Invasive Species Compendium

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Abstract

Variation among neighbouring and distant provenances of Eucalyptus grandis and E. tereticornis in Zimbabwean field trials.

Abstract

An international series of trials of E. grandis and E. tereticornis provenances was set up in 1980. This paper reports the results of the Zimbabwean trials (planted in 1981), in which provenances were tested from most of the natural distributions of the two species. A total of 24 E. grandis provenances, including 3 Zimbabwean seedlots and a South African seed-orchard seedlot, and 22 E. tereticornis provenances, including 2 Zimbabwean seedlots, were planted. The most productive E. grandis provenances at age 3.5 yr were those from Bulahdelah and Coffs Harbour in northern New South Wales (nearly 11 m in height), but some northern Queensland provenances approached them in productivity. There were also significant differences in stem form score, with superior provenances again in both southern and northern groups. Selection indices were constructed to combine productivity traits with stem form for both species. For E. tereticornis the selection index showed that the most desirable provenances came from northern New South Wales and southern Queensland (about 7 m in height), with Papua New Guinea and northern Queensland provenances giving generally poor results. There were significant differences in all traits between E. grandis provenances collected from the Atherton region, located within 25 km of each other, and between E. tereticornis provenances collected along the Cooktown-Laura road. Some provenances of both species located far apart were no more different than some of these neighbouring provenances. This suggests that differentiation is a very local effect, depending either on very local selective forces or on different amounts of inbreeding in adjacent stands. Local Zimbabwean seedlots grew significantly slower than the best of the natural provenances, despite probable inbreeding effects in the latter. The idea of a local 'land race', adapted to local Zimbabwean conditions, is not supported by the results of these experiments. On the contrary, the results suggest that trees derived more directly from superior provenances should be included in the Zimbabwean breeding programmes and that this would lead to a substantial improvement in growth rate.