Picea Crassifolia Research Articles

Effects ofAbietinella abietinaExtracts on the Germination and Seedling Emergence ofPicea crassifolia: Results of Greenhouse Experiments

ABSTRACT 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 ...

A Picea crassifolia Tree-Ring Width-Based Temperature Reconstruction for the Mt. Dongda Region, Northwest China, and Its Relationship to Large-Scale Climate Forcing.

The historical May–October mean temperature since 1831 was reconstructed based on tree-ring width of Qinghai spruce (Picea crassifolia Kom.) collected on Mt. Dongda, North of the Hexi Corridor in Northwest China. The regression model explained 46.6% of the variance of the instrumentally observed temperature. The cold periods in the reconstruction were 1831–1889, 1894–1901, 1908–1934 and 1950–1952, and the warm periods were 1890–1893, 1902–1907, 1935–1949 and 1953–2011. During the instrumental period (1951–2011), an obvious warming trend appeared in the last twenty years. The reconstruction displayed similar patterns to a temperature reconstruction from the east-central Tibetan Plateau at the inter-decadal timescale, indicating that the temperature reconstruction in this study was a reliable proxy for Northwest China. It was also found that the reconstruction series had good consistency with the Northern Hemisphere temperature at a decadal timescale. Multi-taper method spectral analysis detected some low- and high-frequency cycles (2.3–2.4-year, 2.8-year, 3.4–3.6-year, 5.0-year, 9.9-year and 27.0-year). Combining these cycles, the relationship of the low-frequency change with the Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) and Southern Oscillation (SO) suggested that the reconstructed temperature variations may be related to large-scale atmospheric-oceanic variations. Major volcanic eruptions were partly reflected in the reconstructed temperatures after high-pass filtering; these events promoted anomalous cooling in this region. The results of this study not only provide new information for assessing the long-term temperature changes in the Hexi Corridor of Northwest China, but also further demonstrate the effects of large-scale atmospheric-oceanic circulation on climate change in Northwest China.

Climate–growth relationship stability of Picea crassifolia on an elevation gradient, Qilian Mountain, Northwest China

Climate affects Picea crassifolia growth and climate change will lead to changes in the climate–growth relationship (i.e., the “divergence” phenomenon). However, standardization methods can also change the understanding of such a relationship. We tested the stability of this relationship by considering several variables: 1) two periods (1952–1980 and 1981–2009), 2) three elevations (2700, 3000, and 3300 m), and 3) chronologies detrended using cubic splines with two different flexibilities. With increasing elevation, the climatic factor limiting the radial growth of Picea crassifolia shifted from precipitation to temperature. At the elevation of 2700 m, the relationship between radial growth and mean temperature of the previous December changed so that the more flexible spline had a greater precipitation signal. At the elevation of 3000 m, positive correlation of radial growth with mean temperature and precipitation in September of the previous year became more significant. At the elevation of 3300 m, positive correlation between radial growth and precipitation of the current summer and the previous spring and autumn was no longer significant, whereas the positive correlation between radial growth and temperature of the current spring and summer strengthened. The detrending with the most flexible spline enhanced the precipitation signal at 2700 m, while that with the least flexible spline enhanced the temperature signal at 3300 m. All results indicated that the divergence phenomenon was affected by the climatic signals in the chronologies and that it was most dependent on the detrending method. This suggests it is necessary to select a suitable spline bootstrap for studies of growth divergence phenomena.

Drought fluctuations based on dendrochronology since 1786 for the Lenglongling Mountains at the northwestern fringe of the East Asian summer monsoon region

The Lenglongling Mountains (LLM) located in northeastern part of the Tibet Plateau, belong to a marginal area of the East Asian summer monsoon (EASM) and are sensitive to monsoon dynamics. Two tree-ring width chronologies developed from six sites of Picea crassifolia in the LLM were employed to study the regional drought variability. Correlation and temporal correlation analyses showed that relationships between the two chronologies and self-calibrated Palmer Drought Severity Index (sc_PDSI) were significant and stable across time, demonstrating the strength of sc_PDSI in modeling drought conditions in this region. Based on the relationships, the mean sc_PDSI was reconstructed for the period from 1786 to 2013. Dry conditions prevailed during 1817–1819, 1829–1831, 1928–1931 and 1999–2001. Relatively wet periods were identified for 1792–1795 and 1954–1956. Spatial correlations with other fourteen precipitation/drought reconstructed series in previous studies revealed that in arid regions of Northwest China, long-term variability of moisture conditions was synchronous before the 1950s at a decadal scale (1791–1954). In northwestern margin of the EASM, most of all selected reconstructions had better consistency in low-frequency variation, especially during dry periods, indicating similar regional moisture variations and analogous modes of climate forcing on tree growth in the region.

