The theme of bachelor thesis is problematic, that in the last few years grown to be even more of a serious problem for forests not only in Slovakia and it is the activation of harmful agents after wind calamity, where it’s about biotic harmful agents. Even on The territory of Slovakia wind calamities occur multiple times, they affect forests and make ideal terms for the occurrence and spreading of under bark insect as a secondary harmful agent. In this bachelor thesis are described the most significant species of harmful agents, whether on economically important woods or on other less important woods, next we describe risks, which are caused by these phenomena and mainly countermeasures so that we are able to predict whether wind calamities of spreading under bark pest. One chapter of this work is dedicated to description of occurrences of random logging, wind calamities and also logging as a result of infected undergrowth by under bark insect on the territory of Mestské lesy Dobšiná, spol. s.r.o.