Sacred trees and groves in Germanic paganism and mythology

Trees hold a particular role in Germanic paganism and Germanic mythology, both as individuals (sacred trees) and in groups (sacred groves). The central role of trees in Germanic religion is noted in the earliest written reports about the Germanic peoples, with the Roman historian Tacitus stating that Germanic cult practices took place exclusively in groves rather than temples. Scholars consider that reverence for and rites performed at individual trees are derived from the mythological role of the world tree, Yggdrasil; onomastic and some historical evidence also connects individual deities to both groves and individual trees. After Christianisation, trees continue to play a significant role in the folk beliefs of the Germanic peoples.
The pagan Germanic peoples referred to holy places by a variety of terms and many of these terms variously referred to stones, groves, and temple structures. From Proto-Germanic *harugaz, a masculine noun, developed Old Norse hǫrgr meaning 'altar', Old English hearg 'altar', and Old High German harug meaning 'holy grove, holy stone'. According to philologist Vladimir Orel, the term was borrowed from the continental Celtic *karrikā or, alternately, the same non-Indo-European source as the Celtic source. A more general term for a sacred place was *wīhą reflected in Old Norse vé.
The Proto-Germanic masculine noun *nemedaz, which developed into Old Frankish nimid ('holy grove'), similarly either developed from, or is otherwise connected to, Gaulish nemeton, Latin sacellum and Old Irish nemed 'holiness'.
Another Proto-Germanic masculine noun *lauhaz, has given rise to words with a variety of meanings in various Germanic languages, including Anglo-Saxon lēah, 'meadow', Middle Low German lo, 'bush', and Old High German laoh, löh, 'grove, copse, bush'; it is cognate with Latin lūcus, 'sacred grove'.
Scandinavian placenames occur with the name of a deity compounded with lundr, 'grove', or viðr, 'wood'.
Sacred trees and groves are widely attested among the records of the ancient Germanic peoples. Some scholars hypothesize that they even predated the development of temples (according to Rudolf Simek, "there were sacred woods long before there were temples and altars").
In his Germania, Tacitus says that the Germanic peoples "consecrate woods and groves and they apply the name of gods to that mysterious presence which they see only with the eye of devotion", Tacitus describes the grove of the Semnones and refers to a castum nemus ('chaste grove') in which the image of the goddess Nerthus was hallowed, and other reports from the Roman period also refer to rites held by continental Germanic peoples in groves, including the sacrifices in forest clearings of survivors by the Cherusci after their victory at the Battle of the Teutoburg Forest, recounted by Tacitus in his Annals based on a report by Germanicus. Such groves were sometimes dedicated to a particular deity: in addition to the case of Nerthus, there was a silva Herculi sacra ('wood sacred to Hercules', an interpretatio romana) near the River Weser, and the Semnones reportedly held their rituals in honor of the regnator omnium deus ('god the ruler of all'). The scholar of Germanic religion Jan de Vries noted that placenames such as Frølund (Denmark), and Ullunda, Frösvi, and Mjärdevi (Sweden), in which the name of a deity is compounded with words meaning "grove" or "wood", suggest a continuation of the same practice, but are found almost exclusively in eastern Scandinavia; however, there is a Caill Tomair recorded near Dublin, an oak forest apparently sacred to Thor.
Reverence for individual trees among the Germanic peoples is a common theme in medieval Christian denunciations of backsliding into paganism. In some cases, such as Donar's Oak (according to legend, felled by Christian missionary Saint Boniface), these were associated with particular gods, and the association of individual trees with saints can be seen as a continuation of the tradition into modern times.
The Landnámabók, which describes the settlement of Iceland and dates from the 13th century, tells of a skáld by the name of Þórir snepill Ketilsson who, after his crew encountered and fended off raiding vikings, arrived in Iceland and founded a sacred grove there:
Sacred trees and groves leave few archaeological traces, but two such sites may have been identified, both in Sweden. A mouldering birch stump surrounded by animal bones, especially from brown bear and pig, was discovered under the church on Frösön in Jämtland in 1984. The finds have been carbon dated to the late Viking Age. Possible burnt offerings have been found on a hill at Lunda near Strängnäs in Södermanland; the archeologist Gunnar Andersson has argued that the combination of the finds and the placename—which can mean "the grove"—point to this being the remnants of a sacrificial grove. Scholars have proposed that publicly revered trees such as that at the temple in Uppsala were regarded as counterparts to the mythic world tree Yggdrasil.
The present section divides particularly notable examples into texts discussing the religious activities of the ancient Germanic peoples involving trees and groves (Germanic paganism) and their appearance in the myths of the Germanic peoples, particularly the North Germanic peoples (Germanic mythology).
Sacred trees and groves are mentioned throughout the history of the ancient Germanic people, from their earliest attestations among Roman scribes to references made by medieval Christian monks. Notable examples of sacred trees and groves in the historical record among the ancient Germanic peoples include the following:
In Norse mythology, the northernmost extension of Germanic mythology, several sacred trees are mentioned. The most prominent of these trees is the holy tree central to the cosmos, Yggdrasil. Prominent trees mentioned in Germanic mythology include the following:
After the nominal Christianisation of Anglo-Saxons and Saxons in the 7th and 8th centuries, many heathen practices centered on trees such as worship and giving of gifts were made punishable crimes. Despite this, 11th century accounts describe the continuation of votive offering deposition at trees in England and worship in groves in Saxony. English Penitential laws made in the 11th century explicitly forbid the use of a friðplott or friðgeard—a peaceful area around stones, trees or springs.
In later folklore, offerings are made to tree spirits such as Askafroa in Scandinavia and Germany, and the Women of One Tree Hill in England. In the latter case, gifts to the trees are explicitly linked with a returned gift of increased land fertility. There exists also a Scandinavian folk tradition of farmers making small offerings to a "warden tree", regarded as exercising a protective function over the family and land.