Effect of environmental gradients on the quantity and quality of fallen logs in Tsuga longibracteata forest in Tianbaoyan National Nature Reserve, Fujian province, China

We investigated the quantity and quality 0f fallen l0gs in different Tsuga l0ngibracteata f0rest c0mmunities in the Tianba0yan Nati0nal Nature Reserve. We used redundancy analysis t0 determine the spatial distributi0n 0f fallen l0gs in the different f0rest c0mmunities and t0 analyze the relati0nships am0ng stand structure, t0p0graphic fact0rs and human disturbance. The v0lume, c0vered area, mean l0g length and number 0f fallen l0gs differed significantly am0ng f0rest types （P 〈 0.05）, but mean diameter at breast height sh0wed n0 significant difference （P 〉 0.05）. The l0g v0lume and c0vered area in different f0rest types sh0wed the f0ll0wing trend： T. l0ngibracteata pure f0rest 〈 T. l0ngibracteata ＋ Olig0staehyum scabrifl0rur 〈 T. l0ngibraeteata ＋ hardw00d 〈 Rh0d0dendr0n simiarum ＋ T. l0ngibraeteata 〈 T. l0ngibraeteata ＋ Phyll0stachys heter0cycla pubescens. The spatial distributi0n patterns 0f l0gs quantity and quality indicated that l0g v0lume and c0vered area were str0ngly affected by envir0nmental fact0rs in the f0ll0wing 0rder： human disturbance 〉 elevati0n 〉 sl0pe p0siti0n 〉 b0le height 〉 tree height 〉 sl0pe aspect 〉 density 〉 basal area 〉 sl0pe gradient. The relative c0ntributi0n 0f envir0nmental variables 0n the t0tal variance was t0p0graphy （76%） 〉 disturbance （42%） 〉 stand structure （35%）. T0p0graphy and disturbance c0mbined explained 8.2% 0f the variance. Fallen l0~s auantitv and aualitvwere negatively related t0 elevati0n and sl0pe p0siti0n, and p0sitively ass0ciated t0 human disturbance. The l0g v0lume decreased fr0m n0rthern t0 s0uthern sl0pes. Envir0nmental fact0rs had the highest impact 0n class I （slightly decayed）, and l0west impact 0n class V （highly decayed）.     

Micro-site conditions of epiphytic orchids in a human impact gradient in Kathmandu valley, Nepal

We studied distribution and site conditions of epiphytic orchids in a gradient of human interference in Kathmandu valley, central Nepal. The aim was to understand the recent distribution pattern of epiphytic orchids, with respect to (i) the micro-site conditions and (ii) the type and intensity of land use. The occurrence of epiphytic orchids was recorded for a grid with 1.5 km cell size. The cells represent different types and intensities of human impact. Site factors such as bark rugosity, bark pH, diameter at breast height (dbh; 1.3 m) of host trees, exposure to wind and sunlight intensity were recorded. With regard to the species richness and abundance of epiphytic orchids, we compared different human impact categories from very strong human impact (settlement area) to very low human impact (national park). Remote sensing was used for a supervised classification of land cover. Ficus religiosa turned out to be the most important host species for orchids in urban areas, while Schima wallichii and Alnus nepalensis significantly host orchids in the other categories. Both species richness and abundance of epiphytic orchids were significantly higher under very low human impact (forest in national park) and also some remaining patches of primary forest than the other regions. Micro-climate is crucial for orchid populations. Host bark pH, bark rugosity, sunlight intensity and host exposure were significantly different for all human impact categories in order to harbour epiphytic orchid species. Habitats with a mixture of mature trees are suitable and essential for the conservation of viable populations of epiphytic orchids in settled areas. The study reveals that to improve the population size of orchids it is essential for future urban forestry to: (i) Protect old trees as carriers of existing epiphytic orchid diversity, (ii) protect medium old trees to ensure that they may become old trees, (iii) plant new host trees for the future, (iv) plant in groups instead of single isolate trees. Trees should especially be planted in areas where orchids still exist to provide more trees for orchid population enlargement (e.g. along riparian system). Native species should be favoured; the pool of such native host species is wide.     

Rapid changes of sediment dynamic processes in Yalu River Estuary under anthropogenic impacts

The response of the Yalu River Estuary to human activities was investigated.Changes of sediment dynamics during the past 10 years were explored through hydrodynamic calculation,as well as heavy mineral...     

