1- Department of Forest Sciences, Faculty of Agriculture, Ilam University, Ilam, Iran
2- Department of Rangeland and Watershed Management, Faculty of Agriculture, Ilam University, Ilam, Iran
2- Department of Rangeland and Watershed Management, Faculty of Agriculture, Ilam University, Ilam, Iran
Abstract: (743 Views)
Extended Abstarct
Background: The Zagros forests, one of the most vital ecosystems in Iran, play a crucial role in climate regulation, biodiversity conservation, and the provision of ecosystem services. However, anthropogenic activities and climate change have increasingly threatened these forests, leading to declines in aboveground biomass and species diversity. Biodiversity is a key characteristic of forest ecosystems and significantly contributes to maintaining ecosystem functions, such as aboveground biomass production. Nevertheless, the influence of topographic factors—particularly elevation- on mediating the relationship between biodiversity and ecosystem function across different climatic regions of the Zagros forests remains insufficiently studied. This study aims to investigate the relationship between biodiversity indices (diversity, richness, and evenness) and aboveground biomass through a comparative analysis across various climatic regions, assessing how biodiversity–ecosystem function relationships change along an elevational gradient in Ilam Province.
Methods: Areas with distinct climatic conditions, semi-humid cold (Manesht-Qalarang) and semi-arid cold (Kabir-Kuh), were selected to achieve the study objectives. Study sites were chosen based on their climatic, topographic, and vegetation characteristics to evaluate the influence of these factors on species diversity and ecosystem function. In each region, four transects were established along a 300-meter elevational gradient, with sampling points set at 100-meter intervals. Along these transects, 30×30 meter plots were established systematically and randomly. Data on woody species, including species identity, diameter at breast height (DBH), total height, and crown diameters, were collected within each plot. Biodiversity indices, Shannon and Simpson diversity indices, species richness indices (Margalef and Menhinick), and evenness index (Pielou), were calculated using PAST software. Aboveground biomass was estimated using species-specific allometric equations. For statistical analysis, t-tests were used to compare biodiversity indices between two climatic regions. Simple linear regression models were applied to examine the relationships between aboveground biomass (dependent variable) and biodiversity indices (independent variables), as well as the relationships between biodiversity indices and elevation. Additionally, Principal Component Analysis (PCA) was performed to assess the degree of separation between two regions based on biodiversity indices. All data were standardized prior to PCA, and variables with correlation coefficients above 0.7 were excluded to avoid multicollinearity. PCA was conducted using R software with the “FactoMineR” and “factoextra” packages.
Results: The results showed that aboveground biomass (AGB) was significantly higher in the semi-humid cold region (2,973.18 ± 278.57 kg/ha) than in the semi-arid cold region (1,948.25 ± 158.34 kg/ha). This substantial difference is likely due to more favorable climatic conditions in the semi-humid region, which support a longer growing season and enhanced tree growth. In contrast, species diversity indices were higher in the semi-arid region (Kabir-Kuh) than in the semi-humid region (Manesht–Qalarang). This pattern may be attributed to the presence of drought-tolerant species, reduced competition, and higher ecological niche differentiation under stressful environmental conditions. These findings are consistent with ecological theories, such as the Intermediate Disturbance Hypothesis and the Dynamic Equilibrium Model, both of which propose that moderate levels of stress can enhance species diversity. Regression analyses revealed a negative relationship between elevation and AGB in the semi-humid region (R² = -0.368), likely due to the reduced abundance of dominant species, such as Persian oak (Quercus brantii L.) at higher altitudes, as well as the adverse effects of elevation on temperature, precipitation, and vegetation structure. Regarding the relationship between biodiversity indices and AGB, Menhinick’s richness index showed a significant correlation with biomass in the semi-humid region, while other indices, such as Shannon-Wiener and Pielou’s evenness, did not. Conversely, Pielou’s evenness index exhibited the strongest explanatory power for AGB in the semi-arid region, with other diversity indices also significantly correlated with biomass. These differences likely reflect variations in vegetation structure, climatic conditions, and forest degradation levels between the two zones. Under stress conditions, limited resources and harsh environmental factors often lead to the dominance of low-performing species, reducing ecosystem function and biomass. Thus, a negative correlation between diversity indices and biomass is expected in semi-arid climates. In the semi-humid region, only species richness showed a negative correlation with biomass, possibly due to intensified interspecific competition and functional redundancy among species. PCA results confirmed a clear separation between the two climatic regions based on biomass and biodiversity components. The semi-humid region was characterized by higher biomass and crown cover, whereas the semi-arid region exhibited greater species diversity and richness. These findings indicate that forest management should be tailored to the climatic conditions of each region. In arid and semi-arid areas, in particular, the conservation and development of drought-resistant species, along with soil moisture management, can help enhance biomass stability and species diversity.
Conclusion: This study underscores the significant influence of climate and elevation on biodiversity patterns and aboveground biomass in the Zagros forests. The results indicate that intense interspecific competition may result in higher biomass but lower species diversity in more humid climates. Conversely, semi-arid environments tend to support greater biodiversity, albeit with lower biomass accumulation. These findings highlight the necessity of developing sustainable forest management strategies that are tailored to the ecological variability of different regions. Specifically, biodiversity conservation efforts should be prioritized in semi-arid areas, where species richness and ecological niche differentiation are more pronounced, while carbon storage initiatives can be more effectively targeted in semi-humid regions with higher biomass potential. Implementing management practices that consider local climatic and topographic conditions is essential for preserving the ecological integrity and functional resilience of the Zagros forest ecosystem.
