Volume 13, Issue 1 (3-2025)
Ecol Iran For 2025, 13(1): 72-84 |
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Izadi M, Habashi H, Rafiee F, Kazemi S. (2025). Variations in the Frequency and Biomass of Corticolous Earthworms in the Eastern Hyrcanian Forests. Ecol Iran For. 13(1), 72-84. doi:10.61186/ifej.2024.559
URL: http://ifej.sanru.ac.ir/article-1-559-en.html
URL: http://ifej.sanru.ac.ir/article-1-559-en.html
1- Department of Silviculture and Forest Ecology, Faculty of Forest Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
Abstract: (873 Views)
Extended Abstract
Background: Earthworms make up a significant portion of the soil's invertebrate biomass and play a vital role in enhancing the physical, chemical, and biological characteristics of the soil. Earthworms enhance ecosystem performance and boost primary production by altering the soil structure and decomposing organic matter. Earthworms are classified into different categories based on their behavior and feeding habits. The most important ones include epigeic, anecic, and endogeic earthworms. Additionally, some earthworms, such as arboreal and corticolous species, inhabit unusual environments. This study aims to investigate the effect of dead wood on the biodiversity and abundance of corticolous earthworms in the forests of the eastern Hyrcanian region. In this regard, earthworm species found beneath the bark of deadwood (four species) were identified and classified in this research. Additionally, an attempt was made to analyze the effect of different deadwood species and their degrees of decay on various indices of earthworm biodiversity and evenness. To evaluate the impact of different locations within the deciduous temperate forests of eastern Hyrcania, the abundance of earthworms was examined and compared under the forest canopy and in forest gaps.
Methods: The study area is located in District-1 of Dr. Bahramnia Forestry Project, the eastern part of Hyrcanian forests. The research was conducted in parcels 1, 4, 7, 8, 31, and 32, which respectively include tree cover types of oak-hornbeam, ironwood-hornbeam, hornbeam-ironwood, beech-hornbeam, and beech-hornbeam. In this study, 119 samples of fallen deadwood from four species (beech, hornbeam, oak, and ironwood) were randomly selected from beneath the forest canopy and forest gaps at two elevations, 150 and 950 meters. These samples were classified into four degrees of decay based on their physical characteristics. After separating the bark with a sharp knife, the earthworms underneath were collected and initially stored in 15% ethanol, then transferred to 75% ethanol after one day, and finally to a 4% formalin solution. The earthworms were identified to the genus level using available identification keys. Their mass was measured after drying in an oven for 48 h, with an accuracy of 0.0001 g. Data analysis included the calculation of diversity indices (Shannon and Simpson), evenness (Pielou), and richness (Margalef and Menhinick) indices to investigate the diversity of earthworms. Diversity indices were analyzed using PAST (version 3.04) software. Statistical tests were conducted using SPSS to assess the diversity, abundance, and biomass of earthworms across variables.
Results: In a study of four deciduous tree species (hornbeam, beech, oak, and ironwood), four genera of corticolous earthworms were identified: Eisenia, Dendrobaena, Dendrodrillus, and Apporecoeda, with respective abundance percentages of 32%, 20.46%, 45.94%, and 1.6%. Notably, Eisenia showed the highest abundance and biomass among corticolous earthworms, primarily in hornbeam trees. The impact of tree species was significant on corticolous earthworm biodiversity, though differences in earthworm abundance and biomass were not statistically significant. The highest Shannon and Simpson diversity indices were recorded for oak (0.16 and 0.23, respectively), while the lowest values were found in ironwood (0.02 and 0.03). The Margalef richness index was highest in hornbeam (0.14) and lowest in ironwood (0.01). Notably, the greatest abundance and biomass of corticolous earthworms were associated with hornbeam, followed by oak, beech, and ironwood. The Pielou evenness and Menhinick richness indices varied significantly across different stages of deadwood decay. The highest values for Shannon diversity (0.34), Menhinick richness (0.32), and Margalef richness (0.24) were found in hornbeam deadwood at decay stage 2, indicating that biodiversity indices differed significantly across decay stages in this species. ANOVA results also showed that the degree of decay significantly affected the abundance and biomass of corticolous earthworms, with the highest abundance and biomass observed at decay stage 3 and the lowest at stage 1.
