The sensitivity of tree growth to external climatic factors varies with tree age; however, most previous studies have primarily focused on natural forest species, while comparable investigations on plantation species remain limited, especially in China's sandy lands. In this study, we developed ring-width chronologies for four age classes-young, middle-aged, mature, and overmature-of Simon poplar (Populus simonii Carr.) plantations located in a representative distribution area of the Ordos Plateau, northern China. our objective was to quantify the age-dependent sensitivity of radial growth to climatic variability for Simon poplar plantations. The results indicated that the statistical quality of the Simon poplar chronologies exhibited a consistent improvement with increasing stand age: chronologies from younger stands displayed lower statistical quality, whereas those from older stands demonstrated higher statistical quality. The climate-growth relationship of Simon poplar chronologies showed a distinct age-related pattern, characterized by a progressive increase in sensitivity from young to mature stands, followed by a decline in old stands. These findings enhance our understanding of age-dependent variations in climatic sensitivity and provide empirical evidence to evaluate the temporal stability of growth-climate relationships in plantation forests of northern China under climate warming.

The asynchronous changes in vegetation greenness and resilience (the capacity of ecosystems to absorb disturbances and maintain their functions) may threaten the long-term sustainability of ecological restoration. However, their coupling mechanisms and responses to climate change and human activities in desertification areas remain poorly understood. Here, we used the kernelized Normalized Difference Vegetation Index (kNDVI) and its temporal autocorrelation to characterize vegetation greenness and resilience from 2000 to 2020 in Yellow River Basin in Inner Mongolia, China. Random forest (RF) models were employed to quantify the dominant drivers of vegetation resilience. Results indicate a persistent greening trend across the study region, 96.62% of pixels experienced kNDVI increases. Meanwhile, resilience exhibits a pronounced turning point around 2011, transitioning from an increasing to a declining trajectory, while the proportion of resilience-declining areas increased from 18.09% in 2000–2010 to 45.85% in 2011–2020. The greenness–resilience relationship transitioned from synchronous increases to systematic decoupling, resulting in a high-greenness–low-resilience regime. The dominant drivers of vegetation resilience shifted from climate factors during 2000–2010 (contributing 51.57%) to grazing pressure during 2011–2020 (contributing 32.12%). Threshold analysis further revealed that vegetation resilience decline in the later decade resulted from the combined effects of intensified hydrological constraints and grazing pressure. Therefore, we recommend incorporating ecosystem resilience into restoration frameworks and coordinating the regulation of water availability and grazing pressure to promote the synergistic enhancement of greenness and resilience, thereby ensuring long-term ecosystem stability.

Introduction:Global climate change-induced extreme drought has triggered widespread forest growth decline and tree mortality worldwide, making the processes of forest decline and their responses to environmental conditions a major research focus. In the Longtan Catchment of the Loess Plateau, Chinese pine (Pinus tabulaeformis Carr.) plantations exhibit varying levels of degradation, yet the growth trends and climate-growth relationships across different health gradients remain poorly understood. Methods:We developed tree-ring width chronologies for Chinese pine plantations representing five distinct health conditions: healthy, relatively healthy, slightly declining, moderately declining, and severely declining. Standard dendrochronological techniques were employed to compare growth rates, chronology statistical quality, and the sensitivity of radial growth to climate variables during both the growing and non-growing seasons. Results:The results showed that the healthy chronology exhibited a clear increasing trend in growth rate over time and relatively high statistical quality. In contrast, declining chronologies showed no evident long-term increase in growth rate and were characterized by lower chronology quality. Regarding climate responses, the strength of climate signals during the growing season decreased progressively with increasing decline severity. While healthy trees displayed strong positive correlations with climate variables, these relationships weakened and shifted toward negative associations in the moderately and severely declining stages. Similarly, positive climate signals in the non-growing season declined markedly along the health gradient, weakening substantially in the severely declining stage. Discussion:These findings deepen our understanding of growth decline and its environmental drivers in the Loess Plateau. The health-dependent sensitivity shifts identify a critical window for proactive intervention. Our study suggests that early detection and timely density regulation, such as thinning during mild-to-moderate decline, are essential. Furthermore, management strategies should prioritize conserving non-growing-season water-especially spring moisture-to mitigate the risk of severe forest decline and support sustainable ecological restoration.

