Annual Growth Rings Research Articles

Influence of pine (Pinus sylvestris L.) growth rings width on the strength properties of structural sawn timber

Annual growth ring width was considered relative to the mechanical properties of timber from the Silesian Forestry Region in Poland. The timber was acquired from raw wood aged approximately 120 years old, with log quality A, B, and C. The study was conducted on 210 pieces of timber; 70 of them were from each part of the log: butt, middle, and top. The tested parameters, modulus of elasticity (MOE) and modulus of rupture (MOR), were measured on fully dimensional timber (40 × 138 × 3500 mm3) that had been dried and planed in industrial conditions. The density of wood (stereometric method) and annual rings width were calculated after MOR and MOE determination on samples including the entire cross-section cut near the failure zone. The tests revealed that the correlation between the width of growth rings and MOE or MOR depended on the log area: it was the highest for timber from butt logs and the lowest for timber from top logs. Moreover, the correlation between growth ring width and MOE or MOR depended also on the quality class of the logs from which the samples were obtained: it was the highest for timber from class A, and the lowest for class C.

Neotropical Hypericum irazuense shrubs reveal recent ENSO variability in Costa Rican páramo

Climate-vegetation relations in alpine systems play a pivotal role in regulating hydrology and have thus become a research priority in a context of ongoing climate change. In this paper, we investigate how one of the most dominant shrub species in alpine páramo ecosystems of Central America, Hypericum irazuense, responds to changes in precipitation, temperature and El Niño-Southern Oscillation. To this end, we performed dendrochronological and wood-anatomical analyses on H. irazuense to determine the limiting climatic factors driving shrub growth, using a bootstrapped correlation and response function analysis. To validate our results further, we also applied Structural Equation Models (SEM), an approach commonly used in ecology, so as to check for climate-growth relations which consider the control of ENSO on growth through its influence on various climatic parameters. Results support a relation between climate and annual growth of H. irazuense and demonstrate that the latter is sensitive to precipitation and temperature during boreal winters. In addition, we observe a statistically significant correlation between annual growth and La Niña events. The presence of annual growth rings holds H. irazuense as one in only few neotropical species suited for dendrochronological studies. Results of this study could thus contribute to an improved understanding of how changing climatic conditions affect the fragile and threatened páramo ecosystem and the ensuing services it offers in the form of hydrology regulation over the next decades.

Experimental assessment of the annual growth ring’s impact on the mechanical behavior of temperate and tropical species

An innovative experimental protocol is presented, linking a nondestructive (on computed tomography scanner) and destructive approach (bending test on electrostatic press). This study aimed to evaluate the annual growth ring’s impact on the mechanical behavior of wood. The tests were carried out on temperate specimens (Pseudotsuga menziesii and Abies alba Mill) from the Massif Central Region of France and tropical specimens (Aucoumea klaineana Pierre, Milicia excelsa, and Pterocarpus soyauxii) from Gabon. The connection between the mechanical parameters, taken from these tests and their structural characteristics, are also highlighted. Based on these results, a database was formed of the annual growth ring’s impact on the mechanical characteristics of these species. A link was found between the annual growth ring and the mechanical and physical characteristics of the species. The number and width of the earlywood ring and its mechanical properties were also investigated for each type of species. This comparison and the link highlighted was possible due to the study of the impact of dry density’s specimens, considered in this work as an adjustment parameter on the study of the mechanical behavior of these species.

Preserving air pollution forest archives accessible through dendrochemistry

Plants are continuously exposed to human air pollution, absorbing pollutants in their tissues. Trees can store pollutants in wood, in the annual growth rings, retaining traces of pollutants in the environment. Information on past pollution events are archived by trees, which dendrochemistry, a dendrochronological science combined with chemistry, is able to access. Many authors have suggested that trees could complement the conventional environmental monitoring: a forest archive of pollution events. However, the implications of trees occurrence in polluted areas on planning and management have not yet been discussed. In this article, we investigate whether forest archives exist and whether they should be integrated into the network of existing monitoring stations. We use a case study, the Veneto region of Italy, one of the most polluted areas in Europe, to examine the occurrence of trees around 28 industrial plants retrieved from a European pollution register. We propose planning actions to develop the latent potential of these forest archives for environmental monitoring, which society may benefit. We follow three steps: (a) assessing the cover and composition of tree canopies around the industrial plants, (b) inventorying the existing artificial air monitoring stations in order to discover whether pollutants around the industrial plants are already monitored, (c) assessing land use patterns in order to identify which are the receptors of air pollution and enhance the forest archive in the future. These spatial analyses are conducted in a 1-km radius buffer with the industrial plant as the centre. Results show that forest archives are available, with cover and composition suitable for dendrochemistry studies. Artificial monitoring stations are too far from industrial plants or have been installed recently, unable to provide historical data. Trees are an alternative source of pollution data. Receptors of air pollution include a diversity of urban, rural and agricultural lands, where forest archives can be managed and conserved through a variety of actions. Environmental protection agencies should value these trees, preserving them and accessing the records held in this forest archive. Similar inventories must be promoted in other industrialised regions of the world even at larger scales. Studies like this one should also be incorporated into landscape or urban planning processes.

