The Three-North Shelterbelt Project is the largest ecological engineering initiative in China to date, distinguished by its immense scale, extended construction period, and widespread benefits for the population. The gross ecosystem product (GEP) serves as a crucial indicator for assessing ecological benefits. This study focuses on the Three Northern Protection Forest Project Area, utilizing GEP calculations for the years 2000 to 2020. This study evaluates variations in the production values of different ecosystem services to reflect the ecological conservation benefits of the restoration project. Additionally, it analyzes the spatiotemporal evolution and trends of the GEP calculations, offering data references and decision support for the enduring efficacy of ecological restoration projects. The findings are as follows. (i) Between 2000 and 2020, the GEP of the Three-North region exhibited significant growth with continuous enhancement of various ecosystem service functions; the most substantial rate of change was observed in the water conservation function, followed by carbon sequestration and oxygen release, soil retention, windbreak and sand fixation, flood regulation, and environmental purification functions. (ii) The per-unit area value of different ecosystem types generally increased; the forest ecosystem displayed the largest growth rate at 61.18%, followed by shrubland ecosystems at 49.84%. (iii) The spatial distribution of ecosystem service in the Three-North region displayed a clustering trend alongside notable spatial heterogeneity. High-high clustering zones were identified in areas such as the Tianshan Mountains, Altai Mountains, Qilian Mountains, and Greater and Lesser Khingan Mountains. Conversely, low-low clustering areas were scattered, forming patchy distributions in regions like the Tarim Basin, northern Qinghai-Tibet Plateau, and the Hexi Corridor. This study, by analyzing the gross ecosystem product of the Three-North Shelterbelt Project region, unveils the spatial distribution characteristics, trends, and variations in ecosystem service values over the past two decades. It provides data support and decision guidance for the long-term efficacy of future ecological conservation and restoration projects. This study incorporates the GEP accounting method into the assessment of the effectiveness of major conservation projects. Compared to the traditional methods of effectiveness assessment, this represents a significant exploration and innovation.

The traditional volume-derived biomass method is limited because it does not fully consider the carbon sink of young trees, which leads to the underestimation of the carbon sink capacity of a forest ecosystem. Therefore, there is an urgent need to establish an allometric biomass model of young trees to provide a quantitative basis for accurately estimating the carbon storage and carbon sink of young trees. The destructive data that were used in this study included the biomass of the young trees of the two dominant species (Betula pendula subsp. mandshurica (Regel) Ashburner & McAll and Populus × tomentosa Carrière) in China, which was composed of the aboveground biomass (B_a), belowground biomass (B_b), and total biomass (B_t). Univariate and bivariate dimensions were selected and five candidate biomass models were independently tested. Two additive allometric biomass model systems of young trees were established using the proportional function control method and algebraic sum control method, respectively. We found that the logistic function was the most suitable for explaining the allometric growth relationship between the B_a, B_t, and diameter at breast height (D) of young trees; the power function was the most suitable for explaining the allometric growth relationship between the B_b and D of young trees. When compared with the independent fitting model, the two additive allometric biomass model systems provide additive biomass prediction which reflects the conditions in reality. The accuracy of the B_t models and B_a models was higher, while the accuracy of the B_b models was lower. In terms of the two dimensions—univariate and bivariate, we found that the bivariate additive allometric biomass model system was more accurate. In the univariate dimension, the proportional function control method was superior to the algebraic sum control method. In the bivariate dimension, the algebraic sum control method was superior to the proportional function control method. The additive allometric biomass models provide a reliable basis for estimating the biomass of young trees and realizing the additivity of the biomass components, which has broad application prospects, such as the monitoring of carbon stocks and carbon sink evaluation.

Climate change is heavily altering plant distributions, posing significant challenges to conventional agricultural practices and ecological balance. Meanwhile, mixed species planting emerges as a potent strategy to enhance agricultural resilience, counteract climate change, preserve ecological balance, and provide a solution to economic instability. The MaxEnt model was used to predict the suitable area of Citrus reticulata under five climate scenarios and to explore affecting environmental factors. Litchi chinensis, Punica granatum, and Lycium chinense were selected as mixed species to analyze the spatial distribution and centroid migration trend of potentially suitable areas. The research results show the following: (1) The primary environmental factors impacting C. reticulata distribution are annual precipitation (1000–4000 mm), precipitation of driest quarter over 100 mm, and mean temperature of coldest quarter (12–28 °C). Crucially, the mixed species exhibited similar environmental sensitivities, indicating mutual mixing suitability. (2) Currently, the C. reticulata suitable area is of 240.21 × 10⁴ km², primarily in South, East, Central, and Southwest China, with potential for expansion to 265.41 × 10⁴ km² under the 2090s SSP1-2.6 scenario. (3) The geometric center of the moderately-to-highly suitable areas for C. reticulata is located in Hunan Province. Future scenarios show the C. reticulata’s centroid migrating northwest, with distances of less than 110 km. Mixed planting trends toward higher latitudes, fluctuating from 6 km to 210 km. (4) Mixed planting area planning: C. reticulata and L. chinensis are suitable for mixed planting in South China. C. reticulata and P. granatum, C. reticulata and L. chinense are suitable for mixed planting in most areas of Central, East, Southwest, and South China. This research presents a new perspective on using mixed design principles for ecological adaptation and the sustainable mixed planting of C. reticulata, in response to China’s changing climate. This approach is expected to help the economic fruit tree industry enhance ecological resilience and economic stability in the face of future climate change challenges.