ABSTRACT Terracing is widely applied for soil and water conservation in semi‐arid regions; however, its influence on forest ecohydrological processes remains insufficiently quantified, as previous studies have largely emphasized erosion control rather than plant–soil–atmosphere interactions. This study evaluated how terracing regulates these interactions in Pinus tabuliformis plantations on the Loess Plateau, China. Field measurements during the 2023–2024 growing seasons quantified soil water content (SWC), canopy conductance (Gc), and stand transpiration (T_stand) under terraced and unterraced conditions. Terraced plots maintained higher SWC (0.11 vs. 0.09 m 3 m −3 ; +17%–23%) and greater T_stand (0.39–0.52 vs. 0.20–0.29 mm d −1 ), with peak differences of 80%. Terracing delayed diurnal transpiration peaks and enhanced midday fluxes, indicating differences in vegetation water‐use dynamics under improved soil water availability. T_stand correlated strongly with SWC ( R 2 = 0.362, p < 0.001), whereas transpiration stability improved by 38%. These findings demonstrate that terracing increases soil water availability, regulates soil–plant–atmosphere interactions and supports more stable vegetation water use under water‐limited conditions in semi‐arid forests.

Introduction:Climate warming-induced extreme drought has led to substantial growth decline and extensive tree mortality in forests worldwide, with such phenomena being particularly pronounced in plantation ecosystems. This study aimed to assess the divergent climatic responses of radial growth between healthy and declining Simon poplar (Populus simonii Carr.) plantations. Methods:Separate ring-width chronologies were developed for healthy (1996-2024 period) and declining (1994-2024 period) Simon poplar plantations in the Engebei Ecological Demonstration Zone of Ordos, to explore their differing responses to climate factors. Results:All statistical parameters of the declining chronologies were higher than those of the healthy ones, indicating that the declining chronologies exhibited higher quality and stronger common signals, whereas the healthy chronologies were comparatively weaker. Climate-growth response analyses revealed that radial increments of declining trees displayed significantly greater sensitivity to climatic variability than healthy trees, while the basal area increment showed the opposite pattern-declining trees had markedly lower climatic sensitivity than healthy individuals. As Simon poplar trees enter the growth decline phase, drought stress exerts increasingly strong suppressive effects on radial growth, while the warming-induced stimulation of basal area increment becomes progressively weaker. Discussion:The divergent responses of radial growth and basal area increment to climate variability underscore the key climatic determinants shaping the decline of poplar plantations across the study area. Overall, this study contributes to a mechanistic understanding of climate-driven growth decline in poplar plantations of the Ordos area and provides a scientific basis for ecological restoration and sustainable management of local degraded plantations.

Stand thinning is a globally implemented forest management practice to alleviate resource competition and optimize stand productivity. However, how thinning dynamically reshapes intra-annual growth phases (contraction, expansion, and net increment) and vertical water-uptake strategies under changing climate conditions remains poorly understood. Here, we conducted a four-year (2022–2025) continuous monitoring experiment across a thinning gradient (T0%, T45%, T55%, T65%, T80%) in a Robinia pseudoacacia plantation on China’s Loess Plateau. The results demonstrated that thinning significantly enhanced radial growth following a non-linear pattern, with optimal performance at 55% intensity (T55%), achieving cumulative increment of 20.81 mm. This enhancement was primarily driven by delayed seasonal cessation by approximately 20 days during drought years, creating an additional growth window. Although thinning intensified daytime stem contraction under high vapor pressure deficit (VPD), thinned trees demonstrated superior nocturnal rehydration capacity, enabling rapid recovery and transition to net growth. Deep soil water (100–200 cm) significantly contributed to nocturnal expansion, with T55% treatment exhibiting the highest water-refilling baseline. This finding demonstrated that moderate-to-heavy thinning (T55%) represents an evidence-based approach to enhance plantation resilience and productivity through optimized micro-scale phenology and deep-water utilization, providing scientific support for the transition from vegetation expansion to functional enhancement on the Loess Plateau.

