A Network Guardian is like a Blakian angel (see above) who mentally flies over the network, notices what could make a difference for the network at that point in time and helps makes that happen. A Network Guardian might see the need for an article in the paper about the importance of networks, or might work with a local funder to set up an innovation fund that provides seed money to self-organized collaboratives.
This a a great role for foundations. They often have lots of information about the many organizations in their community or region and their networks and thus have the birdseye view needed to be a Network Guardian. They also have the resources to put in place the structures that most networks need: training for Network Weavers, Innovation Funds, communications systems, Network mapping, deep reflection sessions, etc. They have access to the public venues where they can "reframe": extolling the importance of openness to new ideas, explaining the intricacies of self-organization, and encouraging collaboration.
See also her "How do Good Practices Spread and Become Transformative?"