Semi-shady Slopes Research Articles

The competitive relationship of scrub plants for water use in the subalpine zone of the Qilian Mountains in China.

Samples of scrub plants and soil were collected from May to October 2019 in the subalpine scrub zone of the Qilian Mountains. Based on measured oxygen isotope values (δ18O) in plant xylem water and soil water, the multivariate linear mixed model (IsoSource) and the proportional similarity index (PS index) were used to analyze the using proportion for each potential water source and the competition relationship for water use of scrub plants in different growing periods and habitats. The results showed that the soil water content gradually decreased with increasing depth of the soil layer, with the maximum value in the soil layer of 0-10cm. Most of the scrub plants mainly used soil water in the soil layer of 0-30cm during the different periods of growing season, but Salix sclerophylla Anderss. and Salix oritrepha Schneid. on the semi-sunny slope habitat mainly used soil water in the soil layer of 40-80cm during the middle period of growing season (July-August), with the proportion of 59.5% and 52.1%, respectively; and Potentilla fruticosa Linn. and Salix cupularis Rehd. on the semi-shady slope habitat mainly used soil water in the soil layer of 30-60cm during the early period of growing season (May-June), with the proportion of 61.1% and 49.7%, respectively. The competition relationships of scrub plants for water use varied during different periods of growing season (P < 0.05). On the semi-sunny slope habitat, they were fiercest for Salix cupularis Rehd. and Rhododendron thymifolium Maxim., Potentilla fruticosa Linn., and Salix sclerophylla Anderss. during the early period of growing season; Salix cupularis Rehd. and Rhododendron thymifolium Maxim. during the middle period of growing season, and Salix sclerophylla Anderss. and Salix oritrepha Schneid. during the end period of growing season (September-October). On the semi-shady slope habitat, they were fiercest for Salix oritrepha Schneid. and Caragana jubata (Pall.) Poir. during the early period of growing season; Rhododendron przewalskii Maxim. and Rhododendron thymifolium Maxim. during the middle period of growing season; and Salix cupularis Rehd. and Salix oritrepha Schneid. during the end period of growing season. This study reveals the competitive relationship of scrub plants for water use in the subalpine zone and their response to environmental changes, so as to provide theoretical references for the ecological conservation in the ecologically fragile areas of the Qilian Mountains.

Effects of topography and stand spatial structure on the diameter at breast height growth of major pioneer tree species of natural broad-leaved mixed forests in Zhejiang Province, China.

Based on the continuous inventory data of forest resources in Zhejiang Province in 2019 and 2021, we used statistical methods such as polynomial regression to analyze the impacts of topography and forest spatial structure on average annual diameter at breast height (DBH) growth of main pioneer tree species in natural broad-leaved mixed forests. The results showed that DBH of Schima superba, Quercus glauca, Quercus fabri, Lithocarpus glaber, Castanopsis eyrei, and Castanopsis sclerophylla were between 5-50.8, 5-41.5, 5-50.8, 5-43.9, 5-55.5, and 5-46.1 cm, respectively. We classified all the trees into three classes based on DBH: small (6-12 cm), medium (12-14 cm), and large (>26 cm). The average annual DBH growth of S. superba and Q. glauca was the highest on semi-shady slope and shady slope, with increases of 2.9%-15.7% and 1.1%-41.2%, respectively. The average annual DBH growth of large-diameter S. superba, L. glaber, C. eyrei and C. sclerophylla decreased with the increase of slope, with a maximum decrease of 27.0% for S. superba, with no significant difference among small- and medium-diameter trees as a whole. The slope position did not affect the annual DBH growth of small-diameter trees, while that of medium- and large-diameter S. superba, Q. glauca, and large-diameter Q. fabri, L. glaber decreased with the change of slope position from downhill, mesoslope, uphill to ridge, with a maximum decrease of 28.1% for L. glabe, and the major-diameter C. eyrei was on the contrary. Appropriate increase in the mingling was beneficial to the average annual DBH growth of medium- and large-diameter trees. Moderate mixing was suitable for S. superba, while low degree mixing and moderate mixing was suitable for Q. glauca, Q. fabri and L. glaber, and intensive mixing was suitable for C. eyrei and C. sclerophylla. No significant difference was observed for minor-diameter trees under the mingling. The neighborhood comparison only had a significant effect on the average annual DBH growth of large-diameter Q. glauca, Q. fabri, and L. glaber, which was significantly higher under subdominance-moderation than moderation-inferiority. The average annual DBH growth in the study area was mainly affected by aspect and mixing degree.

Effects of season and slope orientation on stable isotopes of different water bodies in the subalpine shrub zone of the eastern Qilian Mountains in China.

