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The Qinghai–Tibet Plateau in China is a region strongly impacted by climate change, yet its effects on the keystone endemic forest species Picea crassifolia Kom. are unknown. Understanding the changes in potential distribution and habitat suitability of P. crassifolia forest with climate change will contribute to water conservation, forest management, and ecological protection in the upper reaches of the Yellow River. A total of 129 records of species distribution data and 19 environmental variables were chosen for modeling. The MaxEnt (maximum entropy) model was used to analyze the main environmental factors affecting the potential distribution of P. crassifolia in two periods (2050s and 2070s) and four representative emission pathways (RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5). The main results are follows: (i) the most important environmental variables affecting distribution of P. crassifolia and percentage variance explained were altitude (41.85%), precipitation of driest month (19.76%), slope (12.35%), annual precipitation (6.56%), precipitation of wettest month (5.73%), and precipitation of warmest quarter (5.12%); (ii) habitat suitability of P. crassifolia shifted to the northwest and into high-altitude areas under climate change scenarios, but its core distribution areas were concentrated in northeastern Qinghai–Tibet Plateau, Qilian Mountains, southern Ningxia, and Helan Mountains; and (iii) the total area of potential suitable habitat of P. crassifolia will change significantly in the future, and change of habitat area of not suitable, low, moderate, and high suitability exceed 60%.

Transcriptome combined with morpho-physiological analyses were performed on female, male and vegetative buds to investigate gender determination regulators, especially genes involved in gibberellin and ethylene metabolism, in Qinghai spruce. Coniferous species are mostly monoecious. Their usage in forest plantations is largely limited by the low and unstable yields of seed cones. Gibberellins (GAs) and ethylene are central gender regulators in flowering, although knowledge about their metabolism is limited in conifers. Here, we explore gender determination regulators, especially GA and ethylene metabolism genes, in Qinghai spruce (Picea crassifolia Kom.) by transcriptome analysis of female, male and vegetative buds during bud formation and development. Year-round observations were performed to determine the window of bud differentiation. Samples of buds before and after differentiation were collected for RNA sequencing, which showed that the bud gender determination process occurred before the morphological differentiation of female, male and vegetative buds. Sixteen homologs of GA metabolism genes were identified in the transcriptome. Concentrations of GA1, GA3, GA9, and GA15 were identified and quantified using ultra-high-performance liquid chromatography—high-resolution mass spectrometry (UPLC-HRMS). Furthermore, phylogenetic analysis was performed on 9 putative ACC synthesis (ACS) genes identified in the transcriptomes, and quantitative real-time PCR was conducted to examine gene expression. Our study provides information on GA and ethylene metabolism genes in female, male and vegetative buds during bud differentiation. Overall, fine-tuned regulation of GA metabolism contributes to both the reproductive transition and gender differentiation in this species, whereas ethylene might affect male cone bud formation. The current findings could further our knowledge about the regulatory mechanisms underlying the gender differentiation of cone buds.

The temperature in northwestern China has increased significantly since the 1990s. However, the responses of mountainous forests to warming have not been extensively examined. We collected tree rings of two dominant coniferous species of Qinghai spruce (Picea crassifolia) and Chinese pine (Pinus tabulaeformis) in the eastern part of the Qilian Mountains, and analyzed the differences in the response dynamic of the radial growth of two species to climate change. The results showed that (1) the annual radial growth of Qinghai spruce was mainly restricted by the minimum temperature in July and October, and the growth of Chinese pine was mainly restricted by the mean temperature in September of the previous year, January, and July and the maximum temperature in March, May, and July. In particular, Qinghai spruce increased its sensitivity to total precipitation in the growing seasons in March, May, and July after the temperature abruptly increased. (2) In comparison to Qinghai spruce, Chinese pine showed a consistent response to the main climatic factors and was more severely affected by drought stress. Qinghai spruce had divergent responses to mean temperatures in March and May and minimum temperatures in April and June. (3) The growth of Qinghai spruce increased with a significant fluctuation at the end of the twentieth century, while the growth of Chinese pine first showed an increase and then a significant decreasing trend. At present, the increase in temperature has adversely affected the growth of Chinese pine in the eastern Qilian Mountains and promoted the growth of Qinghai spruce. However, a continuous temperature increase could negatively affect the growth of Qinghai spruce because of the increasing probability of drought stress. Therefore, we should pay more attention to the growth dynamics of Qinghai spruce, especially with the different water supply and demand, and to the effects of drought on Chinese pine in forest ecosystems in arid and semiarid areas.

Ecological stoichiometry is an effective tool for analyzing and explaining changes and connections between plants and the environment. However, the changes in ecological stoichiometry throughout the leaf-root-litter-soil continuum during different seasons in plantation ecosystems are not fully understood. In this study, the C, N and P contents of leaves, roots, litter and soil were measured in four plantations growing Larix principis-rupprechtii, Picea crassifolia, Betula platyphylla and Populus cathayana in spring, summer and autumn. The stoichiometric characteristics and seasonal dynamics along the continuum were analyzed to reveal nutrient limitations on the plantations and coupling relationships among the components. Our analysis revealed that the C and N contents and C:P and N:P ratios of leaves, the P content of litter, and the C:N ratio of roots were the highest among all components. The seasonal dynamics showed that the N and P contents of leaves and roots and the P content of soil and litter were the highest in spring on all plantations, while the C:N, C:P and N:P of leaves, the C:N and C:P of roots and soil, and the C:P and N:P of litter were the lowest in spring. In all plantations, the N contents of BP and PR in each component were higher, while the P content and C:P and N:P ratios in roots of LR in summer were lower. The N element between litter-soil-root-leaf had a strong coupling relationship, and the P element between leaf-litter-root had a strong coupling relationship. Our results demonstrated that plants and the environment in each season on the Loess Plateau were mainly coupled and regulated by the N element in litter-soil-root-leaf and by the P element in leaf-litter-root. The plants absorbed N mainly from the soil and P mainly from litter. Plantations were limited by N in spring and summer and by P in autumn; this information may help guide plantation restoration and management.

In situ observations indicate that different levels of micro-standing could induce divergent temperature responses in trees at similar elevations but different slope aspects, which is supported by physiological process model simulation of radial incremental growth. The unstable response of tree growth to climate change is a well-documented, yet poorly understood phenomenon. It has been reported that Picea crassifolia exhibits a systematically variable response to climate forcing at a single high-mountain study area located at the upper treeline in the Qilian Mountains, China. This study used in situ meteorological observations to force a simplified but nonlinear mechanistic model of tree-ring width to identify how variable conditions translate into differences in radial growth within this site. The simulations suggest no significant difference in soil moisture between sites, but disparate diurnal micro-site temperature maxima, apparently amplified by a uniform warming, drive the divergent growth trends between subsites. For tree-ring-based reconstructions of surface temperature, such divergent growth trends challenge the validity of the assumption that a linear growth response to environmental conditions within and across study sites. Therefore, we recommend the development of precise, high-resolution data sets for calibrating, validating and reconstructing climatic change, given the potential for emergent non-stable tree growth–climate relationships.

