Plants rule

While humans make up just a tiny fraction—only 0.01 percent—of the mass of all living things, we are responsible for a hefty amount of destruction across other species.

Human activity has caused a decline in the total biomass of wild mammals—both marine and terrestrial— by a factor of six, or over 80 percent, since the dawn of civilization, according to a new Weizmann Institute-led study. Meanwhile, the total plant biomass has declined twofold since the emergence of people on the planet due to the cutting down of forests.

But the surprising finding was that plants still rule the Earth—comprising about 450 gigatons of carbon (Ct C) out of the total 550 Gt C of biomass on Earth. In comparison, humans make up a staggeringly low 0.06 Gt C, despite our enormous impact.

The study, recently published in the Proceedings of the National Academy of Sciences, includes a census of the total biomass distributed among all kingdoms of life. Performed by PhD student Yinon Bar-On from Prof. Ron Milo’s laboratory in the Department of Plant and Environmental Sciences, in collaboration with Caltech Prof. Ron Phillips, the research provides a holistic view of the biosphere’s composition while characterizing patterns according to taxonomic categories, geography, and nutrition. To assemble the census, the scientists conducted extensive analyses based on hundreds of existing studies.

 Another insight from the study was that while the biomass of wild animals has declined steeply, the total mass of mammals—including humans and livestock—increased fourfold.

“Over the relatively short span of human history, major innovations, such as the domestication of livestock, the adoption of an agricultural lifestyle, and the Industrial Revolution, have increased the human population dramatically and have had radical ecological effects,” the authors observe. “The impact of human civilization on global biomass has not been limited to mammals but has also profoundly reshaped the total quantity of carbon sequestered by plants.”

Prof. Ron Milo is the incumbent of the Mary and Tom Beck-Canadian Center for Alternative Energy Research, which he heads, the Larson Charitable Foundation; the Ullmann Family Foundation; and the Zuckerman STEM Leadership Program. He is the incumbent of the Charles and Louise Gartner Professorial Chair.