The subalpine shrub zone of the Qilian Mountains is an important water-retaining area, and it is crucial to clarify the processes of its hydrological cycle. Therefore, based on the stable isotope values of different water bodies in the subalpine shrub zone of the eastern Qilian Mountains from May to October 2019, the characteristics of δD and δ18O of different water bodies and their hydraulic relationships with each other were studied. The results showed that the stable isotope values of precipitation exhibited the largest fluctuations, while they were the most stable for groundwater. Plant transpiration was stronger than the evaporation of other water bodies. The stable isotope of precipitation was enriched in high temperature and low humidity environments. Isotopic values of plant and soil water were higher and more stable on the semi-sunny slope than on the semi-shady slope. According to the stable isotopes, there was a strong hydraulic relationship between the different water bodies in the study area, and precipitation was the ultimate source of all of them. Precipitation replenished soil water through infiltration. Part of the soil water was absorbed by plants, while the rest continued to infiltrate to replenish groundwater. Groundwater and precipitation replenished the river water.

Change Characteristics of Soil Organic Carbon and Soil Available Nutrients and Their Relationship in the Subalpine Shrub Zone of Qilian Mountains in China

Studying the spatial and temporal distribution of soil organic carbon (SOC) content in high-altitude mountainous areas and its correlation with soil nutrients provides a basis for understanding soil carbon stocks and the factors affecting the local carbon cycle. Based on soil samples collected from a semi-sunny slope and semi-shady slope in the subalpine shrub zone of the eastern Qilian Mountains from May to October 2019, we studied the temporal and spatial changes in SOC and soil available nutrients and their relationships. The results showed that SOC content and soil nutrients were greater on the semi-shady slope than on the semi-sunny slope during the growing season and decreased with an increase in soil depth in different slope directions, showing obvious surface aggregation. The soil available nitrogen (SAN) content was consistent with the SOC content and exhibited greater synchronization. SOC was significantly positively correlated with soil available nutrients in the study area during the whole growing season. However, the correlation between SOC and soil nutrients varied among the different soil layers and slope orientations. The SOC content was more obviously correlated with the SAN content in the soil layer at a depth of 30–40 cm (r = 0.67, p &lt; 0.05) on the semi-shady slope. The SOC content was more obviously correlated with soil-available phosphorus (SAP) content in the soil layer at a depth of 30–40 cm (r = 0.57) on the semi-sunny slop. The SOC content was more obviously correlated with the SAP content in the soil layer at a depth of 60–70 cm (r = 0.55) and with the soil-available potassium (SAK) content in the soil layer at a depth of 70–80 cm (r = 0.84) on the semi-sunny slope.

Automatic Extraction of the Spatial Distribution of Picea schrenkiana in the Tianshan Mountains Based on Google Earth Engine and the Jeffries–Matusita Distance

As a distinct species in the Tianshan Mountains (TS) of Central Asia (CA), Picea schrenkiana plays a significant role in water purification, soil and water conservation, and climate regulation. In the context of climate change, rapidly and accurately obtaining its spatial distribution has critical decision-making significance for maintaining ecological security in the arid area of CA and the sustainable development of the “Silk Road Economic Belt”. However, conventional methods are extremely challenging to accomplish the high-resolution mapping of Picea schrenkiana in the TS, which is characterized by a wide range (9.97 × 105 km2) and complex terrain. The approach of geo-big data and cloud computing provides new opportunities to address this issue. Therefore, the purpose of this study is to propose an automatic extraction procedure for the spatial distribution of Picea schrenkiana based on Google Earth Engine and the Jeffries–Matusita (JM) distance, which considered three aspects: sample points, remote-sensing images, and classification features. The results showed that (1) after removing abnormal samples and selecting the summer image, the producer accuracy (PA) of Picea schrenkiana was improved by 2.95% and 0.24%–2.10%, respectively. (2) Both the separation obtained by the JM distance and the analysis results of eight schemes showed that spectral features and texture features played a key role in the mapping of Picea schrenkiana. (3) The JM distance can seize the classification features that are most conducive to the mapping of Picea schrenkiana, and effectively improve the classification accuracy. The PA and user accuracy of Picea schrenkiana were 96.74% and 96.96%, respectively. The overall accuracy was 91.93%, while the Kappa coefficient was 0.89. (4) The results show that Picea schrenkiana is concentrated in the middle TS and scattered in the remaining areas. In total, 85.7%, 66.4%, and 85.9% of Picea schrenkiana were distributed in the range of 1500–2700 m, 20–40°, and on shady slope and semi-shady slope, respectively. The automatic procedure adopted in this study provides a basis for the rapid and accurate mapping of the spatial distribution of coniferous forests in the complex terrain.

