Zhang Yangjian

Huge Carbon Sequestration Potential in Global Forests

Abstract: Forests play an important role in mitigating climate change by absorbing carbon from atmosphere. The global forests sequestrated 2.4±0.4 Pg C y-1 from 1990 to 2007, while the quantitative assessment on the carbon sequestration potential (CSP) of global forests has much uncertainty. We collected and compiled a database of site above-ground biomass (AGB) of global mature forests, and obtained AGB carbon carrying capacity (CCC) of global forests by interpolating global mature forest site data. The results show that: (i) at a global scale, the AGB of mature forests decline mainly from tropical forests to boreal forests, and the maximum AGB occurs in middle latitude regions; (ii) temperature and precipitation are main factors influencing the AGB of mature forests; and (iii) the above-ground biomass CCC of global forests is about 586.2±49.3 Pg C, and with CSP of 313.4 Pg C. Therefore, achieving CCC of the existing forests by reducing human disturbance is an option for mitigating greenhouse gas emission.

The trend of tree line on the northern slope of Changbai Mountain

In order to decipher phenomenon of tree line changing with climate variety, the trend of tree line on the northern slope of Changbai Mountain was studied. Based on the meteorological data of Changbai Mountain, the January temperature (the limiting effect for tree line) and annual mean temperature were mainly investigated. In the ecotone betweenBetula emanii and alpine tundra, the number and diameter at ground level ofBetula ermanii in the plots were measured. According to the correlation between diameter at ground level (DGL) and age, the diameter at ground level can represent age directly. The results showed that the distribution age ofBetula ermanii was in the trend of decreasing with elevation rising. In resent years, the annual mean temperature near Changbai Mountain is rising, which has led to the tree line ascending.

Satellite-Based Estimation of Gross Primary Production in an Alpine Swamp Meadow on the Tibetan Plateau: A Multi-Model Comparison

Abstract: Alpine swamp meadows on the Tibetan Plateau, with the highest soil organic carbon content across the globe, are extremely vulnerable to climate change. To accurately and continually quantify the gross primary production (GPP) is critical for understanding the dynamics of carbon cycles from site-scale to global scale. Eddy covariance technique (EC) provides the best approach to measure the site-specific carbon flux, while satellite-based models can estimate GPP from local, small scale sites to regional and global scales. However, the suitability of most satellite-based models for alpine swamp meadow is unknown. Here we tested the performance of four widely-used models, the MOD17 algorithm (MOD), the vegetation photosynthesis model (VPM), the photosynthetic capacity model (PCM), and the alpine vegetation model (AVM), in providing GPP estimations for a typical alpine swamp meadow as compared to the GPP estimations provided by EC-derived GPP. Our results indicated that all these models provided good descriptions of the intra-annual GPP patterns (R2>0.89, P<0.0001), but hardly agreed with the inter-annual GPP trends. VPM strongly underestimated the GPP of alpine swamp meadow, only accounting for 54.0% of GPP_EC. However, the other three satellite-based GPP models could serve as alternative tools for tower-based GPP observation. GPP estimated from AVM captured 94.5% of daily GPP_EC with the lowest average RMSE of 1.47 g C m-2. PCM slightly overestimated GPP by 12.0% while MODR slightly underestimated by 8.1% GPP compared to the daily GPP_EC. Our results suggested that GPP estimations for this alpine swamp meadow using AVM were superior to GPP estimations using the other relatively complex models.

Livestock Dynamic Responses to Climate Change in Alpine Grasslands on the Northern Tibetan Plateau: Forage Consumption and Time-Lag Effects

Abstract: Climate change and forage-intake are important components of livestock population systems, but our knowledge about the effects of changes in these properties on livestock is limited, particularly on the Northern Tibetan Plateau. Based on corresponding independent models (CASA and TEM), a human-induced NPP (NPPH) value and forage-intake threshold were obtained to determine their influences on livestock population fluctuation and regrowth on the plateau. The intake threshold value provided compatible results with livestock population performance. If the forage-intake was greater than the critical value of 1.9 (kg DM d-1 sheep-1), the livestock population increased; otherwise, the livestock population decreased. It takes four years to transfer a disturbance in primary productivity to the next trophic level. The relationships between livestock population and NPPH value determined population dynamics via the forage-intake value threshold. Improved knowledge on lag effects will advance our understanding of drivers of climatic changes on livestock population dynamics.

Recognizing the Scientific Mission of Flux Tower Observation Networks—Lay the Solid Scientific Data Foundation for Solving Ecological Issues Related to Global Change

Abstract: As the Earth entering into the Anthropocene, global sustainable development requires ecological research to evolve into the large-scale, quantitative, and predictive era. It necessitates a revolution of ecological observation technology and a long-term accumulation of scientific data. The ecosystem flux tower observation technology is the right one to meet this requirement. However, the unique advantages and potential values of global-scale flux tower observation are still not fully appreciated. Reviewing the development history of global meteorological observation and its scientific contributions to the society, we can get an important enlightenment to re-cognize the scientific mission of flux observation.

Vegetation Pattern in Northern Tibet in Relation to Environmental and Geo-spatial Factors

Abstract: Environmental and Geo-spatial factors have long been considered as crucial determinants of species composition and distributions. However, quantifying the relative contributions of these factors for the alpine ecosystems is lacking. The Tibetan Plateau has a unique ecological environment and vegetation types. Our objectives are to quantify the spatial distributions of plant communities on the Northern Tibetan Alpine grasslands and to explore the relationships between vegetation composition, Geo-spatial factors and environmental factors. We established 63 field plots along a 1200-km gradient on the Northern Tibetan Plateau Alpine Grassland and employed the two-way indicator species analysis (TWINSPAN) and the detrended canonical correspondence analysis (DCCA). Fourteen communities of alpine grassland were identifiable along the transect and consisted of three vegetation types: Alpine meadow, Alpine steppe, and desert steppe. Vegetation composition and spatial distribution appeared to be largely determined by mean annual precipitation and less influenced by temperature. A large fraction (73.5%) of the variation in vegetation distribution was explained by environmental variables along this transect, somewhat less by Geo-spatial factors (56.3%). The environmental and Geo-spatial factors explained 29.6% and 12.3% of the total variation, respectively, while their interaction explained 43.9%. Our findings provide strong empirical evidence for explaining biological and environmental synergetic relationships in Northern Tibet.

Impact of Water Vapor on Elevation-Dependent Climate Change

Abstract: Elevation dependency amongst climate change signals has been found in major mountain ranges around the world, but the main factors causing this dependency have not been clarified. In this study, four different datasets of observation and reanalysis for China were used to examine the elevation dependency of climate change. A lack of consistency was found in dependency between warming magnitude and elevation across the Tibetan Plateau and China. However, a dependency of climate change on water vapor was detected whereby the temperature trend initially increased at low specific humidity, and then decreased as specific humidity increased. At ground level the maximum trend in temperature appeared in the specific humidity range 2.0–3.0 g kg-1. This suggests that water vapor is a mediator of climate change and may be responsible for elevation-dependent climate change.