# Linking Dendrometry and Dendrochronology in the Dominant Azorean Tree Laurus azorica (Seub.) Franco

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

^{−1}. Given the known dominance of this species and the threats affecting natural forests, this baseline study will allow a better understanding of forest distribution and dynamics, and support a more effective forest management approach.

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Study Area

^{2}, a coastline length with 213 km and the highest peak at 1105 m [31].

^{2}that correspond to the total land area in the Azores, about 43% is now dominated by pastures, planted or exotic forests (22%), with natural vegetation occupying about 13% [33,34]. Table 1 includes a climatic characterization and the type of soil at each of the study sites.

#### 2.2. Target Species

#### 2.3. Stand Characterization

#### 2.4. Field Sampling

^{®}, Deltalab S.L., Barcelona, Spain, tubes to the lab.

#### 2.5. Wood Sample Preparation for Macroscopic Analysis

#### 2.6. Wood Sample Preparation for Microscopic Analysis

^{TM}Thermo Fisher Scientific and paraffin infiltration were performed in an automatic tissue processor. After that, microcore samples were paraffin blocked, and trimmed for section cutting. In a rotary microtome, sections with a thickness of 8 µm were prepared, transferred to Glycerin-Albumin Sigma-Aldrich Corporation, St. Louis, MO, USA coated slides, and stored at 37 °C overnight. Two sets of histological slides were prepared for two distinct staining methods. Paraffin was removed using D-limonene and rehydration was performed with alcohol solutions CHEM-LAB, Zedelgem, Belgium with decreasing concentration. The first set of slides was stained with Toluidine Blue Sigma-Aldrich Corporation, St. Louis, MO, USA and the second set was stained with a water solution of 100 mL demineralized water, Astrablue (150 mg), Santa Cruz Biotechnology, Dallas, TX, USA safranin (40 mg) CHEM-LAB, Zedelgem, Belgium and 2 mL acetic acid CHEM-LAB, Zedelgem, Belgium (adapted from [52]). Sections were then dehydrated and mounted in DPX (Distrene Plasticizer Xylendene The samples were observed under a light microscope LEICA DM1000 Leica Microsystems Inc., Buffalo Grove, IL, USA, associated to CoolSnap-Pro, Media Cybernetics and images taken using Image Pro-Plus 5.0. software.

#### 2.7. Statistical Analyses

#### 2.7.1. Dendrometric Traits

#### 2.7.2. Annual Increment

#### 2.7.3. Relationship between Tree Age and Dendrometric Traits

## 3. Results

#### 3.1. Tree Ring Structure

#### 3.2. Dendrometric Traits

^{2}= 109.027, df = 5, p < 0.001) trunk diameter (K-W test, χ

^{2}= 88.102, df = 5, p < 0.001), and tree age (K-W test, χ

^{2}= 95.774, df = 5, p < 0.001), forming three homogeneous groups (results of a multiple comparison test, with p > 0.05 within each group): (i) Povoação; (ii) Sete Cidades, Lombadas and Pinhal da Paz; and (iii) Achada das Furnas and Tronqueira. As expected, there were significant differences between samples at the base of the tree or at breast height, both for trunk diameter (M-W test, U = 5574.0, p < 0.001, mean rank base = 150.90, mean rank breast = 113.17) and tree age (M-W test, U = 5579.5, p < 0.001, mean rank base = 148.93, mean rank breast = 114.52). As expected, there were significant differences between the three defined diameter classes both for tree height (K-W test, χ

^{2}= 78.147, df = 2, p < 0.001) and tree age (K-W test, χ

^{2}= 64.779, df = 2, p < 0.001), with significant differences among the three classes for both parameters (all p values from the multiple comparison tests <0.05).

#### 3.3. Tree Age and Dendrometric Traits

^{2}value, particularly for Pinhal da Paz. Dendrometric parameters also showed a better predictive ability to estimate tree age for several stands when outliers were removed from the data set, namely for Lombadas, Achada das Furnas and Tronqueira (a selection of models is shown in Table 2 and Figure 9). The full set of tested models for each stand, and with or without outliers are shown in Tables S2–S7.

#### 3.4. Estimated Annual Increment

^{−1}, and with a concentration of values between 0.300 and 0.833 cm·year

^{−1}(Table 3).

