DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 1-2/1966 str. 91 <-- 91 --> PDF |
More specifically the requirements for provenance experiments can be summarized under 8 headings: 1. The experiment must provide a reliable estimation of tree quality, growth vigour, resistance to climatic and pathogenic agents, wood quality etc. for each provenance separately, and irrespective of the site variability within the experimental area. 2. Apart from the information about the quality and productivity of individual trees within a provenance, the trials have to provide information about the productivity of the stand per unit area, both in terms of wood volume and money returns. 3. The experiment must permit a reliable comparison of the provenances with respect to the characters mentioned in par. 1° and 2°. The lay-out must therefore be such as to enable an elimination of environmental influences as far as the variability within the experimental site is concerned. 4. In view of the fact that the growth and shape of a tree are affected by its neighbours, it would be useful if each experimental plot had a surround of trees that would permit an evaluation of the provenances irrespective of the neighbour effect. 5. The experiment should be so conceived as to permit a comparison of early and late results. Any juvenile-mature correlations established will permit a reduction of the trial period for future studies. 6. In view of the high expense involved in the establishment of provenance experiments they have to be so laid out as to provide maximum information for the work performed. 7. As already stated, the provenance experiments must contain a sufficient number of trees at a time when a reliable comparison of provenances is available in order to permit a reconstruction of these populations which have been selected for reproduction in forest practice. 8. Finally, the experimental stand must be established and tended according to the forestry practices which are standard for the local conditions. It is not realistic to rely on empirically chosen silvicultural innovations or to integrate provenance studies with silvicultural experiments. A brief glance at the eight requirements specified above is sufficient to realize that no single experiment will fully satisfy them all. The older experiments with large plots gave a good estimation of productivity per unit area and permitted elimination of the boundary effects, yet they were not replicated in sufficient numbers, and therefore the provenances are not comparable. The very small or even single tree plots suggested by Wright and Freeland (1958) do not permit an evaluation of productivity per unit area; they are very complicated in the lay-out, which may lead to mistakes during the beating up and later during the recording of the data, and finally some plots will disappear as a result of thinning. The pilot tests laid out in Waldsieversdorf (East Germany), where rows of 6 trees are used per plot are useful only to the early part of the rotation, when some information can already be obtained, but it will not be possible to confirm it later. Nor will the productivity per unit area be calculable. The situation would seem to be such that, on one hand, large plots are too expensive and cover an area too large, thereby introducing an unnecessarily large site variability that may obscure the genetic differences, wheres, on the |