Species interactions: In New Zealand Trachycarpus fortunei has recently been identified as major food source for the lesser short-tailed bat (Mystacina tuberculata). Flowers from just four plant groups appear to be regularly used by this endemic bat species: Collospermum spp., Knightia excels, Metrosideros spp. and apparently, T. fortune. The pollen of the exotic palm amounts to up to 57% of the analyzed diet (Peterson et al. 2006).\r\n

Climate change: While T. fortunei is native to sub-tropical China (along with Myanmar and the Himalayas), it is one of the most cold-hardy palms. T. fortunei is thus cultivated as an ornamental in many countries and its cold-tolerance is well documented (Caramyshev et al. 2006; Essig & Dong 1987; Koike 2006; Khurram & Miyamoto 2005; Walther & Berger 2007). Outside of its native range, T. fortunei has established itself in Australia, Japan, New Zealand, Spain, the United States, and more recently, Switzerland (Armengol et al. 2005; GCW 2007; USDA-ARS 2010; Hodel et al. 2006; Walther 2003). \r\n

The establishment of T. fortunei in the south of Switzerland is further north than the previous northernmost palm population in Europe, and exists outside the usual latitude range for palms (Walther et al. 2007). It is thought that this invasion and range expansion of T. fortunei may be being aided by climate change effects; in this case milder winter conditions. Research has linked the effects of climate change with an increase in survival of species outside their normal ranges (e.g. Berger et al. 2007; Niinemets & Peñuelas 2008; Pyšek et al. 2003; Van der Veken et al. 2007; Walther et al. 2009). This can be most easily seen in places of higher latitude and altitude where temperature previously constrained the survival of thermophilous species such as T. fortunei (Walther et al. 2009). \r\n

Palms have long been recognised as bioindicators for warm climates in palaeontology (Walther et al. 2007). While the range expansion of T. fortunei in Europe had been previously noted, in 2007 Walther et al. investigated the climactic factors underlying this expansion. Using information on conditions of actual and modelled data of the native and introduced ranges of T. fortunei, a larger picture was built of climactic constraints on T. fortunei establishment and growth. This enabled the authors to determine whether establishment of populations in southern Switzerland were a function of changing climactic conditions or due to chorological causes, such as increased availability of seed sources. \r\n

Examination of meteorological data in the native range in China and in Switzerland gave a minimum average temperature of 2.2°C of the coldest month as a threshold for seedling survival and successful growth to maturity. Viewing the mean monthly temperature data for Switzerland from 1864 – 2008 showed a marked increase in favourable conditions since the 1950s. Continuously favourable conditions in terms of temperature and length of the growing season have occurred since the 1970s (Walther & Berger 2007) which is correlated with the establishment of wild T. fortunei populations in this area over the past few decades. \r\n

Based on this temperature threshold, other areas in Europe that were previously unsuitable for palms may have appropriate climactic conditions to support the growth and establishment of seedlings (Walther & Berger 2007). It is extrapolated that new areas of the world will become increasingly suitable for T. fortunei survival under current climactic trends. This will likely continue the expansion in range of T. fortunei, as in southern Switzerland (Walther et al. 2007). T. fortunei and other palms may therefore be good bioindicators for climactic changes occurring globally.

The spread of T. fortunei can be controlled by cutting the frutescence before seeds have ripened, physically removing plants, by digging out small individuals and seedlings and felling larger ones. This can then be followed up with treatment using herbicides. However, from a certain stem height the palm is no longer able to resprout, thus herbicide application is not necessary (G.-R. Walther, pers. comm.). It is recommended that sites be monitored and any seedlings or regrowth be treated (Ishii & Iwasaki 2008; Weedbusters 2010). \r\n

There are implications for management regarding the effects of climatic change, as new areas become suitable for invasion by species that were previously constrained by factors such as temperature. These invasions will change the composition of habitats and the functioning of ecosystems on both the macro- and microorganism level (Walther et al. 2009). The formation and potential importance of non-analogue communities as a consequence of the development of non-analogue climates with global warming should be considered in the context of management options (Walther 2010).