A dataset of the observations of carbon, water and heat fluxes over an alpine shrubland in Haibei (2011–2020)

Alpine shrubland is one of the important vegetation types on the Qinghai-Tibet Plateau, which mainly lies in the shady or semi-shady slope of snowpack mountains or the high-altitude alluvium and diluvium on plains. It plays a crucial role in carbon sequestration, water conservation and climate regulation. Since 2002, Haibei National Field Research Station for Alpine Grassland (Haibei Station) has been using eddy covariance techniques to continuously observe the carbon, water and heat exchange between an alpine Potentilla fruticosa shrubland ecosystem and the atmosphere and has accumulated nearly 20-year data. On the basis of the previous publication of relevant data from 2003 to 2010, the carbon, we further released water and heat fluxes of the alpine shrubland and supplementary meteorological data from 2011 to 2020. This dataset consists of the subsets of meteorological factors, covering air temperature, air relative humidity, water vapor pressure, wind speed, wind direction, ambient pressure, total solar radiation, net radiation, photosynthetically active radiation, precipitation, soil temperature, and soil moisture, as well as net ecosystem CO2 exchange, ecosystem respiration, gross ecosystem CO2 exchange, latent heat flux, and sensible heat flux. The temporal resolutions of the dataset include half-hourly, daily, monthly, and yearly scales. This dataset can not only be used to scientifically evaluate the environmental drivers and evolution trends of the ecological functions of carbon, water and heat in alpine shrub ecosystems, but also provide ground data support for parameter validation and optimization of remote sensing-based ecological process models.

Soil Moisture Dynamics and Its Temporal Stability under Different-Aged Caragana korshinskii Shrubs in the Loess Hilly Region of China

Soil moisture has a great influence on vegetation growth and survival in arid and semiarid regions. Information about deep soil moisture dynamics is vital for restoring vegetation and improving land management on the water-limited Loess Plateau. The spatiotemporal dynamics and temporal stability of deep soil moisture (at a soil depth of 600 cm) were observed in situ under Caragana korshinskii shrubs that had various stand ages (named CK-10yr, CK-20yr and CK-35yr) in the Loess hilly region of China. The results showed that under C. korshinskii, soil moisture generally decreased as the stand age rose. Meanwhile, its moisture was consistent with precipitation variation, and an obvious time lag in soil moisture was found compared to that in precipitation during the entire growing season. Along the soil profile, a transition belt linking the shallow with deep soil moisture occurred at a 200 cm soil depth in different slope positions and aspects. At the slope scale, both the slope aspect and slope position significantly affected soil moisture variation in the areas with planted C. korshinskii shrubs, experiencing a decreasing trend from semi-shady slopes to sunny ones and from lower positions to upper ones. However, the variance in soil moisture between different positions and slope aspects was small. For the slope aspect, except for CK-20yr, the different-aged C. korshinskii shrubs had higher soil moisture content on sunny slopes than on semi-shady slopes at the upper 0–200 cm soil depth, while the opposite was true at the 200–600 cm soil depths. For slope positions, the soil moisture variation was small between the 0 and 200 cm soil depths and larger between the 200 and 600 cm soil depths. Within the whole profiles, the representative depth under the C. korshinskii shrubs for the soil moisture content was mainly concentrated between the 400–500 cm soil depths, on average, showing a gradual deepening trend with increasing restoration age. In summary, the findings indicate that natural recovery with low-water consumption grasslands and manual management measures, such as thinning and mowing, should be strengthened to minimize the high soil moisture consumption rates that occur in a healthy soil moisture environment and maintain sustainable vegetation restoration.

Assessment of Carbon Storage under Different SSP-RCP Scenarios in Terrestrial Ecosystems of Jilin Province, China.

Carbon storage is one of the key factors determining the global carbon balance in the terrestrial ecosystems. Predicting future changes in carbon storage is significant for regional sustainable development in the background of the "dual carbon" objective. This study which coupled the InVEST model and the PLUS model and is based on land use in different future scenarios evaluated the evolution characterization of terrestrial carbon storage in Jilin Province from 2000 to 2040 and explored the impact of related factors on it. The results show that: (1) from 2000 to 2020, the area of cultivated land and built-up areas increased continuously in Jilin Province, while the area of forest land, grassland, and wetland decreased with time; the ecological land has been restored to a certain degree. (2) Due to the continuous reduction in ecological land, the overall carbon storage in Jilin Province from 2000 to 2020 showed a downward trend, with a total reduction of 30.3 Tg, and the carbon storage in the western part of Jilin Province changed significantly. The SSP2-RCP4.5 scenario shows a minimum value of carbon storage in 2030 and a small increase in 2040; the SSP1-RCP2.6 scenario shows an increasing trend in carbon storage from 2020 to 2040; the area of built-up areas and cultivated land increases and the loss in carbon storage is more serious under the SSP5-RCP8.5 scenario. (3) On the whole, with the increase in elevation and slope, the carbon storage showed a trend of increasing first and then decreasing, and the carbon storage of shady and semi-shady slopes was higher than that of sunny and semi-sunny slopes; forest land and cultivated land were the keys to carbon storage changes in Jilin Province.

