Systematic variation of soil infiltration rates within and between the components of the vegetation mosaic in an Australian desert landscape

Vegetation mosaics have commonly been thought to include two principal zones with distinctly different hydrology: relatively bare and impermeable runoff source zones (intergroves) and more strongly absorbing vegetated runon zones (groves). However, the data required to verify the internal uniformity of hydrologic response within these components of mosaic landscapes have been lacking, as have data on the nature (abrupt or gradational) of the boundaries between them. This study examines the degree of internal uniformity of key soil properties in the intergroves and groves of an Australian vegetation mosaic. Infiltration rates, soil water content, shear strength, bulk density and texture were determined at intervals of 1·5–2·5 m across several grove–intergrove cycles of an Australian banded shrubland. Results demonstrate that order‐of‐magnitude variability in soil infiltration rates can occur across intergroves, with lesser variation in groves. Patterns of infiltration are systematically related to slope position. Rates are relatively high in the uppermost parts of the intergrove, and fall to low values only in the lowermost intergrove where soils are mechanically strong. Infiltration rates increase rapidly from the lowermost intergrove to reach maxima within the upper to middle grove, from where rates once again decline toward the next intergrove. However, there is only a gradational change in infiltration rates across the pioneer zone–grove boundary, which is the sharpest of the mosaic boundaries when identified using plant cover data. Hydrologic models built on the presumption that mapped plant cover units are equally distinct hydrologically may need to be refined to incorporate the presence of systematic internal variability of infiltration rates and gradational change in soil hydraulic properties. Copyright © 2002 John Wiley & Sons, Ltd.     

Response of fish communities in rivers subjected to a high sediment load

Erosion and sediment yield are a significant problem in the Guadalquivir River basin. Such phenomena are largely driven by a land use devoted to intensive cultivation of olive trees, with a large socioeconomic influence in Andalusia. This sediment overload in rivers causes serious impacts on all fluvial ecosystem components.In this study we assess the chronic effect of sediment yield on fish communities at 104 river sites located in two different sub-catchments – the Bembézar and Guadajoz rivers – both with different lithological composition and erosion rates. Sediment yield was estimated using a semi-quantitative Factorial Score Model (FSM), developed specifically for Spanish rivers. The fish populations of both basins were evaluated in composition and abundances by the study of Fernández-Delgado et al., 2014. The influence of sediment yield on the fish community was analyzed using General Additive Models.The sediment yield was higher in the Guadajoz basin (921 T/Km2 per year) than in Bembézar (701 T/Km2 per year). In the former, fish communities were poorer in both fish density and diversity, with Luciobarbus sclateri as the only substantially present species and a significant relationship between sediment yield and load, and fish density. In contrast, in the Bembézar basin, sediment yield was correlated with total fish density, including Luciobarbus sclateri, Pseudochondrostoma willkommii, Cobitis paludica, Iberochondrostoma lemmingii, Anaecypris hispanica, and Cyprinus carpio. Intermediate values of sediment yield led to maximum densities, while those higher decreased the density of these species.     

Riparian vegetation dynamics across two different landscapes along the river Cauvery in the Kodagu region of Western Ghats

Decades of commercial planting and other anthropogenic processes are posing a threat to the riparian landscapes of the Cauvery river basin, which supports a high floral diversity. Despite this, the habitats in the upstream sections of the River Cauvery are still intact, as they are located in sacred groves. To understand the dynamism of riparian forests exposed to anthropogenic pressures, the upstream stretch of Cauvery extending from Kushalanagara to Talacauvery (~102 km) was categorized into two landscapes: agro ecosystem and sacred (i.e. preserved). The tree species were sampled using belt transects at 5 km intervals and the regeneration status of endemic species assessed using quadrats. A total of 128 species belonging to 47 families, and representing 1,590 individuals, was observed. Amongst them, 65% of unique species were exclusive to sacred landscapes. A rarefaction plot confirmed higher species richness for the sacred compared to the agro ecosystem landscapes, and diversity indices with more evenness in distribution were evident in sacred landscapes. A significant loss of endemic tree species in the agro ecosystem landscapes was found. Overall, this study demonstrates that an intense biotic pressure in terms of plantations and other anthropogenic activities have altered the species composition of the riparian zone in non-sacred areas. A permanent policy implication is required for the conservation of riparian buffers to avoid further ecosystem degradation and loss of biodiversity.     