For trees in the east from 1980 to 2001 and after 2001 and trees in the west from 1980 to 2001, younger trees responded to precipitation and older trees responded to temperature more strongly. Global warming has now persisted for more than 100 years, but an unusual pause in this rising temperature began in the 2000s, at least for the climate of China. This shift presents an unusual opportunity to investigate possible differences in the radial growth of trees during a climate warming period (1980–2001) and the warming hiatus (after 2001) for different age groups under different moisture conditions. We sampled a total of 304 tree-ring cores of Picea crassifolia in the eastern and western Qilian Mountains, which were divided into four age groups for study. The results indicate that trees of the young group and half-mature group in the wetter eastern region showed insignificant growth trend, while all trees in the drier west showed significant growth reduction related to climate warming. Radial growth of trees in the east showed weak correlation with precipitation, and that in the west positively correlated with precipitation from the previous August–September and current May–June from 1980 to 2001. In contrast, trees in the east positively correlated with precipitation from the previous August–September and current July, and those in the west positively correlated with precipitation from the current April–May during the temperature pause after 2001. Trees in the east showed negative correlation with temperature in the winter dormancy period, and those in the west negatively correlated with temperature from the previous July, November and the current June from 1980 to 2001. Trees in both the east and west showed weak correlations with temperature after 2001. Older trees (> 150 years old) showed a weaker response to precipitation than the younger trees (

Climate change has been documented in the Qilian Mountains of China, and the response of tree stem growth to environmental factors may be changed, affecting regional estimates of seasonal growth patterns and carbon sequestration. The objective of this study was to provide initial evidence for responses of intra-annual tree stem radial changes of sapling Qinghai spruce (Picea crassifolia) to climate warming in the Qilian Mountains. We monitored stem radial changes of Qinghai spruce in an open-top chamber (OTC) and out of chamber (OC) over three growing seasons (2014–2016) using high-resolution point dendrometers. Statistical analysis indicated that the differences in annual average air temperature between OTC and OC were about 1 °C. Our results showed that the onset of the main growth period in OTC was about one week earlier than in OC, and soil temperature played an important role in controlling the onset of growth in sapling Qinghai spruce. However, the timing of radial growth cessation exhibited large variability in different growth conditions. These results indicated that the end of growth may not be related to environmental factors. Daily average air temperature, vapor pressure deficit, relative air humidity, and precipitation were significantly correlated with daily stem radial increment (SRI) and tree water deficit (TWD). Further, soil water content and TWD were also correlated. SRI in OTC was larger than that in OC, while TWD exhibited no significant differences between the two growth conditions. However, cumulative seasonal growth may not be influenced by air temperature alone, but by interacting environmental factors.

Vegetation reconstruction from fossil pollen records depends on an adequate understanding of the relationship between modern pollen and vegetation. In this study, we present the modern pollen dispersal and representation of the “Forest Island” and its surrounding areas within the Chinese desert-loess transitional zone. Forty-four pollen carpet traps, which imitate the natural pollen sediment process, were collected from the Ningxia Daluoshan Mountain and its surrounding areas along a southeast–northwest transect included five vegetation types. The pollen spectra, spatial distribution patterns of the main pollen types and discriminant analysis of pollen data show that: Pinus Diploxylon-type has high pollen production and good dispersal ability and that the over-represented, with values exceeding the 20% (> 100 grains cm− 2 year− 1) within vegetation dominated by Pinus tabuliformis, below 7% ( 100 grains) within the spruce forest, decreased abruptly and even disappeared completely outside the forest. Another interesting finding of this study is that Poaceae have higher values and higher pollen production. The modern pollen assemblage of the desert steppe, mountain steppe and Picea crassifolia forest, but especially the desert steppe and mountain steppe, can be separated from each other as follows: (1) desert steppe: Chenopodiaceae–Poaceae pollen assemblage; (2) mountain steppe: Poaceae–Artemisia–Aster type pollen assemblage; and (3) Picea crassifolia forest: Picea–Artemisia–Poaceae pollen assemblage. However, overlap occurs between deciduous broadleaved shrubs and coniferous and broadleaved mixed forests. The very low concentration of deciduous broadleaved shrubs may due to an increased contribution of pine pollen. Our study may facilitate the confident use of fossil pollen data to reconstruct vegetation in the desert-loess transitional zone in China and may be able to be used to correctly interpret fossil pollen records from similar areas.

Global climate change is reshaping the geographical distribution of forests, especially in mountain regions. The alpine forest ecotone is expected to be affected first, due to the climatic limitations on tree growth, and is thus considered as an indicator of the forest succession to climate change. However, current studies involving tree radial growth and their responses to climate change at alpine forest ecotone remain scarce, posing challenges for predictions of forest dynamics and management strategies under different climate scenarios. Here, we studied 94 Chinese Pine (Pinus tabulaeformis; Pinaceae) and 86 Qinghai Spruce (Picea crassifolia; Pinaceae) trees along the alpine forest ecotone [2100–2400 m above sea level (a.s.l.)] to assess tree growth differences and corresponding responses to climate change in the Helan Mountains, northwestern China. The results revealed that growth rates of Chinese Pine at lowest altitudes and Qinghai Spruce at highest altitudes are strongly affected by water shortage and intraspecific competition, respectively, leading to the tree growth in these regions are inferior to those of other trees in the ecotone (the tree age at maximum width is about 20 years later than in the ecotone), especially for seedling and sapling stages. The responses of tree radial growth to dryness were broadly similar in each sample site, but wetness was more positive in trees at low altitudes than at high altitudes. Climate warming has inhibited the radial growth of Qinghai Spruce at lower distribution limits since 2005, while for Chinese Pine in the same area was not significantly affected by rising temperature, and even the upper limits of the Chinese Pine might migrate to higher altitudes as the calorific limit becomes higher. If climate warming continues, the above process may erode the Qinghai Spruce habitat, resulting in the transitional zone between Chinese Pine and Qinghai Spruce also moving to higher elevations.

Background Large-scale afforestation can significantly change the ground cover and soil physicochemical properties, especially the soil fertility maintenance and water conservation functions of artificial forests, which are very important in semi-arid mountain ecosystems. However, how different tree species affect soil nutrients and soil physicochemical properties after afforestation, and which is the best plantation species for improving soil fertility and water conservation functions remain largely unknown. Methods This study investigated the soil nutrient contents of three different plantations (Larix principis-rupprechtii, Picea crassifolia, Pinus tabuliformis), soils and plant-soil feedbacks, as well as the interactions between soil physicochemical properties. Results The results revealed that the leaves and litter layers strongly influenced soil nutrient availability through biogeochemical processes: P. tabuliformis had higher organic carbon, ratio of organic carbon to total nitrogen (C:N) and organic carbon to total phosphorus (C:P) in the leaves and litter layers than L. principis-rupprechtii or P. crassifolia, suggesting that higher C:N and C:P hindered litter decomposition. As a result, the L. principis-rupprechtii and P. crassifolia plantation forests significantly improved soil nutrients and clay components, compared with the P. tabuliformis plantation forest. Furthermore, the L. principis-rupprechtii and P. crassifolia plantation forests significantly improved the soil capacity, soil total porosity, and capillary porosity, decreased soil bulk density, and enhanced water storage capacity, compared with the P. tabuliformis plantation forest. The results of this study showed that, the strong link between plants and soil was tightly coupled to C:N and C:P, and there was a close correlation between soil particle size distribution and soil physicochemical properties. Conclusions Therefore, our results recommend planting the L. principis-rupprechtii and P. crassifolia as the preferred tree species to enhance the soil fertility and water conservation functions, especially in semi-arid regions mountain forest ecosystems.

