QUERCUS ILEX: CHARACTERISTICS, HABITAT, CULTIVATION, CARE, USES - BIOLOGY - 2024

Quercus ilex is a species of evergreen tree belonging to the Fagaceae family. Known as holm oak, holm oak, chaparro, alzina, artea, enciño or azinheira, it is a forest species native to the Mediterranean region.

It is a tree that reaches 15-25 m in height, up to 30 m depending on its maturity, which can reach 700 years. With a dense and leafy crown, as well as intense green foliage, it is a characteristic floral species of the Iberian Peninsula, cultivated in different environments since ancient times.

Quercus ilex. Source: Picamaderos

Under certain climatic or edaphic conditions it remains in a shrubby state, but develops a dense and extensive root system. The short, robust and straight stem has a thin, smooth and grayish bark when young, brownish and fissured in adult specimens.

The wide and closed crown is oval in its natural state, with numerous branches mid-height above ground level. The firm and thick branches are arranged in an ascending position in the middle and upper part of the crown.

Holm oak is an undemanding tree in relation to the type of soil, although it prefers porous and deep soils. It requires full sun exposure or half shade, being highly resistant to eventual drought, hot environments and frost.

In its initial growth phase it is very sensitive to adapt to transplant conditions, while developing a robust root system. On the other hand, it tolerates pruning very well, since in the wild it easily sprouts its root after fires or severe felling.

Its wood is solid, compact and hard, being used in the manufacture of water resistant tools and in carpentry in general. The bark contains useful tannins for leather tanning, in addition the leaves and acorns are used for medicinal purposes. Firewood is effective for obtaining charcoal due to its great caloric power.

General characteristics

Appearance

- Subgenus: Quercus.

- Section: Quercus.

- Species: Quercus ilex L.

Subspecies

- Quercus ilex subsp. ilex: this species is characterized by its lanceolate leaves with 7-14 pairs of secondary veins. Likewise, it is distributed to the south of France, along the Cantabrian coast and the Mediterranean coast, Italy and the Balearic Islands.

- Quercus ilex subsp. ballota: the leaves tend to be rounded with 5-8 pairs of secondary veins, adapted to the continental climate and of acorns with greater commercial value. It is located in the interior regions of the European continent and in the Balearic Islands.

Quercus ilex leaves. Source: Krzysztof Ziarnek, Kenraiz

Habitat and distribution

Quercus ilex is a rustic species that is not very demanding in terms of soil quality, however, it sits on sandy loam soils. It usually forms pure forests or large meadows, being strongly resistant to dry environments and extreme temperatures.

Under natural conditions it is located in coastal environments with a mild climate, as well as in continental areas up to 1,400 meters above sea level and with an extreme climate. It is a species that adapts to summer climates, frosts down to -12 ºC, prolonged droughts and high solar radiation.

On the other hand, it adapts to urban conditions or spaces with a certain degree of environmental pollution on forests or urban bushes. Due to the ability to thrive on moist, but well-drained soils, it has occasionally thrived in areas such as the Canary Island laurel.

The Quercus ilex ballota subspecies is more tolerant of cold climates, drought and high temperatures, so it adapts to continental regions. It is generally more rustic than the Quercus ilex ilex subspecies, which prefers littoral environments and is more demanding in terms of humidity.

Holm oaks are one of the most common tree species on the Iberian Peninsula and the Balearic Islands. It is part of unique forests or meadows, in association with climbing plants or thick bushes on a wide variety of soils.

In general, they are distributed throughout the Mediterranean region, from where it was transferred to the Canary Islands. At present it is sporadically found in the wild in Gran Canaria, La Gomera, La Palma and Tenerife.

Quercus ilex forest. Source: pixabay.com

Cultivation and care

Reproduction

Holm oaks are monoecious species that reproduce effectively through seeds (sexual reproduction) as well as root shoots (vegetative reproduction). It blooms during the months of March-May or June-July, after a period of stress. When there is an average of 20 ºC and 10 hours of solar radiation per day.

Pollen dispersal and subsequent pollination is anemophilic, that is, it occurs thanks to the intervention of the wind as the main pollinating agent. In Quercus ilex, autogamy or self-pollination occurs in the same individual, and allogamy or reproduction occurs between different individuals.

The fruits are dry and indehiscent acorns, light green when young and dark brown when ripe. The oaks start their production at 15-20 years of age, and their fruits usually ripen during the months of October-November.

Multiplication

As already noted, Quercus ilex multiplies both by seeds and by root shoots during the spring. Seed propagation requires the selection of fresh material from healthy and productive plants, free of pests or diseases.

Sowing is done under nursery conditions in polyethylene bags using a fertile, well-draining and disinfected substrate. The seeds, of 1-2 units, are placed in the center of the humid substrate trying to cover with a thin layer of soil.

Subsequently, the sowing surface is sprinkled with sulfur or copper, in order to prevent the appearance of fungal diseases or pests. It is covered again with loose substrate and irrigated this time with a sprinkler system, avoiding flooding the substrate.

The containers are placed under 65% polyshade, ensuring adequate humidity and temperature conditions. In this way, the seeds will start the germination process between 45-60 days after sowing.

