# Characterisation of Pinus canariensis C.Sm. ex DC. Sawn Timber from Reforested Trees on the Island of Tenerife, Spain

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

^{−3}), modulus of elasticity (MOE) (14,023–11,276 N∙mm

^{−2}) and bending strength (MOR) (26–14 N∙mm

^{−2}) were determined for both grades (ME-1 and ME-2), strength class C24 was assigned to grade ME-1, with similar values to Pinus radiata D.Don and Pinus pinaster Aiton, and C14 was assigned to grade ME-2. Density, number of growth rings, growth ring width, and presence/absence of resinous wood have a significant influence on MOE and MOR, for a confidence level of 95%. Reforestation of Canary Island pine not only allows restoration of the forest cover, but also provides an opportunity, through thinning, to obtain quality wood, helping to create employment and associated industry. This local example with an endemic species can be extrapolated to other parts of the world.

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Sample Collection and Preparation

^{3}, with 122 corresponding to first logs and 141 to second logs. Samples were marked with numbers 1 and 2 in the forest according to their position in the log and this code was maintained until sample preparation. According to EN 384 standard [9], sample is defined as a number of ungraded specimens of one timber species or species combination, one source, with sizes and quality representative of the timber population, and sub-sample is defined as part of one or more samples consisting of specimens of one grade.

#### 2.2. Visual Strength Grading

#### 2.3. Physical and Mechanical Properties

#### 2.4. Reference Conditions and Adjustment Factors

_{0}: modulus of elasticity in the bending parallel to grain;

_{ref}: reference moisture content (12%).

^{−3}or less, bending strengths must be divided by correction factor k

_{h}(Equation (3)).

_{0}: modulus of elasticity in the bending parallel to grain (free of the shear effect);

_{m,global(uref)}: global modulus of elasticity.

#### 2.5. Characteristic Values

_{05,i}and the 5-percentile value of density ρ

_{05,i}were obtained, following standard EN 14358 [15]. The mean value of modulus of elasticity ${\stackrel{\_}{\mathrm{E}}}_{\mathrm{i}}$ of each subsample was obtained using the same standard.

_{k}: characteristic value of strength (5-percentile);

_{0,mean}: mean characteristic modulus of elasticity (50-percentile);

_{k}: characteristic density (5-percentile);

_{05,i}: 5-percentile value of strength of sub-sample i;

_{05,i,min}: lowest 5-percentile value of strength of i-sub-samples;

_{05,i}: 5-percentile value of density of sub-sample i;

_{05,i,min}: lowest mean value of 5-percentile value of density of i-sub-samples;

_{s}: number of sub-samples;

_{i}: number of test pieces of sub-sample i;

_{n}: adjustment factor obtained by number of sub-samples (Table 2).

#### 2.6. Data Analysis

## 3. Results

#### 3.1. Visual Strength Grading and Characteristic Values

#### 3.2. Density, Number of Growth Rings, Growth Ring Width and Presence of Resinous Wood

#### 3.3. Influence of the Variables on MOR and MOE

## 4. Discussion

^{−2}, a density of 290 kg∙m

^{−3}and a mean value of modulus of elasticity of 7.0 kN∙mm

^{−2}, while grade C24 corresponds to a 5-percentile bending strength of 24 N∙mm

^{−2}, a density of 350 kg∙m

^{−3}and a mean value of modulus of elasticity of 11 kN∙mm

^{−2}.

^{−3}and 452.8 kg∙m

^{−3}) and modulus of elasticity (14,022.7 N∙mm

^{−2}and 11,275.6 N∙mm

^{−2}) also exceed the requirements of grade C27, the values of bending strength (26.4 N∙mm

^{−2}and 14.1 N∙mm

^{−2}) do not (Table 3 and Table 4).

^{−2}and 478.8 kg∙m

^{−3}) and the 5-percentile values (37.7 N∙mm

^{−2}and 544.1 kg∙m

^{−3}) of visual grade ME-1 (Table 3) and the characteristic values (14.1 N∙mm

^{−2}and 452.8 kg∙m

^{−3}) and the 5-percentile values (20.2 N∙mm

^{−2}and 514.5 kg∙m

^{−3}) of visual grade ME-2 (Table 4) is due to the penalisation imposed by EN 384 [9] when only one sub-sample is used. Standard EN 384 [9] penalises density and bending strength with a factor to adjust for the number of subsamples k

_{n}of 0.88 and 0.70, respectively. As a result, wood in visual grades ME-1 and ME-2 cannot be assigned to a class higher than C24 or C14, respectively.

## 5. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Distribution of pine forests on the island of Tenerife. Based on a map from Área de Sostenibilidad, Medio Ambiente, Aguas y Seguridad, Cabildo de Tenerife.