Large-scale forest plantations have been established worldwide to promote ecological restoration. However, the effects of climate change on the radial growth of these plantations remain unclear. To fill this research gap, we collected tree-ring data from 82 sampling sites including three typical plantation species across the Loess Plateau, aiming to analyze growth trends and their climatic drivers. The results showed that the majority of plantation sites (64 sites, 78%) exhibited a growth increase followed by decline, with most transition years to growth decline occurring after 2010. Climate variables explained more than 78% of the variation in tree radial growth, among which deep soil water content (30-300 cm) and precipitation were identified as the dominant influencing factors. Compared with those at sites showing growth increase, those experiencing growth decline were generally characterized by more unfavorable climatic conditions, including lower precipitation and deep soil water content, with the turning years from increase to decline often corresponding to abnormal weather events. This study reveals the decline of plantations after 2010 in the Loess Plateau and highlights the critical role of climate change in this process, emphasizing the importance of rational plantation planning and enhanced management under future climate change.

IntroductionWater scarcity severely constrains the sustainability of plantations in semi-arid regions by reducing soil water availability and increasing drought stress. Thinning is a crucial silvicultural practice for forest restoration and water regulation, yet the responses of soil water content (SWC) to varying thinning intensities during a dry year and a normal year remain insufficiently understood.MethodsThis study evaluated the effects of thinning on SWC in Chinese pine (Pinus tabuliformis) plantations on the Loess Plateau of China, with five thinning intensities: 0% (control), 15% (light), 30% (moderate), 45% (heavy), and 60% (extremely heavy). SWC at depths of 0 -200 cm was repeatedly monitored during the growing seasons of 2023 (dry year) and 2024 (normal year). Vegetation structure, rainfall redistribution, and soil properties were periodically measured.ResultsThinning increased mean 0 -200 cm profile SWC by 4.96 -18.06% in the dry year (2023) and by 5.33 -18.87% in the normal year (2024), compared with the 0% thinning control. Although SWC in 2024 was higher than in 2023, thinning exerted a similar effect on SWC in both study years, with the 30% thinning intensity yielding the most pronounced positive improvement in deep SWC (30 -200 cm; +19.14% -25.26%). Thinning significantly improved the temporal stability of deep SWC in 2024, and the 15% and 30% thinning treatments consistently exhibited relatively low coefficient of variation values during the monitored observation period. Redundancy analysis (RDA) indicated that SWC was positively associated with net precipitation in both soil layers and in both study years. Additionally, deep SWC exhibited a positive association with soil organic carbon during both years, as well as with fine-root traits in 2024.DiscussionBased on the above results and the regional soil water carrying capacity, we recommend prioritizing an initial thinning intensity of approximately 30% (≈2,000 stems ha−1) to alleviate soil desiccation in Chinese pine plantations. This finding informs adaptive eco-rehabilitation strategies for plantation restoration on the Loess Plateau and other semi-arid regions and provides a practical basis for improving soil-water regulation and plantation resilience under increasing climatic stress.

Revegetation has been proposed as one of the effective methods for enhancing carbon (C) and nitrogen (N) sequestration. However, the magnitude and direction of soil C and N changes following revegetation remain unclear. To address this issue, we conducted a synthesis analysis based on 6,171 observations of soil organic carbon (SOC) and total nitrogen (STN) from 183 studies in 0–200 cm depth across the Chinese Loess Plateau. Our results revealed revegetation type-specific soil C and N stocks of four soil profiles (0–20, 20–100, 100–200, and 0–200 cm) following five restoration ages (0–5, 6–10, 11–20, 21–30, and > 30 years). In general, significant increases in soil C and N stocks were respectively, observed 21 and 31 years after revegetation for the whole soil layer. In addition, the soil C and N stocks of shrub and grassland were chronologically asynchronous between the deep layer (deeper than 100 cm) and shallow layers, whereas that of forest showed more or less similar temporal dynamics only with slight differences in change rates. Such cross-layer asynchronous were also presented for precipitation and temperature, of which the influences in different soil layers exhibited great nonlinear patterns with different turning points in response to the two climatic factors. Furthermore, compared with natural succession, planted vegetation induced relatively more intensive changes of soil C and N, especially for the forest. Overall, our results revealed revegetation-induced asynchronous changes of soil C and N particularly in the deep layers, and suggest that different patterns of soil C and N stocks should be incorporated into soil C and N modeling and estimation.

