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Surface runoff is a major component of the hydrological cycle, and it is essential for supporting the ecosystem services provided by grassland and forest ecosystems. It is of practical importance to understand the mechanisms and the dynamic processes of runoff in a river's basin, and in this study, we focused on the restored montane Pailugou Basin in the Qilian Mountains, Gansu Province, China, since its water status is extremely important for the large arid area and local economies therein. Our purpose was to determine the annual variation in the surface runoff in the Pailugou Basin because it is important to understand the influence of climate fluctuations on surface water resources and the economy of the basin. In addition, little is known about the annual variations in precipitation and runoff in this region of the world. Daily atmospheric precipitation, air temperature and runoff data from 2000 to 2019 were analyzed by the calculation of the uneven annual distribution of surface runoff, the calculation of the complete adjustment coefficient, and the vector accumulation expressed by the concentration degree. We also used the cumulative anomaly approach to determine the interannual variation trend of runoff, while the change trend was quantified by the sliding average method. Finally, we used the Mann–Kendall mutation test method and regression analysis to establish the time-series trend for precipitation and runoff and to determine the period of abrupt runoff changes. The results indicated concentrated and positive distributions of surface runoff on an annual basis, with a small degree of dispersion, and an explicit concentration of extreme flows. The relative variation ranges exhibited a decreasing trend, and the distribution of the surface runoff gradually was uniform over the year. The runoff was highest from July to September (85% of the annual total). We also determined that annual surface runoff in the basin fluctuated over the 20-year period but showed an overall increasing trend, increasing by 3.94 × 105 m3, with an average increase rate of 0.42 × 105 m3 every ten years. From 2005 to 2014, the annual runoff and the proportion of runoff in the flood season (July to September) to the annual runoff fluctuated greatly. The correlation between the runoff and precipitation was significant (r = 0.839, p < 0.05), whereas the correlation between air temperature and surface runoff was low (r = 0.421, p < 0.05). [ABSTRACT FROM AUTHOR]

Litter plays a key role in maintaining the nutrient cycle of the forest ecosystem. The dynamics of litter trace elements (TEs) can influence litter decomposition and biogeochemical cycling across plant and soil systems. However, our understanding of the biogeochemical cycle of TEs during litter decomposition remains limited. We investigated litter production, the concentrations and fluxes of needle litter TEs over 1 year, and the accumulation and release patterns of TEs at different elevations and canopy coverage during litter decomposition over 3.9 years for the Qinghai spruce in the Qilian Mountains. The concentrations and fluxes of TEs in the needle litter decreased in the following order: Zn > Ni > Cr > Cu > Pb > Co > Cd > Ag. TEs concentrations increased with decomposition time at different elevations, and Co, Cr, Cu, Ni, Pb, and Cd accumulated the fastest at 2850 m. Zn and Ag accumulated the fastest at 3450 and 3050 m, respectively. The fastest accumulation trends were for Co, Cu, Ni, Pb, Zn, Ag, and Cd concentrations at low canopy coverage. Cr accumulated the fastest at middle canopy coverage. The concentrations of Co, Cu, Pb, Zn, Ag, and Cd followed the trend of enrichment–release–enrichment, while Ni and Cr concentrations followed the trends of release–enrichment and sustained enrichment, respectively. Our study is important for an improved understanding of the TE cycle during litter decomposition. It provides theoretical support for healthy soil management and element cycling in the forest of the Qilian Mountains. [ABSTRACT FROM AUTHOR]

In the context of continued global climate change, the intensity and frequency of droughts have increased to varying degrees in many places. Due to the complexity of drought events, the mechanisms by which trees respond to drought are not well understood. In this study, we analyzed the growth trends of Qinghai spruce (Picea crassifolia) at different elevations in the western part of Qilian Mountains and the dynamic response to climate change. We also compared the differences in radial growth of trees at different elevations in response to drought events in the growing and non-growing seasons based on resistance (Rt), recovery (Rc), and resilience (Rs). The results showed that (1) trees at all three elevations were limited by drought stress and the lower the elevation the more sensitive the trees were to drought. (2) The response of middle- and low-elevation trees to the standardized precipitation evaporation index in June of that year was stable. (3) Growing season drought limits radial growth of trees more than non-growing season drought, and Rt is smaller and Rc is larger at low elevations. With increasing drought severity, trees at all three elevations exhibited a trend of decreasing Rt and Rs and increasing Rc. (4) There were significant differences in the growth trends of trees at the three elevations. Therefore, we should continuously pay attention to the dynamics of the forest ecosystem in the western part of Qilian Mountains and take improved measures to cope with the adverse effects of drought on Qinghai spruce. [ABSTRACT FROM AUTHOR]

