Arboriculture & Urban Forestry 45(1): January 2019 5 Figure 5. Representative graph of the average values and the variability of amplitude obtained in the different zones of the discs in different species. Figure 4. Superposition of the amplitude graph of drilling resistance to the photographic image obtained from the disc, in the position of the needle passage of the resistograph. Species: Liquidambar styraciflua. from 0% to 25% in zones with different levels of wood degradation. In this research, in the species for which it was possible to define the heartwood and sapwood regions, there was amplitude variation (Figure 3). In the two species for which it was not possible to visu- alize the distinction between heartwood and sapwood (Tabebuia ochracea and Liquidambar styraciflua), the amplitude of the drilling-resistance graph also does not show variations (Figure 4). Similar graphs, without heartwood and sapwood visual distinction, were obtained by Kubus (2009). In the heartwood, the values of amplitudes were higher than those obtained in the sapwood. For the four species for which it was possible to define the heartwood and sapwood regions (Figure 2), this result was statistically demonstrated (Figure 5). The analy- sis of variance showed that amplitudes were always lower in deteriorated regions (with or without voids), Table 3. Average drilling resistance amplitude by species and Multiple Range Test for analyzing statistical differences. Species Platanus spp. Caesalpinia pluviosa Centrolobium sp. Copaifera sp. Sapwood 23.3 (a) 14.0 (b) 10.4 (bc) 8.1 (c) Heartwood 32.9 (a) 29.8 (a) 15.3 (b) 13.8 (b) Note: Different letters indicate statistically significant differences at the 95.0% confidence level. but always higher in the heartwood regions and in sapwood and bark intermediate regions (Figure 5). Considering only the heartwood and sapwood regions without apparent deterioration, there was a differentiation between species. For sapwood, the amplitudes of drilling resistance were higher and sta- tistically different for Platanus spp. and statistically equivalent for the other species (Table 3). For heart- wood, the amplitudes of drilling resistance were also higher for Platanus spp., but statistically equivalent for Caesalpinia pluviosa, and smaller for the other two species (Table 3). This result is not expected, since Platanus spp. has the lowest density (Table 2) and the drilling resistance, in general, has a positive correlation with density (Costelo and Quarles 1999; Couto et al. 2013). However, it is noteworthy that the amplitude of drilling resistance in this device type is affected by the selected advance velocity, which for Platanus spp. was higher (Table 2), and that in order to properly interpret and compare amplitude results obtained in the resistance test, it was necessary to know, in advance, the profiles obtained in the whole condition (Martinez 2016; Matheny et al. 1999). This is different from resistance drills automatically adopt- ing the speed to the wood, as tested by Brashaw (2013), and resulting in a high correlation to wood density (R2 > 0.9), because a high correlation to wood density is necessary to allow for reliable evaluations of the profiles concerning the wood condition. For Tabebuia ochracea, which sustained a beetle insect attack (Figure 2), the amplitude of drilling resis- tance did not show variations that allowed, in an inspec- tion, researchers to visualize the wood state (Figure 6). ©2019 International Society of Arboriculture
January 2019
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