Natural disturbances are rather rare for the urban forests compared to the anthropogenic ones. However, forcible natural impact may be substantially destructive such as severe storms. Instantaneous defoliation is one of the significant signature of the storm severity. A multipurpose vegetation parameter, Leaf Area Index (LAI) is used as an indicator of instantaneous defoliation which may occur as a result of immediate leaf fall jointly with the stem and branch breakages or uprooting. Enhancing the idea, LAI of the Carpinus betulus trees were analyzed before and after the devastating storm in Balamba urban forest patch of Bartın Province at the northwestern of Turkey. The maximum speed of the severe storm was 117 km/h and enough to destruct the trees. Consequently LAI ceased 24% as a result of instantaneous defoliation both in recreation and control sites indicating the severity of damage. Southwester which is associated with heavy rainfall and represent the winds with maximum speeds in the region led to this change. The inexistence of extraordinary meteorological data before and after the severe storm indicates that the wind speed was the main reason for such damage. The same percentage of LAI decrease within the recreation and control sites supports the situation that the soil compaction due to recreation has no definite influence on the severity of windthrow. Scattered pattern of annual maximum wind speeds particularly for the last fifteen years are possible to be the implications for climate change.