Weed community dynamics in perennial medicinal crops of organic agricultural systems

To investigate the typical weed communities of perennial medicinal crops, floristic analyses were conducted both in spring-summer and autumn-winter throughout the four years of the agronomic cycle of ten different medicinal herbs cultivated with organic methods. The data were analyzed using the most commonly adopted parameters for determining plant communities (relative density percentage, relative abundance) and the Shannon and Simpson diversity indices. Although a predominance of certain species was observed in the warm season (Amaranthus retroflexus, Chenopodium album and Portulaca oleracea) and the cool season (Poa annua, Stellaria media and Veronica persica), altogether 69 species were found, 38 of which were detected in autumn-winter samplings, and 31 during spring-summer samplings. During the four-year period there was an increase in perennial species (geophytes and hemicryptophytes) and a consequent decrease in annual species (therophytes). Also, an increase in relative density of warm-season and cool-season grasses was observed, the relative density percentage being confirmed by significant linear regressions (p<0.05). Furthermore, probably on account of the minimum agronomic soil disturbance during the four-year period, significant increases (p<0.01 and/or 0.05) in species diversity were noted. The study showed the high biodiversity level of weed communities of medicinal crops cultivated with organic agricultural systems.