Effects of plant species on soil quality in natural and planted areas of a forest park in northern Iran.

Reforestation may help protect the health of endangered forest ecosystems. To implement this action, it is important to evaluate the effects of the planted species on soil quality. Previous studies have demonstrated that soil properties are closely driven by the effects of plant roots and plant remains (quantity and quality) reaching the soil surface. However, little research is available about the effects of plant species on soil quality of reforested sites compared to natural forest ecosystems. This study evaluates the changes in the main soil properties between two 30-40 year-old stand types in forest areas of northern Iran: i) two stands, each one comprising a natural species (Parrotia persica or Pinus taeda); and ii) two stands, each one with planted trees (Quercus castaneifolia or Alnus glutinosa). Compared to reforested sites, the soils with natural trees showed higher root weight density (+43%), pH (+17%), and organic carbon (+64%). These differences led to higher nutrient contents, microbial respiration, aggregate stability, and water retention in soils with natural trees, as confirmed by the correlation analysis. A principal component analysis provided a meaningful combined factor (the first principal component) that showed a clear discrimination in soil quality and fertility among natural and reforested species. The calculation of a soil quality index confirms that planted species may lead to an overall lower quality of soils with planted species compared to natural forest. Since the lower soil quality of planted forests can be also the result of unsuitable management practices, this study suggest that forest operations in reforested areas should be avoided, since this could lead to negative effects on soil quality and contribute to an increase in the risk of soil degradation.

Influence of crops on soil properties in agricultural lands of northern Iran.

This study evaluates the effects of land use and soil management on a combination of physico-chemical, biological and hydrological properties of soil, in order to assess its quality. Three land uses were selected at the Fuman area, near Masouleh (Iran), grouping soils covered by tea, garden crops and rice. A total of 24 soil samples (3 land uses × 4 replications × 2 soil layers, topsoil and sub-surface soil) was collected; microbial respiration, available water, stability of soil aggregates, pH, organic matter, cation exchange capacity and nutrient content (P, K, N, Mg and Ca) were determined in each land use/soil layer. In comparison with other land uses, garden showed the highest available water, aggregate stability, microbial respiration, nutrient contents and cation exchange capacity, whereas the latter three soil properties had the lowest values in soils covered by tea and rice crops. Based on these results, under the experimental conditions garden had the highest soil quality among the investigated land uses. Conversely, much caution must be paid to some soil properties of tea and rice crops, such as cation exchange capacity, microbial respiration and nutrient contents, which are the lowest among the investigated land uses. Moreover, the differences in the analysed soil properties between the two soil sampling depths were statistically significant (p < 0.05). Finally, a Principal Component Analysis clearly clustered soils covered by garden, tea and rice crops in three differentiated groups according to the sampled soil properties. This study provides a contribution in understanding the variability of soil properties under different land uses, indicating that some of these properties must be considered with caution, in order to avoid a decay of soil health.