Effects of slope aspect and age class on diseases of Juglans regia in Wild Walnut Nature Conservation Area of Xinjiang, China.

To understand the disease situation of vulnerable plant Juglans regia, we investigated the proportions of four diseases of J. regia with different age classes in different slope aspects in the Wild Walnut Nature Conservation Area of Xinjiang. We analyzed the correlation of disease types and disease grades with the diameter at breast height (DBH) of J. regia and slope aspects. The results showed that the main diseases of J. regia in the reserve were walnut brown spot disease (95.8%), walnut deadwood disease (90.5%), walnut black spot disease (74.4%), and walnut rot disease (7.7%). J. regia was susceptible to walnut brown spot disease in all the four slope aspects, with walnut deadwood disease on shady and semi-shady slopes, walnut black spot disease on sunny and shady slopes, and walnut rot disease on semi-sunny and semi-shady slopes. The proportion of diseased plants with the four diseases decreased with the increases of disease grades (1-4 grades) in the four slope aspects. Across the four slope aspects, the middle-aged trees had the largest proportion of walnut deadwood disease, walnut black spot disease and walnut brown spot disease, followed by old trees and young trees. No diseased seedlings were found. Walnut rot disease only occurred in old trees. There was significant positive correlation between DBH of J. regia and the four diseases. Walnut black spot disease had significant negative correlation with slope aspect. There was correlation between different disease grades of walnut deadwood disease, walnut rot disease and walnut black spot disease with DBH and slope aspects.

Spatial distribution characteristics of discontinuous hillslope gullies on the Loess Plateau of China: A special focus on spoon gullies

Gullies characterized by frequent material exchanges and dramatic morphological changes sculpt fragmented surface landscapes and generate severe soil erosion, yet research on discontinuous gullies is currently lacking on the Loess Plateau of China. A special kind of discontinuous gully isolated on a hillslope, termed a spoon gully, was observed during a field investigation on the Loess Plateau. Spoon gullies are permanent gullies that are basically spoon-shaped with fat heads and thin tails. The confluences between spoon gullies and other gullies mainly occur in the subsurface. According to image interpretations and field verifications, 4077 spoon gullies were recognized on the Loess Plateau. These gullies were mainly distributed in the western part and northern fringes of the Loess Plateau with an obvious spatial clustering tendency, forming four concentrated areas with high gully densities. The topography distinctly affects the spatial distribution of spoon gullies. A total of 81.92% of the spoon gullies were located on slopes of 10–30°, and 73.29% of these gullies were located on semi-sunny or semi-shady slopes. Furthermore, the spatial distribution of spoon gullies was associated with loess landforms and soil erosion intensities. A total of 66.37% of the spoon gullies occurred in loess ridge, loess tableland, or loess hill regions, and more than 50% of them arose in areas of strong or moderate water erosion. Overall, spoon gullies were mainly distributed in areas where continuous gullies developed insufficiently, and this finding can be regarded as the integrated result of precipitation, loess thickness and texture, vegetation coverage, and agricultural activities, suggesting that spoon gullies may represent an early stage in the development of continuous loess gully systems. These results not only provide new insights for understanding the formation and evolution of gully landforms but also have significant implications for soil erosion management on the Loess Plateau.

