Spatial-temporal variations of ecological vulnerability in the Tarim River Basin,Northwest China

As the largest inland river basin of China,the Tarim River Basin(TRB),known for its various natural resources and fragile environment,has an increased risk of ecological crisis due to the intensive exploitation and utilization of water and land resources.Since the Ecological Water Diversion Project(EWDP),which was implemented in 2001 to save endangered desert vegetation,there has been growing evidence of ecological improvement in local regions,but few studies have performed a comprehensive ecological vulnerability assessment of the whole TRB.This study established an evaluation framework integrating the analytic hierarchy process(AHP)and entropy method to estimate the ecological vulnerability of the TRB covering climatic,ecological,and socioeconomic indicators during 2000-2017.Based on the geographical detector model,the importance of ten driving factors on the spatial-temporal variations of ecological vulnerability was explored.The results showed that the ecosystem of the TRB was fragile,with more than half of the area(57.27%)dominated by very heavy and heavy grades of ecological vulnerability,and 28.40%of the area had potential and light grades of ecological vulnerability.The light grade of ecological vulnerability was distributed in the northern regions(Aksu River and Weigan River catchments)and western regions(Kashgar River and Yarkant River catchments),while the heavy grade was located in the southern regions(Kunlun Mountains and Qarqan River catchments)and the Mainstream catchment.The ecosystems in the western and northern regions were less vulnerable than those in the southern and eastern regions.From 2000 to 2017,the overall improvement in ecological vulnerability in the whole TRB showed that the areas with great ecological improvement increased by 46.11%,while the areas with ecological degradation decreased by 9.64%.The vegetation cover and potential evapotranspiration(PET)were the obvious driving factors,explaining 57.56% and 21.55%of the changes in ecological vulnerability across the TRB,respectively.In terms of ecological vulnerability grade changes,obvious spatial differences were observed in the upper,middle,and lower reaches of the TRB due to the different vegetation and hydrothermal conditions.The alpine source region of the TRB showed obvious ecological improvement due to increased precipitation and temperature,but the alpine meadow of the Kaidu River catchment in the Middle Tianshan Mountains experienced degradation associated with overgrazing and local drought.The improved agricultural management technologies had positive effects on farmland ecological improvement,while the desert vegetation in oasis-desert ecotones showed a decreasing trend as a result of cropland reclamation and intensive drought.The desert riparian vegetation in the lower reaches of the Tarim River was greatly improved due to the implementation of the EWDP,which has been active for tens of years.These results provide comprehensive knowledge about ecological processes and mechanisms in the whole TRB and help to develop environmental restoration measures based on different ecological vulnerability grades in each sub-catchment.

Perspectives in restoration: storage and pretreatments of seeds for better germination of Sudanian savanna-woodland species

Insufficient knowledge of the germination ecology of local species is one of the main constraints to restoration of degraded rural lands. We tested seeds from fourteen Sudanian savanna species targeted for restoration for their response to two different pretreatments（conventional and prolonged acid pretreatments） and two different storage conditions（ambient room conditions and refrigerator at 4 C）. For 6 of the studied species, longer soaking in sulphuric acid significantly improved germination rates and also reduced the germination time of some species. Storage condition, in general did not affect germination rates except for two species where cool storage depressed germination. The practical implication is that, for the species tested, when mature seeds are collected for plantation in the upcoming rainy season, there is no need to invest in infrastructure and energy for storing in cold conditions.The study also revealed that in general when seeds are stored in ambient conditions from the time of collection up to seeding time, although germination rate does not increase, germination time is shortened and this could be of great interest in synchronizing germination in real field conditions.

Invaders’ control on post-disturbance succession in coastal mangroves

Aims In recent years,coastal mangroves have been frequently affected by large disturbances(cyclones,hurricanes,flooding and tsunamis)and post-disturbance vegetation is often dominated by small stature mangrove,mangrove-associate and non-mangrove species potentially affecting ecosystem functioning.Knowledge on the processes of mangrove vegetation development and recovery(succession)following normal and large disturbances will benefit practitioners in designing robust ecosystem management/restoration plans.Here we propose a conceptual model of disturbance-mediated succession in mangroves.Methods Based on field observations and species’life history traits,we develop conceptual models of mangrove succession under normal disturbance regime and recently experienced increased frequency of large disturbances.We evaluate our conceptual models by conducting a scenario testing experiment.Important Findings We suggest two predominant processes affecting mangrove succession after disturbance:propagule limitation due to damage of seed producing mature trees and dispersal barrier resulting from biological invasion associated with large disturbance.We argue that large disturbances affect mature trees more than the small-stature non-tree(shrubs,herbs and climbers)species creating a larger propagule shortage for mangrove tree species than non-tree species.Secondly,large disturbances facilitate invasion of free-floating aquatics,which may interfere with the flow-facilitated propagule dispersal and seedling establishment of mangrove species.In a scenario testing experiment,we have shown that similar levels of disturbance impact vegetation development and recovery differently depending on the presence or absence of invasive species.We conclude that since biological invasion is one of the major drivers of post-disturbance mangrove succession,the dimension of biological invasion should be included in prediction,management and restoration of mangrove forests.