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Abstract

The difference in days between the images was not very important to diminish the effects of phenology. The images were geometrically and atmospherically corrected by means of a mixed method based on physical and statistical procedures. Using the NDVI images we calculated coefficients of variation within a radius of 150 meters by means of a moving window procedure. This approach allows to analyse the spatial variability of the vegetation cover. The results show that the NDVI changes have not been important in the analysed period. Nevertheless, there are noticeable modifications in the spatial structure and variability of the NDVI, resulted in homogenization/heterogenisation processes. The forests located at high altitudes have suffered the most important homogenisation processes. On the contrary at low elevated areas the spatial diversity of the vegetation activity increases. Nevertheless, in these areas some spatial differences are found: the heterogenisation of the vegetation cover is less important in the forests than in areas dominated by sclerophyllous vegetation and those characterised by the transition from shrubs to forests. These areas show less mature successional phases after the land abandonment and they are characterised by an increase of the spatial heterogeneity of the NDVI.

Una revisión sobre las tierras abandonadas en España: de los paisajes locales a las estrategias globales de gestión

“…La diversidad de especies vegetales parece estar condicionada por la edad de abandono, el mosaico vegetal circundante, las perturbaciones humanas tras el abandono, y los factores abióticos, especialmente litología, fertilidad de suelo, topoecología y clima. La edad de abandono condiciona la estructura del paisaje y su biodiversidad; se ha observado que habitualmente en las fases iniciales hay un incremento de la riqueza de especies, mientras que en fases posteriores la riqueza se reduce muchísimo (Suárez-Seoane et al, 2002;Vicente-Serrano et al, 2006). Montalvo et al (1993) señalan el rápido incremento en la riqueza de especies como consecuencia de la entrada de herbáceas en un campo recién abandonado.…”

Temporal Indices of Landscape Change: A Proposal to Measure Variations in the Conservation Status of Vegetation at Fine Resolution

“…In general terms these changes reflect a recovery in the vegetation, but also a homogenization of the landscape. This phenomenon has also been reported in areas of the Pyrenees, where the homogenization has been linked to the expansion of mature woodlands and with processes prior to heterogenization [19]. These authors link both phenomena to the elimination of preceding crops, which paves the way to the colonization of pioneering species and communities related to the natural succession and, subsequently, to the stability of the mature woodland.…”

“…The disappearance of dryland crops, shepherd-led livestock, certain management practices (e.g., irrigation of pasture, burning of gorse), and the replacement of small livestock (sheep and goats) with large animals (horses and cows) were the most important changes in the factors influencing the landscape. In general terms, the phenomenon of plants recolonizing a territory as a consequence of crop farming and other traditional practices being abandoned is one that has been observed in various parts of Europe [19,33,34].…”

“…Specifically, near the study area, attempts have been made to study the recent dynamics of the landscape through aerial photographs [16]. Based on the previous attempts to detect changes in the vegetation cover, various indices have been proposed, most of them based on remote sensing data for land-cover change analysis, using measurements derived from infrared radiation and Landsat images [15,[17][18][19][20]. Some of these indices are widely used, such as the normalized difference vegetation index (NDVI) [21] and the enhanced vegetation index (EVI) [22].…”

Analysis of the Temporal and Spatial Evolution of Recovery and Degradation Processes in Vegetated Areas Using a Time Series of Landsat TM Images (1986-2011): Central Region of Chihuahua, Mexico

“…Several studies have identified changes in vegetation dynamics on a continental (Slayback et al, 2003;Delbart et al, 2006), local and regional (Andreu et al, 2007;Martínez-Villalta et al, 2008;Alatorre, et al, 2011;Vicente-Serrano et al, 2012) scale in recent decades. Most of the changes have been caused by human activity, particularly deforestation (Giglio et al, 2006;Achard et al, 2002;DeFries et al, 2002) and forest fires (Riano et al, 2007); moreover, rural abandonment and the consequent marginalization of some regions has contributed to the process of vegetation recovery (Sluiter & de Jong, 2007;Vicente-Serrano et al, 2004;Vicente-Serrano et al, 2006a, 2006bLasanta & Vicente-Serrano, 2007;Alatorre et al, 2011;). In addition, several studies have shown that current climate trends may favor an increase in vegetation activity in different ecosystems around the world (Myneni et al, 1998;Kawabata et al, 2001;Lucht et al, 2002) or a decrease of it (Maselli, 2004;Sarris et al, 2007;Vicente-Serrano et al, 2012).…”