## 4. Discussion

#### 4.1. Laurel Forest in São Miguel Island

#### 4.2. Growth Ring Anatomy

#### 4.3. Dendrometry and Dendrochronology

^{−1}, with an estimated average of 5 years to reach breast height. A higher growth rate than the values reported for the widespread invasive species P. undulatum, with a radial growth rate of 0.38 cm·year

^{−1}, and an average of 8 years needed to attain breast height [2,4]. Therefore, other factors might be affecting growth and dispersal of those species, and a local comparison of growth rates would be needed, if the invasion process is to be better understood, since growth rate can provide a general representation of the growth dynamics at certain conditions (climate, hydrology, soil, and successional stages) [78]. These analyses are essential to support the sustainable management and conservation of natural forests [78].

## 5. Conclusions

## Supplementary Materials

_{0}); Adjusted determination coefficient (Adj R

^{2}); Akaike Information Criterion (AIC); Root Mean Square Error (RMSE); Mean Relative Error (MRE), Correction Factor (CF). Diameter (D); Tree Height (H); Basal Area (BA); Table S2: Allometric equations tested for 25 Laurus azorica (Seub.) Franco trees (ALL) and for 19 samples (without outliers, WO) of Laurus azorica trees from Lombadas, São Miguel Island. Allometric models: * [54]; ** [2]; *** Current study. Regression model equations; Null Model (M

_{0}); Adjusted determination coefficient (Adj R

^{2}); Akaike Information Criterion (AIC); Root Mean Square Error (RMSE); Mean Relative Error (MRE), Correction Factor (CF). Diameter (D); Tree Height (H); Basal Area (BA); Table S3: Allometric equations tested for 20 Laurus azorica (Seub.) Franco trees (ALL) and for 16 samples (without outliers, WO) of Laurus azorica trees from Achada das Furnas, São Miguel Island. Allometric models: * [54]; ** [2]; *** Current study. Regression model equations; Null Model (M

_{0}); Adjusted determination coefficient (Adj R

^{2}); Akaike Information Criterion (AIC); Root Mean Square Error (RMSE); Mean Relative Error (MRE), Correction Factor (CF). Diameter (D); Tree Height (H); Basal Area (BA); Table S4: Allometric equations tested for 49 Laurus azorica (Seub.) Franco trees from Pinhal da Paz, São Miguel Island. Allometric models: * [54]; ** [2]; *** Current study. Regression model equations; Null Model (M

_{0}); Adjusted determination coefficient (Adj R

^{2}); Akaike Information Criterion (AIC); Root Mean Square Error (RMSE); Mean Relative Error (MRE), Correction Factor (CF). Diameter (D); Tree Height (H); Basal Area (BA); Table S5: Allometric equations tested for 49 Laurus azorica (Seub.) Franco trees from Sete Cidades, São Miguel Island. Allometric models: * [54]; ** [2]; *** Current study. Regression model equations; Null Model (M

_{0}); Adjusted determination coefficient (Adj R

^{2}); Akaike Information Criterion (AIC); Root Mean Square Error (RMSE); Mean Relative Error (MRE), Correction Factor (CF). Diameter (D); Tree height (H); Basal area (BA); Table S6: Allometric equations tested for 48 Laurus azorica (Seub.) Franco trees (ALL) and for 33 samples (without outliers, WO) of Laurus azorica trees from Tronqueira, São Miguel Island. Allometric models: * [54]; ** [2]; *** Current study. Regression model equations; Null Model (M

_{0}); Adjusted determination coefficient (Adj R

^{2}); Akaike Information Criterion (AIC); Root Mean Square Error (RMSE); Mean Relative Error (MRE), Correction Factor (CF). Diameter (D); Tree Height (H); Basal Area (BA); Table S7: Allometric equations tested for 47 Laurus azorica (Seub.) Franco trees from Povoação stand, São Miguel Island. Allometric models: * [54]; ** [2]; *** Current study. Regression model equations; Null Model (M

_{0}); Adjusted determination coefficient (Adj R

^{2}); Akaike Information Criterion (AIC); Root Mean Square Error (RMSE); Mean Relative Error (MRE), Correction Factor (CF). Diameter (D); Tree Height (H); Basal Area (BA).

