Changing climate conditions are known to influence forest tree growth response and the CO2 cycle. Dendroclimatological research has shown that the climate signal, species composition, and growth trends have changed in...Changing climate conditions are known to influence forest tree growth response and the CO2 cycle. Dendroclimatological research has shown that the climate signal, species composition, and growth trends have changed in different types of forest ecosystems during the last century. Under current and demonstrated changes in climate variability at the geographic, regional, and local levels tree growth shows also variability and trends that can be non-stationary during time even at relatively short distance between sites. In forest planning and management, yield tables, site quality indices, age class, rate of growth, and spatial distribution are some of the most used tools and parameters. However, these methods do not involve climate variability during time although climate is the main driver in trends of forest and tree growth. Previous research warns about the risk that forest management under changing climatic conditions could amplify their negative effects. For example, changing climate conditions may impact on temperature and/or precipitation thresholds critical to forest tree growth. Forest biomass, resilience, and CO2 storage may be damaged unless forest planning and management implement the relationships between climate variability and trends of tree growth. A positive aspect is that, periods of favorable climate conditions may allow harvesting higher amount of wood mass and storing more CO2 than traditional planning methods. And, the average length of both favorable and adverse periods appears to occur within the validity period of a forest management plan. Here, we show a conceptual development to implement climate variability in forest management in the view of continuing the research.展开更多
The rapid growth of grain yield in China accelerates a discussion on whether the grain system in China is sustainable. To answer the question, a comprehensive assessment from economic and environmental points is neces...The rapid growth of grain yield in China accelerates a discussion on whether the grain system in China is sustainable. To answer the question, a comprehensive assessment from economic and environmental points is necessary. This study jointly used economic analysis(ECA), emergy evaluation(EME) and carbon footprint(CF) to analyze the environmental and economic sustainability of the grain production system in China based on the national statistical data during 2000–2015. Results showed that the costs of maize, wheat, rice and soybean had increased by 252-346% from 2000 to 2015, causing the lower profit of grain system in recent years. The situation resulted in a serious problem on economic sustainability of grain system in China. Meanwhile, the emergy sustainability index(ESI) of maize, wheat, rice and soybean systems were increasing during 2000–2015, and the CF on unit yield of the crops had been reduced by 10-30% in the study period. The results reflected the improved environmental sustainability of grain system in China during 2000–2015. Nevertheless, the emergy flow of industrial inputs for the crops were increased by 4-22% in the study period, and the CF from the inputs presented a growth rate of 16-23% as well during the same period. The results implied that the grain system in China was relying more on fossil-based inputs. Finally, according to the key points of cost, emergy and CF, we suggest that improving labor efficiency, advanced agricultural practices and optimizing cropping pattern will be effective ways to further improve the economic and environmental sustainability of grain system in China.展开更多
车载网VANETs中的车间通信V2V(vehicle to vehicle)有利于车辆信息的共享、提高交通安全;然而,在VANETs中,车辆快速移动、车辆分布不均匀以及拓扑结构动态变化等特性,导致车辆间通信链路断裂频繁、路由稳定性差、车间通信V2V数据传输效...车载网VANETs中的车间通信V2V(vehicle to vehicle)有利于车辆信息的共享、提高交通安全;然而,在VANETs中,车辆快速移动、车辆分布不均匀以及拓扑结构动态变化等特性,导致车辆间通信链路断裂频繁、路由稳定性差、车间通信V2V数据传输效率低。为此,以车辆间通信链路的可持续时间为选择路由指标,择优选取可持续时间长的链路组建路由。从而提高路由的稳定性。利用车辆的实时移动信息,包括移动速度、移动方向以及位置估计链路的可持续时间;同时,车辆周期地广播路由表,邻居节点利用收到其他节点的路由表更新自己的路由表,通过这种方式使车辆共享实时的链路信息。仿真结果表明,提出的路由方案有效地提高数据传输速率、降低了端到端传输时延,并提升了吞吐量。展开更多
文摘Changing climate conditions are known to influence forest tree growth response and the CO2 cycle. Dendroclimatological research has shown that the climate signal, species composition, and growth trends have changed in different types of forest ecosystems during the last century. Under current and demonstrated changes in climate variability at the geographic, regional, and local levels tree growth shows also variability and trends that can be non-stationary during time even at relatively short distance between sites. In forest planning and management, yield tables, site quality indices, age class, rate of growth, and spatial distribution are some of the most used tools and parameters. However, these methods do not involve climate variability during time although climate is the main driver in trends of forest and tree growth. Previous research warns about the risk that forest management under changing climatic conditions could amplify their negative effects. For example, changing climate conditions may impact on temperature and/or precipitation thresholds critical to forest tree growth. Forest biomass, resilience, and CO2 storage may be damaged unless forest planning and management implement the relationships between climate variability and trends of tree growth. A positive aspect is that, periods of favorable climate conditions may allow harvesting higher amount of wood mass and storing more CO2 than traditional planning methods. And, the average length of both favorable and adverse periods appears to occur within the validity period of a forest management plan. Here, we show a conceptual development to implement climate variability in forest management in the view of continuing the research.
基金financially supported by the Natural Science Foundation of Guangdong Province,China(2017A030310055)the National Key Research and Development Program of China(2017YFD0201305)
文摘The rapid growth of grain yield in China accelerates a discussion on whether the grain system in China is sustainable. To answer the question, a comprehensive assessment from economic and environmental points is necessary. This study jointly used economic analysis(ECA), emergy evaluation(EME) and carbon footprint(CF) to analyze the environmental and economic sustainability of the grain production system in China based on the national statistical data during 2000–2015. Results showed that the costs of maize, wheat, rice and soybean had increased by 252-346% from 2000 to 2015, causing the lower profit of grain system in recent years. The situation resulted in a serious problem on economic sustainability of grain system in China. Meanwhile, the emergy sustainability index(ESI) of maize, wheat, rice and soybean systems were increasing during 2000–2015, and the CF on unit yield of the crops had been reduced by 10-30% in the study period. The results reflected the improved environmental sustainability of grain system in China during 2000–2015. Nevertheless, the emergy flow of industrial inputs for the crops were increased by 4-22% in the study period, and the CF from the inputs presented a growth rate of 16-23% as well during the same period. The results implied that the grain system in China was relying more on fossil-based inputs. Finally, according to the key points of cost, emergy and CF, we suggest that improving labor efficiency, advanced agricultural practices and optimizing cropping pattern will be effective ways to further improve the economic and environmental sustainability of grain system in China.
文摘车载网VANETs中的车间通信V2V(vehicle to vehicle)有利于车辆信息的共享、提高交通安全;然而,在VANETs中,车辆快速移动、车辆分布不均匀以及拓扑结构动态变化等特性,导致车辆间通信链路断裂频繁、路由稳定性差、车间通信V2V数据传输效率低。为此,以车辆间通信链路的可持续时间为选择路由指标,择优选取可持续时间长的链路组建路由。从而提高路由的稳定性。利用车辆的实时移动信息,包括移动速度、移动方向以及位置估计链路的可持续时间;同时,车辆周期地广播路由表,邻居节点利用收到其他节点的路由表更新自己的路由表,通过这种方式使车辆共享实时的链路信息。仿真结果表明,提出的路由方案有效地提高数据传输速率、降低了端到端传输时延,并提升了吞吐量。
