First of all, there's no doubt that voluntary stewardship can have a very positive effect. For both the Canadian Wildlife Federation and other conservation organizations I have been associated with, there's lots of evidence of that. The crux of the issue I think depends on how long and how important that particular piece of habitat may be.
Different tools are useful in different areas. Communication can help with some landowners. Different incentives work with different landowners, for example, financial incentives. Joint planning can help share values and help people become more committed. There's a wide range of potential stewardship tools. All work in some situations better than others.