The Response of Erica arborea L. Tree Growth to Climate Variability at the Afro-alpine Tropical Highlands of North Ethiopia

The important ecosystem services of the high altitude tropical afro-alpine Erica arborea L. forests are under increasing environmental and human pressure. The Erica treeline ecotone in the Ethiopian highlands forms a temperature-responsive vegetation boundary that is potentially affected by climate change. The cambium of 10 Erica arborea trees in Lib Amba Mountain and Ferrah Amba Mountain in the North Ethiopian highlands was marked in 2012, and corresponding tree disks were sampled after 498 days. Microphotographs of these cambial marks confirmed the formation of annual growth rings (0.76 ± 0.24 mm) with higher vessel density in earlywood and radially flattened fibers in the last layers of the latewood. In-continuum measurements of vessel size and density on microphotographs indicated the formation of inter-annual density fluctuations (IADFs) related to early rainfall in March-May. The same stem disks and 40 increment cores were used for detailed tree-ring analyses—a tree-ring chronology with 18 trees spanning from 1966 to 2014 could be derived. A significant (p < 0.1) positive correlation with minimum temperature in the growing season (August) and a negative correlation with minimum temperature in the spring season (March) were indicated as the most important climate factors regulating tree growth of Erica trees in the afro-alpine forest. The existence of annual tree rings and the proven potential for chronology building encourages further tree-ring analyses of Erica arborea in the afro-alpine tropical highlands in order to link it with climate variability and climate change.

Sea whip coral Leptogorgia virgulata in the Mid-Atlantic Bight: Colony complexity, age, and growth

Sea whip coral Leptogorgia virgulata are a common structural component of both natural and artificial hard-bottom reef habitats in the mid-Atlantic region and may serve as essential habitat for commercially valuable species. However, they are slow-growing, easily damaged, and especially vulnerable to damage by passive fishing gear such as pots and traps. Despite their potential importance, until recently, sea whips have been generally understudied in this region. We examined the colony complexity, length, age, and growth of sea whips from four artificial reef sites in the mid-Atlantic region to gain a better understanding of their biology in the area. There were no significant differences in the bifurcation (Rb) and tributary to source (T/S) ratios between sites, with the Rb ≈3 for all sites, indicating similar complexity between sites. The total length distribution was 8.3 cm to 85.3 cm, and 50% of corals in the range of 34.2–56.4 cm. Age, estimated from annual growth ring counts, ranged from 2 to 15 y, with 50% of corals in the range of 6 to 8 y. The large proportion of middle-sized and middle-aged corals suggests episodic recruitment. Age-length keys showed the trend of age increasing with total coral length, and a von Bertalanffy growth model demonstrated size-dependent growth following the equation: E[L—t] (cm) = 86.1(1−e−0.14(t−1.44)). This is the first study providing such data for sea whips in the coastal mid-Atlantic region, and the baseline created will be a useful reference to study changes over time.

The Growth Pattern of <i>Chamaecyparis obtuse</i> Stand along Longevity in Gyeongnam Province, South Korea

Tree growth is affected by environmental factors, climate condition and tree age. The objective of this study was to evaluate the growth patterns of Chamaecyparis obtusa (C. obtusa) stand in the Gyeongnam province. Data was collected from two cities and one county by using sample quadrats of 20 * 20 m. A total of 11 quadrats were used to collect tree height, diameter at the breast height (DBH), annual growth rings and soil data. The data analysis of soil moisture content, pH, organic matter (%), EC (cmol + /kg of soil), and available phosphorous was conducted. Growth ring was analyzed by using computer based software and the ages of the trees were identified. Average growth of height and DBH was computed from the surveyed data and annual growth of each tree was assessed by computer based reading of annual growth rings. The results of the study revealed that tree growth showed a reducing trend along the longevity. It was identified that soil pH, age, variation in annual average temperature, and altitude were the main factors related with growth of C. obtusa trees along the life of the stand.