Shiyang River streamflow since AD 1765, reconstructed by tree rings, contains far‐reaching hydro‐climatic signals over and beyond the mid‐latitude Asian continent

AbstractIn this study, the regional tree‐ring chronology of Picea crassifolia was used to estimate annual (September to August) streamflow of the Shiyang River for the period from AD 1765 to 2010. The linear regression model was stable and could explain 41.5% of the variance for the calibration period of 1955–2005. According to the streamflow reconstruction, dry periods with below average streamflow occurred in AD 1775–1804, 1814–1823, 1831–1856, 1862–1867, 1877–1885, 1905–1910, 1926–1932, 1948–1951, 1960–1963 and 1989–2002. Periods of relatively wet years are identified for AD 1765–1774, 1805–1813, 1824–1830, 1857–1861, 1868–1876, 1886–1904, 1911–1925, 1933–1947, 1952–1959, 1964–1988 and 2003–2010. Comparisons with the precipitation reconstructions from surrounding areas supplied a high degree of confidence in our reconstruction. Our reconstructed streamflow is significantly correlated with sea surface temperature in the eastern equatorial Pacific Ocean and the North Atlantic Ocean. The Multitaper spectral and correlation analyses also suggested that the reconstructed streamflow variation in the Shiyang River could be associated with large‐scale atmospheric‐oceanic variability, such as El Niño‐Southern Oscillation (ENSO). The linkages among the streamflow reconstruction, NAO and ENSO suggest the connection of regional streamflow variations to the Asian monsoon and westerlies circulations. Copyright © 2016 John Wiley & Sons, Ltd.

Qinghai spruce (Picea crassifolia) growth–climate response between lower and upper elevation gradient limits: a case study along a consistent slope in the mid-Qilian Mountains region

Tree-ring width chronologies are important records of climate change. Mounting evidence suggests that tree-ring climate response is elevation dependent. In this study, even-aged Qinghai spruce (Picea crassifolia Kom.) chronologies from six sites along a consistent slope in the Qilian Mountains region were selected to investigate altitudinal variability of growth–climate response. Results showed that growth–climate response of this species at different elevations was limited by identical factors. In the Qilian Mountains, P. crassifolia tree-ring growth was limited primarily by drought conditions which are determined by precipitation and temperature in the Qilian Mountains along the entire elevation gradient, exhibiting a positive correlation with PDSI in growth season, a positive correlation with precipitation in May and a negative correlation with the maximum temperature in June. Moreover, P. crassifolia recruitment dynamics coincided well with the temperature variations, suggesting that recruitment rates at different elevations were all primarily influenced by temperature. What was noteworthy was that the great decrease in the mean sensitivity and standard deviation of chronologies directly indicated that P. crassifolia climate–growth response weakened at higher elevations. Furthermore, tree-ring-climate correlation coefficients, and spatial correlation fields of tree-ring width indices to regional climate factors also significantly decreased at higher elevations, indicating that P. crassifolia climate–growth response at higher elevations was weaker than that at lower elevations. Additionally, response of P. crassifolia recruitment dynamics to changes in temperature decreased with increasing elevation, confirming results from chronology and response analyses that showed that P. crassifolia climate–growth response weakened at higher elevations.

Changes in soil physicochemical and microbial properties along elevation gradients in two forest soils

ABSTRACTThe 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.

Association of ectomycorrhizal fungi with Picea crassifolia (Pinaceae, Piceoidae) from high-altitude stands in Mount Helan Nature Reserve, China.

