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CURATOR
A pinboard by
AIMEE HALIM

PhD Student, University of Malaya

PINBOARD SUMMARY

Malaysia is experiencing high precipitation especially during the monsoon season. The hilly areas, specifically the cut slopes are prone to soil erosions. Erosion is happened by force when water hits and runs over the soil surface and this contributes to unstable condition of the slope. Not only soil erosion, soil deterioration including landslide will occur. There has been increasing focus in mitigating soil erosion via various engineering techniques. In order to promote the sustainable development, we provide more eco-sound solution to encounter this issue and reveal the most appropriate mechanism for slope stability. The establishment of vegetative elements has become an alternative way for slope stabilizing against erosion. It provides many advantages including low cost of establishment and maintenance, and the most importantly, self-sustainability. Our results underscore the significant influence of vegetation in controlling the soil hydrological properties of the slope. Remarkable changes in the soil structure were observed via increase the root systems in soil, enhancing the soil-root connectivity and subsequently increased the soil strength. On the other hand, suitable plants chosen for re-vegetation purpose may accelerate the process of vegetation restoration, suggesting that the slopes are to a greater extent regulated by plants. As the plant covers increases, this contributes to lowering the water content in soil and reduces the erosion rate on slope. Thus, the slope re-vegetation projects are suggested to be applied for slope stability. Although it cannot mitigate all risks, it can provide the long-term solution and beneficial for soil fertility improvement.

9 ITEMS PINNED

Gully erosion: A comparison of contributing factors in two catchments in South Africa

Abstract: Gully erosion is an environmental, agricultural and social problem requiring extensive research and mitigation actions to control. This study assesses the influence of factors contributing to gully erosion using Geographic Information System (GIS) and Information Value (InfVal) statistics from two catchments coded X12 and W55 in the Mpumalanga province of South Africa. Existing spatial data representing contributing factors; soil, geology, vegetation and land use were analyzed. Topographic variables were extracted from a 10 m Digital Elevation Model (DEM) interpolated from map contours, and gullies were mapped from aerial photos with 0.5 m spatial resolution. A zonal approach was used to extract the proportion of gullies in each of the contributing factor classes using GIS software packages, and InfVal weighting was performed to determine the influence of each class. Comparison of the results shows the variation in the level of influence of factors contributing to gully erosion. The findings in catchment X12 support a commonly held assumption that gully formation is influenced by duplex soils underlain by colluvium and alluvial deposits on a lower slope position where overland flow converges and accumulates, resulting in high soil moisture. Gullies were also influenced by soils developed over weathered granite, gneiss and ultramafic rocks. The influence of a granite rock was further highlighted in catchment W55 where there is a variable thickness of very deep Hutton dominant soil form and shallow Lithosols with sandy texture, on an area of moderate to steep slopes where overland flow converges and accumulates, with high stream power in overgrazed grassland. An understanding of these factors will assist future modelling of the vulnerability to gully erosion over a wider geographical area.

Pub.: 30 Mar '17, Pinned: 26 Sep '17

Do functional diversity and trait dominance determine carbon storage in an altered tropical landscape?

Abstract: Altered landscapes play a major role in biodiversity conservation and carbon (C) storage in the tropics. There is increasing evidence that C storage potential is controlled by tree functional diversity, but underlying mechanisms are debated. We analyzed the effects of trait dominance (mass-ratio hypothesis), species diversity, and trait variation (species complementarity) on C storage in the soils and vegetation of 20 agroforestry systems (AFS) and seven forested sites in Costa Rica. AFS consisted of organic and conventional coffee farms and pastures with trees. We used the community weighted mean (CWM) to measure trait dominance, and functional divergence (FDvar) to evaluate trait variation of wood densities (WD) and maximum heights (H max) of woody plants at each site. Species richness, the number of woody plants per hectare, and slope of the terrain were also considered as independent variables. Soil organic carbon (SOC) increased with higher CWMWD and with higher variability of H max ([Formula: see text]) across land-use types. Aboveground carbon (AGC) was controlled by the number of woody plants per hectare and by species richness. Our results suggest that dominant traits as well as species complementarity play an important role in determining C storage. Diverse, multilayered AFS which incorporate trees with high WD, combined with the conservation of remnant forests, can maximize C storage in the soils and vegetation of altered tropical landscapes.