**Figure 2.**(

**a**–

**c**) Constructions made from Canary Island pine wood in the municipality of La Orotava (Tenerife). Casa de Los Balcones, 17th century. (

**a**) Wooden ceiling structure; (

**b**) exterior carpentry and wooden balcony; (

**c**) typical wooden balconies; (

**d**) Canary Island pine wounded to obtain pitch for caulking ships and subsequently affected by fire; (

**e**) Icod Pine Forest, 1951 (Fototeca Forestal Española DGB-INIA (Ref. 418) [6]); (

**f**) Icod Pine Forest, 2019 (Photo by Javier León); (

**g**) plantations in Mount Teide forest, 1951 (Montse Quintero photographic archive).

**Figure 3.**Sample collection. (

**a**) Canary Island pine forest on the north slope; (

**b**) plantation thinning tasks; (

**c**) plantation with and without thinning; (

**d**) boles in the sawmill yard; (

**e**) sawing boles; (

**f**) stacks of sawn timber from log 2.

**Figure 4.**Bending test. (

**a**) Diagram of EN 408 test [14] to determine modulus of elasticity (F: load applied, h: depth of cross-section, w: deformation); (

**b**) piece under load.

**Figure 5.**Distribution histograms of (

**a**) density, (

**b**) number of growth rings and (

**c**) growth ring width.

**Figure 6.**Least significant difference (LSD) diagrams of the influence of presence/absence of resinous wood on (

**a**) MOR (Grade ME-2) and (

**b**) MOE (Grade ME-2).

**Table 1.**Visual grading specifications from Spanish standard UNE 56544 [7] for coniferous sawn timber of a rectangular cross-section and a width b ≤ 70 mm.

SPECIFICATIONS | ME-1 | ME-2 | |
---|---|---|---|

FACE KNOT DIAMETER (h) | d ≤ 1/5 “h” | d ≤ 1/2 “h” | |

EDGE KNOT DIAMETER (b) | d ≤ 1/2 “b” and d ≤ 30 mm | d ≤ 2/3 “b” | |

MAXIMUM GROWTH RING WIDTH ^{(1)} | |||

Scots pine | ≤4 mm | No limit | |

Salzmann pine | ≤5 mm | No limit | |

Maritime pine | ≤8 mm | No limit | |

Radiata pine | ≤10 mm | No limit | |

FISSURES | Drying cracks ^{(2),(3)} | f ≤ 2/5 | f ≤ 3/5 |

Drying cracks are considered only if their length exceeds ¼ of the length of the piece or 1 m, whichever is shorter. | |||

Lightning shakes | Not permitted | ||

Frost shakes | Not permitted | ||

Felling shakes | Not permitted | ||

RING SHAKES | Not permitted | ||

RESIN AND BARK POCKETS | Permitted if length is ≤1.5·“h” | ||

COMPRESSION WOOD | Permitted in 1/5 of cross-section or external surface of the piece | Permitted in 2/5 of cross-section or external surface of the piece | |

SLOPE OF GRAIN | 1:10 (10%) | 1:6 (16.7%) | |

WANE | Length | ≤1/4 “L” | ≤1/3 “L” |

Width and thickness | g ≤ 1/4 | g ≤ 1/3 | |

PITH ^{(1)} | Permitted Not permitted if wet graded | Permitted | |

BIOLOGICAL DAMAGE | Mistletoe (Viscum album L.) | Not permitted | |

Blue stain | Permitted | ||

Rot | Not permitted | ||

Xylophagous insect tunnels | Not permitted | ||

MAXIMUM DISTORTIONS ^{(2)(3)(4)} | Bow | 10 mm (over a length of 2 m) | 20 mm (over a length of 2 m) |

Spring | 8 mm (over a length of 2 m) | 12 mm (over a length of 2 m) | |

Twist | 1 mm (for every 25 mm “h”) (over a length of 2 m) | 2 mm (for every 25 mm “h”) (over a length of 2 m) | |

Cup | No limit | No limit |

^{(1)}Applicable only when timber is sold wet;

^{(2)}not applicable to wet grading;

^{(3)}in reference to 20% moisture content;

^{(4)}larger distortions can be accepted provided they do not affect the stability of the construction (because they can be corrected during erection) and the supplier and the client have an express agreement to that effect. Scots pine—Pinus sylvestris L.; Salzmann pine—Pinus nigra Arnold ssp. salzmannii (Dunal) Franco; Maritime pine—Pinus pinaster Aiton; Radiata pine—Pinus radiata D.Don. Symbols—f: fissure depth; L: piece length; g: wane dimension in width or thickness; h test piece depth in mm.

Number of Sub-Samples | 1 | 2 | 3 | 4 | ≥5 |
---|---|---|---|---|---|

k_{n} for modulus of elasticity and density | 0.88 | 0.91 | 0.94 | 0.97 | 1.00 |

k_{n} for strength parallel to grain | 0.70 | 0.80 | 0.90 | 0.95 | 1.00 |

**Table 3.**Results of properties corresponding to grade ME-1. f

_{m}: bending strength; ρ: density; E

_{0}: modulus of elasticity in the bending parallel to grain.