Background: The Zagros forests, one of the most vital ecosystems in Iran, play a crucial role in climate regulation, biodiversity conservation, and the provision of ecosystem services. However, anthropogenic activities and climate change have increasingly threatened these forests, leading to declines in aboveground biomass and species diversity. Biodiversity is a key characteristic of forest ecosystems and significantly contributes to maintaining ecosystem functions, such as aboveground biomass production. Nevertheless, the influence of topographic factors—particularly elevation- on mediating the relationship between biodiversity and ecosystem function across different climatic regions of the Zagros forests remains insufficiently studied. This study aims to investigate the relationship between biodiversity indices (diversity, richness, and evenness) and aboveground biomass through a comparative analysis across various climatic regions, assessing how biodiversity–ecosystem function relationships change along an elevational gradient in Ilam Province.
Methods: Areas with distinct climatic conditions, semi-humid cold (Manesht-Qalarang) and semi-arid cold (Kabir-Kuh), were selected to achieve the study objectives. Study sites were chosen based on their climatic, topographic, and vegetation characteristics to evaluate the influence of these factors on species diversity and ecosystem function. In each region, four transects were established along a 300-meter elevational gradient, with sampling points set at 100-meter intervals. Along these transects, 30×30 meter plots were established systematically and randomly. Data on woody species, including species identity, diameter at breast height (DBH), total height, and crown diameters, were collected within each plot. Biodiversity indices, Shannon and Simpson diversity indices, species richness indices (Margalef and Menhinick), and evenness index (Pielou), were calculated using PAST software. Aboveground biomass was estimated using species-specific allometric equations. For statistical analysis, t-tests were used to compare biodiversity indices between two climatic regions. Simple linear regression models were applied to examine the relationships between aboveground biomass (dependent variable) and biodiversity indices (independent variables), as well as the relationships between biodiversity indices and elevation. Additionally, Principal Component Analysis (PCA) was performed to assess the degree of separation between two regions based on biodiversity indices. All data were standardized prior to PCA, and variables with correlation coefficients above 0.7 were excluded to avoid multicollinearity. PCA was conducted using R software with the “FactoMineR” and “factoextra” packages.
Results: The results showed that aboveground biomass (AGB) was significantly higher in the semi-humid cold region (2,973.18 ± 278.57 kg/ha) than in the semi-arid cold region (1,948.25 ± 158.34 kg/ha). This substantial difference is likely due to more favorable climatic conditions in the semi-humid region, which support a longer growing season and enhanced tree growth. In contrast, species diversity indices were higher in the semi-arid region (Kabir-Kuh) than in the semi-humid region (Manesht–Qalarang). This pattern may be attributed to the presence of drought-tolerant species, reduced competition, and higher ecological niche differentiation under stressful environmental conditions. These findings are consistent with ecological theories, such as the Intermediate Disturbance Hypothesis and the Dynamic Equilibrium Model, both of which propose that moderate levels of stress can enhance species diversity. Regression analyses revealed a negative relationship between elevation and AGB in the semi-humid region (R² = -0.368), likely due to the reduced abundance of dominant species, such as Persian oak (Quercus brantii L.) at higher altitudes, as well as the adverse effects of elevation on temperature, precipitation, and vegetation structure. Regarding the relationship between biodiversity indices and AGB, Menhinick’s richness index showed a significant correlation with biomass in the semi-humid region, while other indices, such as Shannon-Wiener and Pielou’s evenness, did not. Conversely, Pielou’s evenness index exhibited the strongest explanatory power for AGB in the semi-arid region, with other diversity indices also significantly correlated with biomass. These differences likely reflect variations in vegetation structure, climatic conditions, and forest degradation levels between the two zones. Under stress conditions, limited resources and harsh environmental factors often lead to the dominance of low-performing species, reducing ecosystem function and biomass. Thus, a negative correlation between diversity indices and biomass is expected in semi-arid climates. In the semi-humid region, only species richness showed a negative correlation with biomass, possibly due to intensified interspecific competition and functional redundancy among species. PCA results confirmed a clear separation between the two climatic regions based on biomass and biodiversity components. The semi-humid region was characterized by higher biomass and crown cover, whereas the semi-arid region exhibited greater species diversity and richness. These findings indicate that forest management should be tailored to the climatic conditions of each region. In arid and semi-arid areas, in particular, the conservation and development of drought-resistant species, along with soil moisture management, can help enhance biomass stability and species diversity.
Conclusion: This study underscores the significant influence of climate and elevation on biodiversity patterns and aboveground biomass in the Zagros forests. The results indicate that intense interspecific competition may result in higher biomass but lower species diversity in more humid climates. Conversely, semi-arid environments tend to support greater biodiversity, albeit with lower biomass accumulation. These findings highlight the necessity of developing sustainable forest management strategies that are tailored to the ecological variability of different regions. Specifically, biodiversity conservation efforts should be prioritized in semi-arid areas, where species richness and ecological niche differentiation are more pronounced, while carbon storage initiatives can be more effectively targeted in semi-humid regions with higher biomass potential. Implementing management practices that consider local climatic and topographic conditions is essential for preserving the ecological integrity and functional resilience of the Zagros forest ecosystem.
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