We investigated the diversity of ectomycorrhiza associated with the endemic Picea crassifolia in Mount Helan National Nature Reserve in Inner Mongolia, China. Toward this objective, we conducted morphological and molecular identification of ectomycorrhizae in soil cubes taken from pure P. crassifolia stands. Eleven types of ectomycorrhizal (ECM) organisms were separated, briefly described, and identified. Nine morphotypes belonged to the phylum Basidiomycotina [Amphinema byssoides, Cortinarius sp (cf. limonius), Cortinarius vernus, Inocybe cf. nitidiscula, Inocybe sp 1, Sebacina incrustans, Sebacina sp, Suillus luteus, and Piceirhiza tuberculata x Picea crassifolia (comb. Nov.)], and two morphotypes to the phylum Ascomycotina (Cenococcum geophilum and Helvella sp). The diversity of ECM organisms in P. crassifolia was lower than that reported by other studies on spruce or pine forests, or on sporocarp diversity in the high-mountain forests of China. Most of the fungi in the rhizosphere did not correspond to species previously recorded as sporocarps above ground. Here, several new ectomycorrhiza morphotypes are proposed and described. We also confirmed the ectomycorrhizal status of the genus Sebacina (order Sebacinales).

Precipitation Variations in the Eastern Part of the Hexi Corridor During AD 1765–2010 Reveal Changing Precipitation Signal in Gansu

ABSTRACT We reconstructed August–May precipitation from AD 1765 to 2010 for the eastern part of the Hexi Corridor, northwest China, using tree rings of Picea crassifolia. The precipitation reconstruction explains 44.1% of the actual precipitation variance during the common period of 1951–2010. The precipitation reconstruction is representative of precipitation conditions over a large area of the Hexi Corridor. Multi-taper spectral analysis reveals the existence of significant variability with periods of 9.3, 6.7, 3.1, and 2.6 years. Comparison between the precipitation reconstruction of the eastern part of the Hexi Corridor and other nearby precipitation/drought reconstructions shows high coherency in the timing of dry/wet episodes on annual to decadal scale. The divergences existing between the reconstructions may reflect the influence of different geographic features in Gansu and differences in seasonality of the various precipitation/drought reconstructions.

Global warming-related tree growth decline and mortality on the north-eastern Tibetan plateau

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.

Assessing the influences of tree species, elevation and climate on tree-ring growth in the Qilian Mountains of northwest China

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.

Patterns and environmental controls of soil organic carbon and total nitrogen in alpine ecosystems of northwestern China

Soil carbon (C) and nitrogen (N) in alpine ecosystems are of special interest because of high concentration and potential feedbacks to climate changes. Alpine ecosystems of the Qilian Mountains in the northern margin of the Tibetan Plateau are characterized by complex topography, suggesting large variability in the spatial distribution of soil C and N. However, the patterns and environmental controls on C and N storage are not well understood. This study was conducted to determine the soil organic carbon (SOC) and total nitrogen (TN) stocks under different vegetation types and environmental conditions in a typical catchment in the Qilian Mountains, and explore their environmental control factors. The results showed that SOC and TN stocks varied significantly with vegetation type, ranging from 9.50 to 31.09 and 1.07 to 3.14kgm−2, respectively, at 0–50cm soil depth. SOC storage in grasslands on sunny slopes and in Picea crassifolia forest together accounted for about 80% of the total SOC storage in the catchment due to the extensive distribution area of these vegetation types. SOC stocks in grasslands on sunny slopes and in P. crassifolia forest were generally higher than their counterparts in other regions. SOC stocks on shady slopes were mainly regulated by elevation-induced differences in temperature and precipitation, with temperature being the most important factor influencing the distribution of SOC. For the whole catchment, the distribution of SOC stocks was significantly affected by topographic aspect and elevation; aspect and elevation together explained 97.5% of the overall variation in SOC stocks at a soil depth of 0–50cm, and aspect alone explained 68.2% of the overall variation. These results confirmed that topography was the most significant factor controlling the distribution patterns of SOC in alpine ecosystems.

