Chuanyan Zhao

Effect of vegetation on soil water retention and storage in a semi-arid alpine forest catchment

The runoff generated from mountainous regions is recognized as the main water source for inland river basins in arid environments. Thus, the mechanisms by which catchments retain water in soils are to be understood. The water storage capacity of soil depends on its depth and capacity to retain water under gravitational drainage and evapotranspiration. The latter can be studied through soil water retention curve (SWRC), which is closely related to soil properties such as texture, bulk density, porosity, soil organic carbon content, and so on. The present study represented SWRCs using HYDRUS-1D. In the present study, we measured physical and hydraulic properties of soil samples collected from Sabina przewalskii forest (south-facing slope with highest solar radiation), shrubs (west-facing slope with medium radiation), and Picea crassifolia forest (north-facing slope with lowest radiation), and analyzed the differences in soil water storage capacity of these soil samples. Soil water content of those three vegetation covers were also measured to validate the soil water storage capacity and to analyze the relationship between soil organic matter content and soil water content. Statistical analysis showed that different vegetation covers could lead to different soil bulk densities and differences in soil water retention on the three slope aspects. Sand content, porosity, and organic carbon content of the P. crassifolia forest were relatively greater compared with those of the S. przewalskii forest and shrubs. However, silt content and soil bulk density were relatively smaller than those in the S. przewalskii forest and shrubs. In addition, there was a significant linear positive relationship between averaged soil water content and soil organic matter content (P<0.0001). However, this relationship is not significant in the P. crassifolia forest. As depicted in the SWRCs, the water storage capacity of the soil was 39.14% and 37.38% higher in the P. crassifolia forest than in the S. przewalskii forest and shrubs, respectively, at a similar soil depth.

Soil water content and water balance simulation of Caragana korshinskii Kom. in the semiarid Chinese Loess Plateau

Abstract In this paper, to evaluate the hydrological effects of Caragana korshinskii Kom., measured data were combined with model-simulated data to assess the C. korshinskii soil water content based on water balance equation. With measured and simulated canopy interception, plant transpiration and soil evaporation, soil water content was modeled with the water balance equation. The monthly variations in the modeled soil water content by measured and simulated components (canopy interception, plant transpiration, soil evaporation) were then compared with in situ measured soil water content. Our results shows that the modeled monthly water loss (canopy interception + soil evaporation + plant transpiration) by measured and simulated components ranges from 43.78 mm to 113.95 mm and from 47.76 mm to 125.63 mm, respectively, while the monthly input of water (precipitation) ranges from 27.30 mm to 108.30 mm. The relative error between soil water content modeled by measured and simulated components was 6.41%. To sum up, the net change in soil water (ΔSW) is negative in every month of the growing season. The soil moisture is approaching to wilting coefficient at the end of the growth season, and the soil moisture recovered during the following season.

Characteristics of Caragana korshinskii and Hippophae rhamnoides stemflow and their significance in soil moisture enhancement in Loess Plateau, China

Stemflow of xerophytic shrubs represents a significant component of water replenishment to the soil-root system and influences water utilization of plant roots at the stand scale, especially in water-scarce semi-arid ecosystems. The stemflow of two semi-arid shrubs (Caragana korshinskii and Hippophae rhamnoides) and its effect on soil moisture enhancement were evaluated during the growing season of 2011 in the semi-arid loess region of China. The results indicated that stemflow averaged 12.3% and 8.4% of the bulk precipitation for C. korshinskii and H. rhamnoides, respectively. Individual stemflow increased in a linear function with increasing rainfall depth. The relationship between funneling ratios and rainfall suggested that there existed a rainfall depth threshold of 11 mm for both C. korshinskii and H. rhamnoides. Averaged funneling ratios were 156.6±57.1 and 49.5±30.8 for C. korshinskii and H. rhamnoides, respectively, indicating that the canopy architecture of the two shrubs was an effective funnel to channel stemflow to the root area, and C. korshinskii showed a greater potential to use stemflow water in the semi-arid conditions. For individual rainfall events, the wetting front depths were approximately 2 times deeper in the rooting zone around the stems than in the bare area outside canopy for both C. korshinskii and H. rhamnoides. Correspondingly, soil water content was also significantly higher in the root area around the shrub stem than in the area outside the shrub canopy. This confirms that shrub stemflow conserved in the deep soil layers may be an available moisture source for plant growth under semi-arid conditions.

