Abstract
Individual tree architecture and the composition of tree species play a vital role for many ecosystem functions and services provided by a forest, such as timber value, habitat diversity, and ecosystem resilience. However, knowledge is limited when it comes to understanding how tree architecture changes in response to competition. Using 3D-laser scanning data from the German Biodiversity Exploratories, we investigated the detailed three-dimensional architecture of 24 beech (Fagus sylvatica L.) trees that grew under different levels of competition pressure. We created detailed quantitative structure models (QSMs) for all study trees to describe their branching architecture. Furthermore, structural complexity and architectural self-similarity were measured using the box-dimension approach from fractal analysis. Relating these measures to the strength of competition, the trees are exposed to reveal strong responses for a wide range of tree architectural measures indicating that competition strongly changes the branching architecture of trees. The strongest response to competition (rho = −0.78) was observed for a new measure introduced here, the intercept of the regression used to determine the box-dimension. This measure was discovered as an integrating descriptor of the size of the complexity-bearing part of the tree, namely the crown, and proven to be even more sensitive to competition than the box-dimension itself. Future studies may use fractal analysis to investigate and quantify the response of tree individuals to competition.
Highlights
In Europe, the conversion of pure stands into mixed stands is still ongoing [1,2,3]
The intercept of the Db-regression line was the attribute that was most sensitive to competition strength and the relationship was again negative, with the Generalized Additive Modeling (GAM) resulting in the highest explained deviance of all tested measures (Figure 5D and Table 2)
We hypothesized that competition strength affects the architecture of beech trees in terms of branching pattern, as already indicated by Bayer et al [27], as well as measures of tree structural complexity derived from fractal analysis
Summary
In Europe, the conversion of pure stands into mixed stands is still ongoing [1,2,3]. The corresponding silvicultural interventions are made under the assumption that they result in ecologically and economically beneficial stands [4,5]. Site conditions, competition processes and ontogenetic stage all affect the growth of an individual tree, be it in a mixed or pure stand [6,7]. The growth response of the individual tree depends on the species identity of the surrounding neighbors [9,10,11]. In order to understand and model the dynamics in mixed stands, it is necessary to look into the development of tree morphological characteristics and branching architecture under competition in mixed neighborhoods
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