Mechanical site preparation (MSP) is often performed prior to planting to improve the growth and survival of planted seedlings. In this study, we compared root development of 5-years-old
Quercus ...petraea
and
Pinus nigra
seedlings planted in plots that had been prepared with different methods, i.e. deep scarification, deep scarification combined with mounding-subsoiling, herbicide and a control without preparation. Seventy-two trees were excavated (36 per species) and their root system was measured by recording points in a three-dimensional space along their roots. The variation of the number of roots with depth and distance to root collar was assessed and analysed, as well as the root projection area. Our results showed that root development was better in the plots with mechanical preparation, for both
Q. petraea
and
P. nigra
, when compared to the control. Combining mounding to subsoiling made the roots extending deeper, especially for
Q. petraea
. A strong relationship was found between root projection area and root collar diameter, indicating the primary effect of lateral root spread on tree growth. The herbicide treatment induced the highest root growth, which raised questions about the potential negative effects of changes in soil properties caused by MSP methods.
• Introduction
The use of terrestrial LiDAR (light detection and ranging) scanners in forest environments is being studied extensively at present due to the high potential of this technology to ...acquire three-dimensional data on standing trees rapidly and accurately. This article aims to establish the state-of-the-art in this emerging area.
• Objectives
Terrestrial LiDAR has been applied to forest inventory measurements (plot cartography, species recognition, diameter at breast height, tree height, stem density, basal area and plot-level wood volume estimates) and canopy characterisation (virtual projections, gap fraction and three-dimensional foliage distribution). These techniques have been extended to stand value and wood quality assessment. Terrestrial LiDAR also provides new support for ecological applications such as the assessment of the physical properties of leaves, transpiration processes and microhabitat diversity.
• Results
Since 2003, both the capabilities of the devices and data processing technology have improved significantly, with encouraging results. Nevertheless, measurement patterns and device specifications must be selected carefully according to the objectives of the study. Moreover, automated and reliable programmes are still required to process data to make these methodologies applicable specifically to the forest sciences and to fill the gap between time-consuming manual methods and wide-scale remote sensing such as airborne LiDAR scanning.
Key message
This article presents a specific methodology for assessing the scaling of the frequency distribution of the branch diameters within a tree from terrestrial laser scanning (TLS), using ...large oak trees (
Quercus petraea
(Matt.) Liebl.) as the case study. It emphasizes the potential of TLS in assessing branch scaling exponents and provides new insights in forest ecology and biomass allometric modelling.
Context
Many theoretical works invoke the scaling allometry of the frequency distribution of the branch diameters in tree form analyses, but testing such an allometry requires a huge amount of data that is particularly difficult to obtain from traditional measurements.
Aims
The aims of this study were (i) to clarify the theoretical and methodological basics of this allometry, (ii) to explore the possibility of establishing this allometry from terrestrial laser scanning (TLS) and geometric modelling for the solid wood structure (i.e. diameters > 7 cm) of large trees, and (iii) to highlight the major methodological issues.
Methods
Three large oak trees (
Quercus petraea
(Matt.) Liebl.) were digitized in leaf-off conditions from multiple points of view in order to produce accurate three-dimensional point clouds. Their woody structure was modelled using geometric procedures based on polyline and cylinder fitting. The allometry was established using basics found in literature: regular sampling of branch diameters and consideration of the living branches only. The impact of including the unpruned dead branches in the allometry was assessed, as well as the impact of modelling errors for the largest branch diameter classes.
Results
TLS and geometric modelling revealed a scaling exponent of − 2.4 for the frequency distribution of the branch diameters for the solid wood structure of the trees. The dead branches could highly influence the slope of the allometry, making essential their detection in TLS data. The accuracy of diameter measurement for the highest diameter classes required particular attention, slight errors in these classes having a high influence on the slope of the allometry.
Conclusion
These results could make it possible automated programs to process large numbers of trees and, therefore, to provide new insights in assessing forest structure, scaling, and dynamics for various environments in the context of climate change.
► The woody structure of 42 trees was measured using terrestrial laser scanning (TLS). ► TLS data were processed using geometric fitting to extract wood volume information. ► Data processing was ...semi-automated and involved an operator (interactive processing). ► The comparison with destructive measurements shows the accuracy of laser scanning. ► Our modelling protocol performed well regardless of the tree species or size.
