More than 100 world leaders will promise to end and reverse deforestation by 2030, in the COP26 climate summit’s first major deal.
Brazil, where large parts of the Amazon rainforest have been cut down, will be among the signatories on Tuesday.
The pledge includes almost £14bn ($19.2bn) of public and private funds.
Experts welcomed the move, but warned a previous deal in 2014 had “failed to slow deforestation at all” and commitments needed to be delivered on.
Felling trees contributes to climate change because it depletes forests that absorb vast amounts of the warming gas CO2.
The two-week summit in Glasgow is seen as crucial if climate change is to be brought under control.
The countries who say they will sign the pledge, including Canada, Brazil, Russia and Indonesia, cover around 85% of the world’s forests.
Some of the funding will go to developing countries to restore damaged land, tackle wildfires and support indigenous communities.
Governments of 28 countries will also commit to remove deforestation from the global trade of food and other agricultural products such as palm oil, soya and cocoa.
These industries drive forest loss by cutting down trees to make space for animals to graze or crops to grow.
More than 30 of the world’s biggest companies will commit to end investment in activities linked to deforestation.
And a £1.1bn fund will be established to protect the world’s second largest tropical rainforest – in the Congo Basin.
On the second day of the two-week climate summit, the US and EU are also launching an initiative that aims to drive global efforts to cut emissions of methane, a greenhouse gas which comes from sources including fossil fuel extraction and livestock farming.
Dozens of heads of state will join the pledge, which commits countries to cut their emissions of the gas by 30% by 2030.
The opening day of the conference in Glasgow saw India pledge to cut its greenhouse gas emissions to net-zero by 2070 – missing a key goal of the COP26 summit for countries to commit to reach that target by 2050.
Among those to address the summit was the Queen, who urged world leaders in a video message to act “for our children and our children’s children” and to “rise above the politics of the moment”.
Under present targets, the world is on track for warming of 2.7C by 2100 – which the UN says would result in “climate catastrophe”.