Individual tree growth efficiency of Norway spruce

The relationship between forest stand growth and stand density is an expression of the efficiency of growing space on the stand level. Many authors confirm the existence of an optimum density, i.e. all other factors constant, a stand density, where growth exhibits a maximum. Below this optimum density, the individual trees have better growing conditions, i.e. more light and other resources, thus grow better, but cannot compensate anymore the growth of the trees that have been removed in order to lower the stand density. At densities above the optimum it is hypothesised that the proportion of trees which use their part of the stand area inefficiently, is so high, that total stand growth declines. However, there is a lack of investigations in individual tree growth efficiency related to the potentially available area of trees. Individual tree efficiency is frequently defined as growth per unit of crown projection area, or per unit of individual tree leaf area. Both measures do not add up to stand area, and cannot separate the effect of growing space available for the given crown projection area or leaf area. The hypothesis to be tested in this project is that there is an optimum individual tree leaf area index. Besides its size and social position, a tree will be characterised by (i) its volume increment, (ii) its leaf area, and its potentially available part of the stand area. The latter one will be derived by dividing stand area into very little squares, which are attributed to that tree, for which the ratio of its distance to the square and its leaf area is a minimum. In this way, the a found potentially available stand areas are distributed proportionally to leaf area and all together add up to the stand area, because every square of the stand is attributed to one of its trees. Growth efficiency is then defined as volume increment per attributed area, and individual tree leaf area index is defined as leaf area per attributed stand area. The data will be gathered in 8 pure Norway spruce (Picea abies L. Karst.) stands. There will be four stand types, each of them in a thinned and in an unthinned version. The four stand types will represent three age classes and one uneven-aged structured stand. All trees in the stands will be mapped, and increment cores will be taken. For appropriate leaf area determination in each stand 30 trees will be felled, representing three crown classes and each of the whole range of estimated individual leaf area index, taking early sapwood area as a proxy for leaf area. The felled trees will be used to determine (i) their volume increment, and (ii) their leaf area. From the mapping and the leaf area the attributed stand area will be calculated. With these data the hypothesis of an optimum individual tree leaf area index will be tested in each stand individually, and afterwards tested, if it differs by the factors age class, and even-aged-uneven-aged structure, recently thinned or not thinned.

The relationship between forest stand growth and stand density is an expression of the efficiency of growing space on the stand level. Many authors confirm the existence of an optimum density, i.e. all other factors constant, a stand density, where growth exhibits a maximum. Below this optimum density, the individual trees have better growing conditions, i.e. more light and other resources, thus grow better, but cannot compensate anymore the growth of the trees that have been removed in order to lower the stand density. At densities above the optimum it is hypothesised that the proportion of trees which use their part of the stand area inefficiently, is so high, that total stand growth declines. However, there is a lack of investigations in individual tree growth efficiency related to the potentially available area of trees. Individual tree efficiency is frequently defined as growth per unit of crown projection area, or per unit of individual tree leaf area. Both measures do not add up to stand area, and cannot separate the effect of growing space available for the given crown projection area or leaf area. The hypothesis to be tested in this project is that there is an optimum individual tree leaf area index. Besides its size and social position, a tree will be characterised by (i) its volume increment, (ii) its leaf area, and its potentially available part of the stand area. The latter one will be derived by dividing stand area into very little squares, which are attributed to that tree, for which the ratio of its distance to the square and its leaf area is a minimum. In this way, the a found potentially available stand areas are distributed proportionally to leaf area and all together add up to the stand area, because every square of the stand is attributed to one of its trees. Growth efficiency is then defined as volume increment per attributed area, and individual tree leaf area index is defined as leaf area per attributed stand area. The data will be gathered in 8 pure Norway spruce (Picea abies L. Karst.) stands. There will be four stand types, each of them in a thinned and in an unthinned version. The four stand types will represent three age classes and one uneven-aged structured stand. All trees in the stands will be mapped, and increment cores will be taken. For appropriate leaf area determination in each stand 30 trees will be felled, representing three crown classes and each of the whole range of estimated individual leaf area index, taking early sapwood area as a proxy for leaf area. The felled trees will be used to determine (i) their volume increment, and (ii) their leaf area. From the mapping and the leaf area the attributed stand area will be calculated. With these data the hypothesis of an optimum individual tree leaf area index will be tested in each stand individually, and afterwards tested, if it differs by the factors age class, and even-aged-uneven-aged structure, recently thinned or not thinned.