Dynamic Changes of Sediment Discharge and the Influencing Factors in the Yellow River,China, for the Recent 90 Years

The dynamic changes in the sediment discharge over 90 years from 1919 to 2008 in the Yellow River in China were assessed on the basis of annual rainfall series and annual sediment series in Shan County hydrological station. The key factors affecting sediment discharge, such as rainfall, and human activities were studied. Anomaly accumulation method and double mass curve were employed to test the stage changes of sediment discharge, and to determine the main factors of sediment decline. Results showed that the annual average sediment discharge under natural conditions was about 16 × 10⁸ t, but the measured annual average sediment during 1919–2008 was 12.71 × 10⁸ t. The highest annual average during the study period was 39.10 × 10⁸ t in 1933 while the lowest was 1.77 × 10⁸ t in 2008. Sediment discharge in the Yellow River experienced two low sediment stages (1924–1931 and 1979–2008) and a high sediment stage (1932–1971), respectively. Since 1979, there was a significant decreasing trend in the sediment discharge, and the main influencing factor was fierce human activities. Annual average sediment discharge in the post‐development period (1979–2008) was 69.7% lower than that in the pre‐development period (1919–1978), with average reduction of 81 and 19% caused by human activities and rainfall, respectively. These results provide important evidence for making protecting policy for water resources quality and environmental safety of the Yellow River.     

Live bait capture and crayfish trapping as potential vectors for freshwater invasive fauna

Fishing activities strongly contribute to biological invasions in freshwaters. The purpose of this study was to investigate the potential risks of live bait capture using dip nets and of crayfish trapping as vectors for invasive freshwater macrofauna dispersal. In the Tagus river basin (Portugal), where both activities are common, we evaluated the probability of capture and the electivity of the local aquatic macrofauna according to the method used. During the compulsory removal of the invasive species captured we also quantified fish desiccation survival capacities. We found, for both vectors, that the species exhibiting the highest probability of capture and the highest electivity were invasive, respectively, Gambusia holbrooki and Crangonyx pseudogracilis with the dip net, Procambarus clarkii and several invasive species with special relevance for Ameiurus melas with the crayfish trapping. Moreover, the desiccation survival capacities, of all invasive fishes analyzed, are compatible with long distance dispersal out of water, with special relevance to G. holbrooki. This study demonstrates that fishing activities contribute to long-distance dispersal of invasive fauna. Therefore, according to our findings, it is important to update the fishing regulation and simultaneously to raise fishermen awareness of this problem.     

Advantages of longer–term tracing -- three case studies from Slovenia

A variety of human activities can negatively impact on sensitive karst environments, especially on karst water. To protect such water adequately it is necessary to obtain as much information as possible on the extent of the recharge zones and characteristics of the groundwater flow. The authors experience has shown tracer tests to be a very useful tool in acquiring such information. Three examples from Slovenia are presented in this paper. In the first, an estimate was made of the danger of water contamination resulting from a petrochemical storage depot. In the second, the possible impacts of an area used for military training were studied. In the third, the effects of the construction of a railway line on regionally important water resources were assessed. Besides basic information about the direction and velocity of groundwater flow, some methodological principles were also identified by the studies. In all three test areas sampling was carried out for a lengthy period and continued after the detection of the peak concentrations. The results show that only the use of such lengthy tracer tests enable the definition of those flow paths, which are activated in extreme hydrological conditions.     

Assessing the influence of environmental parameters on the hydrological cycle

Human activity is exerting an increasing influence on the hydrological cycle. In order to avoid adverse impacts and to establish optimum conditions for the water balance, it is necessary to understand the role of environmental parameters in influencing the hydrological cycle. Work is currently in progress in China to study the relationships between environmental parameters and the hydrological cycle to provide a basis for planning future development.     

Temporal variations of sandstorms in Minqin oasis during 1954–2000

The purpose of this present study is to investigate in detail the frequency and variation of sandstorms in the Minqin oasis. Using daily observational data from sandstorms and other meteorologic data from 1954 to 2000, the relationship between a sandstorm and meteorological parameters and human activities, which can be used for daily weather forecasting, have been illuminated. The results of the analysis show that sandstorms have a clear daily and monthly variation. Monthly mean and annual mean duration of sandstorms in the Minqin oasis coincide well with the frequencies of sandstorm occurrence.