ПРОЧНОСТНЫЕ ХАРАКТЕРИСТИКИ ЭЛЕМЕНТОВ ФЕРМЫ ИЗ ЭКОЛОГИЧЕСКИХ КОНСТРУКЦИОННЫХ ПИЛОМАТЕРИАЛОВ

Introduction: Softwood lumber is widely used to manufacture load-bearing structures. However, the quality of round wood used to manufacture such lumber has been deteriorating lately. Round wood decreases in diameter and often has heart rot. The article looks into the possibility of manufacturing elements of load-bearing structures using beams made of round wood of small diameter that have not been previously used to manufacture structural materials for construction purposes. It is suggested to make beams of such round wood preserving the trunk structure to the maximum (heartwood beams). Due to the preservation of the annual growth ring pattern, such beams have better strength properties as compared to traditional structural lumber. Purpose of the study: The study is aimed to determine the strength properties of engineering structures’ elements made of heartwood beams sawn from round wood of small diameter. Methods: The authors tested an experimental truss made of heartwood beams by means of incremental loading until destruction. Results: The strength properties of the truss elements made of heartwood beams sawn from round wood of small diameter were determined. There is a good fit between the calculated values of stress in the truss elements and the experimental data. The structure was damaged in the panel points connecting the compression strut with the elements of the tension and compression chords. The tension elements and their joints remained undisturbed. The experimental structure has a safety factor of 2. Compared to the design load, such a value shows that the experimental truss has the required bearing capacity and is robust. The findings confirm that the strength properties of heartwood beams match the requirements for elements of load-bearing structures. The strength properties of heartwood beams make it possible to use them to manufacture load-bearing structures.

Warmer temperatures promote shrub radial growth but not cover in the central Canadian Arctic

ABSTRACT We assessed the response of Salix richardsonii, a deciduous shrub, to climate change by determining the combination of climatic factors that regulated its growth over the past half-century. We tested whether increasing arctic temperatures promote shrub growth and increased cover. We analyzed fifty-four stems (out of seventy sampled) from S. richardsonii shrubs near the Walker Bay research station in Nunavut, Canada (68°21′ N, 108°05′ W) and surveyed shrub cover in 1996 and 2010. We measured annual growth rings, removed the age-related pattern, and used a response function analysis to explore the climate–growth relationship. The standardized chronology was positively associated with mean July temperature, corroborating other evidence that summer temperature is an important driver of shrub radial growth. Basal area increment revealed a long-term increase in radial growth, although it has stabilized this century. Surveys showed no significant increase in shrub cover at Walker Bay from 1996 to 2010. Our results support a growing body of evidence that increased shrub growth does not necessarily translate into a prolonged increase in shrub cover. Instead, we conclude that the heterogeneity of the arctic shrub response to climate change may be associated with variation in the proximate factors limiting recruitment such as water table saturation and herbivory.

Growth ring formation of Dichrostachys cinerea and Senegalia mellifera in arid environments in Namibia

Dichrostachys cinerea and Senegalia mellifera trees are the most widespread invasive encroacher species in Namibia. Understanding their growth performance under arid conditions is key to understanding and managing the arid ecosystems of Namibia. To determine their utility in dendrochronology, we analyzed the formation of growth rings for two species from three sites in Namibia. We applied cross-dating techniques to 69 tree discs, the analysis of which confirmed the formation of annual growth rings. The rings are characterised by alternating layers of low and high vessel density and are separated by bands of marginal parenchyma. D. cinerea shows a well-defined pattern of growth rings, whereas the ring patterns of S. mellifera are more complex. Because aging trees tend to display narrower rings toward the outside of the stem, we applied both ring-width index and basal area increment methods in developing ring-width chronologies for the two species. Descriptive statistics for the chronologies indicate that the average ring chronologies are of good quality and that the trees are responding to common environmental signals. The basal area increment methodology produced better statistics than the ring-width index for these two species. Furthermore, statistical characteristics of the chronologies indicate that D. cinerea has a higher mean sensitivity (MS), expressed population signal (EPS), and signal-to-noise ratio (SNR) than S. mellifera. Thus, we find that both species are suitable for dendrochronological study, with D. cinerea being better than S. mellifera.