Pub.: 19 May '17, Pinned: 26 Sep '17

Hydroclimatic and ecohydrological resistance/resilience conditions across tropical biomes of Costa Rica

Abstract: Water resources management in the tropics is challenged by climate variability and unregulated land use change and their impacts on the complex interactions between vegetation, soil, and atmosphere. This study focuses on the analysis of hydroclimatic and ecohydrological conditions across 6 major biomes in Costa Rica. Using the Budyko and the Tomer–Schilling frameworks, 31 reanalysis data points located across the Caribbean and Pacific domains were classified according to their ecohydrological resistance and resilience between 1989 and 2005. Observed data were used to evaluate the reanalysis products. Resistance was defined as the standard deviation in the water excess (Q/P), whereas resilience was defined as the standard deviation of the energy (AET/PET) to the water excess. A strong orographic separation was obtained between the water-limited Pacific slope and the energy-limited Caribbean slope. The Caribbean slope is characterized by low resistance and high resilience to changes in the hydroclimatic conditions, with small relative changes in water excess (−18% to 2.0%), whereas the Northern Pacific slope has high resistance and low resilience and exhibited strong changes in water excess (−34% to 0%). Some regions of the Northern Pacific region covered by lower and premontane forests have recently suffered significant increments in the dryness index (PET/P). This study demonstrates the need for national–regional strategies to effectively optimize water use efficiency and water storage and to include a climate vulnerability component in future water management plans.

Pub.: 07 Jun '17, Pinned: 26 Sep '17

Landscape controls on long-term runoff in subhumid heterogeneous Boreal Plains catchments

Abstract: We compared median runoff (R) and precipitation (P) relationships over 25 years from 20 mesoscale (50 to 5,000 km2) catchments on the Boreal Plains, Alberta, Canada, to understand controls on water sink and source dynamics in water-limited, low-relief northern environments. Long-term catchment R and runoff efficiency (RP−1) were low and varied spatially by over an order of magnitude (3 to 119 mm/year, 1 to 27%). Intercatchment differences were not associated with small variations in climate. The partitioning of P into evapotranspiration (ET) and R instead reflected the interplay between underlying glacial deposit texture, overlying soil-vegetation land cover, and regional slope. Correlation and principal component analyses results show that peatland-swamp wetlands were the major source areas of water. The lowest estimates of median annual catchment ET (321 to 395 mm) and greatest R (60 to 119 mm, 13 to 27% of P) were observed in low-relief, peatland-swamp dominated catchments, within both fine-textured clay-plain and coarse-textured glacial deposits. In contrast, open-water wetlands and deciduous-mixedwood forest land covers acted as water sinks, and less catchment R was observed with increases in proportional coverage of these land covers. In catchments dominated by hummocky moraines, long-term runoff was restricted to 10 mm/year, or 2% of P. This reflects the poor surface-drainage networks and slightly greater regional slope of the fine-textured glacial deposit, coupled with the large soil-water and depression storage and higher actual ET of associated shallow open-water marsh wetland and deciduous-forest land covers. This intercatchment study enhances current conceptual frameworks for predicting water yield in the Boreal Plains based on the sink and source functions of glacial landforms and soil-vegetation land covers. It offers the capability within this hydro-geoclimatic region to design reclaimed catchments with desired hydrological functionality and associated tolerances to climate or land-use changes and inform land management decisions based on effective catchment-scale conceptual understanding.

Pub.: 09 Jun '17, Pinned: 26 Sep '17

Characteristics and applications of ecological soil substrate for rocky slope vegetation in cold and high-altitude areas.

Abstract: Ecological restoration of steep rocky slopes generated by road cutting is usually difficult especially, in the cold and high-altitude environment, which is unfavorable for the growth of vegetation. With the focus on slope vegetation, an ecological soil substrate, synthesized with polyacrylamide (PAM), carboxymethyl cellulose (CMC), and Fly ash (FA) as the main components, was developed for spray seeding on the rocky slopes in cold and high-altitude regions, to provide a favorable environment for vegetation growth. The compositional effect of individual compound addition on the growth of vegetation and substrate properties was investigated using an orthogonal array experimental design. Based on ANOVA and orthogonal analysis, an ecological soil substrate (PCF) with 400g/m(3) PAM, 600g/m(3) CMC, 1500g/m(3) FA, and 50L/m(3) of water was decided as the optimum PCF substrate. The optimum PCF substrate was then sprayed on a steep rocky slope in a cold and high-altitude region in Sichuan, China, for two years. The vegetation, as well as the physico-chemical properties, nutrient content, and mechanical properties of the field soil substrate, were examined over this duration. The field verification shows that the proposed PCF substrate is able to provide desirable nutrient contents and excellent physical and mechanical properties for vegetating the steep rocky slopes in cold and high-altitude areas.

