Not a botanist, but I would guess that the turpines found in forest plants (such as pinene) play a role. I've experimented with pycnogenol, which is an extract from pine bark, and noticed some mild improvements in respiratory and mental acuity. Completely anecdotal, though there is some science backing pine bark extract and it's benefits. Although from my experience, I would universally recommend spending time in the woods as opposed to consuming trademarked products, despite the hippie nootropic marketing.