Aspects and causes of earlier and current spread of Trachycarpus fortunei in the forests of southern Ticino and northern Lago Maggiore (Switzerland, Italy)

Abstract

During 2013 and 2014, we investigated the process of the spreading of evergreen broad-leaved (laurophyllous) species in the deciduous forests of southern Ticino (Switzerland) and neighboring northern Lago Maggiore (Italy). The mild climate of this region allows a diversity of exotic plants to thrive outdoors. Most noticeable is the Chinese windmill palm (Trachycarpus fortunei), cultivated in almost every private garden and park around the lakes of southern Switzerland. This palm species has been spreading into the nearby forests for decades. Our research deals with several aspects of the spread of Trachycarpus fortunei in the investigated region, such as the occurrence within the vertical layer of the forest structure since earlier surveys. The ecological conditions in which this palm species thrives best in the research area are analyzed. In addition, we discuss possible causes that may have contributed to the spread of Trachycarpus fortunei, such as the environmental dynamics of the past 40 years as global warming and anthropogenic impacts.