Pub.: 30 Jul '17, Pinned: 26 Sep '17

Methods to estimate changes in soil water for phenotyping root activity in the field

Abstract: Abstract Background and aims There is an urgent need to develop new high throughput approaches to phenotype roots in the field. Excavating roots to make direct measurements is labour intensive. An alternative to excavation is to measure soil drying profiles and to infer root activity. Methods We grew 23 lines of wheat in 2013, 2014 and 2015. In each year we estimated soil water profiles with electrical resistance tomography (ERT), electromagnetic inductance (EMI), penetrometer measurements and measurements of soil water content. We determined the relationships between the measured variable and soil water content and matric potential. Results We found that ERT and penetrometer measurements were closely related to soil matric potential and produced the best discrimination between wheat lines. We found genotypic differences in depth of water uptake in soil water profiles and in the extent of surface drying. Conclusions Penetrometer measurements can provide a reliable approach to comparing soil drying profiles by different wheat lines, and genotypic rankings are repeatable across years. EMI, which is more sensitive to soil water content than matric potential, and is less effective in drier soils than the penetrometer or ERT, nevertheless can be used to rapidly screen large populations for differences in root activity. Abstract Background and aims There is an urgent need to develop new high throughput approaches to phenotype roots in the field. Excavating roots to make direct measurements is labour intensive. An alternative to excavation is to measure soil drying profiles and to infer root activity. Background and aimsThere is an urgent need to develop new high throughput approaches to phenotype roots in the field. Excavating roots to make direct measurements is labour intensive. An alternative to excavation is to measure soil drying profiles and to infer root activity. Methods We grew 23 lines of wheat in 2013, 2014 and 2015. In each year we estimated soil water profiles with electrical resistance tomography (ERT), electromagnetic inductance (EMI), penetrometer measurements and measurements of soil water content. We determined the relationships between the measured variable and soil water content and matric potential. MethodsWe grew 23 lines of wheat in 2013, 2014 and 2015. In each year we estimated soil water profiles with electrical resistance tomography (ERT), electromagnetic inductance (EMI), penetrometer measurements and measurements of soil water content. We determined the relationships between the measured variable and soil water content and matric potential. Results We found that ERT and penetrometer measurements were closely related to soil matric potential and produced the best discrimination between wheat lines. We found genotypic differences in depth of water uptake in soil water profiles and in the extent of surface drying. ResultsWe found that ERT and penetrometer measurements were closely related to soil matric potential and produced the best discrimination between wheat lines. We found genotypic differences in depth of water uptake in soil water profiles and in the extent of surface drying. Conclusions Penetrometer measurements can provide a reliable approach to comparing soil drying profiles by different wheat lines, and genotypic rankings are repeatable across years. EMI, which is more sensitive to soil water content than matric potential, and is less effective in drier soils than the penetrometer or ERT, nevertheless can be used to rapidly screen large populations for differences in root activity. ConclusionsPenetrometer measurements can provide a reliable approach to comparing soil drying profiles by different wheat lines, and genotypic rankings are repeatable across years. EMI, which is more sensitive to soil water content than matric potential, and is less effective in drier soils than the penetrometer or ERT, nevertheless can be used to rapidly screen large populations for differences in root activity.

Pub.: 12 Jan '17, Pinned: 26 Sep '17

Root tensile strength and root distribution of typical Mediterranean plant species and their contribution to soil shear strength

