Many wireless sensor network applications like forest fire detection and environment monitoring recommend making benefit from moving humans, vehicles, or animals to enhance network performance. In this research, we had improved our previous protocol (Dynamic Tree Routing DTR) to support mobility in a wireless sensor network. First, we had mathematically approximated the speed threshold for mobile sensors, which enables them to successfully associate with nearby coordinators. Second, we test our (MDTR) protocol in a network with mobile sensors sending packets toward the network's main coordinator. The simulation results obtained from network Simulator (NS2) showed a good approximation of speed threshold, and good performance of MDTR in term of delay, throughput, and hop-count compared with AODV and MZBR Protocols.