Climatic signal in cellulose microfibril angle and tracheid radial diameter of Picea crassifolia at different altitudes of the Tibetan plateau, northwest China

Little attention was given to the climatic signals in wood properties, such as microfibril angle (MFA) and tracheid radial diameter (TRD). In this article, year-to-year variation in MFA and TRD was measured by SilviScan-3 on dated Picea crassifolia trees growing at three altitudes in the northeastern Tibetan plateau. Climatic signals registered in MFA and TRD were analyzed using dendroclimatology methods. The annual variation of MFA and TRD was strongly linked to high-frequency climatic signals. Both MFA and TRD were negatively correlated with temperature and positively correlated with precipitation. The temperature had a similar influence on MFA and TRD at three different altitudes, while the influence of precipitation decreased with the increasing altitudes. MFA was negatively correlated with TRD, and this MFA–TRD internal relationship (R t) varied with calendar year. Temperature and precipitation had a strong influence on R t. Temperature was positively correlated with R t, and precipitation was negatively correlated with R t. The influence of temperature was stronger than that of precipitation. The influence of temperature increased with the increase in altitudes, while the influence of precipitation decreased with the increasing altitudes. Results of this study revealed that the trees could change their internal characteristics to adapt to the changing climate.

The type, position and age effect on the cutting reproduction of Picea crassifolia and its rooting mechanism in the Qilian Mountains

Picea crassifolia Kom, a perennial arbor species is recognized as one of the most adaptable plants found to date in Qilian Mountains. To explore the cutting reproduction technology of P. crassifolia and reveal its rooting mechanism, cuttings of P. crassifolia with different cutting types (softwood, hardwood and root), positions (top, upper, middle and bottom) and ages (7, 10, 15, 20, 25 year-old) were cultivated in a field experiment. One-year old softwood and hardwood cuttings were collected from 7-, 10-, 15-, 20-, and 25 year-old healthy ortets to analyze the changes from endogenous hormones and organic nutrients. Results indicate that the softwood cuttings (0.5–1.0 cm in diameter) from upper branches of 15 year-old ortets shows better growth performance by improving rooting indexes, including a significant increase in rooting rate and a decrease in basal rot rate. Concomitantly, increasing rooting quantity and root length also increased. It is noteworthy that the high rooting rate of P. crassifolia cuttings due to its ability to accumulate high concentrations of indole-3-acetic acid (IAA) and total carbon (TC) rather than abscisic acid (ABA) and total nitrogen (TN). The rooting rate was mainly regulated by the IAA/ABA and TC/TN ratio. In summary, our results suggest that the softwood cuttings (0.5–1.0 cm in diameter) from upper branches of 15 year-old P. crassifolia can be considered as an effective strategy to improve cutting rooting rate, and the IAA/ABA and TC/TN ratio was one of the main factors limiting the cutting rooting rate of P. crassifolia.

Warming-Induced Decline of Picea crassifolia Growth in the Qilian Mountains in Recent Decades.

Warming-induced drought has widely affected forest dynamics in most places of the northern hemisphere. In this study, we assessed how climate warming has affected Picea crassifolia (Qinghai spruce) forests using tree growth-climate relationships and the normalized difference vegetation index (NDVI) along the Qilian Mountains, northeastern Tibet Plateau (the main range of Picea crassifolia). Based on the analysis on trees radial growth data from the upper tree line and the regional NDVI data, we identified a pervasive growth decline in recent decades, most likely caused by warming-induced droughts. The drought stress on Picea crassifolia radial growth were expanding from northeast to southwest and the favorable moisture conditions for tree growth were retreating along the identical direction in the study area over the last half century. Compared to the historical drought stress on tree radial growth in the 1920s, recent warming-induced droughts display a longer-lasting stress with a broader spatial distribution on regional forest growth. If the recent warming continues without the effective moisture increasing, then a notable challenge is developed for Picea crassifolia in the Qilian Mountains. Elaborate forest management is necessary to counteract the future risk of climate change effects in this region.

Reproductive Isolation of Ips nitidus and I. shangrila in Mountain Forests of Western China: Responses to Chiral and Achiral Candidate Pheromone Components.

