Long-Term Abandonment of Forest Management Has a Strong Impact on Tree Morphology and Wood Volume Allocation Pattern of European Beech (Fagus sylvatica L.)

Abstract

The three-dimensional (3D) morphology of individual trees is critical for light interception, growth, stability and interactions with the local environment. Forest management intensity is a key driver of tree morphology, but how the long-term abandonment of silvicultural measures impacts trunk and crown morphological traits is not fully understood. Here, we take advantage of a long management intensity gradient combined with a high-resolution terrestrial laser scanning (TLS) approach to explore how management history affects the 3D structure of mature beech (Fagus sylvatica L.) trees. The management gradient ranged from long-term (>50 years) and short-term (>20 years) unmanaged to extensively and intensively managed beech stands. We determined 28 morphological traits and quantified the vertical distribution of wood volume along the trunk. We evaluated the differences in tree morphological traits between study stands using Tukey's HSD test. Our results show that 93% of the investigated morphological traits differed significantly between the study stands. Significant differences, however, emerged most strongly in the stand where forest management had ceased >50 years ago. Furthermore, we found that the vertical distribution of trunk wood volume was highly responsive between stands with different management intensity, leading to a 67% higher taper top height and 30% lower taper of beech trees growing in long-term unmanaged stands compared to those in short-term unmanaged or managed stands. These results have important implications for management intensity decisions. It is suggested that the economic value of individual beech trees from long-term unmanaged forests can be expected to be very high. This might also translate to beech forests that are extensively managed, but we found that a few decades of implementation of such a silvicultural system is not sufficient to cause significant differences when compared to intensively managed stands. Furthermore, TLS-based high-resolution analyses of trunk and crown traits play a crucial role in the ability to better understand or predict tree growth responses to the current drivers of global change.

Understanding 3D structural complexity of individual Scots pine trees with different management history

“…Tree structure, on the other hand, can be characterized by using morphological measures such as crown dimension (e.g., volume, surface area) and stem attributes (e.g., diameter at breast height (DBH), height, height of crown base) (Pretzsch, 2014). The availability of 3D point clouds from terrestrial laser scanning (TLS) has provided an effective means for such measurements allowing TLS to be utilized in generating stem and crown attributes (Bayer et al, 2013;Calders et al, 2013Calders et al, , 2018Georgi et al, 2018;Juchheim et al, 2017;Liang et al, 2012;Metz et al, 2013;Saarinen et al, 2017Saarinen et al, , 2020Seidel et al, 2011). However, objective and quantitative measures for structural complexity of individual trees are needed to better understand relationship between forest structural diversity and ecosystem services such as biodiversity, productivity, and carbon uptake (Hardiman et al, 2011;Messier et al, 2013;Puettmann et al, 2015;Zenner, 2015).…”

Assessing the effects of thinning on stem growth allocation of individual Scots pine trees

“…Our results did not reveal notable difference in form factor between moderate and intensive thinning whereas tapering below 50% of tree height was smaller for moderate thinnings than for intensive thinnings corroborating results by Jacobs et al (2019). Georgi et al (2018) found significant difference in tapering generated from TLS data between unmanaged and intensively managed beech stands. Most of their attributes were related to crown dimensions or height of branches similar to the study by Juchheim et al (2017) who concentrated on crown expansion in both horizontal and vertical directions.…”

“…In applications related to boreal forests, TLS has been utilized in quantifying stem growth and changes in stem taper (Luoma et al 2019), reparametrizing an existing taper curve model , and assessing timber quality . In Central Europe, on the other hand, impacts of silviculture on stem form of Norway spruce (Jacobs et al 2019) and European beech (Juchheim et al 2017, Georgi et al 2018, Noyer et al 2019) have been studied. In Juchheim et al (2017) and Georgi et al (2018), several attributes characterizing stem size and form were generated from TLS point clouds (e.g.…”

“…In Central Europe, on the other hand, impacts of silviculture on stem form of Norway spruce (Jacobs et al 2019) and European beech (Juchheim et al 2017, Georgi et al 2018, Noyer et al 2019) have been studied. In Juchheim et al (2017) and Georgi et al (2018), several attributes characterizing stem size and form were generated from TLS point clouds (e.g. tree height, DBH, stem volume, crown-base height, height-diameter ratio, taper, lean, and sweep) of which most are attributes that have been generated also from traditional measurements.…”

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

“…The earlier generations of laser scanners, however, mostly lack a high-resolution acquisition of the complex tree crowns in dense mature forests. In this study we make use of state-of-the-art technology of fullwaveform TLS with online waveform processing to measure a large number of individual trees in a highly accurate manner (Bienert et al 2018;Georgi et al 2018).…”