## Author Contributions

## Funding

^{2}-Towards an Ecological and economic valorization of the Azorean Forest ACORES-01-0145-FEDER-000014-Azores 2020 PO, 2016–2019; FEDER funds through the Operational Programme for Competitiveness Factors-COMPETE and by National Funds through FCT-Foundation for Science and Technology under the UID/BIA/50027/2019 and POCI-01-0145-FEDER-006821; DRCT-M1.1.a/005/Funcionamento-C-/2019 (CIBIO-A), Secretaria Regional do Mar, Ciência e Tecnologia, Governo dos Açores; and by MC-Apoio à edição de publicações científicas 2019 PRO-SCIENTIA-Eixo 3-QUALIFICAR-Ação/Medida 3.3. b-“Incentivar a produção, formação e divulgação científica especializada”-Apoio à edição de publicações científicas (03.3.c.2019 (SRMCT/DRCT), Governo Regional dos Açores).

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Distribution of the six selected stands of natural vegetation in São Miguel Island. From left to right: Sete Cidades; Pinhal da Paz; Lombadas; Achada das Furnas; Povoação; Tronqueira. In the map, natural vegetation is not entirely forest.

**Figure 2.**Macroscopic view of L. azorica (Seub.) Francostem disc (

**a**) and of increment cores (

**b**,

**c**,

**d**) taken in São Miguel Island. (

**a**) Pith, distinct tree rings with latewood (lw) and earlywood (ew), and bark. (

**b**) Example of some of the anomalies found in increment cores. (

**c**) Younger tree rings close to cambium, phloem (lighter, ph), ray dispersion (darker, rd) and cork (ck). (

**d**) Tree rings with distinct ring boundaries, and different coloration of early (ew) and latewood (lw), with vessels equally distributed along the ring. Scale bar 1 mm.

**Figure 3.**Cross-section view of L. azorica (Seub.) Franco tree rings under light microscope: First row: (

**a**) General view of growth rings (gr) with thick-wall fibrous boundaries (fb), earlywood (ew) and latewood (lw), xylem rays and vessels with equal size and distribution along annual ring (scale bar 200 μm); (

**b**) Growth ring boundary (fb), paratracheal parenchyma cells around vessels (pp), multiseriate rays (mr), solitary vessels (sv), clustered vessels (cv) and reddish cells (rc) (scale bar 50 μm); and (

**c**) Unlignified tylosis (ty) (scale bar 25 μm). Second row: (

**d**,

**e**), cross section view of bark with phloem wood: (

**d**) Simple construction of phloem, with phloem elements difficult to distinguish but differentiated from ray dilatation (scale bar 150 μm); (

**e**) Bark layers. rd—ray dilatation; ph—phloem; ck—cork layers; bk—bark (scale bar 200 μm); (

**f**) Cross-section of cambial zone from L. azorica, cambium is crossed by xylem rays that dilate in phloem to the bark. xy—xylem; ca—cambium; ph—phloem; rd—ray dilatation (scale bar 200 μm).

**Figure 4.**Tangential section from L. azorica (Seub.) Franco secondary xylem. (

**A**) General view including xylem vessels (v) and multiseriate rays (scale bar 150 μm). (

**B**) A more detailed view showing a closer perspective of multiseriate rays (mr) and the presence of intervessel pits (p) (scale bar 50 μm).

**Figure 5.**The estimated distribution of trunk diameter (

**A**), tree age (

**B**), and maximum height (

**C**), of the 256 L. azorica (Seub.) Franco samples measured in São Miguel Island.

**Figure 6.**First row: Distribution of tree height (

**a**), trunk diameter (

**b**) and tree age (

**c**) for each sampled stand in São Miguel Island. Second Row: Distribution of tree height (

**d**) and estimated tree ages (

**e**) by diameter class (<10, 10–20, >20 cm). From a total of 256 samples of L. azorica (Seub.) Franco collected in São Miguel Island, collected at breast height (130 cm above substrate) or at tree base (20 cm above substrate). In the boxplots, circles represent outliers.

**Figure 7.**Distribution of the cambial age of L. azorica (Seub.) Franco trees obtained at six sites in São Miguel Island. The chart allows to appreciate the age and size structure of the different populations. Diameter classes (cm): (1, <10; 2, 10–20; 3, >20 cm).