In China, flash floods are one of the main natural disasters causing loss of life and damage to infrastructure. The threat of flash floods is exacerbated with climate change and increased human activities, such that the number of disasters has shown a clear upward trend in recent years. However, due to the scarcity of instrumental data or overly short timeseries, we are still lacking critical data to understand spatio-temporal patterns and driving factors of extreme flash floods. This missing knowledge is however crucial for a proper management of these hazards, especially in remote mountain environments. In forested catchments, dendrogeomorphology allows the reconstruction of past process activity based on growth disturbances (GDs) in trees that have been affected by past flash floods. Therefore, in our study, for the first time, we reconstruct past flash floods in the Qilian Mountains, northeast Tibetan Plateau, over past centuries. To this end, we sampled 99 Qinghai spruce (Picea crassifolia) trees affected by flash floods, with a total of 194 increment cores, and identified 302 GDs induced by past flash floods. These GDs have been caused by at least 21 flash floods that we are able to reconstruct over the last 170 years. The position of GDs within tree rings and the intra-seasonal dating of past events also allowed discussion of the likely synoptic situations that may have led to the triggering of flash floods in the past. Logistic regression analysis confirms that significant correlation exists between cumulative maximum 5-day August–September precipitation and reconstructed flash floods, which is corresponding to the majority of scars and related tangential rows of traumatic resin ducts (TRDs) found in the latewood portion of growth rings. These results support the idea that abundant precipitation occurring at the end of the summer season and early fall is the key factor driving flash floods in our study area. Our research not only fills the gaps regarding historical flash flood histories in the Qilian Mountains, but also provides a scientific basis for the region's response to climate change and flood prevention and reduction. [ABSTRACT FROM AUTHOR]

The factors determining litter decomposition incorporated into C and nutrient cycles were examined as part of a broader study investigating the biogeochemical cycle in forest ecosystems. Litter was collected from five altitudes of Qinghai spruce (Picea crassifolia) woodland stands in the Qilian Mountains and placed in litterbags. These litterbags were installed at the crown center (CC) and crown edge (CE) at different altitudes in Qinghai spruce forests during the growing season to study the effect of litter substrate quality on litter decomposition. Results indicate that at varying altitudes in the growing season, the initial mass loss rate and initial decomposition rate of Qinghai spruce litter showed a nonlinear relationship with altitude. The Olson exponential regression equation showed that the decomposition coefficient (k) was the largest at 3050 m (k = 0.709), and the decomposition coefficient (k) was the smallest at 3250 m (k = 0.476). Meanwhile, the initial decomposition rate was highly correlated with initial litter Ca and Mn concentrations. At the CC and CE at different altitudes in the growing season, the initial mass loss rate of CE was significantly higher than that of CC (p < 0.01), and the initial decomposition rate of CE was markedly faster than that of CC (p < 0.01). The Olson exponential regression equation showed that CE's decomposition coefficients (k) were larger than those of CC. The initial decomposition rate of CE was highly correlated with initial litter C and Mn concentrations. However, the initial decomposition rate at CC was independent of the litter substrate quality. Finally, we realize that litter decomposition in the early stages is not ultimately determined by a single common factor, but rather the result of multiple factors working together in different orders and strengths. The results lay a foundation for understanding the process and mechanism of litter decomposition in the alpine mountain forest ecosystem and further understanding the structure and function of the ecosystem. [ABSTRACT FROM AUTHOR]

