A 3-year study was conducted to evaluate growth and survival of trees grafted onto five species of birch rootstocks. `Whitespire' Japanese birch (Betula platyphylla var. japonica Hara.) was grafted onto paper birch (B. papyrifera Marsh), European birch (B. pendula Roth), river birch (B. nigra L.), Szechuan birch [B. szechuanica (C. Schneid.) Janson], and `Whitespire' Japanese birch rootstocks and grown under field conditions. Trees grafted onto river, European, paper, and `Whitespire' birch rootstocks had similar (100% to 60%) survival rates. Trees on Szechuan rootstock had a survival rate of 30%, which was lower than that of all other rootstocks, except `Whitespire'. `Whitespire' scions grafted onto European birch rootstocks had thicker trunks, were higher, and had wider canopies than trees grafted onto `Whitespire' rootstocks. Trees on river birch rootstocks also had thicker trunks but similar tree heights and canopy widths as trees grafted onto `Whitespire'. `Whitespire' Japanese birch rootstocks produced more rootstock suckers than any of the other rootstocks, while trees on river birch rootstocks had the most frost cracks. No signs of graft incompatibility were observed for any of the graft combinations. These results demonstrate that growth of `Whitespire' birch can be enhanced by grafting this cultivar on rootstocks of other species, including European and river birch.
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