A statistical model for the prediction of the number of sapwood rings in Scots pine (Pinus sylvestris L.)

Dendrochronology is a well-established dating method for wooden objects, but due to surface processing of construction timber or natural degradation the dating of historical wood often relies on a prediction of the number of missing rings based on sapwood statistics. Since Scots pine (Pinus sylvestris L.) is one of the most common tree species in north-western Europe, the absence of reliable sapwood statistics and models for the prediction of missing sapwood rings for pine samples is remarkable. We have therefore produced sapwood statistics based on data from 776 pine trees with ages from 15 to 345 years. The material consists of both living trees and historical timber, with varying growth rates, geographic settings, and from different soil types. When the whole material is considered, the average age of the trees is 103 years, and the number of sapwood rings is 54 ± 15 (1 SD), but range from 18 to 129. Trees less than 100-years in age contained 46 ± 11 (1 SD) sapwood rings and had an average tree-ring width (TRW) of 1.76 mm. With increasing age, the average TRW decreased while the number of sapwood rings increased. The average TRW of 101–200-year-old trees is 0.99 mm while the samples contained 63 ± 12 (1 SD) sapwood rings. For trees older than 201 years, the average TRW is 0.64 mm while the number of sapwood rings increased to 85 ± 16 (1 SD). The two most important factors in determining the number of sapwood rings for a given tree when only heartwood statistics are available proved to be (i) the number of heartwood rings and (ii) the average TRW of the heartwood rings. For incomplete samples, we have therefore developed a statistical model based on the sample’s heartwood rings (number and average width) to compute a prediction interval for the total number of rings. The sapwood and heartwood statistics suggest a statistical model for the number of sapwood rings with mean that increase with the number of heartwood rings. Furthermore, the average number of sapwood rings decreases with the mean width of the heartwood rings. However, the predictive power of the mean width is limited when the number of heartwood rings has already been taken into account. Thus, we suggest making predictions for the number of sapwood rings using only the number of heartwood rings. Predictions of the number of sapwood rings based on the statistical model where convincing in the case of the three different datasets that were analysed. The certainty in these predictions was such that the width of the 80% and 95% prediction intervals ranged 28–34 and 45–52 sapwood rings, respectively. Additionally, we demonstrate how make predictions when there is information about the number of remaining sapwood rings in a given sample. To make the sapwood model available, we present a free online R package for fitting our models and an online software dashboard.     

From desert to rainforest, sapwood width is similar in the widespread conifer Callitris columellaris

The process that transforms conductive sapwood to non-conductive heartwood in trees is poorly understood. Here, we use natural variation in climate to examine the environmental control of sapwood width in a widespread conifer species. We hypothesised that if sapwood width is linked to transpirational load, there would be a positive association between sapwood width, and continental gradients in mean annual rainfall, whereas age-related conversion to heartwood would be revealed from estimates of the age of the inner-most sapwood ring. Using the widespread Australian conifer Callitris columellaris we took cores from trees at 85 sites spanning a range of 168–2,117 mm in mean annual rainfall, and 14–28 °C in mean annual temperature. We found that sapwood width was remarkably similar throughout the species range, being only slightly lower in the tropics than the arid or temperate zone. There was a weak negative relationship between sapwood width and mean annual rainfall, which is in the opposite direction expected from transpirational control of sapwood width. Sapwood growth rings were wider, but there were fewer of them in the tropics than elsewhere, indicating conversion to heartwood occurred earlier here. Together with an earlier finding that tracheid diameter was largest in the tropics, our results show that differences amongst climate zones more strongly influence the hydraulic properties of sapwood than its amount.     

Sapwood estimates of pedunculate oak (Quercus robur L.) in eastern Baltic

Pedunculate oak (Quercus robur L.) is one of the widely used and dendrochronologically investigated species in Europe. Still, it is a problematical dating object if its outermost section is missing partly or totally. Thus, we need sapwood estimation of living trees. As sapwood amount varies geographically, numbers of sapwood rings have been published for different regions in Europe but no such estimation has been done for the Baltic States yet. Therefore, this paper deals with the estimation of pedunculate oak sapwood growing in the eastern Baltic region, i.e. in Finland, Estonia, Latvia, and Lithuania.In total, 668 oak core samples of living trees from 43 stands were investigated. Ring widths were measured and the number of sapwood rings was determined according to two criteria: difference of colour and absence of tyloses in earlywood vessels. The samples were divided into two sets, according to the t_H-values between site chronologies and the major geobotanical sub-provinces. Thus, the nine Finnish and western Estonian sites were attributed to the western region and the 34 eastern Estonian, Latvian and Lithuanian sites to the eastern region.As the result of a statistical analysis, we explain that the number of oak sapwood rings ranges from 4.09 to 20.85 and 6.45 to 18.02 within 95% confidence limits in the western and eastern regions, respectively. For the three Baltic countries and southern Finland in general, we recommend to consider a sapwood estimate of 6.18–18.71 rings. Regarding earlier studies, the general European trend of decreasing sapwood ring number towards the east was confirmed. A geographical pattern of eastward decrease of the median sapwood ring number was noticed in the Baltics as well. The chronology based upon 668 samples of living oak trees from all sites covered the period of 1631–2008.     

