I'm very familiar with this percentage argument, and I think it's somewhat artificial. I actually agree with a lot of what Bradley said. I think the percentage of what's conserved or protected should be an output of something else. I think the key is not just the quantity, but the quality of what we protect or conserve.
I headed up the Endangered Spaces campaign. Its goal was to establish a representative system of protected areas in Canada representing all the natural regions of the country. During the 1990s, there were 486 natural regions in Canada. The idea there was just to have baseline representative samples of our natural mosiac. That's an ecological goal; it's not a per cent goal. So I would argue to have an ecological goal and a cultural goal working with first nations, and let the percentage fall where it may.
I was also one of the founders of the boreal framework, which put that 50% number out there. I would observe that when communities are left to their own devices, and they aren't whispered into the ear by big conservation groups, big governments, or big companies, they've tended to protect about 50% of their territory by their own choice. So the 50% does have a historical precedent.