Abstract
An increasing number of investigations into mixed forest stands shows clear interactions between complementarity and stand and site characteristics. One of the least-investigated mixture types are mixed stands of Norway spruce and European larch. We investigated pure and mixed stands of these species in the northern part of the eastern intermediate Alps in Austria, at altitudes between approximately 880 and 1330 m above sea level. In these stands, 12 plots sized between 0.25 ha and 1.6 ha, with varying ages and proportions of Norway spruce, were established. All trees were measured for their coordinates, diameter at breast height, tree height, crown height, and crown projection area. The trees were cored at breast height, and from about 200 felled sample trees, equations for leaf area and for the five-year volume increment were developed. Growth efficiency (volume increment of a species per its fraction of the stand area) exhibited a clear interaction with age: in young mixed stands, spruce as well as larch grew less than the reference from the pure stands, while in the older stands especially spruce grew much better in the mixed stands. When the Clark Evans index was entered into the growth efficiency equations, it could be seen that the spatial distribution of the trees (i) explained more variance than the species proportion and (ii) showed an additional influence of stand density on the complementarity of the species.
Highlights
Rising interest in the growth and yield of mixed forests is well documented by the proliferation of a large number of publications, and even new textbooks (e.g., Pretzsch et al [1]) on mixed forests
From these figures and the species proportions by area given in Table 2, the leaf area index of the species according to Equation (1), the leaf area efficiency (Equation (2)), and the growth efficiency (Equation (3)) were derived
The leaf area efficiency of larch is about 35% higher than that of spruce, the growth efficiency of spruce is more than twice that of larch
Summary
Rising interest in the growth and yield of mixed forests is well documented by the proliferation of a large number of publications, and even new textbooks (e.g., Pretzsch et al [1]) on mixed forests. Liang et al [2] and Vila et al [3] found that a positive biodiversity-productivity relationship is dominant on global and European scales. Paquette and Messier [4] reported a strong, positive effect of biodiversity on tree productivity, they stressed that there is an important difference between their investigated biomes: complementarity seems less important in temperate forests growing in a more stable and productive environment, while, in the more stressful environment of boreal forests, beneficial interactions between species may be more important. When studying different mixture types, more and more interactions between stand and site characteristics and complementarity were found. Pretzsch et al [6] found an interaction effect of site productivity and admixtures in Norway spruce
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