نوع مقاله : علمی- پژوهشی
نویسندگان
1 استادیار، مؤسسه تحقیقات جنگلها و مراتع کشور، سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران
2 دانشیار، موسسه تحقیقات جنگل ها و مراتع، سازمان تحقیقات، آموزش و ترویج کشاورزی، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Background and objectives: Ground vegetation is an important component of forest ecosystems through which many indicators of biodiversity, stand stability, and the effects of global changes caused by human activities can be assessed. Changes in ecosystem components are studied through the process of monitoring. Ground vegetation monitoring is being carried out as part of forest monitoring projects in different regions of the world. However, in the Irano–Turanian forests, such studies have not yet been conducted, and previous studies have generally focused on describing the structural and environmental characteristics of the stands. In this study, ground vegetation in the Irano–Turanian forests of Khojir National Park in Tehran Province, Iran, was investigated and monitored over a three-year period.
Methodology: Khojir National Park is located within the Jajrud protected areas complex in the eastern highlands of Tehran Province, approximately 25 km from the Tehran metropolitan area. The forest habitat has a gentle north–northeast slope and an average elevation of 1,500 m above sea level. Permanent sample plots of 100 m² were used to study and monitor forest cover and regeneration, while permanent microplots of 1 m² were used to monitor ground vegetation cover. The floristic composition, quantitative and qualitative characteristics of vegetation cover, plant species diversity, and regeneration were studied over three consecutive years (2021, 2022, and 2023) during mid-May. All plant species present in the microplots were recorded based on density (individuals per unit area), life form, and phenology. In addition, the cover of ground vegetation, mosses and lichens, shrubs, litter, bare soil, rocky outcrops, and surface gravel was accurately estimated and recorded in the microplots. Comparisons of the studied variables were performed using repeated measures analysis of variance or nonparametric Friedman and Wilcoxon tests.
Results: Ground vegetation cover in the microplots during the first year of the study (22.3%) was higher than in the second and third years (17% and 18.7%, respectively); however, comparisons of the means indicated that these differences were not statistically significant. Moss and lichen cover (mainly soil-surface mosses in the study area) showed a decreasing trend and was significantly lower in 2023 (10%) compared to previous years (16.4% and 15.8%). The percentage of litter cover decreased significantly from 2021 to 2023 (from 43% to approximately 16%), whereas the percentages of bare soil and surface gravel increased significantly. Based on the results, among the 79 species recorded in the microplots of the Khojir site, 62% were annual plants (therophytes), 20% were hemicryptophytes, 13% were chamaephytes, 4% were cryptophytes, and 1% were phanerophytes (seedlings, saplings, or small woody stems). The Asteraceae family, with 15 species, was the largest plant family, followed by Brassicaceae, Poaceae, and Lamiaceae. The density of plant species fluctuated during the three years of the survey, such that no significant difference was observed between the first and third years (average of 242 and 249 individuals per square meter, respectively), whereas density was higher in the second year (average of 344 individuals per square meter). Changes in density were not consistent among all species, and significant interspecific differences were observed. Some therophyte species showed a decrease in density, whereas others showed an increase. The density of hemicryptophytes increased significantly during the study period (average of 2.4, 3.8, and 5.9 individuals per square meter, respectively). Overall, species richness and diversity indices of the ground vegetation showed an increasing trend during the study period, whereas evenness indices did not differ significantly. In the Khojir habitat, only regeneration of mountain almond (Prunus lycioides (Spach) C.K.Schneid.) was recorded in the sample plots, whereas wild pistachio (Pistacia atlantica Desf.) showed no regeneration. Approximately 80% of almond regeneration occurred without nurse plants. The analysis of abundance across height classes also indicated that the number of saplings and young almond individuals has declined in recent years.
Conclusion: Overall, the three-year study of permanent monitoring plots in Khojir National Park revealed that vegetation cover, moss cover, and surface litter decreased during the study period, whereas bare soil, rocks, and surface gravel became more exposed. Changes in the density of different species followed different trends, although species diversity and richness increased overall. The Pistacia–Prunus habitat in Khojir was found to be in poor condition with regard to regeneration.
کلیدواژهها [English]
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