A 781-year oak tree-ring chronology for the Middle Ages archaeological dating in Maramureș (Eastern Europe)

From 1997 to the present, a sustained project in the Maramureș region in Romania was completed with the construction of a 781-year oak tree-ring chronology. A total of 395 samples from living trees and 429 from archaeological wood were analysed with dendrochronological methods. The study aimed to provide the scientific community with a new oak chronology that could be applied in dendroarchaeology, dendroclimatology and dendroecology studies and also for interpreting past socio-economic events. Furthermore, we studied the number of sapwood rings and the growth pattern for different time periods. The chronology covered the continuous period of A.D. 1236‒2016. From the 824 samples collected, we separated 271 tree-ring series into a new chronology (A.D. 1406–2016), which fulfilled all the criteria necessary to reconstruct past climate and environmental changes. The resulting new tree-ring chronology indicated robust signal series intercorrelation (r = 0.55) and an average mean sensitivity of 0.21. Based on an analysis of the sapwood, we recommend estimating a number between 8 and 32 rings to the date of final ring for 95% confidence range of mean on the for felling in the Maramureș region. Additionally, we observed that the number of sapwood rings was not correlated with altitude or oak tree species.     

Estimating missing sapwood rings in three European gymnosperm species by the heartwood age rule

Precise dating of the year of felling is one intended outcome of dendrochronology. However, occasionally some or all sapwood rings might be missing, either due to deterioration or because they were carved off, or for some other reason. Consequently, while heartwood is preserved, sapwood might be fully or partially missing. In such cases, the year of felling must be estimated by adding a suitable number of sapwood rings. A heartwood age rule (HAR) has been advocated for Scots pine and adapted to European larch and Cembra pine, implying a linear relationship between sapwood ring count and the square root of heartwood ring count, largely irrespective of position in the stem. The same rule applied to all observations of a species, irrespective of silviculture, location or fertility of the growth site. Scots pine had twice or thrice as many sapwood rings as Cembra pine, which had 10% more rings than larch. The magnitude of model residuals was proportional to estimated sapwood ring count. Relative residuals were roughly normally distributed. To be applicable in Bayesian modelling in dendrochronology analyses, detailed information on model errors has been provided.     

Sapwood characteristics of Quercus robur species from the south-western part of the Pannonian Basin

We analysed sapwood characteristics in 344 pedunculate oak (Quercus robur L.) samples from the south-western part of the Pannonian Basin. The samples came from 13 sites, located in Slovenia, Croatia and Serbia. The trees had an average of 13.3 sapwood rings, with a minimum of 5 and maximum of 32. Fifteen log-log linear regression models were employed to assess the statistical relationship between sapwood and heartwood variables. The number of sapwood rings (N_SW), which is usually needed in dendroarchaeological dating, is significantly related to the number of heartwood rings (N_HW), heartwood width (W_HW) and heartwood growth rate (G_HW). Older and more slowly growing trees had a higher average number of sapwood rings. Using N_HW and W_HW, we employed an additional multiple regression model and calculated coefficients for N_SW predictions for real-world dendroarchaeological dating from the south-western part of the Pannonian Basin.     

Growth rate and ring width variability of teak, Tectona grandis (Verbenaceae) in an unmanaged forest in East Timor