INFLUENCE OF SOIL FERTILITY ON THE ABILITY OF SCOTS PINE (Pinus sylvestris L.) TO ADAPT TO TECHNOGENIC POLLUTION

ABSTRACT The purpose of the research is to identify the effect of soil factor on the ability of Scots pine to adapt to technogenic pollution based on comparative analysis of radial increment of the species which grows on soils of different fertility. The null hypothesis that soil fertility is a significant factor for adaptation was tested. The research area i.e. the plantation created in 1983 and exposed to pollution of aero-technogenic emissions of magnesium production Satka/Chelyabinsk Region/Russia, is located within the central part of the subzone of coniferous-broad-leaved and South-taiga coniferous forests of the Southern Urals. The analysis of annual growth rings (AGR) of Scots pine growing on soils of different fertility allowed us to estimate the effect of soil factor on the ability of Scots pine to adapt to magnesite pollution. As results of the research it was found that the differences in the AGR of Scots pine growing on soils of different fertility was statistically significant under the same level of technogenic pollution. During the investigation period (1994-2010), the AGR of Scots pine on fertile soils were significantly higher than those of on poor soils for 7 years. It was revealed that the positive effect of soil fertility on the Scots pine growth is leveled at the level of pollution exceeding 6-10 thousand tons per year of gaseous emissions and 25-30 thousand tons per year of total emissions. It was also found that soil fertility allows better adaptation of Scots pine to low temperatures, and more actively grow on sites with increasing precipitation.

Annual Beech (Fagus sylvatica) Growth Rings and Solar-Related Climate Variations in the Central and Western Balkans in the 18th–21st Centuries

Abstract—This work analyzes a time series of annual growth ring widths for beech trees (Fagus sylvatica) in the western and central Balkans (Stara Planina, Bulgaria) to identify solar-related climate cycles. The effects of solar activity on beech growth during the Dalton Grand Solar Minimum (1793/98–1833) are studied based on samples ≥200 years of age. Two different methods (T–R periodogram analysis and wavelet analysis) are used to identify statistically significant variations with periods of 20–22, ~40, 60–70, and 210–220 years in most of the samples. Two samples are found to have a cycle of about 110 years. Statistically significant correlations between the ring widths and precipitation amounts and the temperatures from data of the nearest weather stations for 1899–2012 confidently manifest themselves in all four central Balkan samples and one western Balkan sample. Based on the results, it is concluded that a period of cooling and increased precipitation has likely begun in the climate of Bulgaria. The process is proceeding slowly, having begun approximately in 2007–2010, but it may noticeably accelerate after the end of solar cycle 25 and during cycles 26 and 27. It is concluded that cycle 26 is likely to be delayed in development.

Radial variation of anatomical, morphological and chemical characteristics of Acacia auriculiformis in evaluating pulping raw material

The Variations of anatomical, morphological and chemical characteristics with annual growth ring from first and second generation Acacia auriculiformis were investigated. The fiber length and wall thickness increased and proportion of ray cells decreased with increasing annual growth ring. First generation A. auriculiformis had higher proportion of fiber, longer fiber length than second generation A. auriculiformis. The average percentage of fibers, vessels and rays were 77.56%, 15.14% and 7.31% for first generation A. auriculiformis and 77.19%, 15.64% and 7.16%, for second generation A. auriculiformis, respectively. The holocellulose, α-cellulose and pentosan content increased and lignin and extractives content decreased with increasing annual growth ring. Holocellulose, α-cellulose, pentosan and lignin content in first generation A. auriculiformis were higher than second generation A. auriculiformis.