Dwarf mistletoe (Arceuthobium spp.,Viscaceae) (DM), a hemiparasitic plant, is nutritionally dependent upon its host tree and causes tree mortality in forests worldwide. Dwarf mistletoe infection results in physiological changes in the host, eventually causing the death of the host tree. In this study, we evaluated the changes in leaf reflectance of spruce trees, Picea crassifolia, infected by DM (Arceuthobium sichuanense) with ground‐based hyperspectral technology. A total of 112 sample sites were selected for analysis in the eastern part of Qinghai Province, China, including healthy spruce tree, light DM‐infected spruce tree, moderate DM‐infected spruce tree and high DM‐infected spruce tree in each site. The results showed that leaf reflectance was significantly different among healthy spruce, DM‐infected spruce, DM and dead spruce in the near‐infrared regions ranging from ~750 to 900 nm. Dwarf mistletoe infection resulted in the increase of leaf reflectance of host tree, and the intensity of DM infection was positively related to reflectance. However, five selected hyperspectral indices that commonly used to estimate the physiological status of plants (carotenoid reflectance index, photochemical reflectance index, normalized difference vegetation index, structure‐insensitive pigment index and water index) were not linearly correlated with the intensity of DM infection. Collectively, the hyperspectral characteristics of spruce infected by DM can be potentially used to detect DM‐induced changes on a landscape scale with satellite remote sensing, which can be used as an efficient advanced tool for DM disease monitoring.

Canopy and stem phenology of Qinghai spruce, central Qilian Mountains, respond to different environmental factors depending on season and elevation. To understand vegetation species response to climate change, much research has been devoted to changes in forest phenology. Results of such studies are not only of scientific interest; they are potentially of great use in forest management. This study focuses on variations in canopy and stem phenology as affected by climate and elevation. We collected data on canopy phenology (as recorded in the Normalized Differential Vegetation Index) and stem phenology [using the Vaganov–Shashkin (V–S) model] in Qinghai spruce (Picea crassifolia) growing at two sites in the central Qilian Mountains, Northeast Tibetan Plateau. One site was at a higher elevation, near the local alpine tree-line, and the other was near the local lower tree-line. At both sites, a significant correlation was found between canopy and stem spring phenology. This would seem to be mainly due to spring temperatures. No such correlation was found between canopy and stem autumn phenology. The study suggests that the main factors affecting stem growth after the beginning of growing season would be temperature and soil moisture, and that these have different effects depending on elevation. At the lower elevation, soil moisture seems to be the main factor limiting growth. At the higher elevation, temperature was the determining factor. Climate change will have different effects depending on elevation.

Different tree species exhibit different phenological and physiological characteristics, leading to complexity in inter-species comparison of stem radial growth response to climate change. This study explored the climate-growth responses of Qinghai spruce (Picea crassifolia) and Chinese pine (Pinus tabulaeformis) in the Qilian Mountains, Northwest China. Meanwhile, Vaganov-Shashkin model (VS-oscilloscope) was used to simulate the relationships between radial growth rates and phenology. The results showed that 1) in their radial growth patterns, Qinghai spruce showed a significant increasing trend, while Chinese pine showed a decreasing trend, and Qinghai spruce has a longer growing season than Chinese pine. 2) For the radial growth-climate dynamic response, Qinghai spruce was influenced in an unstable manner by the mean temperature in the mid-growing season of the current year and the late growing season of the previous year and by the mean minimum temperature in the mid-growing season of the current year, while Chinese pine was influenced in a stable manner by the mean temperature and mean maximum temperature during the growing season of the current year. 3) The radial growth rates of the two conifer species were limited by temperature at the initiation and cessation of growth and by soil moisture at the peak of growth. But Chinese pine was more severely affected by soil moisture than Qinghai spruce in the middle of growth. Therefore, different management and restoration measures should be taken based on the differences in ecological responses and physical and physiological properties of the two conifer species to climate change in the subalpine forest ecosystems in the semiarid and arid regions of Northwest China.

The frequency of stem-growth cessation in Picea crassifolia has increased significantly as the frequency of extreme climate events has increased. Extreme climatic events are increasingly recognized as important drivers of tree growth, forest dynamics, and range contractions. Understanding tree growth responses to extreme events is important for forest conservation and management, especially under climate change. Here, we studied the patterns of growth cessation of Picea crassifolia Kom., an endemic species to Central Asia, across its distributional range in the Helan Mountains of Northwestern China, to test the hypotheses that (1) tree growth and growth cessations are limited by moisture availability, and (2) that this relationship is constant over the diverse set of conditions covered in our elevational gradient. While tree growth across our gradient was significantly limited by low precipitation in June, we found growth cessation events at the lower distributional margin to increase in severity and frequency in recent decades. We found that the combination of low precipitation early in the monsoon season (June) and high mid-summer (July) vapor pressure deficit likely caused the increased frequency of growth cessation events. Because these populations are already experiencing a high frequency of growth cessation events, the mortality rate of the lower distributional margin trees could further increase if the current trends of decreasing moisture and increasing heat stress continue into the future. Our results strongly suggest that growth cessation events are more than the dendrochronological curiosity they are usually considered to be, and can be important indicators of increased tree growth stress and be potentially useful in identifying tipping points prior to forest change.

Study of the radial growth response to climate factors at different tree ages is essential for predicting forest dynamics and formulating correct management policies. In this study, we analysed the growth responsiveness of Picea crassifolia to climate conditions, and evaluated its relationship to tree age at the individual tree scale, in the transitional zone between regions affected by the East Asian monsoon and winds blowing from the west (westerlies) in the Qilian Mountains. On three study sites, 150 cores were taken from 75 trees. Pearson correlation coefficients were calculated between the standardized tree-ring series of each core (and chronology) and climatic factors which were utilized to research the climate-growth relationships. Quadratic polynomial fitting was used to test the relationships between tree age, chronological parameters, and the radial growth response to climate. Radial growth was positively influenced by total precipitation for the previous July-September and the current May-July. Additionally, radial growth was negatively correlated with the total monthly precipitation for the current September, and the mean monthly temperature for the previous July. Trees younger than 80 years old showed a stronger response to accumulative precipitation in the previous July-September, those older than 160 years old showed a stronger response to precipitation at the end of current growing season, while those of 140–160 years old showed a weaker response to precipitation in the current May-July.

Ongoing climate changes posed significant threats to forest growth, structure and ecological functions. However, in our field survey in the east Qilian Mountains, we found that growth condition of Qinghai spruce under climate changes was better in anthropogenic management forest than disturbance-free stands. Accordingly, we suggested a hypothesis that the environmental change induced suppression in Qinghai spruce growth could be mitigated by anthropogenic management. Such a hypothesis was tested by comparing Qinghai spruce growth and population dynamic patterns between anthropogenic-managed forests and disturbance-free ones. We found that Qinghai spruce radial growth persistently declined since the late 1950s in the disturbance-free forests, while the radial growth of anthropogenic-managed trees almost kept steady-going trends since the 1970s in which anthropogenic-management appeared. Besides, some anomalous growth-declining years occurred in disturbance-free forests did not appear in anthropogenic-managed forests in the same year after anthropogenic-management emerged. Moreover, missing ring and tree mortality took place in disturbance-free stands and became increasingly frequent after the mid-1980s. The frequencies and proportions of missing rings and tree die-off were much lower in anthropogenic-managed forests than disturbance-free ones. Additionally, the occurrence of Qinghai spruce radial growth decline and increased mortality in recent time in our disturbance-free forests could be well explained by global-change-type drought in conjunction with elevated temperature and warming-related pest outbreaks. These results would be of fundamental significance for the further understanding of the changing forests, which could provide new clues for forest management and conservation in the future.