SACRED GROVES FOR FOREST CONSERVATION IN GHANA'S COASTAL SAVANNAS: ASSESSING ECOLOGICAL AND SOCIAL DIMENSIONS

Despite recent interest in sacred (fetish) groves as remnant forests, few studies have investigated their sustainability and conservation role in West Africa. This article employs a Geographical Information Systems (GIS) analysis of time series images (1960‐98), comprehensive social surveys and ecological field methods to evaluate four sacred groves and eight unprotected tree stands in the coastal savanna of Ghana and compare these with vegetation in the distant forested hinterland. There were strong similarities and substantial differences in tree species between different sacred groves, and between these and the unprotected stands and proximate deciduous forests. In addition, far fewer tree losses were documented in the sacred groves than in the local unprotected stands. Although these sacred groves were on average only partially representative of deciduous forest vegetation, their stronger sustainability compared with unprotected tree stands may be important to consider in detail for conservation.     

Rill and ephemeral gully erosion in a small olive grove catchment in Spain: Interactions between management and conservation measures

Concentrated flow erosion in Mediterranean cultivated areas is considered a major process of land degradation. Rills and ephemeral gullies in a 6.4 ha olive orchard catchment located in an intensive commercial farm, which could represent a common degradation scenario in hilly areas, were measured and compared with the sediment loads at the outlet. Four GPS survey campaigns were carried out between March 2009 and March 2014, for periods with cumulative precipitation ranging between 728 and 121 mm. Chopped pruning residues were kept on the lanes during campaigns 2–4, whereas a grass cover crop was seeded in campaign 4. Rainfall, runoff and sediment loads were measured in a flume gauge station at the catchment outlet. The ratio of concentrated flow erosion to catchment sediment load varied between 1.0 and 35.0. Total concentrated flow erosion ranged between 25.0 and 0.1 t ha⁻¹. Rill erosion was the dominant process on ephemeral gullies for three campaigns, with a mean contribution to the total concentrated flow erosion of 55%. Rills clearly followed tractor tracks along the most parallel lanes to the maximum slope. Therefore, a change in traffic direction would be helpful to reduce the connectivity, controlled by the spatial distribution of rows and lanes in the farm. Olive plantation distributions should prioritize hydrological criteria to adapt traffic patterns in olive farms, as long as the tractor manoeuvrability and risk of overturning are not adversely affected. Although the farmer only kept the cover crop for one campaign, it proved to be an efficient measure for interrupting rills along the lanes, whereas pruning residues were effective for the control of interrill erosion. On-site application of pruning residues reduced their handling and transport costs, while increasing the soil fertility and soil cover. However, guidelines for the efficient application of pruning residues are still necessary in terms of residue rates and orientation.     

Influence of DEM resolution on modelling hydrological connectivity in a complex agricultural catchment with woody crops

Digital elevation model (DEM) resolution influences hydrological simulation. However, its influence when modelling hydrological connectivity (HC) in woody crops remains to be seen. We assessed surface topography, microtopography and HC in an agricultural sub‐catchment (27.4 ha) using six photogrammetry‐derived DEMs with 0.03, 0.05, 0.1, 0.2, 0.5 and 1 m cell sizes. Land uses included vineyards, olive groves, cereal fields, and forestry patches. We ran an updated version of Borselli's HC index (IC) using the D‐Infinity approach. We assessed HC in woody crops at high spatial resolution for the first time. After analysing the differences in the contributing area, the flow width, the soil roughness, the convergence index and the IC (normalised and non‐normalised) at different scales (hillslope, land uses and compartments, ephemeral gullies, depositional areas and the sub‐catchment outlet) and accounting for the field vertical components, we propose an optimum DEM resolution (0.2 m) to improve modelling of structural HC in woody crops. The modelled hydrological features at this threshold resolution matched well with the geomorphic features associated with the short‐ and medium‐term patterns of soil redistribution. Higher DEM resolutions, especially at 0.03 and 0.05 m, introduced bias in the input data and the IC computations. Finally, we observed good agreement between the outputs at the lowest resolution, 1 × 1 m, and the long‐term soil redistribution patterns (functional connectivity). Copyright © 2017 John Wiley & Sons, Ltd.