To disseminate messages from a single source to a large number of targeted receivers, a natural approach is the tree-based application layer multicast (ALM). However, in time-constrained flash dissemination scenarios, e.g. earthquake early warning, where time is of the essence, the tree-based ALM has a single point of failure; its reliable extensions using ack-based failure recovery protocols cannot support reliable dissemination in the timeframe needed. In this paper, we exploit path diversity, i.e. exploit the use of multiple data paths, to achieve fast and reliable data dissemination. First, we design a forest-based M2M (Multiple parents-To-Multiple children) ALM structure where every node has multiple children and multiple parents. The intuition is to enable lower dissemination latency through multiple children, while enabling higher reliability through multiple parents. Second, we design multidirectional multicasting algorithms that effectively utilize the multiple data paths in the M2M ALM structure. A key aspect of our reliable dissemination mechanism is that nodes, in addition to communicating the data to children, also selectively disseminate the data to parents and siblings. As compared to trees using traditional multicasting algorithm, we observe an 80% improvement in reliability under 20% of failed nodes with no significant increase in latency for over 99% of the nodes.