The crown closure of Platycladus orientalis forests has a wide-ranging impact on vegetation and soil, thereby affecting the overall functioning of the ecosystem. There is limited research on the effects of the Platycladus orientalis forest crown closure on changes in community plant functional traits, and their interactions are not yet clear. Therefore, we investigated 50 plots of different types of Platycladus orientalis crown closure, and we measured the functional traits of nine shrub species and 68 herb species in 50 plots under five different densities of Platycladus orientalis forests in the Loess Plateau. The consequence of Pearson’s correlation analysis showed significant positive correlations between LC and LTD, LN and LP, LN and LNP, LN and LV, LN and H, LP and LV, LP and H, and SLA and LV (p < 0.05). LC was significantly negatively correlated with LP, LC with SLA, LC with LV, LN with LTD, LP with LNP, LP with LTD, and LTD with H (p < 0.05). Only the soil phosphorus content (SP) and soil water content (SWC) showed a significant positive correlation with multiple plant functional traits. The crown closure of Platycladus orientalis forests increased significantly, as did the plant functional features. Changes in the Platycladus orientalis forest crown closure significantly increased the LC, LV, LN, LP, and SLA in plant functional traits. An increase in Platycladus orientalis forest crown closure significantly increased the soil organic carbon (SC), soil phosphorus content (SP), soil nitrogen content (SN), soil water content (SWC), field capacity (FC), and soil porosity (PO). Based on a structural equation model, we found that, while changes in the Platycladus orientalis forest crown closure did not directly affect plant functional traits, they could indirectly influence these traits through soil factors, primarily the soil water content (SWC) and soil phosphorus content (SP) (p < 0.05). Additionally, the mechanisms of the Platycladus orientalis forest crown closure’s impact on different functional traits vary. The research results provide scientific elements for the ecological restoration of Platycladus orientalis forests on the Loess Plateau.

Plant functional traits (PFTs) can reflect the response of plants to environment, objectively expressing the adaptability of plants to the external environment. In previous studies, various relationships between various abiotic factors and PFTs have been reported. However, how these factors work together to influence PFTs is not clear. This study attempted to quantify the effects of topographic conditions, soil factors and vegetation structure on PFTs. Four categories of variables were represented using 29 variables collected from 171 herb plots of 57 sites (from different topographic and various herb types) in Xindian SWDP. The partial least squares structural equation modeling showed that the topographic conditions and soil properties also have a direct effect on plant functional traits. Among the topographic conditions, slope (SLO) has the biggest weight of 0.629, indicating that SLO contributed the most to plant functional traits and vegetation structure. Among soil properties, maximum water capacity (MWC) contributes the most and is followed by soil water content (SWC), weighted at 0.588 and 0.416, respectively. In a word, the research provides new points into the quantification of the correlation between different drivers that may be important for understanding the mechanisms of resource utilization, competition and adaptation to the environment during plant recovery.

Competition is an essential driving factor that influences forest community sustainability, yet measuring it poses several challenges. To date, the Competition Index (CI) has generally been the tool of choice for quantifying actual competition. In this study, we proposed using the Total Overlap Index (TOI), a CI in which the Area Overlap (AO) index has been adapted and modified to consider the “shading” and “crowding” effects in the vertical dimension. Next, based on six mixed forest plots in Xiaolong Mountain, Gansu, China, we assessed the results to determine the TOI’s evaluation capability. Individual-tree simulation results showed that compared to the modified Area Overlap index (AO_M), the TOI has superior quantification capability in the vertical direction. The results of the basal area increment (BAI) model showed that the TOI offers the best evaluation capability among the four considered CIs in mixed forest (with Akaike Information Criterion (AIC) of 1041.60 and log-likelihood (LL) of −511.80 in the model fitting test, mean relative error of −28.67%, mean absolute percent error of 117.11%, and root mean square error of 0.7993 in cross-validation). Finally, the TOI was applied in the Kaplan–Meier survival analysis and Cox proportional-hazards analysis. The Kaplan–Meier survival analysis showed a significant difference between the low- (consisting of trees with the TOI lower than 1) and high-competition (consisting of trees with the TOI higher than 1) groups’ survival and hazard curves. Moreover, the results of the Cox proportional-hazards analysis exhibited that the trees in the low-competition group only suffered 34.29% of the hazard risk that trees in the high-competition group suffered. Overall, the TOI expresses more dimensional information than other CIs and appears to be an effective competition index for evaluating individual tree competition. Thus, the competition status quantified using this method may provide new information to guide policy- and decision-makers in sustainable forest management planning projects.

In contrast to intensive management practices focused on wood production, plantations designed to safeguard fragile environments prioritize the sustainable fulfillment of ecological functions. To assess the potential for Chinese pine (Pinus tabuliformis Carr.) plantations in the Loess Hilly Region to effectively serve their ecological protection role over the long term, we selected nine indices representing biological stability, resistance stability, and functional stability. Employing a novel unit circle method, we evaluated the total stability (sum of the three stability components) of 44 plantation plots in Huanglong Mountain. We also explored the connections between total stability and standing spatial structure parameters to offer insights for promptly enhancing stability through thinning. The findings revealed that 79.5% of Chinese pine plantations exhibited moderate total stability, with 20.5% demonstrating good stability. Most plots displayed a random distribution pattern, moderate size differentiation, low species spatial mixing, and high stand crowding. Among the correlations analyzed, mingling exhibited the highest coefficient, followed by differentiation, while the uniform angle index showed the weakest correlation, and crowding displayed an insignificant correlation. While the presence of good functional stability contributed to the moderate total stability, addressing inadequate biological and resistance stability necessitates thinning measures. This study identifies spatial structure types negatively linked to total stability, offering targeted management insights for enhancing the stability of Chinese pine plantations. The stability assessment methodology and indicators presented in this study can serve as a valuable reference for similar plantations with comparable functions and planting conditions.