ME-1 | No. Data | 48 | |
---|---|---|---|

Moisture Content (%) | 12.1 | ||

f_{m} (N∙mm^{−2}) | ρ (kg∙m^{−3}) | E_{0} (N∙mm^{−2}) | |

Mean | 70.6 | 627.1 | 15,138.1 |

Standard deviation | 20.3 | 51.4 | 3947.6 |

Maximum | 121.9 | 723.2 | 21,657.6 |

Minimum | 20.1 | 506.9 | 1843.8 |

Coefficient of variation (%) | 28.8 | 8.2 | 26.1 |

5-percentile value | 37.7 | 544.1 | - |

Characteristic value | 26.4 | 478.8 | 14,022.7 |

**Table 4.**Results of properties corresponding to grade ME-2. f

_{m}: bending strength; ρ: density; E

_{0}: modulus of elasticity in the bending parallel to grain.

ME-2 | No. Data | 824 | |
---|---|---|---|

Moisture Content (%) | 12.0 | ||

f_{m} (N∙mm^{−2}) | ρ (kg∙m^{−3}) | E_{0} (N∙mm^{−2}) | |

Mean | 47.3 | 588.5 | 12,172.5 |

Standard deviation | 19.1 | 53.1 | 3480.1 |

Maximum | 108.4 | 919.5 | 23,588.5 |

Minimum | 11.9 | 245.8 | 1517.1 |

Coefficient of variation (%) | 40.3 | 9.0 | 28.6 |

5-percentile value | 20.2 | 514.5 | - |

Characteristic value | 14.1 | 452.8 | 11,275.6 |

**Table 5.**Density, number of growth rings, growth ring width and pieces with resinous wood by visual grade.

ME-1 | ME-2 | ||
---|---|---|---|

Density (kg∙m^{−3}) | Mean | 627.1 | 588.5 |

Standard deviation | 51.4 | 53.1 | |

Maximum | 723.2 | 919.5 | |

Minimum | 506.9 | 245.8 | |

Number of growth rings | Mean | 12 | 10 |

Standard deviation | 2.8 | 3.1 | |

Maximum | 19 | 26 | |

Minimum | 7 | 5 | |

Growth ring width (mm) | Mean | 3.70 | 4.41 |

Standard deviation | 0.77 | 1.23 | |

Maximum | 5.13 | 7.91 | |

Minimum | 1.08 | 1.72 | |

Resinous wood | Presence | - | 160 |

Absence | 48 | 664 |

**Table 6.**Analysis of variance and correlation between density, number of growth rings, growth ring width and presence of resinous wood; and properties of bending strength (MOR) and modulus of elasticity (MOE), grouping grades ME-1 and ME-2.

Property | Variable | p-Value | Equation | R | R^{2} |
---|---|---|---|---|---|

MOR | Density | 6.40 × 10^{−6} | $MOR=-11.43+0.1\times \rho $ | 0.27 | 0.07 |

Number of growth rings | 2.98 × 10^{−24} | - | - | - | |

Growth ring width | 2.58 × 10^{−4} | $MOR=74.39-5.85\times width$ | −0.37 | 0.14 | |

Presence of resinous wood | 1.83 × 10^{−6} | - | - | - | |

MOE | Density | 5.53 × 10^{−27} | $MOE=-1087.15+22.62\times \rho $ | 0.34 | 0.12 |

Number of growth rings | 6.25 × 10^{−13} | - | - | - | |

Growth ring width | 7.80 × 10^{−5} | $MOR=\text{18,691.6}-1439.94\times width$ | −0.51 | 0.26 | |

Presence of resinous wood | 9.23 × 10^{−15} | - | - | - |

Class | Canary Island Pine | Salzmann Pine | Scots Pine | Radiata Pine | Maritime Pine |
---|---|---|---|---|---|

ME-1 | C24 | C30 | C27 | C24 | C24 |

ME-2 | C14 | C18 |

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**MDPI and ACS Style**

Esteban, L.G.; de Palacios, P.; García Fernández, F.; García-Iruela, A.; del Pozo, J.C.; Pérez Borrego, V.; Agulló Pérez, J.; Padrón Cedrés, E.; Arriaga, F. Characterisation of *Pinus canariensis* C.Sm. ex DC. Sawn Timber from Reforested Trees on the Island of Tenerife, Spain. *Forests* **2020**, *11*, 769.
https://doi.org/10.3390/f11070769

**AMA Style**

Esteban LG, de Palacios P, García Fernández F, García-Iruela A, del Pozo JC, Pérez Borrego V, Agulló Pérez J, Padrón Cedrés E, Arriaga F. Characterisation of *Pinus canariensis* C.Sm. ex DC. Sawn Timber from Reforested Trees on the Island of Tenerife, Spain. *Forests*. 2020; 11(7):769.
https://doi.org/10.3390/f11070769

**Chicago/Turabian Style**

Esteban, Luis García, Paloma de Palacios, Francisco García Fernández, Alberto García-Iruela, Juan Carlos del Pozo, Víctor Pérez Borrego, Juan Agulló Pérez, Eva Padrón Cedrés, and Francisco Arriaga. 2020. "Characterisation of *Pinus canariensis* C.Sm. ex DC. Sawn Timber from Reforested Trees on the Island of Tenerife, Spain" *Forests* 11, no. 7: 769.
https://doi.org/10.3390/f11070769