**Figure 8.**Scatter plots representing the relationship between estimated tree age and trunk diameter at base and at breast height, for six stands of L. azorica (Seub.) Franco in São Miguel Island.

**Figure 9.**Scatter plots of the allometric equations used to predict L. azorica (Seub.) Franco age from dendrometric traits (BA, Basal Area; D, Diameter at Breast Heigth; H, Maximun Tree Height) Comparison of models for all the available samples at breast height, (

**plot 1**, as defined in Table 2), at tree base (

**plot 2**, as defined in Table 2) and for each stand (

**plots 3**–

**8**, as defined in Table 2). This is a selection of the best models. See Table 2 and Tables S1–S7 for the full set of tested models.

**Table 1.**Characterization of the sampling stands of Laurus azorica (Seub.) Franco trees in São Miguel Island. Elevation (E, m), number of trees (N), number of cores at breast or at the base (CB, CA), Annual Mean Temperature (MT, °C), Maximum Temperature of the Warmest Month (TW, °C), Minimum Temperature of the Coldest Month (TC, °C), Annual Temperature Range (TR, °C), Annual Precipitation (AP, mm), Precipitation of the Wettest Quarter (PW, mm), Precipitation of the Driest Quarter (PD, mm). Soil Types: Ins—Insaturated; Ferr—Ferruginous; Shal Aloph—Shallow Alophanic soil; Reg—Regosoil. Climatic data from Karger et al. [35] and Soil data from Ricardo et al. [36]. Native and exotic species as mentioned in the text.

Stands | Code | E (m) | Sampling | Physical Description | Main Species | Other Information | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

N | CB | CA | MT | TW | TC | TR | AP | PW | PD | Soil Type | Native | Exotic | Protection | ||||

Lombadas | LO | 569 | 25 | 25 | 0 | 14 | 22 | 7 | 15 | 1684 | 641 | 167 | Ins And | L. azorica, I. azorica, M. faya | P. undulatum, H. gardnerianum | Habitat/Species Management Area | |

Achada das Furnas | AF | 600 | 20 | 20 | 0 | 13 | 22 | 7 | 15 | 2108 | 789 | 221 | Shal Aloph Ins/Ferr And | L. azorica, I. azorica | C. arborea, P. undulatum, H. gardnerianum | Unprotected | |

Pinhal da Paz | PP | 322 | 25 | 31 | 29 | 15 | 23 | 8 | 15 | 1294 | 494 | 133 | Shal Aloph Reg | L. azorica, M. faya | P. undulatum, H. gardnerianum | Recreational Forest Reserve | |

Sete Cidades | SC | 599 | 25 | 29 | 28 | 13 | 22 | 7 | 15 | 1850 | 698 | 195 | Ins And | L. azorica, I. azorica, M. faya | C. japonica, P. undulatum, H. gardnerianum | Protected Landscape | |

Tonqueira | TR | 629 | 25 | 25 | 25 | 13 | 22 | 6 | 15 | 2092 | 816 | 199 | Shal Aloph Ins/Ferr And | L. azorica, I. azorica, M. faya, J. brevifolia | C. arborea, H. gardnerianum | Habitat/Species Management Area | |

Povoação | PO | 541 | 25 | 25 | 25 | 14 | 23 | 7 | 15 | 1557 | 596 | 152 | Shal Aloph Ins/Ferr And | L. azorica I. azorica | H. gardnerianum | Unprotected | |

Total | 145 | 155 | 107 |

**Table 2.**Selected allometric equations relating tree age and dendrometric parameters tested for 147 L. azorica (Seub.) Franco trees sampled at breast height (BH), for 97 L. azorica trees sampled at base (Base), and for each stand of L. azorica in São Miguel Island. Allometric models: * [54]; ** [2]; *** Current study. Regression model equation (see Tables S1–S7); Stand code (see Table 1). N (number of samples). Plot # (see Figure 9). Adjusted determination coefficient (Adj R

^{2}); Akaike Information Criterion (AIC); Root Mean Square Error (RMSE); Mean Relative Error (MRE); Correction Factor (CF); Diameter (D); Tree Height (H); Basal Area (BA). This is a selection of the best models. See Tables S1–S7 for the full set of tested models.

