Performance and Frost Hardiness of Picea sitchensis x Picea glauca Hybrids in Scotland

The growth of seven Picea sitchensis x Picea glauca hybridswas compared with the growth of two P. sitchensis provenancesand Picea glauca var.albertiana at two sites in northern Scotland.The sites were at Aultmore (an exposed, dry site with a mineralsoil) and Shin (a frosty, wet site with deep peat). They wereof the type considered more suited to Pinus contorta than P.sitchensis. At age 10, in 1984, most of the hybrids, at both sites, wereabout 10 and 20 per cent taller than P. sitchensis of Masset(Q.C.I.) and Ketchikan (Alaska) provenance, respectively. P.glauca var. albertiana grew very poorly, especially at Aultmore. At Aultmore, the frost hardiness of three of the tallest hybrids,the two P. sitchensis provenances, and P. glauca var.albertiana,was tested at about 3-weekly intervals throughout 1982 and 1983.Detached shoots were subjected to artificial frosts in a programmablechamber. P. glauca var. albertiana was frost susceptible atbudburst, but at all other times it was relatively very frosthardy (eg. to^–10°C in mid-August). Also, the hybridswere consistently more hardy than P. sitchensis of even Ketchikan(Alaska) provenance from July onwards. However, the hybridswere less frost hardy than P. sitchensis of Masset (Q.C.I.)provenance in early spring (they dehardened a week earlier inMarch-April) and their buds were equally as frost susceptibleat the time of budburst. In 1983, trees of P. glauca var. albertianaburst their buds about a week sooner than P. sitchensis. It was concluded that P. sitchensis x P. glauca hybrids canperform better than P. sitchensis at sites considered ‘marginal’for P. sitchensis, and that their good performance may be partlyattributed to, or associated with, their greater summer andautumn frost hardiness. A programme of inter-specific hybridizationis being pursued.