Dynamics and Vertical Distribution of Roots in European Beech Forests and Douglas Fir Plantations in Bulgaria

Understanding the Complexity of Drought within the Soil Profile in Beech Ecosystems on Their Lower Altitudinal Limit in Slovakia

Due to the ongoing climate change, decreasing amounts of available water and increasing evapotranspiration during the growing season may impact the stability of some beech ecosystems at lower altitudes. This paper aims to evaluate the risk of drought from a meteorological point of view and the subsequent response in soil hydrology throughout hydrological years 2015 and 2016 in beech forests situated in Central Slovakia. Precipitation sufficiency was assessed by means of a climate irrigation index (CII). Hydrological modelling was carried out using GLOBAL, the simulation model of water movement in a soil profile with an emphasis on the root zone. The greatest drought risk occurs during the summer, when the ecosystem suffers from long periods of water deficiency according to the CII (>20 days). The water content in specific soil horizons responds differently to changing meteorological situations. Simulations indicated a later decrease (approx. 5 days) of the water content in the B horizon (main root zone) compared with the A horizon. Drought lasts longer in deeper layers and retreats only in the case of long-lasting rainfall. Sudden heavy rainfall has proven ineffective at moistening the entire soil profile and impacts only the upper few centimetres while the main root zone suffers from water shortage.

Bioaccumulation of potentially toxic elements within the soil-plant system in Central Balkan region: analysis of the forest ecosystem capacity to mediate toxic elements

The accumulation of potentially toxic elements (PTEs) in terrestrial ecosystems has become a global concern, as PTEs may exert a wide range of negative impacts on forest's ecological state due to local or transboundary pollution. Forest vegetation and soil display great potential as means of coping with the accumulation mechanisms, absorption and dissolving the pollutants. Therefore, it is crucial to study the transfer of PTEs across these basic components of the forest ecosystem. Investigation on the PTEs concentrations in the soil-plant system in relatively non-polluted environment of Central Balkan National Park (Sredna Stara Planina Mountain) provides more information about the role of the forest patterns and soil properties for the bioaccumulation processes in the context of ecosystem services concept. In this paper, the transfer of PTEs in soil-plant system in relatively clean environment is studied in order to assess and map the ecosystem capacity of different types of forest ecosystems to mediate toxic elements. Based on in situ observations and sampling, the PTEs concentrations in soil and aboveground vegetation were analyzed. The potential of each forest type to reduce the impact of PTEs and bioaccumulation as an indicator of ecosystem service is also discussed. The GIS analysis supports the study by creating a common database and setting the basis for ecosystem services assessment. The generated maps represent areas where the forest ecosystems have the greatest capacity to provide related ecosystem service and mediate toxic elements. The bioaccumulation of PTEs in forest territories results in medium to low rates and higher supply capacity is not present at any spatial unit as the accumulation process is focused in the soil. The obtained results highlight the ecological importance of soil in terms of acting as a buffer against pollution, especially in areas with intensive road traffic.

Scaling the Roots Mechanical Reinforcement in Plantation of Cunninghamia R. Br in Southwest China

The degree of mechanical reinforcement provided by plants depends upon its roots distribution in the soil and mechanical properties of the roots. The mechanical properties and distribution of root traits (root diameter and number) in the soil of the standing forest depends on the tree stem diameter. This variation of root traits with tree stem diameter is rarely investigated. Therefore, this research presents the effect of tree stem diameter on the distribution of roots within the standing forest of Cunninghamia in the Longchi forest area, Sichuan province, China. In this area, shallow landslides take place frequently. We investigated the root traits distribution for trees with different stem diameters, i.e., 220 mm, 320 mm, 450 mm, and 468 mm, to show the variation of roots distribution in the soil with stem diameter. The root architecture of the selected trees was studied by step excavation method of the root zone accompanied by measurement of roots physical parameters (roots number and roots diameter) and indices (roots area ratio (RAR), roots biomass (RB), and roots distribution (RD)). We measured the root’s maximum tensile strength by performing root tensile tests in the laboratory. The field and laboratory-measured data were used to estimate the root cohesion by both the commonly used model Wu and Waldron Model (WWM) and Fiber Bundle Model (FBM). The results indicate that the tree stem diameter correlates with both the root distribution and the tensile strength. The roots indices and root cohesion increase with an increase in the diameter of the tree. Further, RAR decreases with depth and lateral distance from the tree stem, while the maximum values were observed in 10 cm depth. The relationship between roots diameter and roots tensile strength is established through power function. The average root cohesion estimated for a tree with stem diameter 220 mm is 23 kPa, 29 kPa for 320 mm, 54 kPa for 450 mm, and 63 kPa for 460 mm. This effect of stem diameter on the increase of soil shear resistance should be considered while evaluating the stability of slopes in standing forests. The comparison between WWM and FBM for investigated species suggests that WWM estimates the cohesion values greater than FBM by 65%.