Does red oak affect the quality of forest soils?

The red oak is a significant introduced tree species in the Czech Republic. In 2010, the area covered by this tree species in the Czech Republic was about 6,000 hectares, with a total supply of approximately 900,000 m3. By 2018, the area had increased to 6,101 hectares and the total supply had risen to 1,138,000 m3. This tree has been commonly used for park improvements and recultivation, although it is not considered to be a productive tree species. Originally, it was intended to replace domestic oak species threatened by tracheomycosis. The debate over whether it is appropriate to plant red oak in Czech forests has been ongoing for several decades, with many scientific institutions contributing their knowledge to the discussion.

The paper “The Influence of Red Oak on the State of Forest Soils” (Vliv dubu červeného na stav lesních půd) was written by scientists from the Faculty of Forestry and Wood Science at the Czech University of Applied Sciences in Prague. It was published in the journal “Reports of Forestry Research 2/2024.” The paper is part of the project NAZV QK22020045: “The potential of geographically non-native tree species in the forestry of the Czech Republic” (Potenciál geograficky nepůvodních druhů dřevin v lesním hospodářství ČR).

The scientists aimed to study how red oak affects the humus forms and the top layer of mineral soil compared to beech-dominated natural stands.

Red oak is known for thriving in arid and semi-arid areas as it can handle low levels of rainfall from its seedling stage.

Additionally, it can tolerate very low temperatures, withstanding as low as -30°C or even -40°C. It is also not affected by late spring frosts as it sprouts later than native oaks.

Red oak usually grows in Europe at altitudes of 250–800 meters with an annual rainfall of only 500–550 mm per year. It is known for its resistance to polluted air.

The root system of the red oak is similar to that of native oaks. A young sapling has a well-developed root, which can reach a length of up to 70 cm in five years, later forming a heart-shaped root system.

As it develops further, it produces strong lateral roots that extend a considerable distance from the stem, creating a strong root system that resists wind damage.

The root system grows throughout the growing season without interruption in the summer, making it suitable for places with a high risk of soil erosion and degradation.

Red oak has the ability to naturally regenerate easily, but it often needs human intervention through forestry practices. Because of this, it is sometimes considered an invasive species.

The success of its seed germination depends on the type of habitat. In less fertile habitats, it can become overly abundant and invasive, while in richer soils, it is less likely to be invasive.

Red oak has lower nutrient requirements and can tolerate acidic sandy soils as well as heavier clay soils. It does not thrive in calcium-rich soils, although its tolerance for higher calcium content seems to increase with age.

Areas with consistently high groundwater levels are also not suitable for its growth. The most suitable habitat for red oak cultivation consists of deeper, slightly acidic soils with minimal calcium content.

The analysis of the impact on soil condition has not yet shown a significant improvement effect of red oak in forest stands.

It is more suitable for the restoration of devastated and degraded areas due to its higher tolerance to environmental stresses.

Red oak can significantly contribute to the restoration of forest soils and their specific character. Thanks to its nature as a preparatory tree species, it can be very beneficial, even in the case of afforestation of agricultural land.

The scientists concluded that:

• Red oak does not significantly improve conditions in deciduous forests.
• Compared to native climax trees and stands dominated by beech, red oak leads to slight acidification, decreased soil reaction, worsened soil sorption complex of base saturation, and reduced nutrient content.
• Red oak can still be used in the restoration of significantly degraded and devastated sites and in creating stands that are more resistant to ongoing climate changes. It can thus play a more significant role than before in addressing the growing problems of native deciduous tree species.

Please find the link below to download the paper on “Influence of red oak on the state of forest soils” (Vliv dubu červeného na stav lesních půd).

Authors: Vilém Podrázský, Ivo Kupka, Czech University of Life Sciences, Faculty of Forestry and Wood, e-mail: kupka@fld.czu.cz

Original prepared by Jan Řezáč, VÚLHM, v. v. i., e-mail: rezac@vulhm.cz

Illustration photo: Stands of red oak in the Czech Republic, VÚLHM archive