During the past several decades, the carbon budget in the dryland ecosystem has experienced great variation under the joint impact of climate change and anthropogenic interference. How the net ecosystem productivity (NEP) responds to climate change and human interference in the Qilian Mountains (QLM), Northwest China, remains unclear. To fill these gaps, we first estimated the NEP in the QLM and then quantified the independent and interactive influences of natural environment factors, climatic factors, and human activity intensity on the NEP change from 2000 to 2020 by linking the Geodetector and structural equation models. The NEP of the QLM showed a significant increase during the recent 20 years, and 78.93% of the QLM experienced a significant increase in NEP; while only 4.83% of the area in the QLM experienced a decreasing trend, which is dominantly located on the southeast edge, surrounding the Qinghai Lake, and the midland of the QLM. The area percentage of the carbon sink region increased from 47% in 2000 to 62% in 2020. The natural environment factors (e.g., altitude and soil type) and climate factors (e.g., temperature and precipitation) were the dominant factors that determine the spatial distribution of NEP. Compared with a single factor, the interaction of pairs of factors enhanced the influence strength on NEP. The natural environment factors indirectly affected NEP change through influencing human activities intensity and climatic factors. Human activities intensity played a medium indirectly negative effect on NEP, while climatic factors exerted strong direct and indirect positive influences on NEP. The contributions of human activity intensity, climatic factors, and natural environment on NEP change in the QLM were 33.5%, 62.3%, and 38.3%, respectively. Overall, warming and wetting shifts in meteorological conditions offset the negative impact of human activities on NEP in the QLM, and the QLM has acted as a growing carbon sink in the past 20 years. [ABSTRACT FROM AUTHOR]

The long-distance transport of toxic elements is a crucial external source of metals accumulated in remote forest ecosystems. Due to the harsh environmental conditions and the complexity and diversity of influencing factors in remote alpine ecosystems, research on toxic elements is very limited, especially in the dry zone. In this regard, mercury (Hg) and arsenic (As) in soil and plant samples were investigated in a Qinghai spruce forest ecosystem at Sidalong Forest Farm (SDL), in the Qilian Mountains, northwest China. The results of the study showed a significant variation in the spatial distribution of Hg and As in soils, but a highly similar spatial distribution trend was found in mosses. High Hg and As concentrations in plants were found in moss, bark, and litterfall; the concentration of Hg was particularly high (BCF > 1). The Qilian Mountain spruce forest ecosystem was contaminated with exogenous Hg and As, with Hg, in particular, being the most serious form of contamination. The study results can provide baseline data for future forest management and research in the spruce forest ecosystem in Qinghai, northwest China. [ABSTRACT FROM AUTHOR]

The genus Cylindroeme Vives, 2019 is taxonomically revised. The type species, Cylindroeme vietnamica Vives, 2019 is redescribed and a second species from Qinghai (China), Cylindroeme shii sp. nov., is described and illustrated. The genus is redescribed and a key to the known species is presented. The genus is also recorded from China for the first time. [ABSTRACT FROM AUTHOR]

• We monitored sap flow for 16 spruces and 14 junipers at 4 arid to semi-arid sites. • Sap flow is almost completely controlled by VPD except for spruce in the arid site. • Increasing site aridity drives a shift towards more anisohydric stomatal behavior. • Spruce exhibits stronger stomatal regulation of transpiration than juniper. • Transpiration may increase first and then decrease from semi-arid to arid forests. Climate change is altering regional aridity and species composition in dryland ecosystems. Understanding the effects of long-term increasing aridity and species-specific stomatal behaviors on transpiration is therefore important for water-resource forecasting. To assess the effects of site aridity levels and species on stand transpiration rate (E s), we monitored sap flux density (J s) and relevant environmental parameters for 16 isohydric Picea crassifolia (spruce) and 14 anisohydric Juniperus przewalskii (juniper) trees over three growing seasons at four arid to semi-arid high-elevation sites on the Tibetan Plateau. Our results show that E s was about 5–9 times higher in semi-arid sites than in arid sites, and about 6–9 times higher in spruce than in juniper. Spruce exhibited stronger stomatal regulation of transpiration than juniper. Soil water supply strongly promoted J s only for spruce in the arid environment (R2 = 0.23), while at the other sites, J s was mostly controlled by atmospheric vapor pressure deficit (VPD) (R2 > 0.82). However, increasing site aridity greatly reduced the sensitivities of both J s and canopy conductance to VPD , especially for juniper. We expect that in the transition from semi-arid to arid alpine forests, E s will initially rise due to increasing VPD. However, in the long term, there may be a stronger decline in E s since both the sensitivity of J s to VPD and the stand sapwood area will decrease. These findings could be used to reduce the impacts of climate change on water resources in high-elevation drylands. [ABSTRACT FROM AUTHOR]

