He's referring to the claims that in the first 5 years, between shedding of leaves and young branches, trees are not carbo neutral. What those studies fail to say is that the carbon the trees shed is turned into composted material within months, adding nitrogen and nutrients to said soil with causes all other plant life to flourish, increasing said carbon capture efficiency. It's like those idiots that say you need to work out for 3 hours to burn off a kit kat. If all your body did was go into stasis between meals then that might be true. But the fact is unless your eating an entire box of kit Kats, or unless you never leave a chair or couch, the average man or woman will burn enough calories just by doing daily activities that a single kit kat won't matter in their calorie scheme of things.