Abstract: In Mediterranean environments, gully erosion is responsible for large soil losses. It has since long been recognized that slopes under vegetation are much more resistant to soil erosion processes compared to bare soils and improve slope stability. Planting or preserving vegetation in areas vulnerable to erosion is therefore considered to be a very effective soil erosion control measure. Re-vegetation strategies for erosion control rely in most cases on the effects of the above-ground biomass in reducing water erosion rates, whereas the role of the below-ground biomass is often neglected or underestimated. While the above-ground biomass can temporally disappear in semi-arid environments, roots may still be present underground and play an important role in protecting the topsoil from being eroded. In order to evaluate the potential of plant species growing in Mediterranean environments to prevent shallow mass movements on gully or terrace walls, the root reinforcement effect of 25 typical Mediterranean matorral species (i.e. shrubs, grasses herbs, small trees) was assessed, using the simple perpendicular model of Wu et al. (Can Geotech J 16:19–33, 1979). As little information is available on Mediterranean plant root characteristics, root distribution data were collected in SE-Spain and root tensile strength tests were conducted in the laboratory. The power root tensile strength–root diameter relationships depend on plant species. The results show that the shrubs Salsola genistoides Juss. Ex Poir. and Atriplex halimus L. have the strongest roots, followed by the grass Brachypodium retusum (Pers.) Beauv. The shrubs Nerium oleander L. and the grass Avenula bromoides (Gouan) H. Scholz have the weakest roots in tension. Root area ratio for the 0–0.1 m topsoil ranges from 0.08% for the grass Piptatherum miliaceum (L.) Coss to 0.8% for the tree Tamarix canariensis Willd. The rush Juncus acutus L. provides the maximum soil reinforcement to the topsoil by its roots (i.e. 304 kPa). Grasses also increase soil shear strength significantly (up to 244 kPa in the 0–0.1 m topsoil for Brachypodium retusum (Pers.) Beauv.). The shrubs Retama sphaerocarpa (L.) Boiss. and Anthyllis cytisoides L. are increasing soil shear strength to a large extent as well (up to 134 and 160 kPa respectively in the 0–0.10 m topsoil). Whereas grasses and the rush Juncus acutus L. increase soil shear strength in the topsoil (0–0.10 m) to a large extent, the shrubs Anthyllis cytisoides (L.), Retama sphaerocarpa (L.) Boiss., Salsola genistoides Juss. Ex Poir. and Atriplex halimus L. strongly reinforce the soil to a greater depth (0–0.5 m). As other studies reported that Wu’s model overestimates root cohesion values, reported root cohesion values in this study are maximum values. Nevertheless, the calculated cohesion values are used to rank species according to their potential to reinforce the soil.

Pub.: 21 Feb '08, Pinned: 26 Sep '17

Desirable plant root traits for protecting natural and engineered slopes against landslides

Abstract: Slope stability models traditionally use simple indicators of root system structure and strength when vegetation is included as a factor. However, additional root system traits should be considered when managing vegetated slopes to avoid shallow substrate mass movement. Traits including root distribution, length, orientation and diameter are recognized as influencing soil fixation, but do not consider the spatial and temporal dimensions of roots within a system. Thick roots act like soil nails on slopes and the spatial position of these thick roots determines the arrangement of the associated thin roots. Thin roots act in tension during failure on slopes and if they traverse the potential shear zone, provide a major contribution in protecting against landslides. We discuss how root traits change depending on ontogeny and climate, how traits are affected by the local soil environment and the types of plastic responses expressed by the plant. How a landslide engineer can use this information when considering slope stability and management strategies is discussed, along with perspectives for future research. This review encompasses many ideas, data and concepts presented at the Second International Conference ‘Ground Bio- and Eco-engineering: The Use of Vegetation to Improve Slope Stability—ICGBE2’ held at Beijing, China, 14–18 July 2008. Several papers from this conference are published in this edition of Plant and Soil.

Pub.: 23 Sep '09, Pinned: 26 Sep '17

Ecological mitigation of hillslope instability: ten key issues facing researchers and practitioners

Abstract: Plants alter their environment in a number of ways. With correct management, plant communities can positively impact soil degradation processes such as surface erosion and shallow landslides. However, there are major gaps in our understanding of physical and ecological processes on hillslopes, and the application of research to restoration and engineering projects.To identify the key issues of concern to researchers and practitioners involved in designing and implementing projects to mitigate hillslope instability, we organized a discussion during the Third International Conference on Soil Bio- and Eco-Engineering: The Use of Vegetation to Improve Slope Stability, Vancouver, Canada, July 2012. The facilitators asked delegates to answer three questions: (i) what do practitioners need from science? (ii) what are some of the key knowledge gaps? (iii) what ideas do you have for future collaborative research projects between practitioners and researchers? From this discussion, ten key issues were identified, considered as the kernel of future studies concerning the impact of vegetation on slope stability and erosion processes. Each issue is described and a discussion at the end of this paper addresses how we can augment the use of ecological engineering techniques for mitigating slope instability.We show that through fundamental and applied research in related fields (e.g., soil formation and biogeochemistry, hydrology and microbial ecology), reliable data can be obtained for use by practitioners seeking adapted solutions for a given site. Through fieldwork, accessible databases, modelling and collaborative projects, awareness and acceptance of the use of plant material in slope restoration projects should increase significantly, particularly in the civil and geotechnical communities.

Pub.: 11 Mar '14, Pinned: 26 Sep '17