This study evaluates the potential of terrestrial laser scanning (TLS) to assess the solid wood volume (i.e., stem and branch diameters of more than 7cm) of adult standing trees in the forest environment. The solid wood volume of 42 trees of different species and size classes was investigated under leafless conditions, both by manual destructive field measurements and by TLS. The trees were first digitised by TLS using a protocol developed to provide fine-scale sampling of trees within acceptable scanning time. TLS data were processed by retro-engineering software using geometric fitting procedures to model tree woody structure and to compute the wood volume. After tree felling, labour-intensive fieldwork was conducted to obtain the solid wood volume of the trees by destructive measurements. The comparison between both methods gave excellent results, regardless of the tree species or size. The relative differences of the TLS estimates remained primarily within a range of ±10% for estimating the volume of the main stem of the trees, and within a range of ±30% for estimating the cumulative branch volumes. Although our semi-automated modelling method makes it possible to overcome the effect of (acceptable) wind, it remains time-consuming and requires further improvement to be used on a large number of trees. However, it demonstrates the appropriateness of laser scanning techniques and simple geometric fitting to characterise the woody structure of a tree in the forest environment and provides new insights for tree growth monitoring, carbon sequestration and bioenergy assessment.
KEY MESSAGE : According to biomechanical processes, tree morphology (trunk inclination, height-to-diameter ratio and crown area) explains statistically silvicultural effects on growth stress ...variation. Growth stresses constitute the main mechanism allowing the tree to control its posture against its mechanical environment, but are also among the most important factors contributing to the depreciation of timber value. This study aimed at assessing the link between stand planting density and growth stress level in European beech (Fagus sylvatica) stands. Beech seedlings were planted in four plots corresponding to four planting densities: 2,500, 5,000, 10,000 and 40,000 stems/ha. They were left to grow for 26 years without any intervention, resulting in trees with highly different morphologies but of the same age and provenance. After 26 years of growth, both the tree morphology and growth stress indicators were measured on the standing trees in each plot and an attempt was made to establish a link between them. Our results showed that initial stand density influences growth stresses of the first order as a result of its impact on tree morphology. The best predictors of high growth stresses were high trunk inclination, high height-to-diameter ratio (slenderness factor) and low crown area. According to mechanosensing theories, these morphological criteria emphasised that growth stresses are due to a global mechanical stimulation rather than to local stem inclination alone. Research now has to be undertaken on new methods that combine the integrative assessment of tree morphology as well as its monitoring over time.
• Premise of the study: Gravitropic movements are unexpected mechanical processes that could disturb tree design allometries derived from the physics of nonliving bodies. We investigated whether the ...scaling law of gravitropic performance (power of −2 of stem diameter) derived from integrative biomechanical modeling is disturbed by ontogeny or environment, then discuss the silvicultural and dendroecological consequences.• Methods: In a beech (Fagus sylvatica) plantation, four plots with different initial planting densities evolved without any intervention for 26 yr. Regular tree inventories and a silvicultural model were used to monitor competition over time in each plot. The radial production of tension wood was quantified using a cross-section of the stems at 1.30-m height, and an integrative biomechanical model computed the tree gravitropic performance over time.• Key results: All trees developed tension wood over the whole period, with higher amounts at the youngest age, resulting in theoretical lean corrections of ca. 20–30° on the first 4 m of the stem over the whole period. The scaling law of gravitropic performance is slightly larger than the power of −2 of stem diameter.• Conclusions: Gravitropic performance in forest ecosystems is mainly limited by size (diameter). Ontogenic acclimation of tension wood formation allows the youngest trees to be more reactive. No additional effect of spacing was found. However, silviculture influences size and, therefore, tree reactivity at a given age. Such results will be helpful for dendroecological approaches that use wood as a marker of environmental disturbances or a trait linked to plant strategies.
Insect pest development is often linearly related to air temperature, without taking into account the multiple interactions between the particular host plant and pest, the microclimatic conditions ...actually experienced by the insect, and the non-linear response of insect development rate to temperature. In this study, using an integrative biophysical model, we have investigated effects of both climatic and tree structure changes on the development of a phytophagous leaf mining moth (Phyllonorycter blancardella), taking into account the heterogeneous microclimatic conditions provided by its host plant, the domestic apple (Malus domestica), the larval body temperature rather than the ambient air temperature, and a non-linear development rate model. Hourly body temperature dynamics of larvae homogeneously dispersed in tree canopies were simulated from hourly meteorological conditions (medium IPCC climate change scenario) within the canopy of apple trees. To analyse the effect of tree architecture on leaf miner development, both pruned and unpruned trees, and one, two and three scaffold branched trees were used. Body temperature dynamics was used to compute larval development time and mortality following the non-linear developmental model for this insect. The results showed that tree pruning influences significantly larval development time and mortality. Nevertheless, the effects of manipulating tree structure on larval development and survival were relatively weak compared with the impact of chosen climate variations. This survey also showed that the variability in insect development time within a year and insect mortality change markedly with climatic variations, and highlights the importance of using non-linear rate curves and insect body temperatures instead of air temperature in forecasting models of climate-related insect pest outbreaks.
