2006. A comparison of the species Á/time relationship across ecosystems and taxonomic groups. Á/ Oikos 112: 185 Á/195.The species Á/time relationship (STR) describes how the species richness of a community increases with the time span over which the community is observed. This pattern has numerous implications for both theory and conservation in much the same way as the species Á/area relationship (SAR). However, the STR has received much less attention and to date only a handful of papers have been published on the pattern. Here we gather together 984 community time-series, representing 15 study areas and nine taxonomic groups, and evaluate their STRs in order to assess the generality of the STR, its consistency across ecosystems and taxonomic groups, its functional form, and its relationship to local species richness. In general, STRs were surprisingly similar across major taxonomic groups and ecosystem types. STRs tended to be well fit by both power and logarithmic functions, and power function exponents typically ranged between 0.2 and 0.4. Communities with high richness tended to have lower STR exponents, suggesting that factors increasing richness may simultaneously decrease turnover in ecological systems. Our results suggest that the STR is as fundamental an ecological pattern as the SAR, and raise questions about the general processes underlying this pattern. They also highlight the dynamic nature of most species assemblages, and the need to incorporate time scale in both basic and applied research on species richness patterns.

No abstract

Vegetation is the main component of the terrestrial ecosystem and plays a key role in global climate change. Remotely sensed vegetation indices are widely used to detect vegetation trends at large scales. To understand the trends of vegetation cover, this research examined the spatial-temporal trends of global vegetation by employing the normalized difference vegetation index (NDVI) from the Advanced Very High Resolution Radiometer (AVHRR) Global Inventory Modeling and Mapping Studies (GIMMS) time series (1982-2015). Ten samples were selected to test the temporal trend of NDVI, and the results show that in arid and semi-arid regions, NDVI showed a deceasing trend, while it showed a growing trend in other regions. Mann-Kendal (MK) trend test results indicate that 83.37% of NDVI pixels exhibited positive trends and that only 16.63% showed negative trends (P < 0.05) during the period from 1982 to 2015. The increasing NDVI trends primarily occurred in tree-covered regions because of forest growth and re-growth and also because of vegetation succession after a forest disturbance. The increasing trend of the NDVI in cropland regions was primarily because of the increasing cropland area and the improvement in planting techniques. This research describes the spatial vegetation trends at a global scale over the past 30+ years, especially for different land cover types.

Seashore reclamation is an important way that humans utilize the oceans. 1 In recent years, expansion of seashore reclamation activities has seriously disturbed 2 natural coastal systems, and especially wetland ecosystems. In this paper, using 3 China's Yellow River Delta as a case study, we evaluated the effects of seashore 4 reclamation activities on the health of coastal wetland ecosystems. We defined a 5 comprehensive assessment index system based on the pressure-state-response model 6 and used the model to explore how wetland health responded to reclamation activities, 7 including the construction of tidal embankments and ports, land reclamation, road 8 construction, and upstream dam construction. We found that the pressure intensity 9 index for seashore reclamation activities ranged from 0.39 to 0.77, and increased until 10 the late 1990s. From 1950 to 2010, increasing pressure on the wetlands caused the 11 comprehensive state and health indices to decrease from 0.87 to 0.51 and from 0.64 to 12 0.52, respectively; both indicate severe risks to ecosystem health. The comprehensive 13 health index decreased continuously until about 2000, then improved. There were 14 strong negative correlations between the comprehensive health and pressure indices 15 and the reclamation activity pressure index (both R 2 > 0.80, p < 0.05). A sensitivity 16 analysis indicated that the assessment model was robust with respect to the effects of 17 tidal embankment and dam construction. Our results indicate that alleviating the 18 reclamation pressure, especially tidal embankment and dam construction, would 19 significantly improve wetland ecosystem health. Our study will help seashore 20 managers assess the combined effects of existing reclamation activities on coastal 21 wetlands, and support future reclamation activity planning.22

No abstract