[Display omitted] • Under the assumption of no change in climate, we used the InVEST model to estimate the response of water yield service to land use change in the Qilian Mountains. • We described the changes in each land use type in the Qilian Mountains and its response of water yield service. • We identified the spatial pattern of water yield service changes in the Qilian Mountains from 1990 to 2020. The Qilian Mountains serve as significant ecological security barriers in the western region of China. Their continuous and stable water supply is essential for the sustainability of the human oasis in the Hexi Corridor, as well as for the maintenance of the desert ecosystem in the north. In the past three decades, land use in this area has changed significantly because of human activities, which has had a profound impact on water yield services. Based on the Water Yield module of the InVEST model, we evaluated the area and water yield of land use during 1990–––2020, and discussed the characteristics of water yield response to changes in land use. As a result of the study, it was found that in the Qilian Mountains during the period 1990–––2020: (1) the areas of swamp, unused land, medium coverage grassland, and woodland reduced, while the areas of high coverage grassland, low coverage grassland, cultivated land, construction land, glaciers, and water area increased, and each land use type exhibited a different degree of transformation. (2) In terms of total water yield, this declined by 1.09 × 108 m3, water yield of medium coverage grasslands, unused land, and swamp decreased, while water yield of other land uses increased, however, the responses to the change in water yield as a result of the change in land use were significant. (3) The areas with decreased water yield fall mainly within the high-altitude areas of the Qinghai Lake and Qaidam river watersheds, while the low-altitude areas were characterized by an increase in water yield. This study may provide decision-makers with guidance for protecting the ecosystem of the Qilian Mountains and developing a national park in the Qilian Mountains. [ABSTRACT FROM AUTHOR]

• The distinct patterns of grassland NDVI changes in different sub-basins within the Qilian Mountains were identified. • The key factors affecting grassland NDVI varied among basins. • In the western Qilian Mountains, sunshine duration and relative humidity emerged as the predominant driving factors, whereas altitude and temperature played a more significant role in the eastern Qilian Mountains. • Grassland NDVI exhibited a response that depended on specific threshold levels when multiple factors interacted. The Qilian Mountains (QLMs) encompass a diverse alpine grassland ecosystem undergoing notable changes due to global climate change. Understanding the driving forces behind these changes is crucial for effective regional vegetation restoration and management, particularly given the contrasting climatic conditions between the eastern and western regions of the QLMs. This study investigated the spatiotemporal evolution of grassland NDVI and the influence of 13 variables on NDVI changes in six distinct QLM sub-basins from 1990 to 2019 using Landsat data and the Geodetector model, respectively. Results revealed a consistent greening trend in all sub-basins, albeit with varying slopes. Notably, the Qinghai Lake basin exhibited a recent slowdown in NDVI, highlighting the need for enhanced vegetation restoration efforts, especially in permafrost-covered areas. Environmental factors affecting NDVI differed among basins. In the western QLMs, sunshine duration and relative humidity emerged as key factors influencing NDVI distribution, while in the eastern basins, altitude and air temperature played significant roles. This study underscored the importance of hydrothermal conditions, both horizontally and vertically, in shaping grassland NDVI. Other factors, such as vegetation types, soil characteristics, and permafrost degradation, also influenced NDVI, while slope and slope aspects had a limited impact. Furthermore, the research identified threshold-dependent responses of NDVI to the interaction of these factors. These findings emphasized the need to customize vegetation restoration strategies based on the specific environmental conditions of each basin within the QLMs. This nuanced understanding of the distinct driving characteristics between the eastern and western QLMs enables more effective and targeted approaches to restoring and managing grassland ecosystems in this region. [ABSTRACT FROM AUTHOR]