Exploring the response of intra-annual tree growth to environmental factors is critical for the understanding of the effects of climate changes on tree seasonal growth patterns. We monitored stem radial changes of Qinghai spruce ( Picea crassifolia ) over two growing seasons (2014 and 2015) in the Qilian Mountains of China using high-resolution point dendrometers. Our results showed that the onset of the main growth period occurred around 11 May. Soil temperature was a key environmental factor influencing the onset of tree growth. Stem radial growth commenced when soil temperature at 40 cm depth was >0 °C. The timing of radial growth cessation exhibited greater variability than onset, ranging from late July to early August, and was probably unrelated to climatic conditions. We found close relationships between maximum daily shrinkage (MDS) and air temperature, precipitation, soil water content, and soil temperature. Maximum and mean air temperature, relative air humidity, vapor pressure deficit, and precipitation had significant effects on daily stem radial increment (SRI). Precipitation was one of the most important factors influencing stem radial growth. Moreover, the number of precipitation days was more significant in promoting cumulative seasonal growth of Qinghai spruce than total precipitation. With climate warming, the onset of radial growth may occur earlier than before, and seasonal growth patterns of trees may change.

The effects of climate warming are widely recognized; however, some studies have suggested that the rate of warming has slowed since the end of the twentieth century. However, the relationships between climate and the radial growth of trees during different periods of climate change have yet to be investigated fully. In the present study, tree-ring core samples were collected from Picea crassifolia and Juniperus przewalskii in the Qilian Mountains of northwest China to study the relationships between climate and radial growth. The core samples were divided into two groups: one with significant tree-growth reduction and another with insignificant reduction. Trees showing with significant growth reduction were more sensitive to climate change than trees showing insignificant growth reduction during the period of climate warming. P. crassifolia exhibited a stronger response to precipitation during May–June of the current year and from August of the previous year to June of the current year, both before and after climate warming. P. crassifolia exhibited a positive coherence with precipitation from August–September of the previous year and a negative coherence with the temperature of the current June during climate warming. After climate warming, J. przewalskii responded positively to precipitation in the current May and from the previous August to the current May. J. przewalskii also responded positively to temperature during January–February of the current year after warming. P. crassifolia responded to precipitation more strongly than J. przewalskii, whereas J. przewalskii showed a closer relationship to temperature than P. crassifolia.

Slope aspect can affect soil temperature and soil type distribution, which, in turn, is likely to influence plant community composition. Three Qilian mountains, located in the northeastern part of the Qinghai–Tibetan Plateau, China, with four distinct slope aspects including south‐facing (SF), southwest‐facing (SW), northwest‐facing (NW), and north‐facing (NF) slope aspects, were studied to investigate the impact of slope aspect on plant assemblages. The results indicated that the environmental conditions were favorable under the NF and NW slope aspects as the soil water, soil organic carbon (SOC), and soil total nitrogen (STN) contents were significantly higher, and soil temperature (ST) and soil bulk density (SBD) were significantly lower than under the SF and SW aspects. Under all slope aspects, however, SOC, STN, and soil total phosphate in the top 0.2 m of topsoil accounted for about 60% of its total quantity, to a soil depth of 0.6 m. The plant communities on the SF and SW slopes were found to be primarily composed of Poa pratensis, Potentilla anrisena, and Carex aridula. In contrast, the plant community on the NW slope was mainly composed of Kobresia humilis, Carex crebra, and Potentilla bifurca, while on the NF slope it was mainly composed of Picea crassifolia, Carex scabrirostris, and Polygonum macrophyllum. The order of the influence of environmental factors on species distributions was ST > SBD > sand > STN. Results suggest that the slope aspect has an important role in the regulation of the soil environment and plant assemblages and that ST and SBD were the main factors influencing plant community composition. Furthermore, evidence from this study suggests that these mountains will become increasingly vulnerable to global warming. Thus, the plant community composition on these mountains must be monitored continuously in order to allow for strategic adaptive management.

Global climate change is expected to affect mountain ecosystems significantly. Phenotypic plasticity, the ability of any genotype to produce a variety of phenotypes under different environmental conditions, is critical in determining the ability of species to acclimate to current climatic changes. Here, to simulate the impact of climate change, we compared the physiology of species of the genus Picea from different provenances and climatic conditions and quantified their phenotypic plasticity index (PPI) in two contrasting common gardens (dry vs. wet), and then considered phenotypic plastic effects on their future adaptation. The mean PPI of the photosynthetic features studied was higher than that of the stomatal features. Species grown in the arid and humid common gardens were differentiated: the stomatal length (SL) and width (SW) on the adaxial surface, the transpiration rate (Tr) and leaf mass per area (LMA) were more highly correlated with rainfall than other traits. There were no significant relationships between the observed plasticity and the species’ original habitat, except in P. crassifolia (from an arid habitat) and P. asperata (from a humid habitat). Picea crassifolia exhibited enhanced instantaneous efficiency of water use (PPI = 0.52) and the ratio of photosynthesis to respiration (PPI = 0.10) remained constant; this species was, therefore, considered to the one best able to acclimate when faced with the effects of climate change. The other three species exhibited reduced physiological activity when exposed to water limitation. These findings indicate how climate change affects the potential roles of plasticity in determining plant physiology, and provide a basis for future reforestation efforts in China., The four species in the genus of Picea analysed in this study exhibited comparatively high photosynthetic plasticity and low stomatal plasticity in the two common gardens. The results also indicated that site-specific conditions can mask habitat variations, and thus should always be considered in studies of habitat trends in the future. Finally, we can make a preliminary suggestion that P. crassifolia should survive best. These findings indicate how climate change affects the potential roles of plasticity in determining plant physiology, and provide a basis for future reforestation efforts in China.

The evergreen coniferous creeping shrub, Sabina vulgaris, is widely distributed in China, from high and cold mountain sites to low-elevation arid desert areas. This paper performed dendroclimatological analysis of the samples of S. vulgaris from three sampling sites (2700–2900 m a.s.l.) at sites in the northern border of the middle Qilian Mountains, Northwest China. We found that the radial growth of S. vulgaris was mainly limited by rainfall during the growing season, especially in May and June, but was also limited by low temperatures in the late growing season. It presents the regional differention of the climate response of the shrub radial growth from the other distributed areas, such as the sandland and mountains. We constructed a 274-year drought record by calibrating growth-ring data and relating this data to the regional monthly Palmer Drought Severity Index (PDSI56), which represents regional moisture conditions. The PDSI56 reconstruction accounted for 35.5 % of the variation of the actual May to June PDSI56 during the period for which meteorological data was available (1950–2014). The most severe drought occurred during the 1920s, followed by the 1950s, 1740s, and the period from the 1870s to the 1880s; the wettest years were during the 1980s, followed by the 2010s, 1770s, and 1750. The changes between drought, normal, and wet periods were consistent with the reconstructed results from previous conifer ring series for Sabina przewalskii and Picea crassifolia in the study area. Our results demonstrate the value of S. vulgaris in dendrochronology.