内蒙古大青山国家级自然保护区植被归一化指数时空变化及其与环境因子的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 内蒙古大青山国家级自然保护区植被归一化指数时空变化及其与环境因子的关系 DOI: 10.5846/stxb202108072161 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 内蒙古自治区科技重大专项项目（zdzx2018060，2019ZD007）；内蒙古自治区退耕还林生态效益监测项目 Spatio-temporal variation of NDVI and influencing factors in the Daqing Mountain National Nature Reserve, Inner Mongolia Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:选取2000-2020年MODIS影像的归一化指数（NDVI）数据及同期的气象数据，采用趋势分析、变异系数、相关分析等方法，从海拔、坡度和坡向的角度分析了内蒙古大青山国家级自然保护区生长季NDVI的时空变化特征，并进一步探讨了NDVI时空变化与气候因子的相关性。结果表明：（1）2000-2020年，内蒙古大青山国家级自然保护区植被总体覆盖状况良好且呈增长趋势，增长速率为0.058/10a；（2）保护区NDVI空间分布呈现出西部低、东部高的从西到东逐渐增加的特征。保护区生长季NDVI均值随着海拔的升高而明显增加，随着坡度的增加呈缓慢增加趋势，在不同坡向上，生长季NDVI均值大小依次为阴坡 > 半阴坡 > 半阳坡 > 阳坡；（3）从NDVI变化趋势分析来看，2000-2020年大青山自然保护区植被覆盖改善的面积占总面积的61.75%，其中，显著改善、极显著改善面积分别占总面积的41.13%、20.62%，基本保持不变的面积占总面积的38.17%，退化面积占总面积的0.07%。在空间分布上，NDVI显著、极显著增加的区域主要分布在保护区西部和东部，中部以变化不显著为主。保护区各功能区NDVI变化趋势看，NDVI极显著增加、显著增加面积百分比大小顺序为实验区 > 核心区 > 缓冲区；（4）2000-2020年，稳定性整体表现为"不同波动变化并存，较低、中等和较高波动变化居多，低波动和高波动变化面积占比相对较小"的特点，高波动变化区域主要分布在保护区西部、中部和实验区，人为影响和降水量是影响稳定性的主要驱动因素；（5）大青山自然保护区生长季NDVI与年均降水量以正相关为主，正相关面积比例达到99.79%，与温度相关性不显著为主，不显著面积占总面积的97.91%，降水量是影响大青山自然保护区植被覆盖的最主要气象因子。 Abstract:Based on the Normalized Difference Vegetation Index (NDVI) data of Moderate Resolution Imaging Spectroradiometer (MODIS) image and the relative meteorological data from 2000 to 2020, the temporal and spatial variation characteristics of NDVI in the growing season of Daqing Mountain National Nature Reserve in Inner Mongolia are analyzed from the perspective of elevation, slope and slope aspect by using the methods of trend analysis, coefficient of variation and correlation analysis. The correlation between temporal and spatial variation of NDVI and climate factors was further explored. The results show that:(1) The overall vegetation coverage of Daqing Mountain National Nature Reserve was good and growing from 2000 to 2020, with a growth rate of 0.058/10a. (2) The spatial distribution of the NDVI shows the characteristics of low in the west and high in the east, and gradually increasing from west to east of the reserve. With the increase of elevation, the mean value of NDVI in the growing season of the reserve increased significantly, but increased slowly with the increase of the slope. In different slope aspects, the mean value of NDVI in growing season was shady slope > semi-shady slope > semi-sunny slope > sunny slope. (3) From the analysis of NDVI change trend in 2000-2020, the area of vegetation coverage improvement in Daqing Mountain National Nature Reserve accounted for 61.75% of the total area, of which the areas of significant improvement and extremely significant improvement accounted for 41.13% and 20.62% of the total area, respectively, the area basically unchanged accounted for 38.17% of the total area, and the degraded area accounted for 0.07% of the total area. In terms of spatial distribution, the areas with the significant and extremely significant increase in NDVI were mainly distributed in the west and east of the reserve, and the change was not significant in the middle. According to the changing trend of NDVI in each functional area of the reserve, the NDVI increased significantly, and the area percentage increased significantly in the order of experimental zone > core zone > buffer zone. (4) From 2000 to 2020, the overall performance of stability is characterized by the coexistence of different fluctuations, the majority of low, medium and high fluctuations, and the proportion of low and high fluctuations being relatively small. The high fluctuations are mainly distributed in the western and central areas of the reserve and the experimental zone, and human disturbance and precipitation are the main driving factors. (5) The average annual maximum NDVI in the growing season of Daqing Mountain National Nature Reserve is mainly positively correlated with the average annual precipitation, and the proportion of the positive correlation area reaches 99.79%. It is mainly insignificant with temperature, and the insignificant area accounts for 97.91% of the total area. Precipitation is the main meteorological factor affecting the vegetation coverage of Daqing Mountain National Nature Reserve. 参考文献 相似文献 引证文献

Sediment connectivity of small watershed affected by gully development and vegetation restoration on the loess plateau

Sediment connectivity can reflect the linkage between sediment source and sink, and identify the hotspot of soil conservation in watersheds. Potential effects of gully development and vegetation restoration on sediment connectivity are not fully understood. This study was performed to quantify the temporal changes in sediment connectivity reflected by the index of connectivity (IC) triggered by the coupling effect of gully development and vegetation restoration in a representative small watershed in the Loess Plateau. Google maps and Landsat images were used to determine gully characteristics and vegetation coverage. Based on the source-sink landscape index, weights of different land use types were computed using the K and C factors of the Universal Soil Loess Equation to calculate the IC. Partial least squares regression was used to quantify the contribution of gully development and vegetation restoration to the IC. The results showed that IC decreased significantly from −1.27 in 2000 to −8.15 in 2020 due to rapid vegetation restoration. Sediment connectivity increased with slope gradient but decreased with vegetation coverage. Compared with grassland, sediment connectivity decreased by 0.35–2.86 for cropland and 1.29–3.56 for forestland from 2000 to 2020. Moreover, the length, width, circumference, and area of gullies increased by at least 73% from 2000 to 2010, and the rate of increase declined greatly with the effective implementation of vegetation restoration. With the increase in slope gradient, gully development became more intense, and the IC increased. The gully length, width, circumference and area, and IC of shady and semi-shady slope aspects were 27.25%, 23.29%, 26.76% and 61.46%, and 5.8%–18.6% less than that of sunny and semi-sunny slope aspects. Vegetation restoration inhibited sediment connectivity, whereas gully development promoted sediment connectivity. Overall, the decrease in sediment connectivity triggered by vegetation restoration was much greater than the increase induced by gully development. The results of this study help understand the change in sediment connectivity over time under the comprehensive impact of vegetation restoration and gully development at small watershed scales in semi-arid regions.

