نوع مقاله : مقاله کامل علمی پژوهشی
نویسندگان
1 دانشجوی کارشناسی‌ارشد گروه جنگلداری و اقتصاد جنگل، دانشکدۀ منابع طبیعی، دانشگاه تهران، کرج، ایران
2 استاد گروه جنگلداری و اقتصاد جنگل، دانشکدۀ منابع طبیعی، دانشگاه تهران، کرج، ایران
3 دانشیار گروه جنگلداری و اقتصاد جنگل، دانشکدۀ منابع طبیعی، دانشگاه تهران، کرج، ایران
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Background and Objectives: Hyrcanian beech forests, as sensitive and valuable ecosystems, are vulnerable to disturbances caused by past skidding operations (before the 2017 "Harvest Suspension" plan) that were conducted without adhering to technical principles. Machinery traffic outside designated trails and the establishment of timber landings in unsuitable locations with dimensions exceeding standards, through canopy removal and altered light regime, have changed the structure and composition of understory vegetation. Although timber harvesting has been halted since 2017, residual effects persist, and this study evaluates these lasting impacts in timber landings. Despite numerous studies, the independent contribution of light regime, separated from soil compaction, to herbaceous cover change in Hyrcanian timber landings after two decades remains unknown, whereas identifying the dominant factor (light or compaction) is essential for designing restoration strategies and mitigating persistent harvesting effects. Using a three-treatment quasi-experimental design (felled landing, unfelled landing, and control), this study disentangles these factors for the first time in Kheyrud Forest.
Materials and Methods: This quasi-experimental study comprised three treatments in Kheyrud Forest timber landings: (1) felled landing with severe soil compaction (compartments 212 and 214), (2) unfelled landing with severe compaction and closed canopy (compartment 213), and (3) adjacent undisturbed control areas (at least 30 m from the landing edge). Six 1-m² plots were systematically established in each landing, and four plots in each control area (81 plots total). Light intensity (LUX) was measured with a digital luxmeter, and photosynthetically active radiation (PAR) with a SunScan device, simultaneously at each plot center. Biodiversity indices (Shannon-Wiener, Simpson, Margalef, evenness, and dominance), floristic composition, and herbaceous abundance were determined. One-way ANOVA and Tukey's HSD tested treatment differences, and principal component analysis (PCA) examined variable relationships.
Results: Mean light intensity was 1225.19 lux in control, 2158.33 lux in the unfelled landing, and 3031.67 lux in the felled landing. Mean PAR was 13.39, 28.84, and 43.09 µmol m⁻² s⁻¹, respectively. Total herbaceous plant count was 85.70, 101.28, and 162.72 individuals m⁻², respectively. Shannon-Wiener index was 1.78, 2.58, and 2.92; dominance index was 0.22, 0.10, and 0.07, respectively. Light-demanding species such as Euphorbia amygdaloides and Oplismenus undulatifolius dominated the felled landing, while shade-tolerant species such as Asperula odorata and Oxalis acetosella declined sharply. No tree species were observed in the felled landing. PCA showed the first two components together explained 82.9% of total variance. The first component (70.2%) was strongly correlated with light intensity, PAR, soil compaction, and biodiversity indices; the second (12.7%) was associated with soil nutrients and shade-tolerant tree species.
Conclusion: Light regime, as an independent environmental filter, shifted herbaceous cover composition from shade-tolerant to light-demanding species; increased PAR in the felled landing (43.09 µmol) led to dominance of Euphorbia amygdaloides and Oplismenus undulatifolius and complete cessation of tree regeneration. Diversity indices increased, but this "spurious diversity" accompanied the loss of forest indicator species. The specific finding is the decisive role of PAR in disentangling light from compaction effects, demonstrating the necessity of reducing landing dimensions and preserving edge canopy cover for sustainable management. These results provide a quantitative basis for revising landing establishment practices and restoring degraded Hyrcanian forests.
کلیدواژه‌ها [English]
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