The selection of seed sources during this early period was, however, not always undertaken systematically. Some reforestation efforts failed as a result, and several countries attempted to restrict the use of imported seed in the late 19th and early 20th centuries ( König, 2005). In the 19th century, more systematic exploration efforts were also extended to North
America, and large quantities of seed of many trees from that region were shipped to other areas. Interestingly, several North American tree species were tested for forestry in Europe before they were assessed for this purpose in their home region (e.g., Samuel, 2007). During the 20th century, the transfer of tree germplasm for R&D purposes increased further when several international provenance trials were established for temperate and boreal species under the auspices of the International Union of Forest Research Organizations (IUFRO) MK-1775 mw (see König, 2005). A series of IUFRO provenance trials was established for P. sylvestris (in 1907, 1938–39 and 1982) and P. abies (in 1938 and 1972), for example. The second IUFRO trial of P. abies, which was planted in Europe and Canada, is probably one of the largest trials ever established, involving 1,100 provenances
( König, 2005). The number of provenances tested in these trials was, however, usually much lower, ranging from 20 to 50. Provenance trials FRAX597 concentration were also established for several other European trees, such as Abies alba, L. decidua, Quercus petraea and Q. robur, as well as for North American species including Abies grandis, Picea sitchensis and Pseudotsuga menziesii. Many of these trials led to the identification of provenances that were superior to local seed sources (e.g., Madsen, 1995 and Eriksson, 2010). The early reforestation and R&D efforts
contributed significantly to the introduction of P. sylvestris and P. abies to 13 and 11 new countries, respectively, in Europe and other regions ( Table 1). Methamphetamine In Canada, initial provenance trials of native trees were established for Picea spp. in the 1930s and 1940s, and for Pinus banksiana, Pinus resinosa and P. menziesii in the 1950s ( Anon, 1997 and Orr-Ewing, 1962). In the USA, one of the earliest provenance trials, established in 1926, was for Pinus taeda ( Rogers and Ledig, 1996). One of the largest provenance trials established in North America included 140 seed sources of Pinus contorta planted in 60 locations in British Columbia, Canada ( Wang et al., 2010). Other tree species received less attention in the Pacific Northwest, but some provenance research was also undertaken on Chamaecyparis lawsoniana, P. sitchensis, Pinus lambertiana, Pinus monticola, Larix occidentalis, Thuja plicata and Tsuga heterophylla. P.taeda and P.