Question

A forest fire destroyed large tracts of forest in California.however, within a few years , the forest regenerated and will soon return to its original state . What is the reason the forest is able to regenerate?

Answer 1

California is very well known for fires so in this case I'd say go with the answer of "SEROTINOUS CONES" which are special "seeds" to easier put it that only spread with the aid of fire. These cones are spread by fire/wind/gravity as time goes by the trees will grow back as a result. 

Another well said answer can be secondary succession. Secondary succession "reduces an already established ecosystem to a smaller population of species" or series of changes that take place after disasters on forests/general like fires.