Although stand age has been shown to strongly affect forest ecosystem processes, little is known about the role that forest stand age plays in tree radial growth processes. The knowledge on geographical patterns of the stand age effect on radial growth along climatic gradients is also scarce. Based on dendrological methods and tree-ring cores from 2276 trees at 14 sampling plots, we confirmed that differences in stand age could result in radial growth dissimilarities of Qinghai spruce (Picea crassifolia Kom.), a moisture-sensitive forest tree species endemic to the Tibetan Plateau. However, the effect that stand age has on the radial growth of Qinghai spruce is not consistent. There is evident dissimilarity in the radial growth dynamics of Qinghai spruce from different-aged forest stands in semi-humid regions, but this dissimilarity is minimal in regions under higher drought limitation. Additionally, we observed significant negative correlations in temporal changes of growth concordance of Qinghai spruce from different-aged stands and regional moisture conditions at each study site. It can therefore be concluded that Qinghai spruce will exhibit greater stand age related growth dissimilarities under lower drought limitation. Findings from this study can improve our understanding of biogeographical patterns of moisture-sensitive tree growth that will be necessary to improve future projections of forest dynamics and to guide forest management under a changing climate.

Understanding the effects of environmental variables on seedling-sapling distributions can help gain insight into changes in population recruitment in the context of global warming. Six transects were used to survey the distribution of seedling-saplings and the variability in environmental variables along altitudinal gradients. In addition, laboratory experiments measuring the effects of moss on Picea crassifolia seedling emergence were conducted to identify seedling development characteristics of Picea crassifolia. The results show that the seedling-sapling distribution of Picea crassifolia is determined by altitudinal gradients over the large scale and is influenced by moss at the small scale. We found the largest number of seedling-saplings occurring at middle altitudes (3050-3250 m a.s.l.). The crucial abiotic factors in the seedling-sapling distribution for this species are precipitation at lower altitudes and temperature at higher altitudes. Moss mats can promote the recruitment of Picea crassifolia when the moss depth is less than 5 cm and moss cover is less than 50%. Conversely, with increasing moss depth and cover, the effects are shifted towards a negative relationship. Moss can promote moist conditions, implying that recruitment may be facilitated by moss in lower altitude areas where drought stress may occur. However, both air temperature in moss layers and soil temperature below moss are reduced, suggesting that the presence of moss may result in a shortened growing season for Picea crassifolia. More research into the seedling-sapling distribution of Picea crassifolia at both the large and small scales is necessary for artificial forestation and forest management, especially for those alpine plant species that are sensitive to climate change. (C) 2016 Elsevier B.V. All rights reserved.

The influence of climate in the previous year on radial growth was stronger than that in the current year and climatic influence became weaker as the altitude increased. The climate conditions during the previous year often influence the radial growth of trees in the current year, which is known as the lingering effect of climate. To explore this lingering effect in depth, we compare the influence of climate in the previous and current year on radial growth and find variations in climatic effects on growth along the altitudinal gradient. We also relate radial growth of Picea crassifolia to climate variables from 24 different timescales (from 1 month to the previous 24 months) at different altitudes in the middle of the Qilian Mountains. In the study area, accumulated monthly precipitation before November in the previous year benefited radial growth in the current year at all altitudes. At lower altitudes, July could be seen as a demarcation point that precipitation from the current May–July significantly affected radial growth in the current year, but precipitation from the current July–October significantly affected radial growth in next year. At the same time, radial growth there responded stronger to precipitation from the previous July–October than that from the current May–July. Radial growth at higher altitudes responded weaker to climatic factors than that at lower altitudes and rarely correlated with precipitation from the current year.

Moss cushion plays an important role in recruitment of vascular plants. In this study, we examined the effects of water soluble extracts (WSE) of Abietinella abietina on germination of Qinghai spruce (Picea crassifolia) and the effects of moss substrates (A. abietina) on seedling emergence of P. crassifolia in two greenhouse experiments. We found that the WSE of moss affected germination of P. crassifolia in two ways: (1) the WSE reducing the risk of fungal infection to the seeds, improve the germination rate; and (2) the WSE affects germination by its concentration, that is, low concentrations of WSE (i.e., 0.5 mg ml-1 and 5 mg ml-1) stimulate, while high concentrations (i.e., 50 mg ml-1) inhibit it. In seedling emergence experiments, we detected that the moss substrates (both thick and thin mosses) facilitate the emergence of P. crassifolia in dry and intermediate moisture conditions, but inhibit it in moist conditions. In bare soil, the P. crassifolia emergence was also controlled by moisture ...

The current work adopted the Biome-BioGeochemical Cycle model to simulate the net primary productivity (NPP) of a subalpine forest (Picea crassifolia forest) under four representative concentration pathway (RCP) scenarios in the Qilian Mountains of northwest China. This study also investigated the responses of forest’s NPP to different combinations of climatic changes and CO2 concentration increase. Results showed that (1) under the RCP scenarios, greater increases in temperature, precipitation, and CO2 concentration caused larger increments in forest NPP; (2) the effect of CO2 concentration (increased NPP from 19.9% to 21.7%) was more significant than that of climate change (increased NPP from 7.5% to 17.1%); (3) the simultaneous increments in climatic change and atmospheric CO2 concentration led to a remarkable increase in P. crassifolia forest NPP (ranging from 33.1% to 41.3%), with the combination of the two exerting strong interactive effects on forest NPP; and (4) the response of the forest’...

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

Global climate change has led to the nonlinear response of the radial growth of trees to climate change at high altitudes and high latitudes in the northern hemisphere, and the responses of different tree species on climate change due to differences in physiological and ecological adaptations are also significantly different. Therefore, we analyzed the response stability and growth trends and the sustainability of two dominant tree species Qinghai spruce (Picea crassifolia) and Chinese pine (Chinese pine) to climate change on the southern edge of the Tengger Desert. The main conclusions were as follows: 1) water stress was the main controlling factor of the two tree species by analyzing the correlations between the radial growth of two tree species and climate factors. 2) Qinghai spruce had a stable response to Standardized Precipitation Evapotranspiration Index (SPEI) in September of the previous year, and the unstable responses to the minimum temperatures in September, December of the previous year and May of the current year, as well as SPEI in June and July of the previous year and June of the current year; Chinese pine had the stable responses to SPEI in September and May of the previous year, and the unstable responses to the minimum temperatures in September, and December of the previous year and May and September of the current year, as well as SPEI in June of the previous year and March of the current year based on the comparing the response variations before and after the abrupt temperature changes and moving correlation function. 3) The basal area increment (BAI) of Qinghai spruce showed a significant downward trend, and that of Chinese pine showed a significant upward trend, which indicated the Qinghai spruce with shade-tolerant and shallow-roots was more severely restricted by climate warming and water stress. Therefore, we must pay more attention to the shade-tolerant and shallow-roots forest ecosystem and strengthen management and protection.

