Shrub encroachment occurs near previously invaded areas in Patagonia (southern South America)

ROMERO-OVALLE, PAULA ESTELÍ ; CAMPANELLA, MARÍA VICTORIA; PASCUAL, MIGUEL A.; GARCÍA ASOREY, M.; PACHECO, CRISTIAN; BARRIONUEVO, CRISTIAN; BISIGATO, ALEJANDRO

Land Degradation and Development

John Wiley and Sons Ltd

Año: 2023 vol. 35 p. 1098 - 1109

During the last century shrub encroachment has occurred in many arid and semiaridareas of the world. Patagonia is a large xeric territory located in the southern tip ofSouth America, which has been grazed by sheep for more than a century. In manyareas overgrazing led to vegetation change (shrub encroachment), which in turnreduced sheep carrying capacity and caused ranch abandonment. However, thesechanges in physiognomy did not occur everywhere, and even some authors did notfind evidence that shrub encroachment is currently occurring. Our objectives were todetermine if encroachment really happened in NE Patagonia and, in the case of confirmingshrub encroachment, to evaluate if the increase in shrub density was spatiallyhomogeneous. We used object-based image analysis to evaluate shrub density andcover in aerial photographs taken in 1970 and 2018. In both dates, shrub densityshowed a clear contrast between two kinds of areas showing higher and lower densitythan was expected by chance. Shrub density and cover more than doubledbetween 1970 and 2018. This increase was concentrated in those areas with moderateor high densities of shrubs in 1970. Our results confirm the occurrence of shrubencroachment in NE Patagonia and demonstrate that it is currently concentratednear previously invaded areas. These findings have implications when defining protocolsfor monitoring shrub encroachment since monitors should focus on both areasthat already have shrubs and areas that lack them.