Phytophthora on Betula spp. (birch)

Birch is an important forest tree especially in colder climates. It is monoecious and wind polli- nated species, and it has wind-dispersed seeds. The genus contains more than 60 taxa including trees and shrubs. B. pendula Roth (silver birch) and B pubescens Ehrh. (downy birch) have both wide distribution in Europe and are also found in northern parts of Asia (Hämet-Ahti et al., 1989, Niemistö et al., 2008). B. alleghaniensis Britton (yellow birch), B. lenta L. (sweet birch), B. papyrifera Marshall (paper birch) B. populifolia Marsh. (grey birch) and B. nigra L. (river birch) are species typical for North America (Hämet-Ahti et al., 1989; Verkasalo, 1990). In Scandinavia and northern Europe B. pendula is an important tree species for forest industry, but also used as amenity trees in parks, alleys and in gardens. B. alleghaniensis, B. lenta and B. papyrifera are also valuable for forest industry. Birches are cold tolerant pioneer species and in southern Europe they are found mainly on higher altitudes. Many Betula species such as B. nana L. (dwarf birch), B. pubescens subsp. czerepanovii (Orlova) Hämet-Ahti (arctic moor birch) and B. utilis D. Don (Himalayan birch) are typi- cal for treeline. B. nana and it’s subspecies are shrubs native to arctic and cool temperate regions of northern Europe, northern Asia and northern North America. They are also present in Greenland as well as in mountains in Scotland and the Alps. B. utilis is growing as a shrub or tree native to the the Himalayas (Hämet-Ahti et al., 1989; http://www.discoverlife.org).