Does Scots pine affect Douglas fir growth?
In recent years, forests in the Czech Republic have been facing extensive calamities, primarily in spruce and pine stands. Given the climate change scenarios, it will be necessary to explore potential partial (but not predominant) substitution for declining commercial tree species within the spectrum of introduced tree species. Douglas-fir is considered one of the promising introduced tree species, and its representation in our forests, currently at around 0.2%, could potentially increase to up to 5% in the future.
The Douglas fir has a wide ecological range and is generally considered to be relatively drought-tolerant. However, its growth is negatively impacted by drought. It outperforms many of our native economic trees in volume production and provides high-quality wood raw material in various habitats.
The impact of Douglas fir on the native understory flora’s biodiversity is minimal to negligible. However, its effect on the fauna has not been extensively studied, and there is speculation about a potential negative impact on bird species. Douglas fir also has a more positive effect on the soil compared to native conifers, but it can also lead to increased nitrification
Its invasive potential is likely minimal in a wide range of habitats, but it is still important to monitor in the future, particularly in nutrient-poor habitats with sparse canopy density.
The latest trend in forestry involves establishing and cultivating stands with a variety of tree species. This is expected to make the stands more resistant to the negative impacts of global climate change. It is recommended to grow Douglas fir in mixtures to prevent monoculture cultivation of this introduced tree. This will help prevent its significant intake of nutrients during rapid growth, among other benefits.
The Douglas fir is only partially shade-tolerant. In certain habitats, it may overgrow when mixed with faster-growing native trees in its youth. Without proper intervention, its quality and vitality could deteriorate or even disappear.
To verify this assumption, scientists from the Opočno Research Station, FGMRI (VÚLHM, v. v. i.), experimentally evaluated the effect of educational interventions on the growth response and prosperity of Douglas firs originating from natural regeneration in habitats relatively poor in terms of nutrients and precipitation. The researchers assessed the development in a stand with a dominant representation of Douglas fir and a stand where Douglas fir is mixed with Scots pine.
Obtained results were published in the paper Růst douglasky tisolisté v mlazinách v závislosti na výchově a konkurenčním tlaku borovice lesní na živinově chudších stanovištích (Growth of young Douglas-fir stands in relation to thinning and competitive pressure from Scots pine on nutrient-poor sites), Reports of Forestry Research (Zprávy lesnického výzkumu), No. 1/2024.
The paper was created in the frame of solution of grant project NAZV QK22020045 „The potential of non-native tree species for forest management in the Czech Republic“(„Potenciál geograficky nepůvodních druhů dřevin v lesním hospodářství ČR“.
Based on the results obtained, the scientists drew the following conclusions:
In nutrient-poor environments, young stands of Douglas fir (young stands and growths) face significant competition from pine, which shows slower growth at this stage.
To grow healthy and high-quality Douglas fir trees in a mixed area with Scots pine, it’s essential to effectively remove competing vegetation and allow the Douglas fir to thrive during its growth stage.
Failing to do so may result in high mortality rates for Douglas fir as Scots pine take over.
In these areas, it is suggested to concentrate on supporting the growth of high-quality Douglas fir trees initially, with the intention of later artificially encouraging the development of valuable assortments. Introducing a large number of Douglas fir trees in a mixture with pine carries the risk of causing the pine trees to become loose and overgrown simultaneously.
The recommended and easier option for artificial regeneration is creating a mixed stands.
Early silviculture interventions are also crucial for achieving the desired tree slimness.
Insufficient or delayed interventions lead to rapid tree thinning, resulting in low stability for both individual trees and entire stands.
Due to the low competitiveness of Douglas fir in the early growth stages in poor habitats, it can be stated that the risk of its invasive spread is negligible here.
The paper Růst douglasky tisolisté v mlazinách v závislosti na výchově a konkurenčním tlaku borovice lesní na živinově chudších stanovištích (Growth of young Douglas-fir stands in relation to thinning and competitive pressure from Scots pine on nutrient-poor sites) can be downloaded here.
Authors: David Dušek, Jiří Novák, FGMRI (VÚLHM, v. v. i.), Opočno Research Station, e-mail: dusek@vulhmop.cz
According to the original, prepared by: Ing. Jan Řezáč, e-mail: rezac@vulhm.cz
Illustrative photo: Examples of forest stands with young Douglas fir, FGMRI (VÚLHM) archive