Preparatory stands of European larch provide an above-average cooling effect
The recovery and establishment of a stand are critical phases during which significant losses in species diversity often occur. A key factor in these processes is the influence of the stand’s microclimate, especially in large areas affected by disasters. To mitigate extreme conditions, preparatory trees are utilised, with European larch being a particularly promising species.
Photo: A preparatory stand of larch in an open area, with an older birch in the background, Krušné hory (Ore Mountains). Author Jan Řezáč
Forest stands have a significant microclimatic effect, particularly in reducing the occurrence of late frosts in spring (in May). Late frosts can persist for extended periods in clear-cut areas during late spring. In contrast, under a loose canopy, these frosts are notably dampened in both temperature and duration. A tighter canopy (full canopy) in forest stands can eliminate the occurrence of late frosts.
Additionally, forest stands moderate daily and seasonal temperature variations when compared to open, uncovered areas, such as clear-cuts. While the absolute air humidity in forest stands may not differ significantly from that in open areas, the relative air humidity is higher in forest stands due to lower air temperatures. This difference can become particularly significant during drought stress, especially when the upper ecological cover of the stand above the regeneration is absent.
The positive impact of ecological cover has been well-documented in past studies involving replacement tree species, such as Norway spruce. This ecological benefit has been used for underplanting target species (like European beech or silver fir) to mitigate the effects of various microclimatic extremes. This effect is especially pronounced in higher-altitude forest habitats, where the positive microclimatic influence can outweigh the reduced light availability caused by shading from the canopy of replacement trees.
Photo: A preparatory larch stand enhances natural conditions at specific sites, Krušné hory (Ore Mountains). Author Jan Řezáč
The impact of preparatory stands of European larch on the microclimate parameters of their habitat was investigated by scientists from various institutions as part of the project QK21010335 LARIXUTOR, titled “„Možnosti využití modřínu opadavého v českých lesích pod dopadem GKZ“ (Possibilities of using European larch in Czech Forests under the impact of GKZ). The National Agency for Agricultural Research (NAZV MZe) funded this project.
The findings were summarized and published in the paper titled “Mikroklimatický účinek přípravného porostu modřínu opadavého (Larix decidua Mill.) na teplotu a vlhkost vzduchu stanoviště ve srovnání s dalšími pěstebně-ekologickými variantami obnovy lesa” [Microclimatic effect of a preparatory forest stand of European larch (Larix decidua Mill.) on air temperature and air humidity of a forest site in comparison with other approaches to forest regeneration], which appeared in the journal Zprávy lesnického výzkumu (Reports of Forestry Research).
In the study, researchers compared the development of temperature and humidity in a vertical gradient across four different forest restoration methods: A) A preparatory stand of deciduous larch alone, B) A preparatory stand of European larch undergoing a two-phase restoration, which is underplanted with forest beech in its loosened form, C) Large-scale catastrophic clear-cutting, and D) Restoration using lateral ecological cover with a renewed leafy vegetation cover.
The researchers conducted a comparison of microclimatic conditions at the Huzová–Dalov research area (49.8067878N, 17.3598294E) during the peak of summer, from July 6 to September 10, 2024. They focused on the daily temperature peak occurring between 10:00 AM and 3:00 PM to capture the full microclimatic extremes of each restoration option and assess their potential for temperature and humidity moderation.
Photo: Older preparatory larch stand; beneath it, more favourable microclimatic conditions exist for planting more demanding target tree species. Krušné hory (Ore Mountains), author Jan Řezáč
The results clearly demonstrated that European larch has the ability to mitigate temperature extremes in open areas, such as those affected by post-disaster clear-cutting, by providing a cooling effect during the midday temperature peak of the growing season. However, as other expert studies indicate, this capability is not uniform across all forest tree species; it can vary significantly or may even be absent in some cases.
For instance, Norway spruce, during its growth phase from young-growth stand to pole-stage stand, does not possess this cooling ability, regardless of the intensity of stand tending. In contrast, silver birch exhibits a strong cooling effect across various levels of stand tending.
The cooling ability of different broadleaved tree species varies significantly. For example, research indicates that small-leaved linden has a notably higher cooling effect compared to black locust, while sessile oak demonstrates greater cooling capacity than European hornbeam. Additionally, the cooling ability of European beech is significantly more developed than that of oak, with daily maximum temperature differences reaching up to 6 °C.
Evidence of European larch’s above-average cooling effect is highlighted by observations from a mixed canopy of larch, oak, and hornbeam. During the midday temperature peak in August, the surface temperature of the upper crown layer was recorded at 25.1 °C for larch, compared to 26.9 °C for oak and 29.7 °C for hornbeam, demonstrating that larch remained significantly cooler than both broadleaved species.
Photo: An older stand of European larch with silver fir trees successfully growing beneath it, Krušné hory (Ore Mountains). Author Jan Řezáč
The ability of trees to provide a cooling effect in the environment during peak midday temperatures in the growing season is primarily influenced by their transpiration intensity, but it is also significantly affected by their albedo. European larch, known for its high albedo, plays a crucial role in this context, especially regarding the temperature balance of landscapes facing the impacts of global climate change. The concern arises when larch is replaced by other evergreen coniferous trees.
The paper titled “Mikroklimatický účinek přípravného porostu modřínu opadavého (Larix decidua Mill.) na teplotu a vlhkost vzduchu stanoviště ve srovnání s dalšími pěstebně-ekologickými variantami obnovy lesa” [Microclimatic effect of a preparatory forest stand of European larch (Larix decidua Mill.) on air temperature and air humidity of a forest site in comparison with other approaches to forest regeneration] can be downloaded here.
Authors: Pavel Bednář, Výzkumný ústav lesního hospodářství a myslivosti, v. v. i., Výzkumná stanice Opočno, Mendelova univerzita v Brně, Lesnická a dřevařská fakulta, Ústav ekologie lesa; Štěpánka Řehořková, Ústav výzkumu globální změny Akademie věd ČR, v. v. i., Brno, kontakt: e-mail: pavelbednar13@seznam.cz
Prepared according to the original by Jan Řezáč, VÚLHM, v. v. i., e-mail: rezac@vulhm.cz