What's Earth's dominant species by mass?

The piece evaluates which single species holds the most biomass on Earth by comparing wet mass and carbon-based biomass across kingdoms. Among animals, humans total about 350 million metric tons, Antarctic krill about 379 million, cattle 650 million and pigs 140 million. Converting to carbon (Bar-On et al. 2018) shows animals total roughly 2 billion tonnes of carbon, far less than bacteria (70 billion) and especially plants (450 billion). That ranking makes bacteria and plants the dominant kingdoms by carbon mass, with a note that most bacterial biomass lives in deep aquifers and sediments.

Focusing on single species, major crops and trees provide the biggest totals: maize harvests about 1.1 billion tonnes yearly, while sugar cane harvests about 2 billion tonnes and as a perennial likely represents greater year-round living mass. Wild trees dominate among plants: black spruce (Picea mariana) exceeds 11 billion tonnes in Canada alone, and Dahurian larch in Russia is estimated at a minimum of 8.4 billion tonnes. With living black spruce wood roughly 51% carbon, the carbon in that single species exceeds the carbon in all animals combined, making boreal trees - not humans, ants or krill - the dominant species by mass.