A biotic agent promotes large-scale catastrophic change in the coastal marshes of Hudson Bay
A biotic agent promotes large-scale catastrophic change in the coastal marshes of Hudson Bay
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DOI：
10.1111/j.1365-2745.2005.01086.x
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发表时间：
2006-01-01
影响因子：
5.5
通讯作者：
Abraham, KF
中科院分区：
文献类型：
--
作者：
Jefferies, RL;Jano, AP;Abraham, KF
1.食草动物可能会对植物-土壤系统产生微小的变化，引发正反馈，导致植物状态迅速发生灾难性变化，包括土壤性质发生不可逆转的变化。在哈德逊湾和詹姆斯湾的沿海沼泽地，越来越多的较小雪雁（Chen caerulescens caerulescens A.O.U.）导致植被丧失，沉积物暴露和部分侵蚀。2对LANDSAT数据进行了多时相分析，以检测这些海湾沿海沼泽中9个地点从1973年到1999年或以后的植被变化，这些海湾每年都会出现集结和/或繁殖的鹅。3图像进行了共配准，并为每幅图像生成归一化植被指数通道。对于每个位置，成对的归一化差异计算这些NDVI图像为每个连续的时期所定义的图像采集日期。由此产生的二次归一化植被指数差异图像表示每个时间间隔的归一化植被指数值的变化，并产生了三个明确界定的类：水，植被衰退和没有检测到的变化植被。4在九个广泛分离的研究地点，潮间带盐沼（生态系列）已经失去（共35 000公顷）和替代稳定状态（暴露沉积物）建立。类似的变化也发生在其他地方沿着2000公里的海岸线，鹅繁殖或舞台。5这些沿海沼泽地的植被重建将需要几十年，因为土壤性质的几乎不可逆转的变化，需要侵蚀和重新沉积的松散沉积物之前，大规模的植物殖民地可以发生，因为大量的鹅继续饲料每年产生这种戏剧性的自上而下的影响。
1 Herbivores may initiate small changes to plant-soil systems that trigger positive feedbacks leading to rapid catastrophic shifts in vegetative states, including irreversible changes in soil properties. In the coastal marshes of Hudson and James bays, foraging by increasing numbers of lesser snow geese (Chen caerulescens caerulescens A.O.U.) has led to loss of vegetation, and exposure and partial erosion of sediment.2 Multi-temporal analysis of LANDSAT data has been carried out to detect vegetation change from 1973 to 1999 or later at nine sites in the coastal marshes of these bays where staging and/or breeding geese are present annually.3 Images were co-registered, and for each image NDVI (Normalized Differential Vegetation Index) channels were generated. For each location, pairwise normalized differences were calculated between these NDVI images for each successive period defined by the imagery acquisition dates. The resulting secondary NDVI difference images expressed changes in NDVI values for each time interval and yielded three well-defined classes: water, vegetation decline and no detectable change in vegetation.4 At the nine widely separated study sites, the intertidal saltmarsh (an ecological sere) has been lost (to a total of 35 000 ha) and an alternative stable state (exposed sediment) established. Similar changes have occurred elsewhere along the 2000-km coastline where the geese breed or stage.5 Re-vegetation of these coastal marshes will take decades because of near-irreversible changes in soil properties that require erosion and re-deposition of unconsolidated sediment before large-scale plant colonization can occur, and because large numbers of geese continue to forage annually producing this dramatic top-down effect.