Precipitation is one of the most important climate factors controlling tree growth, yet it is not fully understood how changes in precipitation affect the relationship between growth and temperature. On the northeastern edge of the Tibetan Plateau, nine tree-ring chronologies of Picea crassifolia were developed along a precipitation gradient from semi-arid (mean annual precipitation, 255 mm) to semi-humid (710 mm). We analyze the growth-climate relationships along this precipitation gradient and assess whether these associations are regulated by local precipitation. From 1960 to 2014, temperature increased significantly while precipitation remained stable at the nine sampling sites. The radial growth of P. crassifolia decreased at the semi-arid sites but increased at the semi-humid sites. Growth-temperature relationships gradually changed from negative to positive along the precipitation gradient (from dry to wet sites), particularly during summer. The moist P. crassifolia sites are also characterized by positive correlations with the Palmer Drought Severity Index. The temporal growth-temperature relationships varied significantly among the different spruce sites over the last five decades. Although temperature remains the main factor controlling the growth of P. crassifolia, local precipitation variability is becoming increasingly important. Our findings indicate that considering species distribution areas supports the analyses of the impact of climate change on tree growth.

Northwestern China has experienced dramatic climate change characterized by rapid warming since the 1980s with the warming trend substantially slowing after 2000. Qinghai spruce (Picea crassifolia Kom.), a key tree species in northwest China, has been predicted to be strongly coupled with climate change. However, how the trends in biomass growth change at different canopy positions under climate change and whether climate–growth responses vary with canopy position remain unclear. A total of 222 trees were sampled by a stand-total sampling strategy in the central Qilian Mountains. Trees were assigned to four canopy positions according to height and distance from neighbors: dominant, codominant, intermediate, and suppressed. Our results indicate that trees in dominant and codominant canopy positions dominate the decreasing trend in stand-level biomass from 1980 to 2000 and the increasing trend from 2000–2013, contributing 81.3 % and 86 %, respectively, whereas trees in the intermediate and suppressed canopy positions contributed less. This result was attributed to a more sensitive response of biomass growth in trees in dominant and codominant canopy positions to climate change. From 1980 to 2000, the stronger decreasing trend in biomass growth at dominant and codominant canopy positions is mostly accounted for by increasing temperature. A more pronounced water deficit might have restricted biomass growth more than that at the intermediate and suppressed canopy positions. However, from 2000 to 2013, drought stress was relieved and summer standardized precipitation evapotranspiration index became a leading factor, which promoted the recovery in biomass at dominant and codominant canopy positions. In a word, compared with intermediate and suppressed canopy trees, those in dominant and codominant positions are less resistant to drought, but dominant and codominant canopy position's biomass can recover more when drought stress is relieved. A more robust understanding of canopy-level growth response and resilience to climate change is crucial to fully understand forest growth dynamics under fluctuating climate conditions.

Examining the growth of trees in response to environmental factors is essential for evaluating the stability of forest ecosystems. In this study, using tree ring data obtained from 18 sites and climate diagnostic methods. we investigated relationships between the radial growth of Picea crassifolia in the mid-western Qilian Mountains and local climate/sea surface temperatures (SSTs) since 1851 C.E. The results revealed that the radial growth of P. crassifolia showed significant upward trends during three time periods (1884–1906, 1929–1946, and 1964–1983) and significant downward trends in a further three periods (1907–1928, 1947–1963, and 1984–1995). Variations in the growth of P. crassifolia showed a significant negative correlation with temperature in June and a positive correlation with precipitation from July in the previous year to June in the current year as a response to climate change. We also found that large-scale anomalies could influence the radial growth of P. crassifolia, which was reflected in results showing that extremely high radial growth is related to El Nino patterns in the central-eastern equatorial Pacific, whereas extremely low growth is related to anomalously warmer SSTs in the southern Indian Ocean. Notably, we found that the extremely low growth of P. crassifolia in response to SST was more stable than that of extremely high growth. Furthermore, on the basis of qualitative methodology, we established that years characterized by extremely high/low growth were largely/little influenced by the time window and threshold values that were selected when determining the positive/negative pointer years. Our results confirm the validity of using the relationships between extremely low growth and SSTs to predict forest dynamics.

Water deficiency is the primary limiting factor for tree growth in arid and semi-arid areas. Droughts associated with rising temperatures have increased in severity and frequency globally over the past few decades, making the trees in the drought-prone sites first be affected by water shortages. However, our understanding of tree growth status in these areas, and of their response to drought, is currently insufficient; especially in the context of global warming. Here, we studied 94 Chinese pine (Pinus tabulaeformis) and 86 spruce (Picea crassifolia) trees from different altitudes [2,100–2400 m above sea level (a.s.l.)] distributed at the desert margins of Northwestern China to explore tree growth and drought response from multiple perspectives using dendroecological approaches. Significant growth decline, across all tree species and altitudes, was detected in response to an interdecadal trend towards a drier climate. Moreover, the extent of tree growth decline, the proportion of affected trees, and the degree of moisture dependence have all tended to increase in each sample site, most likely due to enhanced drought severity and duration in recent decades. The more sensitive and susceptible trees were found at lower elevations (drier sites) and may signify a higher vulnerability to heating-induced drought stress. Tree resistance to drought showed strong negative correlation with drought severity across all sample sites. However, the connection between post-drought tree resilience and drought intensity is weak, perhaps because the samples were all collected from living trees, while those that had died were not sampled. The priority for future work should be to combine surviving and dead trees simultaneously, thus achieving a more representative view of tree resilience to drought; this will improve our knowledge of forest dynamics and even ecosystem succession in these vulnerable and sensitive environments.

Understanding the mechanisms for how tree growth responds to drought is important for forest conservation and management in semi-arid regions, particularly under ongoing climate change. However, most previous studies have been relied on linear statistical analysis, unsupported by insights into tree physiological processes. In this study, we applied process-based Vaganov–Shashkin (VS) model to investigate the stem radial growth response and resilience of Qinghai spruce (Picea crassifolia) and Chinese pine (Pinus tabuliformis) to intense drought in semi-arid region of China from 1960 to 2013. Correlation analysis indicated that soil moisture availability in the early growing season (May to July) significantly limit stem growth for both tree species, but Chinese pine was affected more strongly by drought legacies. The model results validated our statistical modeling results, and quantified the effects of temperature and soil moisture on the intra-seasonal variation of the relative stem radial growth rate. The influence of soil moisture on the relative stem radial growth rate during the early growing season was significantly higher for positive pointer years (years with greater than mean growth) than for negative pointer years (years with less than mean growth) for both tree species. Interestingly, the two species displayed similar patterns of growth resilience in response to drought. Based on our successful application of the VS model, our results provide important insights into the two main tree species in the semi-arid Helan Mountains, and offer a new perspective on tree growth processes and their varying responses and resilience to drought.

