# Short-Term Effects of Pine Plantations on Vegetation and Soil in Northern Mongolia
## 4 Discussion  
The establishment of productive forest plantations is becoming an important silvilvil cultural issue in Mongolia. In the study region, plantations are primarily monocultures,  
Figure 6: Relationships between Shannon diversity index and soil properties across different plots. Shannon index (H\({}^{\prime}\)): ranges from 0.172 to 0.816; assesses species diversity by accounting for both richness and evenness. **(a)** Shannon vs. pH: ranges from 6.8 to 8.2; quantifies soil acidity and alkalinity. **(b)** Shannon versus SOM (%): soil organic matter ranges from 15% to 35%, indicating organic content. **(c)** Shannon versus EC (dS/m): electrical conductivity ranges from 0.3 to 0.8 dS/m and quantifies soil salinity. Note: The blue shading denotes 95% confidence intervals, the trend lines illustrate linear regression fits, and the R\({}^{2}\) values reflect the proportion of variation explained. consisting only of Scots pine (_P. sylvestris_ L.). Scots pine is a light-demanding tree species that plays an important role not only in the domestic wood industry, but also in forest ecosystem sustainability in Mongolia. Several open questions regarding Scots pine in Mongolia include whether to plant or rely on natural regeneration; which regeneration method produces the greatest understory diversity; the optimal spacing for planting; and the effect of planting tree on the growth and development of the over story pine, understory diversity, and soil properties. Soil water content decreased with the increasing tree age, while the thickness of the surface dry layer increased, leading to significantly greater soil drying. In the 4-year-old forests, soil moisture was adequate, and seasonal rainfall could partially compensate for the soil water deficit. However, in 9-year-old forests, water deficit became a serious concern at high tree densities, where seasonal rainfall did not completely offset the soil water deficit at densities greater than 400 trees per hectare (trees ha\({}^{-1}\)). Consequently, the soil remained relatively dry at the end of the rainy season, even after more than 640 mm of rainfall. The 15- and 30-year-old forests also experienced significant drought due to their drying effect on the soil. Overall, the trees promoted soil water loss, creating a serious imbalance between the water supply and demand in this desert environment. High-density planting accelerated the deterioration in the water environment (i.e., soil drying) and threatened the future survival of the trees and other plants. Thus, ecological managers must reduce tree planting and test the effectiveness of reducing the density to 333 trees ha\({}^{-1}\) during the young stage [47]. Natural regeneration in the Tujiin nars Scots pine forests has been impeded by fires and grazing, increasing the emphasis on planting to regenerate these forests. Although this study was not designed to directly compare planting with natural regeneration, we included comparisons of the planted stands to a naturally regenerated stand of approximately the same age to highlight different management effects. On one hand, several studies [48; 49; 50; 51] have noted the importance of establishing forest plantations with native tree species, which can have a highly diverse understory of indigenous species. On the other hand, [PERSON] [52] and [PERSON] [53] stated that plantation forests typically are less favorable as a habitat than naturally regenerated stands for a wide range of taxa, particularly in the case in the even-aged, single-species stands. In our case, species richness (30.57%-75.18%) and plant coverage (18.4%-48.3%) were higher in the planted forests than in the naturally regenerated stand (SR-68.16% and PC-48.3%) (Figure 3). The contrary effects may be due to legacy effects of previous land use [54; 55]. For example, [PERSON] et al. [56] found that understory diversity was greater in pine plantations established after harvesting a forest than on old agricultural fields.