Teak (Tectona grandis) is one of the most valuable timbers in international trade and an important species for tropical forestry. Teak is found on the island of East Timor but no information is available on teak growth from this region. A pure stand planted in 1940-50 in the North of East Timor and left unmanaged was studied. Fifteen trees were sampled in October-November 2003 and stem discs taken at three height levels of its height (1.7m, 9.5m and 18.7m), and cores were collected at DBH. Transverse surfaces of the discs and cores were polished for ring identification. Core cross sections were first digitized and disc cross sections were observed under the microscope. Three randomly selected radii were analyzed in each disc. Ring width measurement and ring counting were done using image analysis software. The distinction between heartwood and sapwood was performed macroscopically by colour difference, and heartwood radius and sapwood width were measured. The relationship between stem and heartwood radius was studied for each disc and heartwood percentage by radius was determined. Radial ring width curves are presented for the different axial positions within the stem, and ring width variability was analyzed. Growth rates were calculated and age-radius relationships were estimated using cumulative growth curves. Growth rings were large and well defined in the juvenile phase, reflecting the specie's fast-growing character. The year-to-year variation of ring width showed a similar pattern among trees. Mean ring width ranged between 4.3-7.3mm for the first 20 years and 3.3-5.1mm for 30 to 45 years. Pith eccentricity was evident in the lower part of the stem and ring wedging occurred. On average, heartwood represented 84% of the radius and sapwood contained 6 to 11 rings. The age-related variation of ring width and the occurrence in the lower part of the tree stems of eccentricity and wedging rings, highlights the importance of appropriate stand management, particularly regarding basal density distribution over time, whenever optimized timber production is envisaged.     

干旱区多枝柽柳的生长特性

多枝柽柳是分布最为广泛的柽柳属植物之一。也是维持干旱区荒漠生态系统的关键植物种。本研究运用树轮年代学和树干解析方法。对额济纳地区不同生境条件下多枝柽柳的年轮生长、高生长和地径生长等方面的特征进行初步探讨。多枝柽柳每年形成1个年轮。树盘偏心生长极为普遍．完整树轮大多在10龄以内区域,10龄以外都呈单个或多个不完整年轮生长区。多枝柽柳单枝在1～4年高生长缓慢．4～8龄之间属于快速生长期,10年以上生长速率急剧下降。不同地下水位条件下三组样本径生长年增长速率达到极大值的年龄分别为21、56和74年,水环境条件是影响多枝柽柳径向生长的主要因素。同一年年轮宽度随枝高呈减小趋势。多枝柽柳边材的树轮数一般在3～5轮之间,进入老龄阶段有增加趋势。边材宽度随年龄增长逐渐减小。     

Xylem water content and wood density in spruce and oak trees detected by high-resolution computed tomography

Elucidation of the mechanisms involved in long-distance water transport in trees requires knowledge of the water distribution within the sapwood and heartwood of the stem as well as of the earlywood and latewood of an annual ring. X-ray computed tomography is a powerful tool for measuring density distributions and water contents in the xylem with high spatial resolution. Ten- to 20-year-old spruce (Picea abies L. KARST.) and oak (Quercus robur) trees grown in the field were used throughout the experiments. Stem and branch discs were collected from different tree heights, immediately deep frozen, and used for the tomographic determinations of spatial water distributions. Results are presented for single-tree individuals, demonstrating heartwood and sapwood distribution throughout their entire length as well as the water relations in single annual rings of both types of wood. Tree rings of the sapwood show steep water gradients from latewood to earlywood, whereas those of the heartwood reflect water deficiency in both species. Although only the latest two annual rings of the ringporous species are generally assumed to transport water, we found similar amounts of water and no tyloses in all rings of the oak sapwood, which indicates that at least water storage is important in the whole sapwood.     

Variation in stem radial growth of the Australian conifer, Callitris columellaris, across the world’s driest and least fertile vegetated continent

Climate change could alter the biogeography of many tree species. However, there have been few studies of tree growth across climatic gradients at a continental scale. Callitris columellaris is a widespread conifer that spans many climates and landscape positions across Australia. Our aim was to determine how stem radial growth of C. columellaris varies with tree size and with the biogeographic factors of rainfall, temperature, soil fertility and inter-tree competition. We sampled cores from trees at 85 sites in biomes ranging from tropical savanna to arid desert and temperate forest, and measured widths of the 100 outermost growth rings. We analysed ring width in relation to changes in tree age and diameter, and also evaluated the influence of the biogeographic factors on the width of the ten most recently formed rings. The average width of outermost rings varied only slightly with stem diameter, because the decrease in ring width with age and diameter within trees is offset by an increase with diameter among trees. Our analyses thus explain the weak, inconsistent relationships often observed between stem diameter and growth rate amongst trees. The most important biogeographic factors were the climatic ones: across Australia, ring width increased with both mean annual rainfall and mean annual temperature. These relationships were largely driven by continental scale differences between the tropical and the southern (arid plus temperate) sites, while relationships within climate zones were comparatively weak. Ring width decreased with intense inter-tree competition but showed little correlation with available soil nitrogen or phosphorus.     

