[GreyFriar]

And here is the Daily Mail with an article saying that we are destroying 15 billion trees a year.

http://www.dailymail.co.uk/sciencetech/article-3219790/Number-trees-Earth-HALVED-beginning-human-civilisation-15-billion-lost-YEAR.html

And how does anyone know how many trees have grown since or before human civilization came about.

[minnesota_bound]

3 trillion divided by 15 billion = never run out as trees grow back.

[JoeProBono]

“We’ve nearly halved the number of trees on the planet, and we’ve seen the impacts on climate and human health as a result,” Crowther said. “This study highlights how much more effort is needed if we are to restore healthy forests worldwide.”

http://phys.org/news/2015-09-trees-previously-believed.html

[zot]

I think this is a SWAG (Scientific Wild-Ass Guess).