21 April 2009

Palms Conquer the North

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The Chusan palm started to spread and regenerate outside the gardens in forests in Southern Switzerland and Northern Italy. (Jan. '08)

Just a few decades ago the Chusan palm (Trachycarpus fortunei) started to spread and regenerate outside the gardens in forests across the borderline region of southern Switzerland and North Italy. This new northernmost wild palm population is a genuine witness of climate change. Due to rising winter temperatures by up to 0,5 degrees per decade, the cold-hard Chusan palm was able to survive also in the forests without protection.

Locarno, Swittzerland. Within the European research project ALARM (Assessing LArge scale Risks for biodiversity with tested Methods) a research team lead by plant ecologist PD Dr. Gian-Reto Walther of the University of Bayreuth discovered a palm species being among those species profiting from recent climate change. Based on the height of the located palms and the stage of rejuvenation the scientists concluded the beginning of the proliferation of the Chusan palm around 1970. Just around that time the climate change got noticeable and winter temperatures began to increase by up to 0,5 degrees per decade.

Originally the Chusan palm – as the name tells – comes from Southeast Asia, China and grows in subtropical regions with winter temperatures up to +2 or +2,5 degrees. Because of their cold-hardiness seamen imported the palm as an ornamental plant to Europe. The first written confirmation of the Chusan palm in Europe goes back to the time around 1830. Soon they were cultivated in many areas of the world at the range margin of global palm distribution.

Based on the new wild palm population members of the ALARM project, representing the scientists either modelling or observing climate change impacts, planted palm seeds all over Europe to contribute a better understanding of the role of changing climatic parameters in limiting the dispersion of the Chusan palm. 50 seeds per test area were planted in the native forests, half in the genuine forest ground, half in potting soil. Astonishingly the seeds were able to germinate nearly in every region between Spain and Scandinavia. Only in dry regions in the south of Spain, Turkey and Romania and the very cold regions in the north of Norway no seedlings were found. During the one and a half year period of growth the germinated plants in Barcelona, Spain dried up totally in the arid summer and the ones in Germany and Scandinavia declined in some extent due to cold winter temperatures and their aftermaths. Despite of all these reactions the seedlings in France, England and Ireland grew surprisingly well in the native forests.

The scientists conclusion is that the warming of the present century ameliorated conditions for the palms immensely. Hence, the Chusan palm is an appropriate indicator and appears to be a witness of global climate change. And if the temperatures continue to rise, the Chusan palm could soon spread over the man-made protected gardens and become part of the natural forest vegetation in central Europe, too.

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