Hybrid strategies generally involve treating biodegradable substrates with preservative compositions having at least two phases in which the metal biocide is distributed among at least the two phases and via equilibrium reactions moves between the two phases. Both phases are caused to contact the substrate in a manner so that the phases are in contact with each other during at least a portion of the treatment. In illustrative embodiments, the first phase is a liquid phase comprising complexed metal biocide dissolved in a liquid carrier, while the second phase comprises particles comprising the metal biocide, often precipitated and/or colloidal particles. The strategies and related compositions, processes, and treatments are hybrid in the sense that the strategies include both heterogeneous (insoluble) and homogeneous metal biocide constituents. Unlike heterogeneous strategies, hybrid strategies are less sensitive to particle size constraints and may use biocide particles with a wider range of particle sizes. Unlike homogeneous strategies, hybrid strategies are less sensitive to pH and may use a wider range of complexing agents, including mildly alkaline amines such as triethanolamine.