Background and objectives: Hyrcanian forests, as one of the most valuable natural forests of Iran, play an important role in the sustainability of regional and global ecosystems. These forests contain a high diversity of vascular plants and provide diverse living conditions for plant species. Iron wood sites, as a part of the Caspian broadleaf forests, have high plant diversity and unique ecological features. This investigation aims to compare the floristic composition and plant diversity between an undisturbed site and a disturbed site in the Persian ironwood (Parrotia persica) site of western Guilan.

Methodology: For this purpose, two Iron wood sites were selected in the Chafroud (undegraded) and the Shafaroud (degraded). Both sites were chosen to have comparable slope, aspect, and elevation, and they were both pure stands of Persian ironwood. Using the selective sampling method, the research was carried out across two study areas, including the undisturbed site of Chafroud (57.49 ha) and the disturbed site of Shafaroud (40 ha). In each study area, a total of 40 circular sampling plots, each measuring 1000 m², were established. Then, within each sample plot, all woody stems with a diameter at breast height (DBH≥ 5.7 cm) were measured and identified. Then, shrub species were recorded in terms of both species composition and individual abundance. To assess the herbaceous layer, five quadrats of 4 m² (2×2 m) were systematically established within each main plot, and the cover percentage of all herbaceous species was visually estimated and documented. In order to examine the diversity indices in the tree, shrub and herbaceous layers, Shannon-Wiener diversity indices, Margalef richness and Smith-Wilson evenness indices were used. In addiion, the importance value of tree, shrub and herbaceous species in all three layers was calculated and a logarithmic diagram was drawn based on the ranking of plant species in each layer. For comparing the diversity indices in two regions in different layers, independent t-test was used. Diversity indices were calculated using Ecological Methodology 6.0 software and all statistical analyses were performed using IBM SPSS 22 statistical software.

Results: The results showed that the number of trees per hectare in Chafroud Iron wood sites is 462.5 and in Shafaroud Iron wood habitat is 408.25 per hectare. Ulmus minor, Ulmus glabra, Albizia julibrissin, Pyrus communis and Malus orientalis were present only in Chafroud sites and two species of Cerasus avium and Castanea sativa were present only in Shafarood sites. Also, the results showed that the mean indices of diversity, richness and evenness in the tree layer in the Iron wood site of Chafroud are higher than the Shafaroud Iron wood site, and there is a significant difference between the mean of the Shannon-Weiner diversity indices and the Margalf richness between the two. The evangelical habitat of Chafroud and Shafaroud was observed. The result in shrub layer indicated that nine shrub species were identified in both sites. The species of Frangula grandifolia only was present in the Chafroud site and the Punica granatum and Cornus australis species were present only in the Shafaroud site.
The results of diversity indices in the shrub layer showed that the mean of all indices of diversity, richness and evenness in the Chafroud site was less than Shafaroud, additionally, there were no significant difference between the mean of in the shrub layer in two sites. A total of 95 herbaceous species were identified in two Iron wood site, of which 40 species only were present in the Chafroud site and 16 species only were present in the Shafaroud site. The results of diversity indices showed that the mean of diversity and richness indices (unless evenness index) in the Chafroud sitet is higher than the Shafaroud site and there is a significant difference between the mean of all diversity indices in two sites in the herbaceous layer. The results of the species importance value in the tree layer demonstrated that in both the Iron wood site of Chafroud and Shafarood, the two species of Parrotia persica and Morus alba had the highest and lowest value of tree species, respectively. Moreover, the results showed that the highest value of shrub species in the site of Chafrood and Shafarood was related to Ruscus hyrcanus and Mespilus germanica species and the lowest in the two sites were related to Danae racemosa and Cornus australis, respectively. In the herbaceous layer in Chafroud site, two species of Cyclamen coum and Geranium molle had the highest and lowest value of the importance of the species, while in Shafarood site, Viola odorata and Rubus hyrtus had the highest and lowest amount. The diagrams in the tree layer showed that in both sites the shape of the diagrams follows the log normal distribution. Also, the graphs of the shrub layer showed that the the diagrams in Chafroud and Shafarood sites follow the log normal distribution and the broken stick model, respectively. The diagrams in the herbaceous layer revealed that in the both sites the diagrams follow the log normal distribution.

Conclusion: The results of this study demonstrated that degradation processes play a key role in changing the vegetation structure and diversity of ironwood (Parrotia persica) stands in the Hyrcanian forests. Comparison of the undisturbed Chafroud stand with the degraded Shafaroud stand revealed that forest degradation reduced the richness, tree diversity, herbaceous species, and changed species composition, with sensitive species predominantly occurring in the undisturbed stand, whereas disturbance-tolerant species became dominant in the degraded stand. The continued effect of degradation processes not only diminishes plant diversity but also threatens the natural regeneration capacity and ecological stability of these valuable forest ecosystems. Therefore, mitigating degradation requires the implementation of integrated forest management practices, including the control of illegal harvesting, prevention of land-use change, regulation of livestock grazing, and effective protection of natural stands. Furthermore, restoring degraded areas using native species and promoting natural regeneration can accelerate ecosystem recovery and prevent further forest degradation.