Estimating realized and potential carbon storage benefits from reforestation and afforestation under climate change: a case study of the Qinghai spruce forests in the Qilian Mountains, northwestern China

Greenhouse gas emission has been scientifically shown to be the primary cause of observed global climate change. The reduction of greenhouse gas levels in the atmosphere deserves international attention. Aside from strategies to reduce emissions, increasing carbon (C) storage by forests has become an alternative method to lower carbon dioxide (CO2) levels. The present study assesses the potential of C storage to decrease gas emission by restoring cleared and disturbed spruce (picea) forests in the Qilian Mountains, northwestern China. We first introduced and tested a new method for live aboveground biomass (AGB) estimation. We then used the method to define the relationship of AGB with topographic wetness index (TWI) and precipitation seasonality for total AGB estimation and quantification of the realized C storage in the live AGB of existing spruce forests. The same strategies were adopted to estimate the total AGB and the related potential C storage in the projected potential spruce forest distribution. A species distribution model was used, and the results showed that the AGB of the Qinghai spruce forests ranged between 2.30 and 4.96 Mg per plot (0.021 ha), i.e., 110 Mg ha-1 to 236 Mg ha-1). Actual total AGB was measured at 33 Tg, and C storage was 17.3 Tg in existing spruce forests. Potential total AGB and potential C storage were greater if the cleared and the potential C storage was ~50 Tg.

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.

Determining the Canopy Water Stress for Spring Wheat Using Canopy Hyperspectral Reflectance Data in Loess Plateau Semiarid Regions

Crop water stress significantly reduces crop yield. Several studies have employed optical and remote-sensing methods to obtain nondamage monitoring crop water content to understand the agriculture drought process. In this paper, the spectral information (i.e., the canopy absorption feature at the 350–2500 nm band range) from the field experiments was used to estimate and identify the canopy water stress. Five different levels of water treatments exist in the spring wheat field in the semiarid regions of Loess Plateau, Northwest China. The hyperspectral reflectance, soil moisture content, soil water potential, canopy water content, amount of chlorophyll, leaf area index, and environmental parameters were measured. The relationship between canopy reflectance and canopy water content was analyzed at different water stress levels. In addition, various spectral indices were tested by measurements. Results showed that a high correlation exists in semiarid water index-1, semiarid water index-2, and red-edge normalized difference vegetation index, thus denoting that these indices can indicate water stress effectively. We can conclude that canopy reflectance can identify crop water stress and can be used to develop a certain index for monitoring agriculture drought.

Mapping Daily Temperature and Precipitation in the Qilian Mountains of Northwest China

Daily meteorological data are the critical inputs for distributed hydrological and ecological models. This study modified mountain microclimate simulation model (MTCLIM) with the data from 19 weather stations, and compared and validated two methods (the MTCLIM and the modified MTCLIM) in the Qilian Mountains of Northwest China to estimate daily temperature (i.e., maximum temperature, minimum temperature) and precipitation at six weather stations from 1 January 2000 to 31 December 2009. The algorithm of temperature in modified MTCLIM was improved by constructing the daily linear regression relationship between temperature and elevation, aspect and location information. There are two steps to modify the MTCLIM to predict daily precipitation: firstly, the linear regression relationship was built between annual average precipitation and elevation, location, and vegetation index; secondly, the distance weight for measuring the contribution of each weather station on target point was improved by average wind direction during the rainy season. Several regression analysis and goodness-of-fit indices (i.e., Pearson’s correlation coefficient, coefficient of determination, mean absolute error, root-mean-square error and modeling efficiency) were used to validate these estimated values. The result showed that the modified MTCLIM had a better performance than the MTCLIM. Therefore, the modified MTCLIM was used to map daily meteorological data in the study area from 2000 to 2009. These results were validated using weather stations with short time data and the predicted accuracy was acceptable. The meteorological data mapped could become inputs for distributed hydrological and ecological models applied in the Qilian Mountains.

