There's certainly been experience in several of the Australian states. As well, I'm familiar with systems in Europe. However, I have to admit that I haven't studied in detail the legislative arrangements that have enabled them.
The state I'm most familiar with, Victoria in Australia, put in place a banking system for native vegetation. It went through several iterations. Legislatively, it was quite simple. It was based on a policy that required permitting for any destruction of native vegetation, and the policy behind that permitting indicated a commitment to no net loss, much like our policy has done for several years with respect to fisheries. It then laid out a system for classifying different types of vegetation in different regions of Victoria, and for the development of credits among third parties and for trading among parties.
It has had various levels of performance as the system has been tweaked. In some ways it was overly complex early on, with very fine distinctions between different vegetation communities, leading to a number of very thin markets. Then a change of political winds there led to quite an expansion of the classification scheme. I'm not familiar with exactly how it turned out, but I did hear early critiques that it may be too broad—that it was designed to encourage large markets but may have been ecologically inappropriate.
I think that points to a key challenge in this endeavour: to get a system that is administered efficiently and encourages private sector participation, yet still upholds environmental standards. That is a tricky balance to find. There may not be immediate success in finding that balance immediately when designing a system, but I think that just speaks to the need for some ongoing review and improvement of the system. It should not deter us from exploring how to do it as well as is feasible at any one time.