The Use of Herbicides in South American Dry Forests to Control Shrub Encroachment: a New Threat to Cactus Species? A First Assessment

Abstract: Dry forests are home to an important diversity of cactus species. In the Americas, these forests are under an increasing pressure due to a growing demand for land to produce pastures for cattle; in addition, the use of herbicides to control shrub encroachment is increasing. As a scientific collaborator of the Environmental Police of Córdoba province, Argentina, I had the opportunity to visit five cattle ranches where herbicides were illegally applied. The product used is Pastar, produced by Dow Agrochemical, and is composed of two hormonal herbicides, aminopyralid and fluroxypyr. Since all ranch owners are in legal dispute with the government, it was not possible to conduct a quantitative research. Therefore, I recorded all cactus species present and their sanitary conditions. A total of nine cactus species were recorded. In general, all species presented low abundance in comparison to the preserved forest, indicating that mechanical control of shrubs (using tractors) had already had a negative effect on species. Moreover, some common species in these forests, such as Gymnocalycium schickendantzii and Echinopsis leucantha, were not recorded. For most cactus species, the herbicide would have minimal or no effect, since individuals were found alive and in good sanitary conditions. In a few individuals of Cereus forbesii and C. aethiops, the end of the stems was damaged. Some individuals of Stetsonia coryne and Cereus forbesii were found dead, but it is not clear whether the herbicide was the cause. Since pressure for more pastures for cattle is increasing worldwide, more studies on the effect of land use changes and the use of chemical products on cactus species in dry forests of the Americas are needed.