Aboveground biomass estimation of black locust planted forests with aspect variable using machine learning regression algorithms

An accurate estimation of forest aboveground biomass (AGB) is important for carbon accounting and afforestation policy making, and the aspect factors that affect forest stand growth are important to the accuracy of AGB estimation. In this study, aspect was incorporated as a variable into three machine learning algorithms (MLAs) (support vector machine (SVM), artificial neural network (ANN) and random forest (RF)), to estimate the AGB of black locust (Robinia pseudoacacia) planted forests in 96 field plots with four different aspects (sunny slope, semi-sunny slope, semi-shady slope and shady slope). The results showed that in the models incorporating aspect variables, the increase in accuracy varied from 36.72% to 41.23% for 29 validation plots based on R2. The A-RF model (RF with aspect variable), which had the highest R2 (0.8519) and lowest RMSE and rRMSE (12.552 Mg/ha and 0.175) was considered optimal for AGB estimation of black locust planted forests. The overestimation of sunny and shady slopes, and the underestimation of semi-sunny and semi-shady slopes are reduced by incorporating the aspect variable. Areas with lower AGB values mainly occur on sunny and shady slopes, and areas with higher AGB values mainly occur on semi-sunny and semi-shady slopes. Overall, our study demonstrates that the introduction of the aspect variable provided the model with a basis for the effects of different growth conditions of black locust planted forests on different aspects, which can improve the accuracy of AGB estimation.

Influence of Slope Direction on the Soil Seed Bank and Seedling Regeneration of Castanopsis hystrix Seed Rain

Objective: To investigate the impact of different slope directions on the quantity and quality of the soil seed bank and seedling germination process of Castanopsis hystrix plantations. Method: Fixed sample plots in forest stands of Castanopsis hystrix were established on different slope directions (sunny slope, semi-sunny slope, semi-shady slope, and shady slope). The characteristics of the forest stand were investigated, and per-wood scaling was carried out. The temporal dynamics of the seed rain and seed bank were quantified using seed rain collectors and by collecting soil samples from different depths. The quantity and quality of the seeds were determined, and the vigor of mature seeds was measured throughout the study. Results: (1) The diffusion of Castanopsis hystrix seed rain started in mid-September, reached its peak from late October to early November, and ended in mid-December. (2) The dissemination process, occurrence time, and composition of the seed rain varied between the different slope directions. The seed rain intensity on the semi-sunny slope was the highest (572.75 ± 9.50 grains∙m−2), followed by the sunny slope (515.60 ± 10.28 grains∙m−2), the semi-shady slope (382.13 ± 12.11 grains∙m−2), and finally the shady slope (208.00 ± 11.35 grains∙m−2). The seed rain on the sunny slope diffused earliest and lasted the longest, while the seed rain on the shady slope diffused latest and lasted the shortest time. Seed vigor and the proportion of mature seeds within the seed rain were greatest on the semi-sunny slope, followed by the sunny slope, semi-shady slope, and the shady slope. (3) From the end of the seed rain to August of the following year, the amount of total reserves of the soil seed banks was highest on the semi-sunny slope, followed by the sunny slope then the semi-shady slope, and it was the lowest on the shady slope. The amount of mature, immature, gnawed seeds and seed vigor of the soil seed bank in various slope directions showed a decreasing trend with time. The seeds of the seed bank in all slope directions were mainly distributed in the litter layer, followed by the 0–2 cm humus layer, and only a few seeds were present in the 2–5 cm soil layer. (4) The seedling density of Castanopsis hystrix differed significantly on the different slope directions. The semi-sunny slope had the most seedlings, followed by the sunny slope, semi-shady slope, and the shady slope. Conclusions: The environmental conditions of the semi-sunny slope were found to be most suitable for the seed germination and seedling growth of Castanopsis hystrix, and more conducive to the regeneration and restoration of its population.

