The effects of climate change are influencing management practices in oak forests

Climate change is leading to more frequent variations in precipitation and rising average air temperatures, which are weakening the resilience of forest species and jeopardizing the health of forest stands, potentially causing their collapse. In Central Europe, this impact is particularly evident in the deterioration of Norway spruce. Additionally, a decline in vitality is noticeable in several other economically significant species, including Scots pine and various types of oak, particularly sessile oak.

Photo: A high-quality stand of sessile oak featuring abundant natural regeneration. VÚLHM archive, Research Station Opočno.

Oak, including both pedunculate and sessile species, is the second most widespread deciduous species in the Czech Republic. This tree species covers approximately 7.4% of the total forest area, which amounts to around 192,000 hectares. Furthermore, oaks contribute to 6.8% of the wood supply, equivalent to about 58.7 million cubic metres.

The current practices of silviculture for sessile oak were examined by scientists from the VÚLHM, v. v. i., at the Opočno Research Station, in the certified methodology titled Postupy hospodaření v porostech dubu zimního pro zmírnění nepříznivých dopadů klimatické změny (Management practices in sessile oak stands to mitigate adverse effects of environmental change).

When developing management guidelines, scientists considered the results of long-term research, published studies, and findings from a survey conducted as part of a project supported by the Grant Service of the Forests of the Czech Republic. This project, titled “Differentiation of habitats and management in pine, oak, and beech stands to mitigate the adverse impacts of environmental change,” (Diferenciace stanovišť a hospodaření v porostech borovice, dubu a buku pro zmírnění nepříznivých dopadů environmentální změny) was carried out between 2019 and 2021.

Photo: Left – When introducing oaks into existing stands, seed renewal can be effective. Successful bowl seeding has been achieved in areas that have been prepared through chipping and plowing. Right – However, increased temperatures and irregular rainfall in recent years have weakened many tree species, including oaks. As the stands age, there is a noticeable decrease in foliage and an increased susceptibility to damage from biotic factors. This information is archived in the VÚLHM records at VS Opočno.

The aim of this methodology is to provide framework recommendations for cultivating sessile oak in the context of ongoing climate change. This period is marked by increased variability in precipitation patterns and a gradual rise in average air temperatures. The methodology outlines procedures designed to optimize the potential of this tree species.

The procedures are presented as framework management guidelines for two stand types: “Oak of Normal Quality” and “Oak of High Quality.” These stand types are part of targeted management sets, which recommend that sessile oak should comprise at least 20% of the target tree species composition.

The specific objective of this methodology is to enhance the likelihood of successfully cultivating sessile oak in suitable habitats. It also outlines the habitat conditions where it is not feasible to replace sessile oak with sedge; in other conditions, both species can be managed.

Sessile oak is a light-loving tree that can thrive in environments with limited moisture availability. It has low soil requirements, and its growth is more influenced by the amount of available water than by soil fertility. Additionally, sessile oak demonstrates greater resistance to drought stress compared to other native commercial tree species, even at a young age.

Photo: If the status of the ungulate population aligns with the forest’s fertility, it is possible to fully harness the potential of natural regeneration; marginal cutting with a control fence, archive of the VÚLHM, VS Opočno.

Scientists have made crucial discoveries that include:

The deterioration of health primarily impacts older stands, particularly those over 60 years old. These older stands tend to be healthier when grown in mixtures rather than in monocultures. Additionally, stands located in sunny exposures, especially on steeper slopes and acidic sites, show poorer health.

Sprout forests (coppices) are more resistant against drought.

Oaks, growing in richer soils, exhibited less root development. In mixed stands of oak, pine, and beech, oak trees showed an increase in volume growth and enhanced drought resistance. However, oak roots tend to grow to shallower depths in these mixtures compared to when they are grown in monocultures.

Trees with a well-balanced canopy demonstrated better overall health. In terms of silvicultural interventions, one can only expect a short-term increase in under-canopy precipitation and an improvement in health status, which will occur only until the crown canopy is fully restored or the shrub layer develops.

Individuals affected by aphids and epicorms experience increased defoliation. Older monoculture stands located on flat terrain or gentle slopes are particularly vulnerable to aphid infestations.

Photo: Silvicultural interventions in oak stands are conducted through negative selection based on their location. Positive selection and the release of target trees typically occur at a later age, most often when the trees reach a height of 16 meters. This information is archived at the VÚLHM, VS Opočno.

Scientists recommend the following actions:

• During restoration efforts, prioritise the removal of individuals affected by aphids.
• In areas with high-density stands, carry out selective clearing at a height of 1 to 2 meters, targeting 10,000 to 14,000 individuals per hectare.
• In high-quality sprout forests (coppices) located in drier areas, maintain the low forest structure.

Implementing the procedures recommended in the methodology will optimize the use, restoration, and cultivation of sessile oak stands. This will enhance safety and, to some extent, improve the quality of production while also fulfilling other forest functions. Additionally, we can expect a reduction in accidental logging and a partial increase in value production. These improvements could lead to cost savings and an increase in forest yields, potentially amounting to tens of thousands of CZK per hectare for these stands.

The certified methodology titled Postupy hospodaření v porostech dubu zimního pro zmírnění nepříznivých dopadů klimatické změny (Management practices in sessile oak stands to mitigate adverse effects of environmental change) can be downloaded here.

Authors: Ing. Ondřej Špulák, Ph.D., doc. RNDr. Marian Slodičák, CSc., Ing. Jiří Novák, Ph.D., Ing. Jan Leugner, Ph.D.; VÚLHM, v. v. i., VS Opočno, e-mail: spulak@vulhmop.cz

Prepared according to the original by Jan Řezáč, VÚLHM, v. v. i., email: rezac@vulhm.cz