The diploma thesis deals with the influence of changes in the humidity of forest waste on its flammability and subsequent spread of fire. The first chapter focuses on the summarizing of the theoretical knowledge about forest fires, a statistical overview of the fire of the natural environment in Slovakia and in the countries of the European Union, as well as fire information systems that are used in the world. We made field research on stand number 365a, which is in the village Kováčová, district Zvolen. We took samples from the field, specifically it was an oak waste. Subsequently, we made laboratory research which was focused on the determining the critical humidity of forest waste, which affects its flammability. We performed measurements for humidity 0%, 5%, 10%, and 15%. At 0%, 5%, and 10% humidity, the oak waste ignited, and the flame spread. At 15% humidity, the oak waste did not ignite after the flame was removed. During the measurement, we also simulated the wind speed and examined how the wind affects the spread of the fire. During the measurement we found that the fire was most affected by the wind of 3,4 - 5,4 m/s, when the flame spread the fastest across the bowl and all the fuel burned. We compared the results with the experience of firefighters from District Directorate Fire and Rescue Corps in Poprad.