Both composting and incineration will lead to a much more rapid release of carbon, while landfilling allows all that carbon to be released at a much slower rate.

Source: https://www.independent.co.uk/voices/christmas-tree-real-artificial-environment-impact-b2464177.html

The new gate fees were first in an effort to incentivise commercial operators to separate their waste before dumping it at WasteServ facilities and to reverse Malta’s historic trend of landfilling the vast majority of its waste.

Source: https://timesofmalta.com/articles/view/new-landfill-fees-discourage-dumping-mixed-waste.1074474