif, Albert; Öllerer, Kinga (2018-04-01). "Seeing the oakscape beyond the forest: a landscape approach to the oak regeneration in Europe". Landscape Ecology. 33 (4): 513–528. doi: 10.1007/s10980-018-0619-y . ISSN   1572-9761.
  11. ↑ Reif, Albert; Gärtner, Stefanie. "Natural regeneration of the deciduous oak species Pedunculate Oak (Quercus robur L.) and Sessile Oak (Quercrus petraea Liebl.) – a literature review with focus on wood pasture" (PDF). waldoekologie online (in German).
  12. 1 2 "The Future of Our Oak Forests: Can Fire and Fences Sustain Oak Forests for the Future?". National Park Service. 2011. Retrieved November 28, 2022.
  13. ↑ "Keystone Research Study: Restoration of Oak-Hicko… | Research | Upland Hardwood Ecology and Management | SRS". srs.fs.usda.gov. Retrieved 2022-12-09.
  14. ↑ US EPA, OA. "Climate Impacts on Forests". 19january2017snapshot.epa.gov. Retrieved 2022-12-09.
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