This read-write INTEGER counts the number of spanning tree topology changes that have occurred since the ES/1 was last booted or since this parameter was last reset by the NMS. An administrator treats a fast-climbing count as a long-term instability indicator pointing to a flapping link or a misconfigured redundant path. For example, the admin notices stTopChangeCount incrementing every few minutes and traces it to a flapping fiber uplink causing repeated reconvergence.