La plantation forestière est un outil important pour l’adaptation des forêts aux changements globaux. Les échecs parfois récurrents dans certains contextes, les coûts associés à la plantation, la ...pénibilité du travail pour les ouvriers forestiers ainsi que les impacts environnementaux parfois négatifs sont autant de facteurs qui freinent le recours à la plantation et peuvent ainsi limiter la capacité d’adaptation des forêts. Un ensemble de travaux ont été menés pour répondre aux besoins en innovation technique sur les méthodes de plantation exprimés par les praticiens. Ces travaux portent sur le processus d’innovation en sylviculture et sur l’amélioration technique des méthodes de plantation. L’analyse du processus d’innovation indique une faiblesse des réseaux sociotechniques associée à un mauvais partage des connaissances entre acteurs, et une réticence à l’investissement dans du nouveau matériel, dans un contexte économique perçu comme incertain. Ces observations suggèrent qu’un des leviers possibles serait une meilleure mise en réseau des acteurs, à travers différents liens fonctionnels: partage d’information, échanges de services, construction de partenariats économiques. Des exemples de méthodes innovantes pour réaliser chacune des différentes étapes de l’itinéraire de plantation (préparation du site, plantation, entretiens), répondant aux besoins d’innovation technique exprimés par les praticiens, sont ensuite présentés.
•Terrestrial laser scanning (TLS) used to examine Fagus sylvatica crown characteristics.•Crowns in mixed stands were wider and lower-reaching than those in pure stands.•Magnitude of mixing effect ...increased in the two sites with higher productivity.•Innovative TLS metrics revealed site effects not captured by traditional metrics.
Competition with neighboring trees of different species can affect crown size and shape. However, whether intra-specific differences in crown characteristics in mixed stands compared to pure stands are dependent on site conditions remains poorly understood. We used terrestrial laser scanning (TLS) to examine the differences in Fagus sylvatica crown characteristics at four sites, each of which contained pure stands of F. sylvatica and their mixture with Pinus sylvestris. These sites covered the area where the mixture occurs in Europe from south to north, representing a gradient of F. sylvatica productivity, defined as the mean increment of annual volume growth in pure F. sylvatica stands. Despite the large range in productivity, F. sylvatica trees in mixtures had larger crowns regardless of site conditions, with a higher proportion of their crown volume in the lower canopy compared to trees in pure stands. Larger crown volumes were related to higher live crown ratios and greater crown expansion, depending on the site. The magnitude of the mixing effect was variable among the crown characteristics evaluated, but overall our findings provide evidence that for a given species combination and density, the effect of mixture increased in the two most productive sites. TLS-derived novel crown metrics revealed that the mixing effect was affected by productivity, which was not captured by traditionally measured crown variables.
This study aimed at evaluating alternative methods to ensure regeneration success in temperate low-mountain forest stands by (1) estimating the effects of seed availability, competition from the ...adult stand and from neighbouring vegetation and interaction with the litter layer on seedling density, and by (2) comparing the effects of various silvicultural methods on regeneration success. The experiment was conducted in a monospecific beech (Fagus sylvatica) stand and a mixed silver fir-beech (Abies alba, Fagus sylvatica) stand with contrasted vegetation communities, in north-east France. Different methods of soil preparation, i.e. chemical (herbicide), mechanical (surface hoeing and deep scarification using light-weight machines) and biological (cover crops after surface hoeing) methods, were applied along a canopy opening gradient. After soil preparation (in 2009), vegetation colonisation and tree seedling density were monitored once a year from 2010 to 2013. Results were similar for the two sites. Seedling density the first year indicated a predominant effect of seed availability and soil scarification over potential competitive effects of adult stand and neighbouring vegetation. Despite continuous vegetation colonisation after soil preparation, seedling density remained stable over the 4 years of the experiment. For each of the 4 years, seedling density increased with canopy cover. Seedling density was higher after mechanical soil preparation than after herbicide application. Cover crops (following surface hoeing) appeared as the best method, ensuring both the lowest vegetation colonisation and the highest seedling density.
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