Sessile Oak (Quercus petraea)
The sessile oak is the rarer type of the two oak species domestic in Germany. Both are considered thermophile, require much sunlight and are resistant to drought. The sessile oak tends to be pushed towards regions which experience less precipitation, while the pedunculate oak (the second of the two common German oak species) also grows in the sporadically flooded areas around lowland rivers. In the “Heisterblock”, central Europe’s largest and oldest oak forest, in the German Spessart mountains, oaks grow slowly and thus in very narrow growth rings, creating outstandingly valuable oak veneer.
Oaks are ring-porous trees. This means that the tree builds mostly tracheae – wood vessels – at the beginning of the growing period. Only later in the summer, the typical hard oak wood is grown. Thus oak with narrow growth rings are visually very appealing, yet does not possess the typical hardness and durability for which the oak tree is known.
Oak lumber with thicker growth rings is particularly sturdy. Its tanning agents and phenolic compounds in the darker heartwood attribute to its durability. This is why oak is commonly used for construction, especially in shipbuilding and houses. Additionally, landing stages for steamers, stilt houses and in earlier years also railroad ties made up the variety of constructions in which oak was often used. The tanning agents in oak were also implemented in leather processing. Furthermore, oak is used for barrique barrels of premium red wine. Portuguese companies make cork from oak. Acorns, the fruits of the oak tree, used to be an important component of pig fodder. The pigs were driven into oak wood pastures with low treetops. Moreover, acorns serve are nutrition for wild animals, yet have also been used as a coffee substitute in times of need. Children commonly use acorns in their handicrafts during the fall season.
The fruits of the sessile oak are commonly arranged in a greater, grape-like infructescence. Its leaves have longer stems than the pedunculate oak’s leaves. The only other difference between the two types of oaks is the shape of their buds: While one has round buds, the other is teardrop shaped with five longer edges. They cannot be distinguished by their lumber. The spread of pathogens in oak wood is hindered through a number of factors. Poisonous substances in the heartwood contain germ growth, so does the high density of the broad beams – this is where the parenchyma of the tree actively fend off threats. Live oak wood is thus only rarely infected with fungi by very few and well adapted types like the sulphur polypore, the oak mazegill, and the Phellinus robustus. The perennial growth of the fungus is commonly found nearby woodpecker’s next excavations.
The Oak Processionary (Thaumetopoea processionea) reached disreputable fame as a thermophile moth which poses an immediate health threat to humans: Its caterpillars’ poisonous setae can cause significant rashes and allergic reactions in humans. The insect profits from the continuous climate change, acquiring habitats in new regions, while the formerly common oak leaf eating cockchafer disappears. Old oak trees sometimes harbor rare types of insect in duff excavations, which can only be found in trees that have reached a certain level of corrosion. These habitats are home to many insects that are found on the IUCN Red List of Threatened Species, such as the Great Capricorn Beetle, Lucanus Cervus, Flower Chafer, and the hermit beetle.