Conclusion: Among the study variables, including deadwood species type, decay stage, canopy cover (under the forest canopy or in canopy gaps), and altitude, only the degree of deadwood decay significantly influenced changes in the abundance and biomass of subcortical earthworms. This suggests that, unlike forest soils where earthworm distribution is highly variable both vertically and horizontally, subcortical earthworms exhibit a relatively uniform distribution. This uniformity points to the consistent, favorable conditions beneath deadwood bark for earthworm survival. Given the impacts of climate change and human disturbances, maintaining various types of deadwood at different altitudes and canopy positions can play a crucial role in supporting earthworm biodiversity.
Background: Earthworms make up a significant portion of the soil's invertebrate biomass and play a vital role in enhancing the physical, chemical, and biological characteristics of the soil. Earthworms enhance ecosystem performance and boost primary production by altering the soil structure and decomposing organic matter. Earthworms are classified into different categories based on their behavior and feeding habits. The most important ones include epigeic, anecic, and endogeic earthworms. Additionally, some earthworms, such as arboreal and corticolous species, inhabit unusual environments. This study aims to investigate the effect of dead wood on the biodiversity and abundance of corticolous earthworms in the forests of the eastern Hyrcanian region. In this regard, earthworm species found beneath the bark of deadwood (four species) were identified and classified in this research. Additionally, an attempt was made to analyze the effect of different deadwood species and their degrees of decay on various indices of earthworm biodiversity and evenness. To evaluate the impact of different locations within the deciduous temperate forests of eastern Hyrcania, the abundance of earthworms was examined and compared under the forest canopy and in forest gaps.
Methods: The study area is located in District-1 of Dr. Bahramnia Forestry Project, the eastern part of Hyrcanian forests. The research was conducted in parcels 1, 4, 7, 8, 31, and 32, which respectively include tree cover types of oak-hornbeam, ironwood-hornbeam, hornbeam-ironwood, beech-hornbeam, and beech-hornbeam. In this study, 119 samples of fallen deadwood from four species (beech, hornbeam, oak, and ironwood) were randomly selected from beneath the forest canopy and forest gaps at two elevations, 150 and 950 meters. These samples were classified into four degrees of decay based on their physical characteristics. After separating the bark with a sharp knife, the earthworms underneath were collected and initially stored in 15% ethanol, then transferred to 75% ethanol after one day, and finally to a 4% formalin solution. The earthworms were identified to the genus level using available identification keys. Their mass was measured after drying in an oven for 48 h, with an accuracy of 0.0001 g. Data analysis included the calculation of diversity indices (Shannon and Simpson), evenness (Pielou), and richness (Margalef and Menhinick) indices to investigate the diversity of earthworms. Diversity indices were analyzed using PAST (version 3.04) software. Statistical tests were conducted using SPSS to assess the diversity, abundance, and biomass of earthworms across variables.
Results: In a study of four deciduous tree species (hornbeam, beech, oak, and ironwood), four genera of corticolous earthworms were identified: Eisenia, Dendrobaena, Dendrodrillus, and Apporecoeda, with respective abundance percentages of 32%, 20.46%, 45.94%, and 1.6%. Notably, Eisenia showed the highest abundance and biomass among corticolous earthworms, primarily in hornbeam trees. The impact of tree species was significant on corticolous earthworm biodiversity, though differences in earthworm abundance and biomass were not statistically significant. The highest Shannon and Simpson diversity indices were recorded for oak (0.16 and 0.23, respectively), while the lowest values were found in ironwood (0.02 and 0.03). The Margalef richness index was highest in hornbeam (0.14) and lowest in ironwood (0.01). Notably, the greatest abundance and biomass of corticolous earthworms were associated with hornbeam, followed by oak, beech, and ironwood. The Pielou evenness and Menhinick richness indices varied significantly across different stages of deadwood decay. The highest values for Shannon diversity (0.34), Menhinick richness (0.32), and Margalef richness (0.24) were found in hornbeam deadwood at decay stage 2, indicating that biodiversity indices differed significantly across decay stages in this species. ANOVA results also showed that the degree of decay significantly affected the abundance and biomass of corticolous earthworms, with the highest abundance and biomass observed at decay stage 3 and the lowest at stage 1.
Conclusion: Among the study variables, including deadwood species type, decay stage, canopy cover (under the forest canopy or in canopy gaps), and altitude, only the degree of deadwood decay significantly influenced changes in the abundance and biomass of subcortical earthworms. This suggests that, unlike forest soils where earthworm distribution is highly variable both vertically and horizontally, subcortical earthworms exhibit a relatively uniform distribution. This uniformity points to the consistent, favorable conditions beneath deadwood bark for earthworm survival. Given the impacts of climate change and human disturbances, maintaining various types of deadwood at different altitudes and canopy positions can play a crucial role in supporting earthworm biodiversity.
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