Introduction:Modern warming and associated aridification have intensified forest growth decline and tree mortality, weakening forest carbon sequestration. This study aims to investigate how Chinese pine (Pinus tabuliformis Carr.) responds to these climatic shifts across the Loess Plateau, a region highly sensitive to environmental changes. Methods:We synthesized tree-ring width chronologies from 60 sites spanning major geomorphological units of the Loess Plateau. To evaluate the impact of rapid warming, we compared climate-growth relationships between two distinct periods: the pre-warming phase (1901-1960) and the post-warming phase (1961-2012). Results:Before 1960, when warming and drying were not pronounced, radial growth generally increased across regions, primarily limited by moisture while temperature had a modest stimulatory effect. After 1960, as warming and aridification strengthened, growth declined across all geomorphological units. Moisture limitation intensified, and higher temperatures shifted from a weak benefit to a clear suppressive influence. Spatially, the southern Loess Plateau showed the highest sensitivity to both growing- and non-growing-season climate, while the western and eastern regions were less sensitive and primarily influenced by non-growing-season conditions. Discussion:The spatially heterogeneous responses identified in this tree-ring dataset underscore the complex impact of recent warm-dry trends on forest ecosystems. These findings are crucial for improving our understanding of forest dynamics in semi-arid regions and can guide adaptive forest management strategies to sustain ecosystem functioning under ongoing aridification of the Loess Plateau.

Plantations are primarily located in arid and semi-arid regions, where they significantly enhance regional ecosystem quality and service functions. Yet, recent climate warming has triggered widespread growth decline and tree mortality in these areas. In this study, we developed tree-ring width chronologies for Simon poplar (Populus simonii) across four age classes-young, middle-aged, mature, and overmature-in a typical area of the desert-shelter forests in the Kubuqi Desert of China. The aim was to examine age-dependent differences in growth decline and climate sensitivity across developmental stages. The results revealed distinct temporal variations in tree growth rates around 2010 across all age classes. Simultaneously, climatic sensitivity exhibited significant divergence during this transition period. Prior to 2010, Simon poplar exhibited relatively high radial growth rates and strong climatic sensitivity, with overall warming conditions promoting tree growth similarly across all age classes. After 2010, however, radial growth rates declined markedly, accompanied by a reduction in climate sensitivity. Climate warming induced drought stress exerted an overall inhibitory effect on growth after 2010, with suppression being more pronounced in mature and overmature stands than in young and middle stands. These findings provide empirical evidence for understanding the age-specific responses and possibility of tree mortality to recent intensified drought stress for desert-shelter forest in the Kubuqi Desert and offer scientific guidance for the sustainable management of plantation forest in northern China under changing climatic conditions.

Tree growth sensitivity to moisture availability is pivotal for assessing the forest adaptability to changing water availability and projecting future carbon sequestration and forest health. Climate warming could reshape the temporal shifts in moisture sensitivity, but both the direction and strength, and the underlying drivers remain unclear. In this study, we compiled a pan-continental tree-ring width dataset consisting of 2505 chronologies across the Northern Hemisphere in the period of 1960-2020. Using this dataset, we quantified the spatial patterns, temporal trends and climatic drivers of temporal variations in tree growth sensitivity to moisture. Specifically, we investigated the factors driving the warming effects on temporal variations in moisture sensitivity. We revealed that tree growth in over 78% of the studied forest stands was limited by moisture availability. The moisture sensitivity of tree growth increased in similar to 50% of forest stands, and it decreased in the remaining similar to 50%. Climate warming has contrasting impacts on moisture sensitivity. It enhances the moisture sensitivity in water-limited forests, and for tree species with drought-adapted hydraulic traits, but reduces that in energy-limited forests and for drought-vulnerable tree species. Our findings highlight the pivotal roles of background climate conditions and hydraulic traits of tree species in determining the forest vulnerability in a warmer climate regime. These insights are essential for guiding effective forest management practices and enhancing the accuracy of forest ecosystem modeling.

