Make it mandatory (and pay) for schools to ensure that each secondary school or higher kid plants 10 trees a year. The motivation multiplier on the rest of society from this policy will take care of the rest.
Used to be a thing in Norway until the 70ies or early 80ies. Now we Norwegians are busily blaming ourselves for planting Sitka spruce instead of native species, but I guess the right answer might not be to stop planting trees but to be a little more considerate in what we plant and where.