Influencia del pastoreo en la cubierta vegetal y la geomorfodinámica en el transecto Depresión del Ebro-Pirineos

Extensive grazing by sheep and goats on fallow land and abandoned fields in the Ebro basin and the Pyrenees impedes the regeneration of vegetation cover by browsing and hoof threads. An association of characteristic patterns of geomorphodynamically highly dynamic animal trails and largely stable areas develops. In the High Pyrenees and the Pre-Pyrenees, even existing matorral scrubss hows clear sign of thinning, while morphodynamic activity increases. Areas affected by erosion rills expand especially where sheep trails encourage their development by very high runoff and erosion rates. Regarding their effects on vegetation cover development and geomorphodynarnic processes, sheep breeding subsidizing programmes by the European Union have to he critically assessed.El pastoreo extensivo de campos en barbecho o abandonados entre la Depresión Central del Ebro y el Pirineo Central impide la regeneración de la cubierta vegetal. Se desarrolla un patrón típico de areas con geomorfodinárnica muy activa en los senderos del ganado, junto a otras extensas superficies estables. En el Prepirineo y el Pirineo Central, se puede incluso observar la reducción de la cubierta de matorral ya existente, de forma simultánea al incremento de la geomorfodinámica. Las zonas afectadas por fuerte erosión lineal aumentan a lo largo de los senderos, ya que éstos muestran tasas de escorrentia superficial y de erosión muy altas. A causa de estos efectos, los incentivos comunitarios a la ganadería ovina han de ser revisados de forma crítica

Global application of an unoccupied aerial vehicle photogrammetry protocol for predicting aboveground biomass in non‐forest ecosystems

This is the final version. Available on open access from Wiley via the DOI in this recordData Availability Statement: The data collected for this publication, including aerial images, marker and plot coordinates and dry sample weights, as well as site and survey metadata, are available from the NERC Environmental Information Data Centre . Code for photogrammetric processing and statistical analysis is available at Zenodo Non-forest ecosystems, dominated by shrubs, grasses and herbaceous plants, provide ecosystem services including carbon sequestration and forage for grazing, and are highly sensitive to climatic changes. Yet these ecosystems are poorly represented in remotely sensed biomass products and are undersampled by in situ monitoring. Current global change threats emphasize the need for new tools to capture biomass change in non-forest ecosystems at appropriate scales. Here we developed and deployed a new protocol for photogrammetric height using unoccupied aerial vehicle (UAV) images to test its capability for delivering standardized measurements of biomass across a globally distributed field experiment. We assessed whether canopy height inferred from UAV photogrammetry allows the prediction of aboveground biomass (AGB) across low-stature plant species by conducting 38 photogrammetric surveys over 741 harvested plots to sample 50 species. We found mean canopy height was strongly predictive of AGB across species, with a median adjusted R2 of 0.87 (ranging from 0.46 to 0.99) and median prediction error from leave-one-out cross-validation of 3.9%. Biomass per-unit-of-height was similar within but different among, plant functional types. We found that photogrammetric reconstructions of canopy height were sensitive to wind speed but not sun elevation during surveys. We demonstrated that our photogrammetric approach produced generalizable measurements across growth forms and environmental settings and yielded accuracies as good as those obtained from in situ approaches. We demonstrate that using a standardized approach for UAV photogrammetry can deliver accurate AGB estimates across a wide range of dynamic and heterogeneous ecosystems. Many academic and land management institutions have the technical capacity to deploy these approaches over extents of 1–10 ha−1. Photogrammetric approaches could provide much-needed information required to calibrate and validate the vegetation models and satellite-derived biomass products that are essential to understand vulnerable and understudied non-forested ecosystems around the globe

Identification of gully-development processes in semi-arid NE-Spain

Gully erosion is considered to be one of the most important soil erosion processes, but its contribution to soil loss is still discussed. Despite the efforts made to understand the occurrence and dynamics of gullies, there is still a lack of knowledge on the factors leading to gully formation and growth. Within this study, the results from monitoring of gully-growth with high-resolution aerial photography are combined with the characterisation of the gully catchments with mapping of soil surface types and morphology and rainfall simulations. The results show an extremely high variability of gully-growth dynamics, being it independent from the size of the contributing catchment and rainfall characteristics. The distribution of soil surface types and their infiltration and erosion characteristics are identified as determinant for gully-growth. Additionally, their position related to the active gully-headcut is identified as determinant for the observed gully developmen

Short to medium - term gully development : Human activity and gully erosion variability in selected Spanish gully catchments

This study investigates how medium-term gully-development data differ from short-term data, and which factors are responsible for their spatial and temporal variability. Eight actively retreating bank gullies situated in Spanish basin landscapes were monitored for up to 11 years with high-resolution aerial photographs using unmanned remote-controlled platforms. The results of planimetric and volumetric change analysis using GIS and photogrammetry systems show a high variability of annual gully retreat rates both between gullies and between observation periods. The varying influences of land use and human activities with their positive or negative effects on runoff production and connectivity appears to play the most important role in these study areas, both for short-term variability and medium-term difference in gully development. The study demonstrates the importance of capturing spatially continuous, high-resolution three-dimensional data for detailed gully monitoring. It also confirms that short-term data are not representative of longer-term gully development, but they are still required to understand the processes - particularly human activity at varying time scales - causing gully-erosion variability

Accuracy of high-resolution photogrammetric measurements of gullies with contrasting morphology

Field techniques allow accurate direct measurements on gully geometry, even in three-dimensional (3D) coordinates. Accuracy and detail reproduction is limited mainly by experimental setup and density of measurements, and less so by the precision of the measuring equipment. In contrast, remote-sensing techniques permit the coverage of large study areas with a minimum of time and effort. However, the indirect measurements from imagery are known to depend on factors like image resolution, quality of ground control, vegetation cover and image evaluation technique, which strongly influence the measurement accuracy. The objective of the present study was to investigate to what extent the accuracy of 3D gully measurement using photogrammetric techniques depends on gully morphology. At a study site in the Bardenas Reales (Navarre, Spain), field measurements of cross-sections were taken for five gullies with contrasting morphology and dimensions and used as reference data for analysing the errors associated with a corresponding dataset obtained using small-format aerial photogrammetry whose pixel size on the ground is 16 mm. Results show that volumetric gully measurements by means of photogrammetric techniques are strongly affected by the gully morphology; in particular by its width/depth (W/D) ratio, because of the increasing sun-shadowing and sight-shadowing effects associated with narrower gullies. Only wide, shallow gullies are little affected by this problem. For gullies of an intermediate typology (W/D between 0·5 and 2·5), the accuracy of photogrammetric measurements will much depend on the time of day and the period of the year when the photographs are taken, and narrow/deep gullies (W/D <0·5) will be likely to be highly inaccurate at any time. Although this study was conducted with a large measurement scale for small (mostly ephemeral) gullies, the W/D ratios judged challenging for photogrammetric analysis in this study are also common for larger-sized gullies of the (permanent) bank gully typ

Gully erosion as a natural and human-induced hazard

status: publishe