Leaves may blow around some, but on most of the forest floor there isn't anywhere for them to go. Some of the leaves get eaten or turned into fungus or whatnot

Leaves may blow around some, but on most of the forest floor there isn't anywhere for them to go. Some of the leaves get eaten or turned into fungus or whatnot, but those die off too and eventually return to the air. There was a time in the Earth's history where this wasn't the case. During the carboniferous phase plant life didn't decay and biomatter piled up on the forest floor in miles-thick layers. The CO2 levels in the atmosphere dropped so low that the planet was verging on an iceball at times. The carbon balance was only maintained via enormous forest fires in the oxygen rich atmosphere.