Monoculture forests formed by Fagus sylvatica L. belong to one of the most sensitive forest ecosystems, mainly at low altitudes. Cultivation of this species in mixed stands should reduce its sensitivity to drought in the vegetation period, which is why we researched the water balance in one pure-beech (i.e., monoculture) and one beech–oak–linden (i.e., mixed) forest. This research was carried out in Drahanská vrchovina in the Czech Republic in the period 2019–2021. The total precipitation was measured, together with its partitions (i.e., throughfall and stemflow), and the crown interception was also calculated. The total forest transpiration was calculated from the values measured on the sample trees. The values of each rainfall partition and transpiration (and their percentages) were compared. The rainfall partitions in the monoculture forest differed from those in the mixed forest. While, on average, the annual percentages of the throughfall, stemflow and crown interception in the monoculture forest were 63%, 6% and 31%, respectively, these partitions in the mixed forest were 76%, 2% and 22%, respectively. The crown interception was greater in the monoculture (31% of precipitation) and the effective precipitation (i.e., the sum of throughfall and stemflow) was greater in the mixed forest (78% of precipitation). The greatest differences (in each rainfall partition) between the monoculture and mixed forest were in the summer and winter. The throughfall was greater in the mixed forest (ca. 22% in the summer and ca. 12% in the winter), and the stemflow was greater in the monoculture forest (ca. 66% in the summer and ca. 51% in the winter). The mean annual transpiration was 318 (±52) mm in the monoculture and 451 (±58) mm in the mixed forest, i.e., about 99 (±65) mm more in the mixed forest than in the monoculture forest. The transpiration, in comparison with the effective precipitation, made up, on average, 70% of the effective precipitation in the monoculture forest. On the other hand, the transpiration reached 71% (in 2019), 74% (in 2020) and even 100% (in 2021) of the effective precipitation in the mixed forest. Our results show that an oak–beech–linden mixed forest can manage water better than a beech monoculture because more precipitation leaked through the mixed forest onto the soil than through the monoculture, especially via the throughfall in the summer. On the other hand, the amount of water that transpired was greater in the mixed forest than in the monoculture. However, the utilisation of the effective precipitation by trees was very similar in the monoculture in all three years, while, in the mixed forest, the utilisation of the effective water by trees increased, which may have been caused by the saturation of the deeper soil layers with water in the first two years of measurement. We can, Therefore, say that, at lower altitudes, it will be more suitable in the future to cultivate beech in mixed forests because of the assumed lack of water (mainly in early spring and summer).
Drought and high evapotranspiration demands can jeopardise trees and shrubs in windbreaks and habitat corridors, where they are more exposed to the effects of extreme weather than in the forest. This study utilised chlorophyll fluorescence to assess how the leaf-level physiological processes of 13 woody species typically planted in Czech habitat corridors responded to the effects of naturally occurring drought and their ability to recover after rain. Linear electron flow (LEF) responded only weakly to the drought, indicating high levels of photorespiration. Trees and shrubs increased the proportion of energy which was dissipated in a harmless way (ΦNPQ) during drought and decreased the proportion of energy dissipated through non-regulated processes (ΦNO). In this way, they reduced processes potentially leading to the production of reactive oxygen species. All species except Tilia cordata Mill. maintained high ΦNPQ even after its release from drought. Tilia cordata was potentially the most susceptible tree to drought due to its low LEF and high ΦNO. The most drought-resistant tree species appeared to be Acer campestre L. and shrubs such as Prunus spinosa L., Viburnum lantana L, and Crataegus monogyna L. These shrubs may be planted at the sunny edges of habitat corridors. The woody species identified as resistant to drought in habitat corridors may also be considered resistant in a warming climate or suitable for planting in the urban environment which is generally warmer and drier than in a forest.
<p>The density of forest canopy is affecting understory light conditions as well as soil water availability. Trees either suppress the herbaceous understory species by competition for resources or help them to cope with increased climatic warming by canopy shading. Nevertheless, little is known about the light &#215; water interaction on herbaceous species performance. In shaded environments, such as in the forest understory, the energy needed for stomatal opening may not be entirely offset by the imminent carbon gain, which may give a partial advantage to anisohydric species. The combination of shade and additional drought might damage the light-harvesting part of the photosynthetic systems because of the strong competition between species for light, which may be specifically critical for the anisohydric species. In this study, we compare seasonal water status, photosynthetic and fluorescence performance of 14 forest understorey herb species in open and closed forest stands, including perennials, annuals and grasses under favourable and mild drought-stress conditions.&#160;<br>We found midday and predawn water potentials are different between several different water-managing species which were divided into rather isohydric, rather anisohydric and neutral species. Most of the species were less drought-stressed during the midday in the closed forest compared to open forest. In contrast, all species under the sparse canopy kept the same or higher light-saturated photosynthetic yield than those growing in the closed forest. Few species growing under the open forest had lower values of intercellular CO2 concentration compared to those growing in the closed forest both under favourable and mild drought-stress conditions. We found that almost every individual species had a different seasonal variation in stomatal conductance values and led to differences in the photorespiration rates, which were mostly driven by light conditions. <br>We conclude that herbaceous species growing in the closed forest were less drought stress and the response of studied physiological traits to the combined effect of drought and light was found to be species-specific.</p>
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