Huanhua Peng

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.

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.

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.

Estimating spatial distribution of radiation below the Qinghai Spruce forest canopy in Qilian Mountains using hemispherical images and Airborne LiDAR data

Solar radiation transmission plays is an important process in the energy exchange in forest ecosystem. There are a lot of transmission models developed for a single canopy, but relatively fewer models for studying spatial distribution of radiation below the forest canopy. In this paper, we used a simple model that was related to canopy cover to calculate the solar radiation below the forest canopy. At the same time, the hemispherical photography integrated with airborne LiDAR to provide a data for the model. Especially, LiDAR data was used to obtain the spatial distribution of the canopy cover. We obtained a spatial distribution of solar radiation below the Qinghai Spruce forest canopy in Qilian Mountains. Results showed that modeled average daily total radiation below the canopy was 21.614 MJ/m2/d, ranging from 4.618 to 54.053 MJ/m2/d in our experimental zone.

Estimating morphological parameters of Tamarix ramosissima by Digital hemispherical image in the lower reaches of heihe river, northwest China

Tamarix ramosissima is a dominant shrub and mainly contributes to total biomass in the lower reaches of Heihe River. In order to study the biomass and growth status of the shrub, we need to measure the morphological parameters. Usually, the morphological parameters are measured by field survey. However, the method is low in efficient and accurate. In this study, the hemispherical photography was used to obtain the morphological parameters of Tamarix ramosissima. The hemispherical images of Tamarix ramosissima were obtained from the top of canopy by digital camera with fisheye lens, then processed and overlaid with the calibration parameter layer to estimate the morphological parameters. The results show that the hemispherical photography had high accuracy in estimating the morphological parameters. The method is a convenient and feasible approach, and can provide a scientific data for the biomass models.