In the 21st century, factors such as global climate change, drought stress, and irrational anthropogenic land use practices have increasingly induced vegetation decline, creating a difficult challenge for sustainable forest management practices and biodiversity conservation. This phenomenon is characterized by a reduction in vegetation quantity, slower growth rate, a diminished biomass production, and the loss or weakening of ecological functions, including soil and water conservation, climate regulation, and air purification. As a significant indicator of ecological environment changes, vegetation decline has been extensively explored all around the world. However, existing studies have merely focused on a specific manifestation or mechanism of decline, lacking a comprehensive synthesis and visual analysis of the hot research areas in this field. Based on the VOSviewer and CiteSpace tools, this paper conducted a systematic investigation of the research hotspots and evolution in the field of vegetation decline by using the literature data published in the Web of Science (WOS) database from 2000 to 2024. Through bibliometric analysis, these indicators such as the number of published papers, citation frequency, and high-frequency co-occurring keywords were thoroughly analyzed. The results indicated that since 2000, both the annual and cumulative publication counts in the field of vegetation decline have demonstrated a pronounced upward trajectory. The research hotspots and focuses have evolved from fundamental to more nuanced inquiries, and from the localized to the holistic perspectives. Notably, "Drought" and "Climate Change" have consistently been the hotspots throughout the whole processes of vegetation decline research. Concurrently, advancements in technology and methodological innovations have facilitated the integration of more sophisticated and precise quantitative approaches into vegetation decline studies, which to a certain extent, helps to enhance the accuracy and reliability of the research. Consequently, in the future, it is essential to strengthen interdisciplinary cross-collaboration, promote the innovative application of research outcomes, and to deeply analyze the process of vegetation decline. Such efforts are imperative for the effective management of vegetation decline and the enhancement of ecosystem functions, ultimately contributing to the sustainability of global ecosystems.

Dryland ecosystems are now exposed to intensifying aridity and plant diversity loss, posing significant threats to the maintenance of ecosystem multifunctionality, defined as the capacity of ecosystems to simultaneously sustain multiple functions. Although many experiments and empirical studies have shown that local plant diversity promotes ecosystem multifunctionality, we have little understanding of the scale dependence of plant diversity effect and the roles of local plant loss (α diversity) and spatial homogenization (β diversity) in mediating ecosystem multifunctionality under shifting environmental conditions. Here, we investigate the effects of plant α- and β-diversity on soil multifunctionality across a 3200 km aridity gradient in China's drylands. We measure 12 variables related to soil carbon, nitrogen, and phosphorus cycling and storage to characterize soil functions, and quantified soil multifunctionality using both averaging and multiple threshold approaches. We examine how the relationships between plant α/β-diversity and soil multifunctionality shift along an aridity gradient, and assess the combined effects of plant α- and β-diversity on soil multifunctionality under aridity stress. We show that although both plant α- and β-diversity promote soil multifunctionality, the positive effect of α-diversity increases as aridity intensifies, whereas the contribution of β-diversity diminishes. In addition, the processes of complementarity and facilitation outweigh competition in community assembly as plant water stress tolerance becomes increasingly important. Despite their opposing patterns, the contributions of plant α- and β-diversity are approximately equivalent. Furthermore, plant α-diversity can promote β-diversity, synergistically enhancing soil multifunctionality. Our study highlights the importance of biodiversity conservation across scales in drylands and provides insights for designing aridity-specific biodiversity conservation policies.

Stretching from Lanzhou to Sanmenxia, the Ji-shaped bend of the Yellow River constitutes a key ecological and economic zone in the upper-middle reaches of the river. It acts as a major sand source and transmission corridor for sandstorms impacting Beijing, Tianjin, and eastern China. Grasping the long-term vegetation dynamics in this bend and forecasting its future trends is crucial for the high-quality development of the Yellow River Basin. In this research, multiple analytical methods were applied to investigate the spatiotemporal dynamics of vegetation: Theil-Sen Median trend analysis, Mann-Kendall test, Moran's I index, coefficient of variation, and GeoDetector model. Additionally, the Hurst index was used to assess potential future changes in vegetation coverage. The results showed that the fractional vegetation cover (FVC) in the Ji-shaped bend of the Yellow River demonstrated a continuous increasing trend at an average annual rate of 0.005 during the period 2001-2020, with areas experiencing improvement accounting for 86.79% of the total study region. This vegetation improvement area confirmed the effectiveness of regional ecological engineering implementation. Vegetation coverage across the study area exhibited substantial spatial heterogeneity while displaying a prominent agglomeration pattern. From the perspective of the coefficient of variation, the overall vegetation coverage in the region maintained high stability. Notably, areas with anti-persistent FVC variation (24.80%) outnumbered those with persistent variation (9.34%), with 65.86% of the area showing random variation, indicating a potential reverse-sustained trend. Among the key factors, soil type, precipitation, and land use type emerged as the primary drivers shaping the spatiotemporal distribution of FVC across the study region. Natural environmental factors exerted a more prominent influence than human activity factors.

