The potential for using goats to control Genista scorpius shrubs in European black pine stands

Abstract

The depopulation of mountain areas, and with it the reduction of livestock that traditionally grazed on the spontaneous vegetation in these areas, has led to an uncontrolled development of bushes and, consequently, a significant increase in fuel material and fire risk. In the Mediterranean basin, Genista scorpius (L.) DC. is of particular interest due to its invasive nature and ignition capacity. In this respect, the value of using goats for the control of G. scorpius, according to grazing season and stocking density, was studied while taking into consideration the morphological alterations, regrowth, surviving and flowering rates of bushes growing on a European black pine ( Pinus nigra Arn. subsp. nigra) revegetated slope of the Pyrenees (Spain). Goat grazing clearly affected G. scorpius' performance. While stocking density showed an effect on morphological modifications, the plant was much affected by the time of grazing. G. scorpius bushes in grazed areas, both in spring and autumn, showed a mean survival and regrowth rate (69% and 49%, respectively), intermediate but significantly different from that of bushes consumed only in autumn (58% and 32%) or in spring (93% and 65%), which did not differ from the non-eaten ones (100% and 66%). This suggests that the timing of herbivory in relation to G. scorpius' phenological stage is the most important factor affecting both, the survival and regrowth rates. Grazing also has an effect on flowering performance the next spring, since the flowering rate decreased from 38.5% in the non-grazed areas to 2.6% in the grazing ones. G. scorpius response to browsing appears to be associated with the section of twigs consumed, suggesting that this parameter could be used as an index of the level of impact on the bushes. While thorns have shown themselves to be efficient enough against most mammalian herbivores, browsing ability displayed by goats and the different response of G. scorpius depending on its phenological stage suggest that autumn is the most adequate season for this bush control and that efficiency increases with stocking density.