Eastern Palearctic conifers are subject to frequent bark beetle outbreaks. However, neither the species responsible nor the semiochemicals guiding these attacks are well understood. Two high-mountain Ips species on Qinghai spruce, Picea crassifolia, I. shangrila and I. nitidus, are typical in this regard. Six synthetic candidate pheromone components that we earlier identified from hindguts of unmated males of these two Ips species were tested for field activity in Qinghai province, P. R. China. For I. nitidus, racemic ipsdienol ((±)-Id) could replace the naturally-produced blend of enantiomers containing 74% (-)-(S)-Id (74:26 S:R), in attractive ternary or binary blends. In contrast, sympatric I. shangrila were attracted mainly to blends including Id of opposite chirality, 97%-(+)-(R)-Id. Of the verbenols, (-)-trans-verbenol was inactive for I. nitidus or inhibitory for I. shangrila, but (-)-cis-verbenol (cV) was a key component of the pheromone in both species. Two fully factorial experiments demonstrated that (±)-Id, cV, and 2-methyl-3-buten-2-ol (MB) are components of the aggregation pheromone of I. nitidus, whereas only (+)-Id and cV are essential components of the aggregation pheromone of I. shangrila. While MB is not necessary for attraction of I. shangrila, it is an active antagonist and likely functions in species isolation. A review of the pheromone production and responses in Palearctic Ips and Pseudoips showed that cV is more common than methylbutenols, and both elicit qualitatively variable responses. Ipsdienol is the most common component with variable chirality, and is a necessary, but often not sufficient, factor for determining pheromone specificity.

Estimation of Canopy and Woody Components Clumping Indices at Three Mature Picea crassifolia Forest Stands

Many previous studies have shown that the underestimation of the plant area index (PAI) by traditional optical instruments is mainly due to the clumping effects of forest canopies. However, the evaluation of the clumping effects of canopy (leaves, stems, branches, fruits, and flowers) and woody components (stems and branches) within forest canopies is still a challenging task for current indirect instruments and algorithms. In this study, two key issues of the gap size distribution algorithm (CC) were discussed first, such as the stop conditions of the gap-removal procedure and gap-removing methods. Four types of gap-removing schemes were compared and their impacts to the estimation of canopy and woody components clumping indices (Ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> and Ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> ) were analyzed. Obvious discrepancies were found between the estimates of Ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> and Ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> from the four gap-removing schemes at each zenith angle. A new gap-removal scheme was proposed subsequently. After that, a solution was presented to estimate Ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> and Ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> at multiple zenithal and azimuthal directions in three mature Picea crassifolia forest stands. These estimates were retrieved based on multispectral canopy imager (MCI) equipment and CC algorithm. The estimates from the MCI equipment were later compared with those from the TRAC instrument. Small differences were found between the Ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> estimates from the MCI and TRAC instruments, indicating that the MCI instrument was effective for evaluating the clumping effects of forest canopies at multiple zenithal and azimuthal directions. Results showed that both of Ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> and Ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> change with the zenithal and azimuthal directions.

Carbon pools of semi-arid Picea crassifolia forests in the Qilian Mountains (north-eastern Tibetan Plateau)

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 2600–2800m elevation, we found ecosystem carbon stocks of 348MgCha−1 with carbon densities of 43MgCha−1 in the live and dead aboveground biomass, 12MgCha−1 in roots, 3MgCha−1 in litter and 305MgCha−1 in the soil (SOC; 0–100cm). 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 >85MgCha−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.

Dendroclimatic reconstruction of temperature in the eastern Qilian Mountains, northwestern China

Understanding the extent to which climate has varied in the past is a prerequisite to assessing current trends. In this study, we present a 225 yr tree-ring width record of Qinghai spruce Picea crassifolia from a mesic site in the eastern Qilian Mountains of northwest China. This tree-ring record showed significant positive correlations (p < 0.05) with temperature for most months from the preceding May to the current September, but none with precipitation or the Palmer Drought Severity Index. Based on the correlation relationships, we developed a regression model to reconstruct the average July temperatures over the period AD 1785-2009, which accounted for 45% of the observed temperature variation during the calibration period (1957-2009). This is the first tree-ring based temperature reconstruction in the eastern Qilian Mountains. The reconstruction indicated a warming trend that began around 1900 and continued through the late 20th century. Eight of the 10 warmest years were recorded during the period 1990-2009. The longest cool period occurred in 1894-1916. Comparisons of our reconstruction with other independent tree-ring based temperature reconstructions from the northeastern Tibetan Plateau suggest coherent variance patterns in these warm season temperature reconstructions regardless of the positive or negative correlation relationships between tree-ring records and temperatures. The results of comparisons also indicated that the warm season temperature variances lag behind the winter temperature variability by about 20 yr in this region.

Modeling stem volume growth of Qinghai spruce (Picea crassifolia Kom.) in Qilian Mountains of Northwest China

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 meteorological data should be improved to obtain high-accuracy BIOME-BGC outputs.