Fractional vegetation cover and topographic effects in Pisha sandstone area of Northwest China in 2000-2018

Based on MODIS-EVI data and binary pixel model, we calculated fractional vegetation coverage (FVC) in Pisha sandstone area of Northwest China from 2000 to 2018. The topographic effects on fractional vegetation coverage was analyzed from elevation, slope, and aspect using digital elevation model (DEM) data. From 2000 to 2018, FVC in Pisha sandstone area of Northwest was relatively low, which increased with a rate of 2.43·a-1. The positive anomaly of FVC existed in 12 years, with higher positive anomaly FVC mainly in 2018 and 2013. The negative anomaly of FVC existed in seven years, with the lower negative anomaly of FVC mainly in 2000 and 2001. The spatial distribution of FVC in Pisha sandstone area decreased from southeast to northwest, which differed significantly among different types, with that in bare Pisha sandstone being the lowest, followed by sand-covered Pisha sandstone, and soil-covered Pisha sandstone area being the highest. The FVC in this area had an average increasing rate of 0.0031, suggesting an improved vegetation growth status. Analysis of elevation-aspect effect showed that aspect had a great influence on FVC at the elevation no more than 1000 m and more than 1500 m in bare Pisha sandstone and sand-covered Pisha sandstone areas, respectively. The aspect of soil-covered Pisha sandstone had a small influence on FVC, its influence was relatively large at 1200-1300 m. When the slope of Pisha sandstone area was no more than 15°, the slope-aspect effect of FVC was not obvious. When the slope was more than 25°, FVC of shady and semi-shady slope in bare and sand-covered Pisha sandstone areas was larger than that of sunny and semi-sunny slopes. For soil-covered Pisha sandstone, when the slope was more than 15°, FVC of semi-shady and semi-sunny slopes was larger than that of shady and sunny slopes.

Stoichiometric characteristics of Artemisia sacrorum communities under different site conditions and their correlation with soil nutrients

We explored the stoichiometric characteristic of Artemisia sacrorum communities and its correlation with soil characters by considering the aspect and slope position, and variation of soil nutrient in Yangqingchuan catchment of Wuqi. Our results showed that total carbon, total nitrogen, total phosphorus contents and C:N ratio in A. sacrorum (both shoot and root) in the top of hillock>sunny slope>semi-shady slope>shady slope. The C:P ratio in shoot and the N:P ratio in root decreased consistently. The N:P ratio in shoot and the C:P ratio in root decreased first and then increased. While the total nitrogen and total phosphorus in shoot, and the organic carbon in root increased first and then decreased with the decreases of slope position, the C:N ratio and N:P ratio in shoot decreased first and then increased. The stoichiometric characteristic of A. sacrorum communities was positively correlated with the soil stoichiometric characteristics. However, the C:N ratio, C:P ratio and N:P ratio of A. sacrorum and the total phosphorus of root were negatively correlated to corresponding soil indices. The correlation between shoot nutrition and soil was greater than that between soil and root nutrition. In conclusion, middle position of shady slope was optimal for the growth of A. sacrorum. The stoichiometric characteristics of plants were significantly correlated with soil nutrient condition. Aspect and slope position had a significant effect on the stoichiometric cha-racteristics of A. sacrorum community and soil. Proper A. sacrorum community could help restore soil nutrition.

Spatial variability of plant community characteristics and its influencing factors in a small watershed of wind-water erosion crisscross region on the Loess Plateau, China

The small watershed is the basic unit of soil erosion control on the Loess Plateau. Consequently, the study of the spatial distribution and influencing factors of vegetation is the basis of vege-tation restoration and reconstruction in this region. A small watershed in the wind-water erosion crisscross region with the most serious soil erosion in the Loess Plateau was selected to investigate the changes of vegetation distribution and soil properties. The spatial variability of plant community characteristics and its main driving factors were studied by geo-statistical method and redundancy analysis (RDA). The results showed that there were 27 plant species in the small watershed, belonging to 12 families and 25 genera. Leguminous, Gramineous and Compositae plants were dominant families, contributing 59.3% of the total species. In general, the community structure was simple and the organization level was low. The aboveground biomass (AGB) and coverage (C) of the community reached 205.7 g·m-2 and 57.7%, which was higher than the mean value of grassland in northern China, but the level of species diversity was lower. There were medium spatial correlation in AGB, but stronger spatial correlation for C, Patrick richness index (R), Shannon diversity index (H), Simpson dominance index (D) and Pielou evenness index (J). The spatial distribution of AGB was mainly patchy and striped, which was highest at the semi-shady slope and near the outlet of watershed. Other community characteristics were relatively fragmented, and R, H and J were higher at the top of the semi-shady slope. AGB and C were mainly affected by soil organic carbon, mineral nitrogen, total nitrogen, soil water content, and altitude, while R, H, D and J were mainly affected by soil saturated hydraulic conductivity, bulk density, sand content, and silt content. The results are helpful for vegetation restoration and evaluation of ecosystem structure and function in the wind-water erosion crisscross region.

