鄱阳湖越冬雁类食源植被适宜取食时间窗口

A study on the suitable time window of feeding vegetation fit for overwintering geese in Poyang Lake

雁类是长江中下游越冬水鸟的优势种群,以苔草(Carex spp)等湿生植被为主要食物来源。作为长江中下游仅存的通江湖泊之一,鄱阳湖显著受到水文波动的影响,湿地植被的生长发育与洲滩淹没和出露时间密切相关。雁类对食物资源具有高度的选择性,建立雁类取食植被的特征和苔草生长过程之间的关系,是刻画适宜栖息地时空分布范围,开展雁类及其食物资源保育的关键。选择鄱阳湖典型子湖泊常湖池作为研究区,对苔草春季生长期开展了原位观测试验,对4个高程梯度的苔草株高和生物量等关键生长因子进行了12次野外监测和采样。同时,结合遥感影像、气温数据及实地观测记录,确定了4个高程梯度洲滩的出露时间和苔草有效生长时间。在此基础上,建立了基于Logistic方程的苔草株高和生物量的生长过程曲线。并根据实地观测的雁类觅食苔草的特征,反推得到雁类适宜取食苔草的时间窗口。结果表明:苔草株高与地上生物量显著正相关,水文条件和气温是影响苔草生长的关键因素,而退水时间的推迟,会导致生长期缩短和低温限制下的有效生长时间减少,影响雁类食物资源的分布。苔草在秋季生长期出露达到12—28 d,而在春季生长期出露达到83—182 d时适宜雁类取食。研究提出了确定越冬雁类苔草适宜取食时间窗口的方法,证实洲滩退水时间推迟超过20 d,苔草生长节律将难以匹配雁类数量峰值期觅食的需要。本研究对鄱阳湖湿地水文调控和湿地资源管理具有重要意义。

Geese are the dominant species among waterbirds overwintering along the middle and lower Yangtze River who prefer Carex spp as their main food source. As the largest freshwater lakes connected to the Yangtze River, the consequent growth of the wetland vegetation at Poyang Lake is greatly affected by hydrological factors which may determine the exposure time of the meadow and as well as the effective growth time of wetland vegetation. However, geese are of highly selectivity of food, Carex spp is just suitable during a specific growing period and plant height is one of the important selection factors. Clarifying the relationship between feeding characteristics of geese and the growth process of Carex spp is therefore significant to determine the spatial-temporal pattern of suitable habitats for geese conservation. Taking Changhuchi Lake, a typical sub-lake of Poyang Lake National Nature Reserve, as the study area, this study undertook in-situ experiments as well as lab analysis of Carex spp during the spring growth season （from early March to early May）, including 12 field surveys of plant height and 7 field surveys of aboveground biomass along four elevation gradients. Data extracted from remote sensing interpretation, meteorological data and field survey data were combined to identify the flood recession dates as well as the effective growth time of different elevation gradients. By incorporating Logistic equation and the feeding characteristics of geese, the time window fit for geese＇s feeding on vegetation was reversely deduced from growth curve model. The results showed that there was a significant positive correlation between plant height and aboveground biomass and both of them fit the Logistic growth model; hydrological regime and temperature jointly affected the growing process of Carex spp. Delayed flood recession will influence the vegetation pattern for geese to feed on due to the low temperature limit. When the exposure time of Carex spp reached 12-28 days in autumn and 83-182 days in spring, they provided an appropriate time window for geese to feed. Our study proposed a method to determine the time window of Carex spp fit for overwintering geese and analyzed the influencing mechanism for hydrological factors on wintering geese＇s food availability. It was evidenced that a 20-day delay of flood recession would cause a great mismatching between the growth patterns of Carex spp and the foraging requirements of wintering geese in their peak period through our field monitoring. This study is of great contribution to the hydrological regulation and management of Poyang Lake wetland.