Phytophthora on Alnus spp. (alders)
The genus Alnus (Betulaceae) includes thirty-fi ve species distributed across northern hemisphere (http://www.discoverlife.org). There are four species native to Europe: A. incana (grey alder), A. cordata (Italian or Corsica alder), A. glutinosa (common or black alder) and A. viridis (green alder). In addition, A. rubra native to North America has been extensively planted in some European countries (Claessens, 2003). Alnus sp. plays important ecological roles. It is a pioneer genus, tolerant of high ground water levels and periodic fl ooding. A. glutinosa is the most common species and is present throughout Europe up to 1800 m. It is well adapted to wet sites and plays a vital role in riparian ecosystems as the root system helps to stabilise riverbanks reducing the eff ect of erosion (Webber et al., 2004). Black alder has a benefi cial eff ect on soil (porosity, symbiosis with Frankia), on water quality (fi ltration, purifi cation) and also on fauna. It contributes to increase the biodiversity of birds and insects and its root system allows fi sh to shelter. Alnus incana is widely distributed in central and eastern Europe. In the south, it grows mainly in mountain areas. As it is a root sprout pioneer that tolerates both dry conditions and fl ooding, A. incana is very important for improving the stability of slopes and riverbanks (Jung & Blaschke, 2004). A. cordata and A. viridis are much less frequent species and are native to Corsica-Italy and mountains of central Europe, respectively (Claessens, 2003).