Abstract. Tree rings serve as precise archives of the environmental conditions that influence tree growth. In this study, we collected tree-ring cores from Schrenk spruce (Picea schrenkiana) in the eastern Tianshan Mountains and developed a robust ring-width chronology. Growth-climate response analysis revealed that total precipitation from the previous July through the current June is the primary factor limiting radial growth in this species, a relationship that remained stable over the period 1961–2020. Based on this strong climatic signal, we reconstructed annual precipitation for the region from 1830 to 2020. The reconstruction explains 37.6 % of the variance in instrumental precipitation records, demonstrating its reliability as a proxy for past climate. The reconstructed series identified distinct dry periods (e.g., 1830–1839, 1863–1868, 1919–1921, 1944–1947, 1975–1979, and 1989–1992) and wet periods (e.g., 1844–1850, 1869–1882, 1886–1899, 1930–1942, 1966–1973, 1980–1988, 1996–2001, and 2004–2018). The validity of our reconstruction is further supported by its strong agreement with other precipitation and drought reconstructions from nearby regions. Moreover, comparison with the Climatic Research Unit (CRU) gridded dataset indicates that our reconstruction captures precipitation variability across a broad spatial domain. By extending the instrumental record, this long-term precipitation series significantly enhances our understanding of climatic variability and its spatiotemporal characteristics in the eastern Tianshan Mountains. Notably, the reconstruction reveals a general upward trend in annual precipitation since the 1990s, which may enhance growth and carbon sequestration potential of Schrenk spruce forests in the region.

Poplar decline has become increasingly widespread in northern China under intensified warming and drought. However, the sensitivity of radial growth to climatic variability and the drought adaptation mechanisms of declining trees remain limited. In this study, we developed standard tree-ring chronologies for healthy and declining Simon poplar (Populus simonii Carr.) in Jungar Banner on the northeastern Ordos Plateau, northern China. Our objective was to assess their climatic responses and ecological resilience. The results indicated that declining trees chronologies exhibited a higher statistical quality, but showed a long-term decreasing growth trend after 2000, contrasting with the increasing growth trend of healthy trees. The climate-growth relationship of Simon poplar chronologies showed that declining trees are more sensitivity to temperature and water availability. Healthy trees maintained consistently higher resistance, recovery and resilience across drought intensities. In contrast, as drought severity increased, both healthy and declining trees showed declining resistance and resilience, accompanied by enhanced recovery. These findings improve our understanding of the climatic sensitivity and drought-adaptation mechanisms of healthy and declining Simon poplar, and provide valuable insights for enhancing poplar management under ongoing climate change.

Species mixtures are widely promoted in ecological restoration because of their potential advantages in productivity, resource complementarity and nutrient cycling. However, whether these benefits translate into deep soil nutrient recovery remains unclear, as most restoration assessments focus on upper soil layers. Here, we quantified soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) stocks and C:N:P stoichiometry across a 0–500 cm profile under seven restoration patterns, including mixed species stands and single species stands, with a grassland reference in a loess hilly catchment. Elemental stocks and stoichiometric ratios were integrated into a nutrient performance index ({\ C}_i) using entropy weighted TOPSIS, and depth specific environmental controls were assessed by variation partitioning. Nutrient responses were strongly depth dependent. Upper profile improvement did not necessarily translate into whole profile recovery, and mixed species stands were not consistently superior to single species stands. The Platycladus orientalis-Hippophae rhamnoides mixture showed the strongest whole profile nutrient performance ({\ C}_i = 0.77; 95% CI: 0.72–0.83) and a clear deep profile advantage (Δ{\ C}_i = +0.25, calculated as {\ C}_i,100–500 cm - {\ C}_i,0–100 cm). In contrast, the Robinia pseudoacacia-Pinus tabuliformis-Prunus sibirica mixture ranked lowest ({\ C}_i = 0.18; 95% CI: 0.15–0.22), despite being the most species rich mixture. Soil water storage capacity, bulk density, porosity and texture dominated the explained variation in nutrient pools, whereas vegetation and topographic effects varied with depth. These findings indicate that restoration planning should move beyond upper soil indicators and simple mixture versus monoculture comparisons, and should prioritize functionally compatible species combinations that maintain nutrient performance throughout the soil profile.