The impact of climate change on potential distribution of species in semi-arid region: A case study of Qinghai spruce (Picea crassifolia) in Qilian Mountain, Gansu province, China

To restore the human-disturbed natural ecosystem and to assess the impact of the projected future climatic change on the natural ecosystem at a plant community level or at a plant species level, the potential distribution of the community and the species under current climate conditions need to be understood. Therefore many methods have recently been developed to simulate the potential distribution of a particular community or species [1]. However, very little has been done to assess the potential distribution of Qinghai spruce (Picea crassifolia) in Qilian Mountains where the spruce forest is extremely important ecologically and hydrologically. This study used Maximum Entropy model to simulate the potential distribution of Qinghai spruce under current climatic conditions. The validity of the model was verified by comparing the simulated potential distribution with the observed distribution of the spruce. The result shows the model is feasible to simulate the potential distribution of Qinghai spruce. Then this model was used to assess the impact of the projected climatic changes on the distribution of the spruce. The distribution of the spruce under current climate condition was compared with that under the projected climatic change scenario. The areal extent of the potential distribution may increase by 1% under the projected climatic change scenario. In addition, this study revealed that Mean Maximum Temperature of Warmest Month and Mean Temperature of Wettest Quarter are the most important factors which controlling the potential distribution of Qinghai spruce among the 19 environmental and climatic factors used in this model.

The canopy rainfall interception in actual and potential distribution of Qinghai spruce (Picea crassifolia) forest

Abstract Interception is one of the most underestimated processes in hydrological cycle in arid and semiarid regions. In Qilian Mountains of northwestern arid and semiarid China, the Qinghai spruce (Picea crassifolia) forest plays an important role in the hydrological cycle of the inland Heihe River basin. The historical disturbance of Qinghai spruce forest has resulted in various ecological problems. In order to realize the sustainable development of Heihe River basin, the Chinese government implemented restoration practices for Qinghai spruce in the past three decades. In this study, we estimated the rainfall interception in the actual and potential distribution of Qinghai spruce forest. Some of the important findings include: (1) The interception ratio of rainfall events ranged from 11-51% with a mean value of 27.02%; (2) Totally, 147 Mt of rainfall is intercepted by canopy of actual Qinghai spruce forest, in the projected potential distribution of the forest, totally 407 Mt of rainfall will be intercepted.

Modeling canopy interception of Picea crassifolia forest in Qilian mountains using QuickBird satellite data

Canopy interception of rainfall plays an important role in hydrologic cycling and water balance of ecosystems in arid and semi-arid regions. At present, most research focuses on the characteristics of interception at the stand or plot scale. Studies of canopy interception at the river basin or landscape scale based on RS and GIS are lacking because the factors influencing canopy interception such as precipitation, vegetation are difficult to model spatially. A semi-theoretical and semi-empirical model of canopy interception was improved based on investigation in the study area. Considering the important influence of canopy structure, LAI was introduced to the model. After parameters in the model were spatialized using remote sensing data and GIS, the spatial distribution of canopy interception was estimated in the study area (i.e. Pailugou catchment). The results show that the amount of canopy interception in Pailugou catchment is between 97.9 mm and 236.6 mm and the mean interception amount is 161.8 mm. The minimum interception appears at the lower altitude area and the maximum interception presents at the higher altitude area. The interception percentage of Picea crassifolia forest is between 27.92% and 58.00%, which increases with increasing altitude and the maximum appears at 3100m, then decreases along with the increase of altitude.