Identifying the effect of density dependence, agricultural practices and climate variables on the long-term dynamics of weed populations

Quantifying the impacts of climate change on weed populations requires an understanding of the relative contributions of endogenous and exogenous factors on their numerical fluctuations. Here, we have used long-term data (26years) of seven weed species growing in a cereal-legume rotation from a locality in central Spain to determine the importance of endogenous (density dependence) and exogenous (tillage system, crop rotation, temperature and precipitation) factors. Density dependence was the main driver of the population dynamics studied, and it was exhibited more frequently under zero tillage (86% of the species) than under minimum tillage (57% of the species). Our results confirmed previous findings and provided stronger support for density dependence under zero tillage than under minimum tillage. Under the latter, temperature negatively affected the population growth rate of Descurainia sophia and positively Atriplex patula. We found no effect of either precipitation or crop rotation on population dynamics. Our findings could underpin an awareness campaign aimed at farmers to prevent them from drawing unwarranted conclusions regarding the efficacy of the particular control method used in a given year.