It is important to explore the responses of radial tree growth in different regions to understand growth patterns and to enhance forest management and protection with climate change. We constructed tree ring width chronologies of Picea crassifolia from different regions of the Qilian Mountains of northwest China. We used Pearson correlation and moving correlation to analyze the main climate factors limiting radial growth of trees and the temporal stability of the growth–climate relationship, while spatial correlation is the result of further testing the first two terms in space. The conclusions were as follows: (1) Radial growth had different trends, showing an increasing followed by a decreasing trend in the central region, a continuously increasing trend in the eastern region, and a gradually decreasing trend in the isolated mountain. (2) Radial tree growth in the central region and isolated mountains was constrained by drought stress, and tree growth in the central region was significantly negatively correlated with growing season temperature. Isolated mountains showed a significant negative correlation with mean minimum of growing season and a significant positive correlation with total precipitation. (3) Temporal dynamic responses of radial growth in the central region to the temperatures and SPEI (the standardized precipitation evapotranspiration index) in the growing season were unstable, the isolated mountains to total precipitation was unstable, and that to SPEI was stable. The results of this study suggest that scientific management and maintenance plans of the forest ecosystem should be developed according to the response and growth patterns of the Qinghai spruce to climate change in different regions of the Qilian Mountains. [ABSTRACT FROM AUTHOR]

Human activities have dramatically changed ecosystems. As an irreplaceable ecological barrier in western China, the Qilian Mountains (QLM) provide various ecosystem services for humans. To evaluate the changes in the intensity of human activities in the QLM and their impact on the ecosystem, the human footprint (HF) method was used to conduct a spatial dataset of human activity intensity. In our study, the NDVI was used to characterize the growth of vegetation, and six categories of human pressures were employed to create the HF map in the QLM for 2000–2015 at a 1-km scale. The results showed that the mean NDVI during the growing season showed a significant increasing trend over the entire QLM in the period 2000–2015, while the NDVI showed a significant declining trend of more than 70% concentrated in Qinghai. Human pressure throughout the QLM occurred at a low level during 2000–2015, being greater in the eastern region than the western region, while the Qinghai area had greater human pressure than the Gansu area. Due to the improvement in traffic facilities, tourism, overgrazing, and other illegal activities, grasslands, shrublands, forests, wetlands, and bare land were the vegetation types most affected by human activities (in decreasing order). As the core area of the QLM, the Qilian Mountains National Nature Reserve (NR) has effectively reduced the impact of human activities. However, due to the existence of many ecological historical debts caused by unreasonable management in the past, the national park established in 2017 is facing great challenges to achieve its goals. These data and results will provide reference and guidance for future protection and restoration of the QLM ecosystem. [ABSTRACT FROM AUTHOR]

• The macroecology of plant tissues and soil nutrients in an arid area were studied. • Climate, soil depth, latitude, and longitude significantly affected soil nutrients. • Plant tissue N and N:P were positively correlated with precipitation. • Plant and soil were closely linked and interacted with each other. • Precipitation is critical to mediating the element circulation in arid areas. Knowledge of nutrient traits, especially carbon (C), nitrogen (N), and phosphorus (P), is essential for understanding the biogeochemical cycle and ecosystem functioning. However, spatial patterns in soil and plant tissues stoichiometry in the arid and semiarid forest ecosystem are not yet fully understood. Here, a regional-scale study was conducted on the Qilian Mountains to illustrate the macroecological patterns of soil C:N:P stoichiometry and the plant tissue N and P contents in Qinghai spruce (Picea crassifolia) forest and their driving forces. Soil C, N, and P contents and C:N:P ratios at all four soil depth layers (0–5, 5–10, 10–20, and 20–40 cm) showed depths, latitudinal, and longitudinal trends (p < 0.01), except for the soil P content and C:N ratios. The plant N and P contents and N:P ratios were found to be correlated with the latitude and longitude (p < 0.05). The N content and N:P ratios of plant tissue showed a negative correlation with the temperature (p < 0.05), which coincides with the temperature-plant physiological hypothesis. Additionally, the N and N:P of both the soil and plant tissue were positively correlated with precipitation (p < 0.05), which led to the plant tissue N and N:P and the soil TN and N:P being tightly related. Variation partitioning analysis revealed that the soil properties (39.31%) contributed more to the plant tissue N:P stoichiometry variations than climate (6.47%). The results demonstrated that the macroecological pattern of plant tissue N:P stoichiometry is mainly regulated by soil traits. These findings contribute to our understanding of the C:N:P macroecological pattern of forest ecosystems in arid regions, providing basic data for future forest cultivation and management in those areas. [ABSTRACT FROM AUTHOR]