Effect of a Windstorm on Gaps Structural Characteristics in the Different Forest Stands in Darabkola Region, Mazandaran Province

In this study, the response of individual trees and the stand structure to windstorm damage were investigated in a mixed broad-leaf forest stands located in Darabkola Forest, northern Iran. A full inventory was performed for all trees with diameter at breast height≥ 10cm and all damaged trees were identified within the study area. The number of the damaged trees varied with species, ranging from 0.04% (2 individuals) in Tilia begonifolia Stev to 53.7% (2709 individuals) in Fagus orientalis L. Among the damaged trees 5054 recorded, 2231 (44.20%) had been snapped and 787 (15.6 %) uprooted, and 2028 (40.20 %) were snags. Among the species, Fagus orientalis L. (47.7%), Alnus subcordata C. A. Mey. (19.7%) and Carpinus betulus L. (18.8%) were most susceptible to uprooting, whereas Populus caspica Bornm, Quercus castaneifolia C. A. Mey. and Ulmus glabra Huds. were the least susceptible to uprooting. Trees ≥60cm dbh were more likely to be snapped (78%) or snags (69%), whereas trees <60 cm dbh were more presumably to be uprooted (50%). Also, about one third (33%) of total trees larger than 60 cm (dbh) have showed distinct effects and individual trees >20 m were more commonly uprooted. Finding showed that Oriental beech and Common hornbeam to be species that were most susceptible to both being snapped and snagged, whereas Caucasian alder had the most uprooting damage among the other species. Overall, features like species, D.B.H, height and height to diameter ratio (H/D.B.H), were intensively related with the type and severity of windstorm damage.