According to one configuration, multiple users in a tiered hierarchy share use of a wireless spectrum. For example, a spectrum access system receives a notification indicating that a first-priority tier 1 user in the hierarchy temporarily needs access to a first wireless spectrum assigned to a second-priority tier 2 user in the hierarchy. In response to the notification, the spectrum access system temporarily allocates the second-priority tier 2 user use of a second wireless spectrum. The spectrum access system protects use of the second wireless spectrum by the second-priority tier 2 user from a third-priority tier 3 user in the hierarchy. In certain instances, the one or more spectrum access systems receive the same notification of use of the first wireless spectrum by the first-priority tier 1 user. The multiple spectrum access systems not serving the second-priority tier 2 user protect the Tier 2 User from any Tier 3 Users in the hierarchy.