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New Zealand Journal of Forestry (1973) 18(1): 36–46
©New Zealand Institute of Forestry

Research article
Die-back of Tawa [Beilschmiedia tawa].

R. M. J. MacKenzie and P. D. Gadgil

Following reports of widespread tawa die-back in the Urewera country, four observation plots, two in logged and two in unlogged areas, were established. They were examined monthly for two years. It was noted that foliage, buds and young shoots were killed off- in autumn and early winter; the dead leaves showed rupture of cells accompanied by a reddish to dark brown mottling. In late winter and spring, wilting of foliage and death of whole branches was observed. Early winter deaths were rarely found on foliage and shoots under a 0.8-1.0 canopy and the incidence of such deaths increased with decreasing canopy closure. Wilting of foliage did occur under a full canopy but the incidence was lower than under a lesser canopy closure. No micro-organisms pathogenic to tawa were found. Field observations and laboratory experiments strongly suggested that the damage in early winter was due to frost. The cause of the wilt is obscure. Most damage occurred in logged areas where the canopy was open; damage on a lesser scale was found in unlogged areas.
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