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New Zealand Journal of Forestry (1998) 42(4): 39–42
©New Zealand Institute of Forestry

Research article
Implications of dioecy for sustainable forest management

S. Van Uden , G.H. Stewart and R.P. Duncan

The dense podocarp forests of New Zealand, and in South Westland in particular, are unusual in that they are dominated by dioecious trees. Females and males of dioecious species perform different reproductive functions and consequently may use resources in different ways. This differential resource use can result in females and males differing in growth rate, age at maturity, and life span, which in turn can result in differences between the sexes in size distribution, age distribution and number within a population. Differences in growth rate and size in particular could result in one sex being harvested at a greater rate than the other, altering the natural sex ratio — an outcome that may have important implications for the long-term sustainability of managed dioecious forests.
We review the differences between the sexes for the two species studied in New Zealand (kahikatea and rimu) and present additional rimu sex data from differently-aged landforms in Saltwater Forest, South Westland. Female dominated, male dominated, and 1:1 ratios of the sexes have all been found, and in some instances differences in growth rate reported. We discuss the implications of dioecy and differences in growth and mortality between the sexes, and suggest areas of research required, for sustainable forest management.

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