Landscape Attributes Best Explain the Population Trend of Wintering Greater White-Fronted Goose (Anser albifrons) in the Yangtze River Floodplain

Biodiversity in the Middle and Lower Yangtze Floodplain has critically decreased during the last several decades, driven by numerous determinants. Hence, identification of primary drivers of animal population decline is a priority for conservation. Analyzing long time-series data is a powerful way to assess drivers of declines, but the data are often missing, hampering effective conservation policymaking. In this study, based on twenty-four years (from 1996 to 2019) of annual maximal count data, we investigated the effects of climate and landscape changes on the increasing population trend of the Greater White-Fronted Goose (Anser albifrons) at a Ramsar site in the Middle and Lower Yangtze Floodplain, China. Our results showed that the availability of a suitable habitat and landscape attributes are the key driving forces affecting the population trend, while the effects of climate factors are weak. Specifically, increasing the area of suitable habitat and alleviating habitat fragmentation through a fishing ban policy may have provided a more suitable habitat to the geese, contributing to the increasing population trend. However, we also observed that the grazing prohibition policy implemented in 2017 at Shengjin Lake may have potentially negatively affected geese abundance, as grazing by larger herbivores may favor smaller geese species by modifying the vegetation community and structure. Based on our results, we suggest several practical countermeasures to improve the habitat suitability for herbivorous goose species wintering in this region.

Recent ecological trajectory of lake Taihu and land-use history reconstructed from lake sediment DNA

<p>More than 80% of shallow lake ecosystems in the Yangtze floodplain suffer significant disturbances from the 50’s, especially eutrophication. These environmental degradations and subsequent loss of services are related with the important and rapid development of the agriculture, industry, urban areas and the population boom in the region. Lake Taihu is one of the largest lakes of the floodplain and represents an important water resource (for drinking and fishing) for the population of the two big cities on the lake shore. This lake experimented two shifts toward the degradation of the trophic state: one in the 50-60’s and a second in 80’s.</p><p>In order to document the causes of these ecological shifts, we applied the DNA metabarcoding approach on lake sediments and focused on plants as proxy of land use. Whereas this proxy has been successfully applied in many lakes over the world, it has never been tested in large shallow lakes and not in China either.</p><p>We show important changes in land use in 50’s and 80’s related with agricultural developments (i.e. intensification) and urban expansion, respectively. In fact, in the 50’s crop plants are increasing (rapeseed and/or cabbage, rice and/or wheat, barley and <em>Poaceae</em>) whereas in 80’s, we record the development of several plants associated to gardens (e.g. ornamental species). Moreover, this last period is characterised by the presence of trees mostly cultivated along stream banks to protect dikes against erosion. Between the 80’s and the years 2000, the plant diversity recorded in the sediment strongly increase, which may be due to higher detrital inputs (i.e. more efficient DNA transfer). The timing in land-use changes corresponds to the main shifts in lake trophic state.</p>

Water Level Fluctuation Requirements of Emergent Macrophyte Typha angustifolia L.

The management of water levels in wetlands is of great importance for the wetland ecosystem, including the conservation and revitalization of plants. However, the water level requirements (WLRs) of wetland plants have not been well investigated. In this study, Typha angustifolia was selected as an experimental plant species. Combining field investigation and simulation experiments, the relationship between the development status of this species and water level fluctuations (WLFs) in different life-history stages were analyzed. The results show that populations in the Yangtze floodplain, China, had two phenotypic forms ‘tall’ and ‘short’, and that these were distributed in lakes with intermittent or quasi-natural fluctuations and reservoir-like fluctuations, respectively. Lakes with high amplitude (>3.2 m) water fluctuations did not contain T. angustifolia. We investigated the distribution and growth of T. angustifolia in lakes of varying hydrology across the Yangtze floodplain, seeking to define its tolerance of water-level fluctuations and submergence at different stages in its life cycle. The upper tolerance limit of static submerged water depth was bounded by 1.5 times the height of plants in the seedling stage, and the upper tolerance limit of the submergence rate in the seedling stage was the average growth rate of seedling, 1.5 cm/d. The plant height had a positive linear correlation with amplitude and water depth from June to July. The autumn biomass was significantly negatively correlated with amplitude and water depth from January to May. This paper is perhaps the first case study on water level fluctuation requirements (WLFRs) of emergent macrophytes. It systematically assessed the WLFRs of T. angustifolia in each life-history stage, and established a comprehensive WLFR conceptual model. The results of this study could provide a quantitative operational basis for the protection and restoration of this species in Yangtze floodplain lakes.