Temporal distribution of cattle and horses grazing on mountain rangelands partially invaded by Euphorbia polygalifolia

摘要

Horse stocking rates have increased significantly in the last decades in many summer rangelands of northern Spain traditionally used by cattle. Additionally, a major type of grassland within these rangelands (Festuca-Agrostis dominated grassland) is experiencing a noticeable invasion by the spurge species Euphorbia polygalifolia. The objective of this study was to compare diurnal grazing distribution of cattle and horses in order to provide information on the relationship between horse grazing patterns and pasture degradation. Temporal distribution of daylight grazing was quantified in eighteen cows and fifteen mares, from June to September 2004, in a representative summer rangeland of northern Spain. Mares spent more diurnal time grazing than cows(81.7 vs. 63.1%; P < 0.001). While cows showed two distinct grazing peaks, at early morning and late evening, mares had a more uniform daily grazing pattern. Finally, mares spent a higher proportion of their grazing time on grasslands prone to spurge invasion than cows (97.2 vs. 77.9; P = 0.001). These results suggest that horses could contribute to grassland overgrazing in this type of European mountain rangelands, favouring in this way spurge invasion.