From CO2Science: Has the so-called unprecedented rise in atmospheric CO2 and temperature caused a weed apocalypse? Writing as background for their study, Özkan and Tepe (2020) say there are concerns that CO2-induced global warming could “cause changes in the spreading limits of weeds in agricultural ecosystems, the emergence of some new species, and the decrease in the effect of some important weeds or the complete elimination of [some] species.” As an initial test of this thesis the two Turkish researchers examined three-decade-long changes in the weed flora inhabiting cereal fields in an area surrounding Van, Turkey.
Paper reviewed: Özkan, R.Y. and Tepe, I. 2020. Changes of weed flora in cereal fields over the last 31 years in Van, Turkey. Pakistan Journal of Botany 52: 2003-2009
In 1986 scientists conducted a weed survey in the area and Özkan and Tepe conducted a similar survey 32 years later in 2017. The results of the study revealed a surprising reduction in both the number of weed species and weed density. With respect to the number of species, in 1986 scientists identified a total of 84 weed species belonging to 24 plant families. In 2017, however, the present researchers identified only 71 species from 23 plant families, signaling an overall 8.5% reduction in this parameter. With respect to weed density, Özkan and Tepe report this measure was also significantly impacted. In 1986 weed density amounted to 82.6 weeds per square meter. In 2017, it was reduced by half to only 41.8.
As for the factor(s) driving these declining trends in overall weed number and density, the authors opine it may have resulted from a “change in cultivation and pest control techniques and climatic factors.” Unfortunately, their study was not designed to discriminate the legitimacy and strength of these potential factors. Nevertheless, what the data do show is encouraging: rising temperatures and atmospheric CO2 levels of the past three decades do not appear to have initiated a weed apocalypse. And even if it tended to do so, the application of simple management techniques (cultivation, fertilization and/or herbicide application) has been more than sufficient to counter any such impetus so as to result in the weed number and density reductions observed here.