The problem of the initial stage of a high altitude radiant energy source effect on the underlying surface of the Earth covered with the forest vegetation is discussed below. The objective of the present research is to define deimensions of the ignition zone and to study photochemical processes which are taking place. Setting up and numerical solutions of problems of the vegetation ignition when meteorites fall and during air explosions in the atmosphere of the Earth are presented with the use of a mathematical model of forest fires.