Role Of Tree Roots Research Articles

The Impact of Bamboo on Rainfall-Triggered Landslide Distribution at the Regional Scale: A Case Study from SE China

It is widely accepted that land use and land cover (LULC) is an important conditioning factor for landslide occurrence, especially when considering the role of tree roots in stabilizing slopes and consolidating the soil. However, it is still difficult to assess the impacts of a specific LULC type on landslide distribution. The objective of the present study is to reveal the relationship between bamboo and landslide distribution at the regional scale. We aim to answer the following question: do the areas covered by bamboo have a higher susceptibility to landslides? Wenzhou City in SE China was taken as the study area, and a landslide inventory containing 1725 shallow landslides was constructed. The generalized additive model (GAM) was employed to assess the significance of LULC and nine additional factors, all of which were generated using the GIS platform. The frequency ratio (FR) method was used to analyze and compare the landslide density in each LULC category. Machine learning models were applied to perform landslide susceptibility mapping of the region. The results show that in the Wenzhou region, LULC is the second most important factor for landslide occurrences after the slope factor, whereas bamboo has a relatively higher FR value than most other LULC categories. The accuracies of the landslide susceptibility maps obtained from the random forest and XGBoost models were 79.6% and 85.3%, respectively. Moreover, 23.8% and 25.5% of the bamboos were distributed in very-high- and high-susceptibility-level areas. The incidents and density of landslides in bamboo areas were significantly higher than those with debris flow and rock collapses, indicating a promotional effect of bamboo on slope failure in the study area. This work will improve our understanding regarding the role of geological and ecological conditions that affect slope stability, which may provide useful guidance for land use planning and landslide risk assessment and mitigation at the regional scale.

Weathering and soil production under trees growing on sandstones – The role of tree roots in soil formation

Rock weathering drives both landform formation and soil production/evolution. The less studied biological component of weathering and soil production caused by tree root systems is the main focus of the present study. Weathering by trees, which likely has been important in soil formation since the first trees emerged in the middle and late Devonian, is accomplished through both physical and biological means, like acids excreted by plants and exudates from associated bacterial communities. However, these processes are relatively poorly known. We assessed the impact of tree roots and associated microbiota on the potential level of biological weathering. Three research plots were selected in two sandstone regions in Poland. Two plots were in the Stołowe Mountains (Złotno, Batorów), a tableland built of Cretaceous sandstones. The third plot (Żegiestów) was in the Sącz Beskidy Mountains, the Carpathians. Soil samples were taken from tree root zones of Norway spruces from predefined sampling positions. Soils from non-tree control positions were also sampled. Soil samples were a subject of laboratory analyses which included the content of Fe and Al (amorphous and labile forms), carbon (C), nitrogen (N), and soil pH. The microbial functional diversity of soil microorganisms was determined using the Biolog (EcoPlate) system. Rock fragments were collected for mineralogical and a subject of optical microscopy and cathodoluminescence analyses in order to examine their mineralogical composition.Significant differences (pHolm-corrected < 0.05) between sample locations were found mostly for the Żegiestów plot: Soils at control positions differed from the crack and bulk soil sample positions in terms of C, N, C/N, and pH.Tree roots were able to develop a great variety of sizes and forms by following the existing net of bedrock discontinuities and hillslope microrelief. They developed along the most accessible surfaces, and caused rockcliff retreat and scree slope formation. These two features can be considered as initial stages of soil production. Trees add to the complexity of the soil system and allow formation of rhizospheric soils, and horizons rich in organic matter which are zones of a high microbial activity. However, as our study shows, rock cracks with roots cannot be considered as zones of microbial weathering. In addition, C content and microbial activity decreases with depth but can stay on a high level along living and dead roots. When entering rock fractures, they change the intensity of biomechanical weathering and soil properties. The highest biological activity of microorganisms was found in the control samples.Overall, tree roots do change the pattern of soil formation and explain the existing pattern of soil chemical properties, microbial activity, and potentially biological weathering intensity, and the intensity of those processes in correlation with root presence varies in space.

Pairing geophysical techniques improves understanding of the near-surface Critical Zone: Visualization of preferential routing of stemflow along coarse roots

