Final results from a trial to test the effect of plot size on <i>Eucalyptus</i> hybrid clonal ranking in coastal Zululand, South Africa

Abstract

Hybrid clones withEucalyptus grandis as one parent and, generally, E. urophylla as the other parent, are deployed commercially as monoclonal blocks by Sappi in the subtropical region of coastal Zululand, South Africa. In monoclonal blocks genotypes are grown in self-competition. Performance under this scenario may not necessarily correlate well with performance where genotypes are competing for resources with a number of genetically dissimilar genotypes. There is an uncertainty whether plot configuration or size influences clonal ranking and therefore selection of clones for commercialisation. Final results at age eight years of a trial testing eight selected Eucalyptus hybrid clones in single-tree, eight-tree line, and eight × eight tree square plots are reported in this paper. Ranking of the eight clones between the half rotation (44 months) and full rotation (94 months) measurement have remained stable in the single-tree and line plots, but there have been some changes in the square plots. At 94 months, clonal ranking between the single-tree and line plots was consistent (r_p = 0.98) with only two clones changing ranks. When comparing the clonal ranking  of the single-tree plots to the large square plots rank changes have been significant (r_p = 0.65). The overall means for the three different plot types are very similar. The range of the clonal means for tree volume in the single-tree plots (0.4042 m³) is more than five times the range for the  square plots (0.0709 m³). Gain predictions using data from the single-tree  plots overestimated the realised gains measured in the square plots. The top-performing clone in the single-tree plots had a predicted gain of 74% over the  trial mean, but only yielded 7% more in the square plots. Similarly, the worst-ranked clone in the single-tree plots did not perform as poorly as what was predicted (−59%) and produced only 13% less than the trial mean on the  square plots.

Keywords: clonal ranking, clones, hybrid, intergenotypic competition, plot size

Southern Forests 2011, 73(3&4): 131–135