Effects of local neighbourhood diversity on crown structure and productivity of individual trees in mature mixed-species forests

Abstract

Background Species-specific genotypic features, local neighbourhood interactions and resource supply strongly influence the tree stature and growth rate. In mixed-species forests, diversity-mediated biomass allocation has been suggested to be a fundamental mechanism underlying the positive biodiversity-productivity relationships. Empirical evidence, however, is rare about the impact of local neighbourhood diversity on tree characteristics analysed at a very high level of detail. To address this issue we analysed these effects on the individual-tree crown architecture and tree productivity in a mature mixed forest in northern Germany. Methods Our analysis considers multiple target tree species across a local neighbourhood species richness gradient ranging from 1 to 4. We applied terrestrial laser scanning to quantify a large number of individual mature trees (N = 920) at very high accuracy. We evaluated two different neighbour inclusion approaches by analysing both a fixed radius selection procedure and a selection based on overlapping crowns. Results and conclusions We show that local neighbourhood species diversity significantly increases crown dimension and wood volume of target trees. Moreover, we found a size-dependency of diversity effects on tree productivity (basal area and wood volume increment) with positive effects for large-sized trees (diameter at breast height (DBH) > 40 cm) and negative effects for small-sized (DBH < 40 cm) trees. In our analysis, the neighbour inclusion approach has a significant impact on the outcome. For scientific studies and the validation of growth models we recommend a neighbour selection by overlapping crowns, because this seems to be the relevant scale at which local neighbourhood interactions occur. Because local neighbourhood diversity promotes individual-tree productivity in mature European mixed-species forests, we conclude that a small-scale species mixture should be considered in management plans.

Effects of Stem Density on Crown Architecture of Scots Pine Trees

“…Laser scanning (or light detecting and ranging LiDAR) has provided new opportunities for characterizing trees in more detail in three-dimensional space. Specifically, terrestrial laser scanning (TLS) has increasingly been used in producing a variety of tree attributes ( Seidel et al, 2011 , 2015 ; Metz et al, 2013 ; Saarinen et al, 2017 ; Hess et al, 2018 ; Chianucci et al, 2020 ; Georgi et al, 2021 ; Owen et al, 2021 ; Rais et al, 2021 ; Zhu et al, 2021 ). One of the challenging stem-related attributes to be measured from standing trees has been taper curve (i.e., diameters at various heights of a stem), and TLS data have been shown to overcome that challenge ( Liang et al, 2014 ; Yrttimaa et al, 2019 , 2020 ).…”

Iterative Method of Discriminant Analysis to Classify Beech (Fagus sylvatica L.) Forest

“…The proposed method is based on an iterative process (Figure 1) in order to achieve an acceptable percentage of success in classified forest inventory plots according to their structure. The method starts with a frequency analysis (FA) for each % BAi variable in order to determine the minimum values from which a diameter class can be considered as sufficiently represented (SR) related to its relative basal area, so the basic definition of The method starts with a frequency analysis (FA) for each % BA i variable in order to determine the minimum values from which a diameter class can be considered as sufficiently represented (SR) related to its relative basal area, so the basic definition of structure typologies is based in that concept, also linked with crown surface and productivity [28]. Thus, it has been considered that a diameter class is sufficiently represented if it exceeds the value of the bottom quartile in each of the % BA i variables.…”

Segmentation of conifer tree crowns from terrestrial laser scanning point clouds in mixed stands of Scots pine and Norway spruce

“…The scanner uses phase shift technology to measure distance to objects that the laser beam hits. We used the following settings when scanning the et al 2008), or implemented for similar objectives (Fang and Strimbu 2019;Georgi et al 2021). Given the sample plot diameter of 26 m and an average distance of 20 m between the 4 m-wide strip roads, varying proportions of strip roads were included in the sample plots.…”

“…Tree crowns are of particular interest, because the location of foliage relative to competing neighbors determines photosynthesis and tree growth. Tree crowns are therefore scanned either individually with scanner positions around each tree (Bayer et al 2013;Seidel et al 2015) or as a group of trees on a sample plot with multiple scanner positions set up across the sample plot (Barbeito et al 2017;Fang and Strimbu 2019;Georgi et al 2021;Wilkes et al 2017). Segmenting individual tree crowns from the resulting point clouds is an essential step in the analysis of these data.…”

“…Many different methods have been applied for segmentation. Most often, deciduous trees have been scanned in the leave-off phase to have complete branch systems visible in the point cloud (Barbeito et al 2017;Bayer et al 2013;Bienert et al 2018;Georgi et al 2021;Seidel et al 2015). Methods tailored for these data are often tracking individual branches in the point cloud with geometric models (Hackenberg et al 2014(Hackenberg et al , 2015Raumonen et al 2013;Tao et al 2015).…”