Effect of Snags on the Species Diversity and Frequency of Tree Natural Regeneration in Natural Forest Ecosystems of Guilan, Iran

Future of natural forests depends on stand regeneration. In this research impact of standing dead trees (snags) on the species diversity and density of established regeneration was studied in district No. 2 Forest of Nav-Asalem، Guilan. In this regard، 32 snags with D. B. H. above 50Cm were taken as the centers of sampling plots. Canopy gap areas caused by snags and their decay degree were measured and determined. Also in a 50m distance from snags with same canopy، one safe tree with same D. B. H. and species were selected as the sampling plots. At each of these plots variables of number، species and growing stage (seedling، small sapling and sapling) of regeneration were counted in a 1000 m2 circular sample area. For each sample plot frequency and species diversity calculated from Shannon Winner diversity index، Pielous evenness index and Minhinich richness index. Mean of frequency and species diversity indices in each statistical population were compared from ANOVA and t-test. Results showed that frequency and species diversity of established regeneration in the snag plots were more than safe tree plots and this different was significant at a=0. 01 statistical level. Reason of different diversity amount was more amount of richness in snag plots. More of frequency and species diversity in snag plots was occurred due the established and growth of more number and species from seed trees. Snags with medium canopy gap areas (50-113m2) had more influence on frequency and species diversity of regeneration. Also، snags with degree 3 of decay had more frequency and snags with degree 2 of decay had more regeneration species diversity. Snags with create of gaps in forest canopy and increasing sun light to forest floor، moreover، have positive influence with preparing suitable condition and resources to establishment and growth of different tree seeds. Saving snags in forest stands in different sizes and species can be useful to regeneration and sustainability in these ecosystems.