When God gives man power over His creation He makes men His surrogates, not His stewards.
The surrogate owns the charge and takes the place of the original owner; it's just that the surrogate has to give it back. The surrogate's ownership is temporary but complete. The class of ownership is intermittent but unattenuated.
Surrogacy is the style of ownership that suits the kind of relationship covenantal partners would have. Relative to stewardship, surrogacy demands a lower load of co-ordination, communication and interaction between the covenantal partners.