The effects of the interaction between tree species composition and altitude on soil microbial properties are poorly understood. In this study, soil samples (0-20 cm) were collected in August 2011 from Betula platyphylla and Picea crassifolia forests along two different altitudinal gradients. Soil microbial activity and biomass were measured using Biolog-ECO plates and phospholipid fatty acid analysis. Both of the forest soils were characterized by a significantly lower soil pH (p < .05) and higher soil organic matter (SOM) and nutrient levels (total nitrogen, available nitrogen and phosphorus) at higher altitudes compared with lower altitudes. Soil microbial activity was significantly lower in the birch forests (p < .05), but changed little in the spruce forests with increasing altitude. Soil microbial biomass decreased in the two forest soils across altitude gradients. With each 100-m drop in altitude, the soil microbial biomass exhibited a sharper decline in the spruce forests than in the birch forests. SOM had significant negative effects on soil microbial biomass, but no effects on soil microbial activity. Soil pH was significantly negative correlated with soil microbial biomass and activity. The tree species composition exhibited more negative effects on soil microbial biomass in the spruce forests, while altitude had a greater effect in the birch forests.

Semi-arid forests at the limit of their existence close to the Gobi Desert in Inner Asia might be vulnerable to warming-induced drought stress. Yet, not much is known about the impact of global-change-type droughts on these forests. Here, we show that warming-related tree mortality is recently taking place in high-elevation semi-arid Qinghai spruce (Picea crassifolia Kom.) forests of the north-eastern margin of the Tibetan Plateau (Qilian Mountains). Tree-ring samples were collected from 24 Qinghai spruce forest plots (20 m × 20 m) at three elevations (2600, 2700, 2800 m) along eight elevation transects on north-facing slopes. Three lines of evidence suggest that these forests are increasingly at risk of increased tree mortality as a consequence of global warming, (i) a strong precipitation and air humidity dependence of radial growth, (ii) increasing frequency of missing tree rings, and (iii) a rising tree mortality rate in recent decades. The recent drought episode on the north-eastern Tibetan Plateau may represent a precursor of future global-change-type drought events in large parts of Inner Asia. Warming-related tree mortality of the semi-arid forests may be interpreted as early-warning signs for the densely populated artificial oases surrounding the Gobi Desert, which largely depend on river run-off from the mountain forests on the edge of the Tibetan Plateau.

The tree species, elevation and climate change jointly influenced the tree-ring growth, directing us to carefully consider the comprehensive effects of these variables when performing large-scale and multi-species-based dendroclimatic studies. The rate of tree growth varies by species and is influenced by elevation and climate gradients. Assessing the influence of these variables on tree-ring growth can improve projections for tree growth under future climate conditions. Here, we evaluate the relationships between tree species, elevation, climate and tree-ring growth in the Qilian Mountains of northwest China by using the tree-ring records of Qinghai spruce (Picea crassifolia) and Qilian juniper (Juniperus przewalskii) trees. The rotated principal component analysis was applied to examine the individual tree growth and the associated influencing factors. The tree-ring chronologies were used to compare tree growth patterns and the climate–growth relationships between the two species and elevations. The results indicated that trees from the Qinghai spruce sites showed similar growth patterns and climate–growth relationships, even though the elevation differed. The Qilian juniper chronologies from the high and low elevation sites revealed different growth patterns during recent decades that were closely related to the discrepant climate–growth relationships with the temperatures and the recent warming trend. The differences in tree growth patterns between both species and elevation could be attributed to plant physiological traits. The results of this study demonstrate the impact of tree species, elevation and climate change on tree-ring growth, suggesting that accounting for the influences of these variables could improve large-scale and multi-species-based dendroclimatic studies.

The vast alpine grasslands of the Tibetan Plateau are lined by a belt of oroboreal coniferous forests in the transition zone to the Central Asian semi-deserts and deserts which may play important roles in the hydrology and biogeochemistry of the region. Many of these forests exist under semi-arid climates, are exposed to rapid climate warming and suffer from intensive human impact. We investigated the carbon stocks in biomass and soil in the Picea crassifolia (Qinghai spruce) forests of the Qilian Mountains, north-eastern Tibetan Plateau. In 18 forest plots at 2600–2800 m elevation, we found ecosystem carbon stocks of 348 Mg C ha−1 with carbon densities of 43 Mg C ha−1 in the live and dead aboveground biomass, 12 Mg C ha−1 in roots, 3 Mg C ha−1 in litter and 305 Mg C ha−1 in the soil (SOC; 0–100 cm). The belowground carbon pools exceed averages reported for northern boreal forests and even more clearly for zonal forest vegetation in the temperate zone. The high SOC density in the P. crassifolia forests are probably the result of slow decomposition rates due to low soil temperatures in combination with low soil moisture. The widespread degradation of mountain spruce forests to shrubland reduces the ecosystem carbon stock by >85 Mg C ha−1, and is partly caused by a 15%-reduction in SOC. We conclude that the remaining mountain forests of spruce and other conifers at the northern fringe of the Tibetan Plateau play an important role in the regional carbon budget and need urgent conservation.

Qinghai spruce (Picea crassifolia Kom.), the dominant species in Qilian Mountains of Northwest China, has an important role in ecological service function, especially in carbon sequestration. The current work simulated stem volume growth of Qinghai spruce at individual and stand levels using a widespread bio-geochemical cycle (BIOME-BGC) model and considering the crown projection area (CPA). CPA was introduced because photosynthesis was only carried out on the vegetation canopy. The results showed that: (1) the CPA-simulated stem volume of individual Qinghai spruce in the three sites fitted well with the observed stem volume; (2) the introduction of CPA corrected the over-predicted stem volume for relatively younger stands and the under-predicted stem volume for relatively older stands in BIOME-BGC; and (3) meteorological factors may be crucial parameters that influence the model accuracy, aside from CPA. Therefore, CPA should be considered in correcting the carbon simulated by BIOME-BGC, and the meteorol...

Large old trees contribute to ecosystem integrity and biodiversity in urban and periurban areas. Quantifying the factors influencing the suitable habitats of large old trees is critical for management. Because tree species are sensitive to changes in the human footprint and soil properties in alpine regions, understanding the effects of these on the habitat suitability of large old trees is crucial for ecological management in urban and periurban areas of alpine regions. Here, we used a habitat suitability model to project the distributions of suitable habitats of six large old tree species (Salix matsudana, Picea crassifolia, Picea wilsonii, Populus cathayana, Populus simonii, and Ulmus pumila) in urban and periurban areas of Qinghai Province, China, based on climate, the human footprint, and soil variables. Then, we used jackknife methods and effect size analysis to quantify the effects of the human footprint and soil properties on the habitats of large old trees. Our results showed that the human footprint and soil properties, especially cation exchange capacity, affected the habitat suitability of the large old trees in Qinghai Province. The tree species in Chengzhong, Chengxi, Ping’an, Guide, and Qilian were all greatly affected by the human footprint and soil properties. We propose the following management strategies based upon our data: 1) protected areas should be established for large old trees where soil nutrient levels are high to ensure the protection of small groups of scattered trees and single isolated trees; and 2) Chengzhong, Chengxi, Huangzhong, Ping’an, Ledou, Minhe, Xunhua, and Guide should be used as recruitment areas of large old trees based on their suitable climate and soil properties in Qinghai Province. Our study provides insight into the effective management of large old trees in alpine regions.

