The us plants about 2.3 trillion corn plants per year. 25,000 per acre, 95,000,000 acres. Considering they plant 68,000,000 trees per year just for paper, in the US, the numbers aren't shocking. Worldwide tree nurseries probably dwarf that 1.6 billion, maybe.

It's not vastly more than every Chinese person planting 1 tree a year. If you pay people to plant 10 trees a day, 5 days a week, 48 weeks a year you only need to employ one person in every 2400 to get close.