European white elm ( Pallas) is a typical species of riparian forest. In Switzerland, at the margin of its distribution range, this tree is rare and poorly known. Its naturalness was often debated, and the species was seen most often as only cultivated. We aimed to clarify its status, ecology and distribution with extensive field work and surveys in Switzerland, as well as historical investigations. has a scattered distribution along large rivers and lakes of Switzerland. It is found mainly on coarse, moderately calcareous soils with good fertility. It generally occurs in hardwood riparian forests and occasionally in softwood forests in more dynamic systems. Our findings indicate that grows naturally in Switzerland. However, the channelization of the large rivers and stabilization of water levels of the main lakes during the 19th century have altered the alluvial dynamics necessary for natural regeneration and thus its long-term survival. Therefore, occurs today mainly as a relict species in ancient floodplain forests with altered dynamics. In this context, regeneration occurs only to a very limited extent and is scarcely sufficient for species persistence. With a total population of less than 1000 naturally occurring individuals, it belongs to the rarest and most threatened trees of Switzerland. By demonstrating the fact that this species was actually present originally in this country, we exemplify the need for a multi-faceted approach to answering questions on the original occurrence versus introduced character of a species, which is very important in regard to land use planning, conservation, and wise use of local plant resources.

中文翻译：

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河漫滩森林遗迹：瑞士榆树的自然分布和生态

欧洲白榆（Pallas）是河岸森林的典型树种。在瑞士，在其分布范围的边缘，这种树很稀有且鲜为人知。它的自然性经常受到争议，并且该物种通常被视为只能人工栽培。我们的目的是通过在瑞士进行广泛的实地工作和调查以及历史调查来阐明其现状、生态和分布。分布于瑞士各大河流和湖泊沿岸。它主要生长在肥力良好的粗质、中钙质土壤上。它通常发生在硬木河岸森林中，偶尔也发生在动态系统中的软木森林中。我们的研究结果表明它在瑞士自然生长。然而，19 世纪大河的渠化和主要湖泊水位的稳定改变了冲积土的自然再生动力，从而改变了冲积土的长期生存。因此，如今，它们主要作为孑遗物种出现在动态变化的古代洪泛区森林中。在这种情况下，再生仅发生在非常有限的范围内，并且不足以维持物种的持续存在。天然存在的总数量不足1000株，属于瑞士最稀有、最受威胁的树木。通过证明该物种实际上最初存在于该国这一事实，我们举例说明了需要采取多方面的方法来回答有关物种的原始出现与引入特征的问题，这对于土地利用规划非常重要，保护和合理利用当地植物资源。