Numerous individual tree parameters can be isolated from a canopy height model derived from light detection and ranging. However, closed canopy forests make isolating individual trees difficult. A watershed method based on morphological crown control is studied in this research to isolate individual trees in a closed canopy forest and find how much the tree density influences the individual tree parameters. Morphological crown control is introduced to ensure that the watershed results locate in the crown area. The local maxima algorithm is used to identify potential tree positions in the crown area. Double watershed transformations, in which a simple reconstruction operation is inserted into the two transformations, are then applied to delineate the tree crowns. Finally, the individual trees are isolated, and their parameters are extracted. An experiment is conducted in a closed coniferous forest dominated by Picea crassifolia Kom. in northwest China. Results show that the proposed method can isolate the ...

Light detection and ranging (LiDAR) has been widely used to estimate forest biomass. In this study, we aim to further explore this capability by correlating horizontal and vertical distribution of LiDAR data with components of biomass in a Picea crassifolia forest. Airborne small footprint full-waveform data were decomposed to acquire higher density point clouds. We calculated LiDAR metrics at the tree level and subplot level and correlated them to biomass components, including branch biomass (BB), leaf biomass (LB) and above-ground biomass (AGB), respectively. A new metric (Horizcv) describing the horizontal distribution of point clouds was proposed. This metric was found to be highly correlated with canopy biomass (BB and LB) at the tree level and subplot level. Correlation between AGB and Horizcv at the subplot level is much lower than that at tree level. AGB for subplot is highly correlated with the mean height metric (Hmean), canopy cover index (CCI) and the product of them. On the other hand, the relationship between the vertical distribution of LiDAR point and biomass was explored by developing two types of vertical profiles, including LiDAR distribution profiles and a biomass profile. Good relationships were found between these two types of vertical profiles and assessed by Pearson’s correlation coefficient (R) and the area of overlap index (AOI). These good correlations possess potential in predicting the vertical distribution of canopy biomass. Overall, it is concluded that not only the vertical, but also the horizontal distribution of LiDAR points should be taken into account in estimating components of biomass by LiDAR.

Each of the last three decades has seen the Earth’s surface get progressively warmer more than any preceding decade since the 1850s. Greenhouse gas emissions from human activities have been scientifically demonstrated as the primary cause of the observed global climate change. The reduction of greenhouse gas levels in the atmosphere has deserved international attention. Aside from strategies to reduce emissions, increasing carbon storage by restoring and protecting destroyed forests has become an alternative method to lower carbon dioxide (CO2) levels. Therefore, effective restoration/conservation plans for deforested lands are urgently needed. The current work focuses on the restoration and conservation potential of destroyed Qinghai spruce (Picea crassifolia) forests in the Qilian Mountains of northwest China and provides a reasonable approach for drafting effective restoration/conservation plans for deforested lands. We first estimated habitat suitability of the Qinghai spruce using a habitat suitability model based on the relationships among the three most influential/significant environmental variables: average annual precipitation (P), average air temperature in July (T), and solar radiation (R) and the corresponding occurrence frequency of Qinghai spruce in the niche space. We then calculated the index of habitat suitability (IHS) for Qinghai spruce by applying a model in the study area. We finally used field data to classify the IHS map and identified the prior restoration and conservation areas for Qinghai spruce. The results show that (1) the optimal combination of T, P, and R for Qinghai spruce is 11.5 °C, 380 mm, and 2 × 103 kWh/m2, respectively; (2) these forests have potential for restoration; (3) areas with priority restoration and conservation potential are about 43 and 56.65 km2. The results of this study will help decision-makers develop and implement effective restoration/conservation strategies in the Qilian Mountains. This study presents a useful approach for helping decision-makers in other regions of the world draft effective restoration/conservation plans for deforested lands. The implementation of these plans will reduce CO2 concentration in the atmosphere, in turn, may retard global warming.

Dryland montane forests conserve water for people living in the fluvial plains. The fate of these forests under climate warming is strongly affected by local environmental factors. The question remains of how internal factors contribute to climate change impacts on forest growth in these regions. Here, we investigated tree ring records for similar-aged stand-grown trees and their neighboring open-grown trees at elevation in a dryland montane forest (Picea crassifolia Kom.) in northwestern China. The growth rate of open-grown trees is much higher than their neighboring stand-grown trees across the entire elevation gradient, and the lower the altitude, the greater the difference. Open-grown trees at different elevations showed similar growth patterns, as tree growth at all sites was accelerated over time. In contrast, growth patterns of stand-grown trees were divergent at different altitudes, as growth at high elevations (3100&ndash, 3300 m a.s.l.) was accelerated, whereas growth at low elevations (2700&ndash, 2900 m a.s.l.) became stable after the year 1990. Analysis of growth&ndash, climate relationships indicated that warming promoted open-grown tree growth across the entire altitude gradient, and also stand-grown tree growth at high elevations, but negatively affected the growth of stand-grown trees at low elevations. Water scarcity can be exacerbated by competition within forests, inhibiting the warming-induced benefits on tree growth. Moving window correlation analysis suggested the negative effect of warming on tree growth at low elevations was diminished after the late 1990s, as the drought stress was alleviated. Our research shows the divergent growth responses to warming of stand-grown and open-grown trees along elevation. It reveals effects of internal factors in determining tree growth response to warming and holds the potential to aid forest management and ecosystem models in responding to climate change.

Understanding the factors that influence the distribution of understory vegetation is important for biological conservation and forest management. We compared understory species composition by multi-response permutation procedure and indicator species analysis between plots dominated by Qinghai spruce (Picea crassifoliaKom.) and Qilian juniper (Sabina przewalskiiKom.) in coniferous forests of the Qilian Mountains, northwestern China. Understory species composition differed markedly between the forest types. Many heliophilous species were significantly associated with juniper forest, while only one species was indicative of spruce forest. Using constrained ordination and the variation partitioning model, we quantitatively assessed the relative effects of two sets of explanatory variables on understory species composition. The results showed that topographic variables had higher explanatory power than did site conditions for understory plant distributions. However, a large amount of the variation in understory species composition remained unexplained. Forward selection revealed that understory species distributions were primarily affected by elevation and aspect. Juniper forest had higher species richness andα-diversity and lowerβ-diversity in the herb layer of the understory plant community than spruce forest, suggesting that the former may be more important in maintaining understory biodiversity and community stability in alpine coniferous forest ecosystems.

In order to investigate the response to climate changes in radial growth of Picea crassifolia at the lower tree line in the middle Qilian mountains in northwestern China, relationships of standardized chronologies of annual ring, earlywood and latewood widths with mean monthly temperature and total monthly precipitation were analyzed by ways of correlation and pointer year analyses. The results show that annual ring, earlywood and latewood widths are significantly negatively correlated with mean monthly temperature in June and July. Annual ring and earlywood widths are significantly and positively correlated with total monthly precipitation in March, May and June and negatively correlated with total monthly precipitation in September. Latewood width is less sensitive to climate changes than the width of earlywood and insignificantly sensitive to precipitation. The results of pointer year analysis revealed that when summer temperatures are higher than the mean summer temperature synchronization and the summer precipitation lower than mean summer precipitation synchronization, narrow annual rings are formed. Wide annual rings are formed when summer temperatures are lower than the mean summer temperature synchronization and summer precipitation higher than mean summer precipitation synchronization. The results indicate that more precipitation in the spring and summer is helpful for radial growth while warmer summer restricts radial growth of P. crassifolia at the lower tree line in the middle Qilian mountains.