Document Type : Research Paper
Authors
1
Associate Prof., Forests and Rangelands Research Department, Khuzestan Agricultural and Natural Resources Research and Education Center, Agricultural Research Education and Extension Organization(AREEO), Ahvaz, Iran
2
Associate Professor, Forest and Rangeland Research Institute, AREEO, Tehran, Iran.
3
Assistant Prof., Forests and Rangelands Research Department, Khuzestan Agricultural and Natural Resources Research and Education Center, Agricultural Research Education and Extension Organization(AREEO), Ahvaz, Iran
4
Assistant Professor, Forest and Rangeland Research Institute, AREEO, Tehran, Iran
10.22092/ijfrpr.2025.367976.1655
Abstract
Background and Objectives: Soil, as one of the essential elements of the ecosystem, plays a major role in the creation, transformation, and diversity of forest species. On the other hand, vegetation type also plays a significant role in the alteration and development of the physical, chemical, and biological properties of soils. Therefore, changes in vegetation types and soil properties should not be considered separately. Since forest degradation begins with soil degradation, understanding the characteristics of soil is vital for maintaining soil health and function for the sustainable management of forest areas. This study was designed and conducted as the first phase of long-term monitoring and evaluation of changes in soil biological, physical, and chemical properties in forest stands and tree plantations in the Sindhi Sahara region.
Methodology: In this study, fixed sample plots with the same geographical orientation were established in natural woodlands along the Karkheh River. In each sample plot, 15 soil samples were randomly collected from a depth of 0 to 15 cm under the crown of the dominant tree species, from the trunk to the outer edge of the crown, in an eastward direction. For the control samples, 15 soil samples were randomly taken from a depth of 0 to 15 cm outside the canopy and in areas without tree cover. In the laboratory, physical and chemical characteristics including soil texture, organic matter percentage, pH, EC, P, K, Mg, Fe, Zn, and Cu, as well as biological soil characteristics including basal respiration, stimulated respiration, microbial biomass, and nitrification potential were measured. After checking the normality of the data, independent t-tests and Mann-Whitney tests were applied to examine the significance of differences in soil characteristics between under-canopy and outside-canopy samples. Correlations among soil characteristics were also examined using Pearson and Spearman tests.
Results: The findings of the study showed that the basal and stimulated respiration rates in the soil under the crowns of Tamarix and Populus euphratica trees were higher than those outside the crowns. Although the increase in basal respiration was not statistically significant, the difference for stimulated respiration was significant. The amounts of microbial biomass and nitrification potential in the control area (outside the tree canopy) were higher, and this difference was significant for microbial biomass at the 99% confidence level but not significant for the nitrification potential index. The levels of chemical elements (P, K, Fe, Zn, Mg, and Cu), organic matter, pH, and EC in the soil under the canopy were higher than in the control area, and the differences in organic matter percentage and pH were significant at the 99% level.
Conclusion: The general findings of the study indicated that the higher levels of chemical elements and organic matter in the soil under the tree crowns compared to the control increased basal and stimulated respiration. However, it is likely that environmental stresses, including high salinity, reduced microbial respiration in the soil under the crown compared to the control area. Given the positive and significant effect of the Tamarix shrub on increasing stimulated respiration and carbon sequestration, the preservation and restoration of this valuable native species in its natural habitat is a priority. However, this plant increases the electrical conductivity (salinity) of the soil due to the secretion of salt from its glandular structures. Therefore, its uncontrolled development and dominance in natural woodlands, which may occur invasively due to deforestation and fire, should be prevented.
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