Global climate warming and intensified urbanization have altered the urban-rural environmental gradient, with consequence on the growth and adaptation processes of urban forest trees. To explore the differences in radial growth and ecological resilience of trees under varying degrees of urbanization, we established plots in forest parks within urban areas of Qingdao and in the rural area of Laoshan Mountain. A total of 342 trees and 626 cores (including 339 Pinus thunbergii and 287 Robinia pseudoacacia) were sampled. Using dendrochronological methods, we quantitatively analyzed the growth characteristics and responses of both species to extreme drought events (in both 1992 and 2015) under different urbanization intensities. The results showed that radial growth rates of both species were 1.87-2.75 mm·a-1 and were generally lower in urban than those in rural areas (on average 1.6% to 4.7% lower). Both species exhibited a decreasing trend during recent years (2004-2020) relative to the past period (1980-2003), with a more significant decline in urban areas. P. thunbergii in urban areas showed significantly higher resistance (18.0%) than those in rural areas, suggesting stronger immediate tolerance to drought stress, whereas R. pseudoacacia displayed higher resistance (25.9%) in rural sites, indicating better adaptation to less urbanized environments. The recovery and resilience of both species in two areas showed relatively small differences, though P. thunbergii (1.34, 1.39) recovered slightly faster than R. pseudoacacia (1.00, 1.20), demonstrating that P. thunbergii has higher ecological resilience. Both resistance and recovery were significantly negatively correlated. P. thunbergii in urban sites exhibited a flatter trade-off curve and a wider range of recovery, reflecting a more flexible ecological adjustment under urban conditions. Overall, the combined effects of urbanization and climate warming have intensified drought stress, limited radial growth, and driven divergent adaptive strategies between resistance and recovery across tree species.

Understory vegetation is essential for maintaining biodiversity and conserving soil and water in degraded plantations. Although thinning and terracing are widely used to optimize eco-rehabilitation in water-limited areas, their combined effects on understory vegetation remain unclear. In this study, we implemented a 2 & times; 5 factorial design crossing terracing type (counter-slope and half-moon terraces) with thinning intensity (0%, 15%, 30%, 45%, and 60%) in Pinus tabuliformis plantations on the semi-arid Loess Plateau, China. We disentangled the combined effects of thinning and terracing on understory taxonomic, functional, and phylogenetic diversity, as well as herbaceous biomass, using variation partitioning (VP) and partial least squares path modeling (PLS-PM). Our results indicated that thinning produced greater increases in understory diversity and biomass in counter-slope terraces than in half-moon terraces. In counter-slope terraces, thinning >= 30% increased understory diversity by 24-130% and herbaceous biomass by 200-640%, peaking at 30-45%. In half-moon terraces, diversity and biomass increased by 8-60% and 180-220% under thinning >= 45%, with the strongest responses at 45-60%. VP and PLS-PM identified thinning as the primary driver, with understory vegetation enhancement mediated by soil moisture and understory light in counter-slope terraces, and by understory light and soil nutrients in halfmoon terraces. We recommend 30-45% thinning on counter-slope terraces and >= 45% thinning on half-moon terraces in these semi-arid P. tabuliformis plantations. These findings support terrace-specific, adaptive thinning strategies, with intensity adjusted stepwise to post-thinning ecosystem responses, providing a feasible basis for effective eco-rehabilitation on the Loess Plateau and other water-limited regions.