Setting aside half the earth's surface sounds like a good idea at first, but when you think about how that would be implemented it just doesn't make sense. The only way it would be possible would be by force. In other words you would be forcefully removed from said lands if you are caught on them. This would cause undue suffering to millions of people.
Paul Simon, who is donating all his proceeds from his current tour to the half-earth project, says that we are destroying the world and once we do there is no going back. What he fails to mention, or realize is that is his attempt to increase biodiversity, he is actually lowering it by removing humans. But we, "human animals" (what E.O. calls us), are actually the best "animals" to have on the land when armed with the right knowledge.
We are the only creatures on this planet that can creatively improve our environment. For example using Sepp Holzer Permaculture, someone would put several ponds, lakes, and terraces on the land, and plant a large variety of every type of plant from grasses to fruit and nut trees.
By putting lakes ponds and terraces, strategically placed for maximum solar gain and prevailing wind exposure, and planting by spreading seed mixes on small plots cleared by a series of different livestock, one can create a micro-climate to extend the growing season for that area, increase biodiversity in the surrounding areas within a year or two, reduce erosion, reduce flooding and landslides, increases humidity in area, attracts more diverse wildlife, provide people with food that has been raised in a happy and healthy environment... I could go on.
And, if the above methods are combined with living in earth-ships(homes that cost nothing to heat or cool, harvest rain water to reuse it four times and leave it clean, composting toilet, solar panels, etc.) We could live in a garden of eden type setting, and one persons labor(spreading seeds, harvesting as there is no weeding or any other major actives besides the initial setup and tending to animals, because the animals manage the land, and the farmer manages the animals, with electric fences, or predator animals) could potentially feed thousands of people. the potential is endless.
My plan is to set up a system like I described above in the next year or two, and make it an eco resort, and tiny home retreat. I believe this idea I have will be profitable and I know it will help the planet, creating a win win situation for everyone. and enabling us to franchise or create an open source model and start more locations everywhere in the world.
We don't need less people, or less people on half the earth. We do need more freedom to build homes like described above, currently it's hard in most city limits because of building codes because the houses use tires, but could actually withstand a earthquake. We need the freedom to live off the land like countless of generations before us did, without the FDA shutting down small farmers in the name of "safety". We need freedom to harvest rainwater, forcing us to build roads and pipes so we can buy our water isn't the best for the planet, nor poor people.
That is what we need on half the earth(really whole thing); FREEDOM, CAPITALISM
My system could revolutionize the way we live, just imagine; you live in a city, where food is plentiful, healthy, and not expensive, your house was built by you and your partner our of tires and cost you only about 20k in material, and is comfortable, spacious and costs nothing to maintain(no water bills, mortgage, gas and electric, etc), and also provides you and your family with some fresh food year around. With the internet, 3-d printing, robotics, drones, and new types of travel all creating a new world for us, we would never have to leave our village/city other then for leisure traveling. People could use this model to populate areas which are now only factory farms doing mono-crop planting on hundreds of thousands of acres. We could spend our time inventing, creating art and music, writing, traveling or just spending more time in nature and or with family, all the while improving the planet for future generations