The oldest, carbon-rich rainforests continue to be lost at a staggering rate, according to satellite data.
Brazil accounted for a third of this, its worst loss in 13 years, in addition to the great peaks in 2016 and 2017 of the fires.
However, Indonesia and the Democratic Republic of Congo have managed to reduce the loss of trees.
Meanwhile, Australia saw a sixfold increase in total tree loss after wildfires in late 2019.
In addition to storing large amounts of carbon, primary tropical forests, where trees can be hundreds or thousands of years old, are home to species such as orangutans and tigers.
The tropics lost 11.9 million hectares (46,000 square miles) of tree cover, according to the study, 3.8 million in older primary forest areas – the third largest loss of primary trees since 2000 and a slight increase in 2018.
"The level of forest loss that we saw in 2019 is unacceptable," said Frances Seymour, of the World Resources Institute.
"And one of the reasons why it is unacceptable is that we already know how to change that.
"If governments adopt good policies and enforce the law, the loss of forests will decrease.
"But if governments relax restrictions on burning, or [are] signaling that they intend to open indigenous territories for commercial exploitation, the loss of forests increases ".
Speaking about the losses in Brazil, Mikaela Weisse, from Global Forest Watch, said: "We have also seen several new hotspots of loss of primary forests in indigenous territories, especially in the state of Pará, related to land grabbing and mining.
"These incursions are of particular concern, since indigenous peoples have been some of the best conservators of forests in Brazil and in the world."
Indonesia, however, has seen losses remain at historically low levels for the third year running, thanks, it seems, to strong government action.
Liz Goldman of Global Forest Watch said: "Several policies in Indonesia have contributed to this positive story, including increased enforcement to prevent forest fires and deforestation and a forest moratorium to prevent further deforestation for oil palm plantations and logging activities, which was first established in 2011 and made permanent only last year ".
And Columbia, which has seen tree losses increase since a peace agreement went into effect in 2016, saw a 35% drop in loss of primary forests compared to 2018.
But Bolivia suffered losses 80% greater than in any other year, after the fires in the agricultural clearing went out of control.
And almost 12% of the dry forest in Chiquitano, in eastern Bolivia, which houses indigenous peoples, jaguars, armadillos and giant tapirs, have been burned.
Follow Matt on Twitter @mattmcgrathbbc.