Seed rain, soil seed bank and seedling regeneration of Quercus aliena var. acureserrata in different slope directions on the middle Qinling Mountains, China

We studied the seed rain, seed pool quantity and quality dynamics, and seedling develop-ment of natural Quercus aliena var. acureserrata forests in different slopes (sunny, semi-sunny, semi-shady and shady slope) of the middle Qinling Mountains, China. The results showed that seed rain of Q. aliena var. acureserrata generally began at mid-August, peaked from mid-late September to early October, and ended in mid-early November. The dissemination process, occurrence time, and composition of seed rain in four slopes were different. The seed rain intensity of the semi-sunny slope was the highest, which was 134.13 seeds·m-2, followed by sunny slope, semi-shady slope, and shady slope. The seed rain on the sunny slope occurred first, and the duration of the whole and peak period were the longest. The seed rain on the shady slope occurred at the latest, and the duration of the whole and peak period were the shortest. The seed viability and mature seeds proportion were semi-sunny slope > sunny slope > semi-shady slope > shady slope. From the end of the seed rain to the August of the next year, the size of soil seed bank was semi-sunny slope > sunny slope > semi-shady slope > shady slope. The number of mature, immature and nibbled seeds and seed vigor of soil seed bank showed a decreasing trend with time, while the number of moldy seeds increased. The seeds in soil seed bank mainly existed in the litter layer, followed by the 0-2 cm soil layer, with few seeds in the 2-5 cm soil layer. The seedling density of Q. aliena var. acureserrata was significantly different among the four slopes. The semi-sunny slope, with the highest seedling density, was more suitable for seed germination and seedling growth of Q. aliena var. acureserrata than other slopes.

Spatial patterns in natural Picea crassifolia forests of northwestern China, as basis for close-to-nature forestry

Close-to-nature forest management has been proposed as an effective method for improving the quality of plantation forests. Knowledge of spatial distribution patterns, structure, and succession trajectories in natural forests can provide guidelines for the establishment of close-to-nature forest plantations. Such knowledge is lacking in natural spruce (Picea crassifolia) forests in the Qilian Mountains of China, impeding the establishment of production forests. We conducted a case study in the Qilian Mountains to analyze the relationships between the naturally-formed forest patches and terrain factors, spatial heterogeneity of stand characteristics, and stand structure following harvesting disturbance. Our results suggested that spruce plantations will be effective on the N, NE, and NW slopes, at elevations between 2700 and 3300 m, and on slopes ranging from 15° to 45°. Further, planted forest patches should occupy 64% of the slope area on semi-shady slopes (NE, NW). Spatial patterns in the studied forest exhibited a strong scale-effect, and an area of 0.25 ha could be used as the most efficient plot scale for the management of spruce plantations. Partial logging is an effective method for the conversion of spruce planted forests into nearnatural forests, and the intensity of partial logging can be determined from the negative exponential function relationship between stand density and DBH. Our results provided critical information for the development of spruce plantations and conversion of existing plantations.

Evaluating relationships between soil chemical properties and vegetation cover at different slope aspects in a reclaimed dump

Conducting research about the relationships between soil chemical properties and vegetation coverage at different slope aspects is especially important in reconstructed ecosystems of vulnerable ecological regions. This study was conducted in the first reclaimed dump within the Pingshuo mining area of Shanxi Province, China, to analyze patterns of soil chemical properties (soil organic matter (SOM), soil total nitrogen (STN), soil available phosphorus (SAP) and soil available potassium (SAp) and vegetation coverage (NDVI) and their correlations at different slope aspects. In the reclaimed dump, 26 quadrats were established along four slope aspects (i.e., shady, semi-shady, sunny and semi-sunny slopes). There was no significant difference in SOM or STN among different slope aspects, while SAP differed between shady slopes compared to semi-shady, sunny and semi-sunny slopes; SAP differed significantly between semi-shady and semi-sunny slopes. The NDVI of semi-sunny slopes differed significantly from that of the other three aspects. There was variation in the relationships between NDVI and soil chemical properties, depending on the slope aspects. The logarithm of SOM and NDVI was related linearly on shady and semi-shady slopes, while NDVI was inversely related to the natural logarithm of the logarithm of SOM on sunny and semi-sunny slopes. STN and NDVI had a first-order function relationship on shady and semi-shady slopes, yet a quadratic function relationship on sunny and semi-sunny slopes. The relationships between SAP and NDVI were inverse on all types of slopes. On shady and semi-shady slopes, NDVI had a quadratic relationship with the logarithm of SAp, but it was well fitted by using a cubic function on sunny and semi-sunny slopes. The sensitivity coefficients of soil chemical properties and NDVI were different, and soil chemical properties changed differently depending on changes in NDVI at different slope aspects.