Effects of harvesting intensity on population structure of Lippia graveolens (Verbenaceae, Lamiales) in the Semidesert of Queretaro, Mexico

Abstract

Whole Oregano (Lippia graveolens) is a wild shrub species that is harvested commercially as an important complement to the income of farmers in the semiarid areas of Mexico. However, the impact of this activity on populations of the species is unknown, particularly in the semi-desert of Queretaro State in Mexico. We quantified the consequences of different harvest rates on the growth and reproduction of five wild populations of L. graveolens, with the goal of improving current practices. We found that, as the harvesting rates of L. graveolens increase, there are changes in the density, size structure, proportion of reproductive individuals and production of inflorescences. For instance, in sites with the lowest harvesting intensity, the density was 2980 individuals/ha, the mean plant height was 100 ± 3.25 cm (mean ± SE) and mean plant cover was 4312 ± 247 cm2; whereas in sites with the highest plant harvesting intensity the density was 1920 individuals/ha, mean plan height was 30 ± 1.93 cm and mean plant cover was 843 ± 73 cm2. Such changes place certain managed wild oregano populations in a vulnerable situation, illustrating the need of close monitoring of species harvested from the wild as cash crops. Key words: Extraction, spices, population dynamics, non-wood forest products.