There is compelling evidence from aboveground observations that trees considerably affect precipitation partitioning through the Critical Zone. However, due to the lack of appropriate methods, the role of root systems (the hidden half of trees) on redistributing precipitation and infiltration into and routing through the soil remains inadequately visualized and understood. Here, we designed a novel experiment to pair two non-invasive geophysical techniques, ground-penetrating radar (GPR) and electrical resistivity tomography (ERT), to trace stemflow through the soil in a forested hillslope after water was released on the trunk of an American beech (Fagus grandifolia Ehrh.) to induce stemflow. We used GPR to locate lateral coarse roots and GPR and ERT together to confirm the wetting areas in response to the non-uniform transport of stemflow. Signal changes between time-lapse geophysical images were used to reveal both the response time and location of stemflow infiltration into and redistribution through the soil. This first known study to investigate the subsurface routing of stemflow by combining GPR and ERT revealed that the belowground funneling of stemflow along laterally oriented coarse roots transported water 2.8 m downslope from the study tree in 30 min after stemflow was initiated. In situ excavation validated the distribution of lateral roots and lateral root-derived preferential flow paths identified in geophysical images, confirming the utility of pairing GPR and ERT to gain insights into the temporal dynamics and spatial distribution of subsurface routing of stemflow. The proposed method visualized and confirmed the funneling effect of roots on belowground water redistribution that contributed to subsurface lateral flow. Pairing GPR and ERT provides a useful combination of geophysical methods to advance our understanding of the complex interactions between plant and soil, such as the role of tree roots in soil hydrological process by revealing areas of funneling in the hidden part of the Critical Zone.

Species mixing boosts root yield in mangrove trees

Enhanced species richness can stimulate the productivity of plant communities; however, its effect on the belowground production of forests has scarcely been tested, despite the role of tree roots in carbon storage and ecosystem processes. Therefore, we tested for the effects of tree species richness on mangrove root biomass: thirty-two 6 m by 6 m plots were planted with zero (control), one, two or three species treatments of six-month-old Avicennia marina (A), Bruguiera gymnorrhiza (B) and Ceriops tagal (C). A monoculture of each species and the four possible combinations of the three species were used, with four replicate plots per treatment. Above- and belowground biomass was measured after three and four years' growth. In both years, the all-species mix (ABC) had significant overyielding of roots, suggesting complementarity mediated by differences in rhizosphere use amongst species. In year four, there was higher belowground than aboveground biomass in all but one treatment. Belowground biomass was strongly influenced by the presence of the most vigorously growing species, A. marina. These results demonstrate the potential for complementarity between fast- and slow-growing species to enhance belowground growth in mangrove forests, with implications for forest productivity and the potential for belowground carbon sequestration.

Do tree-based intercropping systems increase the diversity and stability of soil microbial communities?

There is a need for research projects to provide scientific arguments favouring a greater implementation of tree-based intercropping (TBI) systems in Canada’s rural landscape. We tested the hypothesis that TBI increases the beta-diversity and stability of soil microbial communities compared to conventional monocropping (CM) systems. Soil from TBI research plots in St-Rémi (Québec) and Guelph (Ontario) were intensively sampled along 56-point grid patterns and compared to soil sampled in a similar manner in adjacent CM systems. Phospholipid fatty acids (PLFAs) were extracted from each sample, purified and methylated, and subsequently analyzed by gas chromatography. The spatial heterogeneity (i.e., microbial beta-diversity) of whole PLFA profiles from each field were analyzed using multivariate statistical procedures (PCA and PERMDISP), and those of individual PLFAs were analyzed using Levene’s and Moses’ tests. Microbial beta-diversity, based on a measure of dispersion among PLFA profiles within each sampling grid, was significantly higher in the TBI than in the CM system at the St-Rémi site only. Multivariate multiple regression analyses failed to reveal any significant relationship between soil physico-chemical variables and shifts in soil PLFA profiles. We compared the concentrations of broad microbial groups in both cropping systems using Tukey’s test and found a higher incidence of arbuscular mycorrhizal fungi (AMF) in TBI systems at both sites, and a greater ratio of gram positive-to-gram negative bacteria in the TBI system at the St-Rémi site only. In order to determine microbial stability, we monitored changes in microbial biomass of bulked soil samples from the sampling grids after these had been exposed to varying concentrations of a heavy metal (Cu) contaminant. Data were then fitted to decreasing exponential functions and model parameters were used to derive an index of microbial stability. Higher microbial stability was found in the TBI than in the CM system at the St-Rémi site only. Because our hypotheses regarding soil microbial beta-diversity and stability were confirmed at only one of two sites, our conclusions warrant prudence and discretion. Future research should explore the possible role of tree roots in maintaining AMF and other beneficial soil organisms for alley crops.

Role of tree roots in slope stabilisation

The mechanical stabilisation of soil slopes by means of tree roots depends largely on the strength properties of the roots and their growth pattern within the soil. In particular areas, the selection of indigenous tree species on the basis of their root properties is an essential part of biotechnical slope protection. In order to determine the effects of tree roots on slope stabilisation in the mountainous area of Khao Luang, southern Thailand, seven tree species were studied. The distribution and penetration of the roots was established and their tensile strength and pull-out resistance determined. The paper evaluates the potential contribution of each of these species to slope stabilisation with reference to existing slope conditions.

TREES AND BUILDINGS—6. A Matter of Opinion—Settlement or Heave of Houses and the Role of Tree Roots

(1980). TREES AND BUILDINGS—6. A Matter of Opinion—Settlement or Heave of Houses and the Role of Tree Roots. Arboricultural Journal: Vol. 4, No. 1, pp. 24-30.