Stand | BH/Base | N | Plot ^{#} | Regression Model | Adj R^{2} | AIC | RMSE | MRE | CF ^{##} |
---|---|---|---|---|---|---|---|---|---|

All | BH | 147 | ln(Age) = a + b_{1}ln(D) + ε * | 0.34 | 118.60 | 10.01 | −0.07 | 1.07 | |

All | BH | 147 | ln(Age) = a + b_{1}ln(D) + b_{2}ln(H) + ε *** | 0.38 | 110.29 | 10.05 | −0.06 | 1.06 | |

All | BH | 147 | 1 | ln(Age) = a + b_{1}ln(BA) + b_{2}ln(H) + ε ** | 0.39 | 106.87 | 9.75 | −0.06 | 1.06 |

Null Model | 178.18 | ||||||||

All | Base | 97 | ln(Age) = a + b_{1}ln(D) + ε * | 0.36 | 74.47 | 11.60 | −0.06 | 1.06 | |

All | Base | 97 | ln(Age) = a + b_{1}ln(D) + b_{2}ln(H) + ε *** | 0.41 | 67.46 | 11.70 | −0.06 | 1.06 | |

All | Base | 97 | 2 | ln(Age) = a + b_{1}ln(BA) + b_{2}ln(H) + ε ** | 0.44 | 62.31 | 11.12 | −0.05 | 1.05 |

Null Model | 116.37 | ||||||||

LO | BH/Base | 19 | 3 | ln(Age) = a + b_{1}ln(D) + ε * | 0.61 | −11.26 | 4.41 | −0.01 | 1.01 |

AF | BH/Base | 16 | 4 | ln(Age) = a + b_{1}ln(BA) + ε *** | 0.62 | −6.82 | 4.63 | −0.01 | 1.01 |

PP | BH/Base | 49 | 5 | ln(Age) = a + b_{1}ln(D) + ε * | 0.86 | −22.87 | 3.92 | −0.02 | 1.02 |

SC | BH/Base | 49 | 6 | ln(Age) = a + b_{1}ln(D) + b_{2}ln(H) + ε*** | 0.13 | 1.76 | 8.60 | −0.03 | 1.03 |

TR | BH/Base | 33 | 7 | ln(Age) = a + b_{1}ln(D) + ε * | 0.66 | −69.53 | 3.12 | −0.03 | 1.00 |

PO | BH/Base | 47 | 8 | ln(Age) = a + b_{1}ln(BAH) + ε *** | 0.40 | 17.78 | 10.77 | −0.04 | 1.04 |

**Table 3.**Descriptive statistics estimated for periodic annual increment and tree age difference, from 101 pairs of L. azorica (Seub.) Franco wood cores collected at tree base and at breast height.

Growth Parameters | Mean | Standard Deviation | Standard Error | Minimum | Maximum |
---|---|---|---|---|---|

PAI (cm·year^{−1}) | 0.679 | 0.659 | 0.066 | 0.033 | 4.200 |

Age Diference (years) | 5.010 | 3.413 | 0.340 | 0.000 | 18.000 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Matos, B.; Borges Silva, L.; Camarinho, R.; Rodrigues, A.S.; Rego, R.; Câmara, M.; Silva, L. Linking Dendrometry and Dendrochronology in the Dominant Azorean Tree *Laurus azorica* (Seub.) Franco. *Forests* **2019**, *10*, 538.
https://doi.org/10.3390/f10070538

**AMA Style**

Matos B, Borges Silva L, Camarinho R, Rodrigues AS, Rego R, Câmara M, Silva L. Linking Dendrometry and Dendrochronology in the Dominant Azorean Tree *Laurus azorica* (Seub.) Franco. *Forests*. 2019; 10(7):538.
https://doi.org/10.3390/f10070538

**Chicago/Turabian Style**

Matos, Bárbara, Lurdes Borges Silva, Ricardo Camarinho, Armindo S. Rodrigues, Ruben Rego, Mariana Câmara, and Luís Silva. 2019. "Linking Dendrometry and Dendrochronology in the Dominant Azorean Tree *Laurus azorica* (Seub.) Franco" *Forests* 10, no. 7: 538.
https://doi.org/10.3390/f10070538