PENDUGAAN UMUR CAKALANG, Katsuwonus pelamis (Linnaeus, 1758) YANG DIDARATKAN DI UPT P2SKP PONDOKDADAP SENDANGBIRU MELALUI ANALISIS LINGKARAN UMUR

Abstract Length-growth analysis of fish cannot be completed without age information. Age study on skipjack has been done through analysis of its first-hard dorsal fin. Sampling was done using 11 fish specimen taken from UPT P2SKP Pondokdadap Sendangbiru, from January to February 2018. Species identification follows the FAO standard procedure (species identification sheet) published 2001. A specimen was deposited at Depository Ichtyologicum Brawijaya with code DIB.FISH 111103. The first hard spine of 11 fish samples were cut with IsoMet low speed cutting machine at 50 mm thickness. The preparates were then analyzed using biological binocular microscope at 40x magnification. The results showed differences in number of growth annuli (annual growth-ring) at different fish length (FL). The number of annuli varied between 4 - 6+ age year at fish length (FL) variation between 38 and 62 cm. These values were closely related to those with other methods such as Modal Progression Analysis (MPA). The number of samples successfully analyzed (5 specimen) were not sufficient for analysis of length-growth parameters (L ∞ , k and t 0 ). Also, this technique did not apply for age less than yearly unit, but quite affordable (Rp.50.000,- per sample) for a fairly variable amount of specimens.

Effects of different land-use systems (grazing and understory cultivation) on growth and yield of semi-arid oak coppices

The present study examines the extent of negative effects of traditional multiple land-use systems on oak coppices, from a forest management point of view. The study area was located in approximately 10,000 ha of hilly Brant’s oak (Quercus brantii Lindl.) woodlands in the central Zagros Mountains. In the same site-quality class, three land-use systems were compared: simple coppice (Co), coppice in conjunction with small ruminant grazing (CoG), and coppice with understory rain-fed wheat cultivation plus grazing (CoCG). Data on total wood volume of trunk and major branches, and annual ring growth, were collected and analyzed from 74 stands in 15 coppiced woodland patches. The results showed the advantage of Co over CoG and CoCG land-uses by 43 and 60 m3 of mean accumulated wood volume per hectare, respectively. The diameter growth analysis also revealed an annual increase in wood production of trees in Co land-uses over 43 years, with an exception of the recent decade, when growth coincided with a severe drought. Using a back-extrapolation method, the minimum rotation age of woodlands in Co land-use was found to be 23.6 years, 5 and 7 years shorter than those of CoG and CoCG land-uses, respectively. Unlike CoCG, woodlands located in Co and CoG land-use systems demonstrated a high level of agreement with self-thinning rule of − 3/2. Values for the stand density index for coppiced oak woodlands were between more than 1000 for the least disturbed (Co) and less than 400 for the most disturbed woodlands (CoCG). The structure and growth rate of the coppiced oak woodlands were irreversibly disrupted by understory tillage plus grazing and in less extent by grazing alone. It was concluded that ending undergrowth cultivation in semi-arid oak coppices should be addressed as a priority by adopting minimum regulations.

Uranium quantification of oak tree rings (Quercus petraea) from a former uranium mining site by High Resolution Inductively Coupled Plasma Mass spectrometry in Laser Ablation and Solution modes

Tree ring proxies are employed in dendroanalysis as a valuable tool for evaluating past anthropogenic contamination. A wide variety of analytical methods are used to quantify tree ring content for a broad spectrum of chemical elements. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is often used to investigate element concentrations in the tree rings. However, several issues regarding the representativeness of laser ablation measurements for trace elements have to be addressed before definitive conclusions can be drawn. In this study, High Resolution (HR)-ICP-MS has been implemented to analyze the trace concentration of uranium (U) in annual growth rings of oak trees (Quercus petraea) using both laser ablation (LA) and solution modes. The three tree samples taken for the present study were located upstream (with respect to the hydrologic system) of a former uranium mine site at Rophin (Puy de Dôme, France), where mining operations were performed between 1949 and 1958. According to the LA-HR-ICP-MS technique, two-dimensional quantitative (2D) mapping of uranium has developed to study the spatial distribution of uranium at the tree ring surface. A strong heterogeneity was observed, leading to an average uranium concentration with high uncertainty (50–66%). Pressed pellets of the standard reference material, NIST1570a spinach leaves and uranium doped cellulose powder were adopted as the uranium standards for quantification. No agreement was found between uranium concentrations measured after acid digestion and the values obtained by laser ablation. This comparison highlights the limitations of laser ablation technique; hence the solution mode should be preferred for quantifying uranium trace concentrations in tree rings. However, low uncertainty (< 9%) was found with the HR-ICP-MS solution, this result should be compared with the deviation observed both at the tree scale (≈ 40%) and across the ≈ 10 m sampling area (≈ 50%).