Propagation through root shoots is done by selecting the vigorous buds that appear at the base of the mother plant. To separate the shoots, it is necessary to make a ditch around it and extract it with a clean cut avoiding damaging the roots.

A natural rooting agent or phytohormone can be added to this seedling, and it is sown in a polyethylene bag with fertile and humid substrate. Under nursery conditions, providing constant lighting, humidity and temperature, the plants will establish in a few weeks.

Quercus ilex acorns. Source: Meneerke bloem

Care

Holm oaks grow in open spaces with full sun exposure or semi-shade. They do not develop invasive roots, but their planting is recommended 5-6 m apart from buildings, pipes, paved roads or other shrub species.

They adapt to flat terrain, loose and well-drained soils, of limestone or siliceous origin with a good content of organic matter. For the establishment of the plantation, the use of a fertile substrate with good moisture retention and 30% perlite is recommended.

This particular species is tolerant to certain periods of drought, without reaching extremes of lack of moisture. Indeed, during the summer it requires frequent watering, preventing the ground from drying out completely.

For its establishment and development, a frequency of irrigation is required every 4-5 days. In any case, it is advisable to maintain constant monitoring of the soil humidity, mainly in the development, flowering and fruiting phases.

Regarding the fertilization needs, the application of organic fertilizers is carried out during the spring until early autumn. The oak responds satisfactorily to the application of fertilizers with a high content of phosphorus and nitrogen during the productive phase.

Maintenance and sanitation pruning can be done in late winter. This practice consists of eliminating dry, weak or diseased branches, as well as trimming branches that show irregular or uneven growth.

Plagues and diseases

This species is generally very resistant to attack by pests or diseases. However, it is susceptible to attack by defoliating caterpillars, such as Tortrix viridana and Lymantria dispar, as well as the dry oak.

Tortrix viridana or piral of oak and holm oak is a nocturnal lepidopteran of the Tortricidae family whose caterpillars cause defoliation. Lymantria dispar is a lepidopteran of the Erebidae family with a high invasive potential and constitutes a serious threat to forest species.

Holm oak drying is caused by the phytopathogenic fungus Phytophthora cinnamomi, which causes holm oak to decay and die. Symptoms usually occur when the plant suffers from extreme water deficit, environmental contamination, or improper handling.

An effective agronomic management is vital to obtain a strong and vigorous specimen. For this, the effective application of irrigation is essential and supply the nutritional needs with organic fertilizers, avoiding severe pruning.

Holm oak (Quercus ilex) produces these fruits. Source: Miguel Angel Masegosa Martínez

Applications

Wood

Good quality, fine-grained, hard, heavy and resistant wood is used for the manufacture of agricultural implements and general carpentry. It is ideal for manufacturing parts that support continuous handling such as carts, plows or parquets, as well as hydraulic tools, beams or pillars.

The firewood of the oak is very valuable for obtaining charcoal. Furthermore, the bark contains tannins used for the leather tanning process, especially in the Moroccan region.

Ornamental

Quercus ilex is a tree of landscape importance and is one of the main species in rural meadows and around cities. Indeed, holm oaks are decorative plants that provide excellent shade in open spaces, being widely used to make bonsai.

Nutritional

Acorns are used as a food supplement to feed Iberian pigs. They are also used for human consumption, roasted as nuts, or ground to obtain flour for the production of bakery products.

Medicinal

Holm oak contains certain organic compounds such as tannins, gallic acid and querecitanic acid that provide it with astringent and antiseptic medicinal properties. In addition, acorns have starches, fats, sugars and tannins used for medicinal or food use.

Generally the parts used for medicinal use are the bark, the leaves and the acorns, whether they are dried, crushed or ground. The decoctions of the bark are used as an antidiarrheal; as a Vulnerary it is used to relieve wounds, hemorrhages or nosebleeds; It is also applied topically to the scalp to control dandruff.

References

1. Rodríguez, C., & Muñoz, B. (2009). Phenology of Quercus ilex L. and Quercus suber L. in a meadow in the center of the peninsula. Madrid: Polytechnic University of Madrid-University School of Technical Forestry Engineering.
2. Quercus ilex L. (2013) Iberian Trees. Recovered in: arbolesibericos.es
3. Quercus ilex. Holm oak, holm oak (2018) List of species. TreeApp. Recovered at: arbolapp.es
4. Quercus ilex. (2019,). Wikipedia, The Free Encyclopedia. Recovered at: es.wikipedia.org
5. Sánchez de Lorenzo-Cáceres, JM (2014) Quercus ilex L. Ornamental Trees. Spanish Ornamental Flora. Recovered in: arbolesornamentales.es
6. Sáenz De Rivas, C. (1967). Studies on Quercus ilex L. and Quercus rotundifolia Lamk. An. Inst. Bot. AJ Cavanilles, 25, 245-262.
7. Villar-Salvador, P., Nicolás-Peragón, JL, Heredia-Guerrero, N., & Uscola-Fernández, M. (2013). Quercus ilex L. Production and management of seeds and forest plants, 2, 226-249.