A.R. Proto*
Department of Agriculture, University “Mediterranea” of Reggio Calabria, Reggio Calabria, Italy, andrea.proto@unirc.it
S. Papandrea
Department of Agriculture, University “Mediterranea” of Reggio Calabria, Reggio Calabria, Italy, M.F. Cataldo
Department of Agriculture, University “Mediterranea” of Reggio Calabria, Reggio Calabria, Italy, G. Zimbalatti
Department of Agriculture, University “Mediterranea” of Reggio Calabria, Reggio Calabria, Italy, gzimbalatti@unirc.it
* Corresponding author
Abstract
Sweet chestnut (Castanea sativa Mill.) is one of the most important forest tree species in Europe; it grows commonly in hilly and mountainous areas, where it is traditionally used as timber in construction.
Secondary products are furniture, floorings, windows, external doors, and barrels. In fact, the use of the wood of chestnut tree is potentially unlimited: from the smallest objects up to biggest, and the cultivation and use of chestnut fruit and wood has a long tradition. This wood is appreciated for its durability due to extractives: heartwood shows a pleasant colour and a natural durability against biotic and abiotic agents.
In Italy, the species is currently cultivated for wood production using coppice silvicultural management, in which new trees (shoots) grow from the stumps. One of the main problems, that affect negatively the exploitation of chestnut and decrease the value of its timber, is the risk of ring shake, a defect which occurs as detachment between the annual rings. In certain cases, the frequency of this defect is so high that it causes extended qualitative falloff of the produced timber. Several previous studies have reported the presence of ring shake in sample plots observed immediately after felling and the prediction models for its presence before felling are based related to growth parameters. The aim of this preliminary study is to assess the possibility of ring shake appearance on standing chestnut trees using a tomography approach.
Keywords: standing tree, tomography, sensors, ring shake, non-destructive method
Introduction
Sweet chestnut (Castanea sativa Mill.) is one of the most important forest tree species in Europe; it grows commonly in hilly and mountainous areas, where it is traditionally used as timber in construction.
Secondary products are furniture, floorings, windows, external doors, and barrels. In fact, the use of the wood of chestnut tree is potentially unlimited: from the smallest objects up to biggest, and the cultivation and use of chestnut fruit and wood has a long tradition. This wood is appreciated for its durability due to
extractives: heartwood shows a pleasant colour and a natural durability against biotic and abiotic agents.
In Italy, the species is currently cultivated for wood production using coppice silvicultural management, in which new trees (shoots) grow from the stumps. One of the main problems, that affect negatively the exploitation of chestnut and decrease the value of its timber, is the risk of ring shake, a defect which occurs as detachment between the annual rings. The study of the internal state of this species have a long tradition in Italy (Romagnoli and Spina 2013), as in Europe, due to the high merchantable value of his wood products. The defect of ring shake occurrence greatly reduces the value of the timber assortment and in the worst case, the incidence of ring shake is so high that only few logs of a stand can be brought to the sawmill (Fonti et al. 2002). In certain cases, the frequency of this defect is so high that it causes extended qualitative falloff of the produced timber. Several previous studies have reported the presence of ring shake in sample plots observed immediately after felling and the prediction models for its presence before felling are based related to growth parameters. The aim of this preliminary study is to assess the possibility of ring shake appearance on standing chestnut trees using a tomography approach. Assessing wood quality inn standing trees has been a long – time interest to wood products manufactures end forest managers worldwide. A significant effort has been devoted to develop to develop robust NDT
technologies that are capable of predicting intrinsic wood proprieties of individual trees and assessing wood quality by stands and forest (Wang et al. 2007; Brashaw et al. 2009, Divos 2010; Proto et al. 2017).
The research started four years ago and was funded by the Ministry of Education, University and Research-MIUR, under the National Operative Programme (PON) Research and Competitiveness 2007-2013, to support development and innovation in forestry and wood industry, in Calabrian region by the Mediterranean University with private companies working in the field of wood, computer science and remote sensing. One of the most important object has been to assess the wood quality using NDT methods in the principal’s forestry area of the Calabria region to obtain a correct economic value of Calabrian wood (Proto et al. 2014; Proto et al. 2015). This study present a preliminary examination of the applicability of sonic tomography for evaluate the chestnut wood in standing trees.
Material and Methods
Study sites and tree samples
The test site was situated in Southern Italy (Calabria Region) in the Serre Massif. The study area covering a total area of 5 hectares with an altitude ranged of 610 and 680 m (Table 1). The site study was coppiced with first class standards which derive from coppice shoots growing from the previous cut. The age of the shoots ranged was 12 years, whereas those of the standards were 24 (II cycle) and 36 (III cycle) years.
The breast height (DBH) was measured by using a classic diameter caliper and tree height with a vertex IV hypsometer. Thirty chestnut standards, with a regular cross-section, were randomly selected and each tree was marked and assigned a tracking number, useful to conduct the tomographic study and the subsequent felling phase. The choice of this population was dictated not only by the characteristics favorable to a silviculture of a productive type, but also by the assured presence of ring shake in the trees, identified through a historical inquiry among the local users (Macchioni and Pividori 1996). The main characteristics of the study site are shown in the Table 1. At the conclusion of acoustic measurements, the trees were subsequently harvested by a local company and cross-sectioned in correspondence of acoustic tests and a disk 5-cm thick was collected from each stem and taken to a laboratory where the ring shake characteristics were measured. In particular, ring shake position and the extent of the defect were measured for each wood disk defected.
Field Acoustic Tomography Test and Data analysis
All 30 standards were first nondestructively tested using a commercial ArborSonic 3D acoustic
tomograph device (Fakopp Enterprise Ltd., Hungary). Each monitored tree had regular form of the stem
and then the position of sensor was calculated dividing the circumference with the number of the sensors applied (Figure 1a). At height of 50 cm, the circumference and distances between sensors were measured using a tape measure and this data were used to map the approximate geometric form of the cross-section.
During testing, each position of sensors was marked so that they could be traced back to the original location in the stem disk in order to assess the actual condition of the wood at the area of sampling.
After the test, the velocity of acoustic wave transmission measured from each chestnut trees was finding, studied and used to predict the ring shake presence respect the typical application of tomograms for detect cavity or decay. The comparison between the paths of stress wave measurements on one cross section (sound wood vs. defect wood) was used to determine and localize the area affect by ring shake. Using tomographic technique, a complete data matrix was obtained through measurement of stress wave transmission time and in Figure 1b.
Table 1 - Study area characteristics and dendrometric parameters Parameters Unit Measure Value
Altitude – Range a.s.l. m 610 - 680
Slope - Range % 15 - 20
Average Basal area for tree m2 0.102
Average Basal area for hectare m2 ha-1 26.14
Volume for hectare m3 ha-1 214.15
Coppice shoots diameter cm 20.12
Standard diameter cm 33.03
Number of stump n ha-1 370
Shoots – number of tree n ha-1 1720
Standards – number of tree n ha-1 65
Figure 1 - Acoustic tomography test on standing tree (a) and stress wave propagation paths (b)