The functional implications of tracheary connections across growth rings in four northern hardwood trees.

Deciduous angiosperm trees transport xylem sap through trunks and branches in vessels within annual growth rings. Utilizing previous growth rings for sap transport could increase vessel network size and redundancy but may expose new xylem to residual air embolisms in the network. Despite the important role of vessel networks in sap transport and drought resistance, our understanding of cross-ring connections within and between species is limited. We studied cross-ring connections in four temperate deciduous trees using dye staining and X-ray microcomputed tomography (microCT) to detect xylem connectivity across growth rings and quantify their impact on hydraulic conductivity. Acer rubrum and Fraxinus americana had cross-ring connections visible in microCT but only A. rubrum used previous growth rings for axial sap flow. Fagus grandifolia and Quercus rubra, however, did not have cross-ring connections. Accounting for the number of growth rings that function for axial transport improved hydraulic conductivity estimates. These data suggest that the presence of cross-ring connections may help explain aspects of whole-tree xylem sap transport and should be considered for plant hydraulics measurements in these species and others with similar anatomy.

Dendrogeomorphological analysis of the Sawicki Landslide in the Beskid Niski Mountains (S Poland)

We applied dendrochronological analysis to study an extensive (~2.5 km long) complex-type landslide in the Beskid Niski Mountains (Polish Flysch Carpathians), which was rejuvenated in historical time (the earliest transformation occurred in 1913). We used three complementary methods (dating of eccentricity of annual growth rings, eccentricity indices, and analysis of reaction wood), based on seven species of deciduous and coniferous trees. A total of 204 trees were sampled and 408 cores collected using a Pressler increment borer. Based on the dendrochronological analysis, the activity of various parts of the landslide in the past century is presented, which appears to have been diverse and influenced mostly by precipitation. The upper part of the landslide was active from the 1920s until the 1940s. In the middle section of the landslide, intensifications of gravitational movement were repeatedly recorded after intense rainfalls throughout the entirety of the last century. The highest landslide activity was dendrochronologically detected in the 1980s and 1990s. Increasing landslide activity during so-called “dry years” may have been related to quick drying of the bedrock, resulting in changes in rock strength parameters. Our results indicate significant susceptibility of this particular slope-valley geosystem in response to even slight hydrogeological changes (including dryness), which can trigger ground movement.

Genome-wide association study identified novel candidate loci affecting wood formation in Norway spruce.

SummaryNorway spruce is a boreal forest tree species of significant ecological and economic importance. Hence there is a strong imperative to dissect the genetics underlying important wood quality traits in the species. We performed a functional genome‐wide association study (GWAS) of 17 wood traits in Norway spruce using 178 101 single nucleotide polymorphisms (SNPs) generated from exome genotyping of 517 mother trees. The wood traits were defined using functional modelling of wood properties across annual growth rings. We applied a Least Absolute Shrinkage and Selection Operator (LASSO‐based) association mapping method using a functional multilocus mapping approach that utilizes latent traits, with a stability selection probability method as the hypothesis testing approach to determine a significant quantitative trait locus. The analysis provided 52 significant SNPs from 39 candidate genes, including genes previously implicated in wood formation and tree growth in spruce and other species. Our study represents a multilocus GWAS for complex wood traits in Norway spruce. The results advance our understanding of the genetics influencing wood traits and identifies candidate genes for future functional studies.

Age determination in echinoderms: first evidence of annual growth rings in holothuroids.

While age is fundamental in animal biology, forming the basis of critical concepts such as life-history strategies, longevity and population structures, measuring this variable in some taxa remains problematic. Such is the case of holothuroid echinoderms, which play key roles in marine benthic communities from the shore to the abyss, and which are extensively fished in many regions across the globe. Here, we present and validate a promising ageing technique using the cold-water species Psolus fabricii. The method involves the extraction of the oldest dermal plates (largest dorsal ossicles) to preserve their original pigments and structure. While plates initially appear to have a uniform texture, polishing and dying them reveals layered ring patterns. A study of laboratory-reared juveniles, from settlement to 40 months of age, confirmed that one layer is added annually, making plates both larger and thicker, and generating successive light and dark rings, the latter representing the transition (overlap) between two layers. Therefore, each pair of rings represents an annual growth band. Size-at-age data obtained using this method revealed that growth of P. fabricii is slow and that wild individuals collected at diving depths had reached an age of several decades.