A comparison of ring-width and event-year chronologies derived from white oak (Quercus alba) and northern red oak (Quercus rubra), southwestern Quebec, Canada

In dendrochronology, ring width has been a variable of choice when assessing the radial growth–climate association of tree species. We compared ring-width and event-year chronologies from a dendroclimatic perspective using both white oak (Quercus alba L.) and northern red oak (Quercus rubra L.). The study was conducted in three regions of the Ottawa valley in southern Québec. Twelve mixed red and white oak stands were selected and for each oak species, 12 chronologies were developed from tree-ring measurement and 12 others were derived using visual assessment of narrow or wide rings (event years). Ring-width and event-year chronologies gave almost identical results and revealed the prevalence of drought in the early growing season as the most influential factor in both species. This study emphasizes the utility of event-year chronologies in tree-ring studies and their comparativeness with ring width. Establishing event-year chronologies has the advantage of being faster than measuring ring width, it does not necessitate complex equipment and depending on the purpose of the study may prove to be at least comparable. The choice of species, their mean sensitivity, the ability to recognize narrow or large rings as well as the number of trees and sites to analyze may, however, be factors to consider when choosing to use event-year chronologies over the more commonly used ring-width ones.     

Chloroplast division machinery as revealed by immunofluorescence and electron microscopy

The division of chloroplasts (plastids) is critical for the viability of photosynthetic eukaryotes. Previously we reported on the chloroplast division apparatus, which consists of inner and outer double or triple rings (PD rings). Chloroplasts are assumed to arise from bacterial endosymbionts, while bacterial division is instigated by a bacterial cytokinesis Z-ring protein (FtsZ). Here we present immunofluorescence and electron-microscopic evidence of chloroplast division via complex machinery involving the FtsZ and PD rings in the higher plant Pelargonium zonale Ait. Prior to invagination, the FtsZ protein was attached to a ring at the stromal division site. Following formation of the FtsZ ring, the inner stromal and outer cytosolic PD rings appeared, signifying the initiation of invagination. The FtsZ ring and the PD rings were found at the leading edge of chloroplast constriction throughout division. During chloroplast division, neither the FtsZ nor the inner rings changed width, but the volume of the outer ring gradually increased. We suggest that the FtsZ ring determines the division region, after which the inner and outer PD rings are formed as a lining for the FtsZ ring. With the outer ring providing the motivating force, the FtsZ and inner PD rings ultimately decompose to their base components.     

Heartwood and sapwood development within maritime pine (<Emphasis Type="Italic">Pinus pinaster </Emphasis>Ait.) stems

Heartwood and sapwood development in maritime pine (Pinus pinaster Ait.) is reported based on 35 trees randomly sampled in four sites in Portugal. It was possible to model the number of heartwood rings with cambial age. The heartwood initiation age was estimated to be 13 years and the rate of sapwood transformation into heartwood was 0.5 and 0.7 rings year^–1 for ages below and above 55 years, respectively. Reconstruction of heartwood volume inside the tree stem was made by visual identification by image analysis in longitudinal boards along the sawn surfaces. This volume was integrated into the 3D models of logs and stems developed for this species representing the external shape and internal knots. Heartwood either follows the stem profile or shows a maximum value at 3.8 m in height, on average, while sapwood width is greater at the stem base and after 3 m remains almost constant up the stem. Up to 50% of tree height heartwood represents 17% of stem volume, in 83-year-old trees and 12–13% in 42 to 55-year-old trees. Tree variables such as stem diameter, DBH and tree total height were found to correlate significantly with the heartwood content.     

大花序桉心边材变异规律和候选基因挖掘研究

为探究大花序桉(Eucalyptus cloeziana)心材比例差异显著的不同家系间心边材变异规律,挖掘心材变异相关的候选基因,为珍贵用材树种高效培育及育种利用提供基因资源。以18 a生的2个心材比例差异显著的大花序桉家系为材料(家系1和2),各制作解析木3株,沿着树干以1 m为区间分段截取圆盘,测量东西和南北2个方向的带皮直径、去皮直径、总年轮数、边材年轮数、边材直径,并开展心材和边材径向和轴向分析。同时利用各解析木胸径处初生木质部样品进行DNA混池测序,发掘等位基因频率差异显著的SNP位点并挖掘相关功能基因。结果表明,大花序桉边材宽度和心材半径的方位变异中家系2大于家系1,平均差值分别为0.7和5.5 cm,在随树高的变异中,家系1和2的心材半径和心材年轮数的下降速率分别为0.40和0.64及0.43和0.36。两家系间基本密度差异显著,家系1为0.80～0.82 g/cm³,家系2为0.75～0.78 g/cm³。基本密度与树高、横截面半径和心材半径呈显著负相关,与顺纹抗拉强度、弦面硬度和部分力学性质呈显著正相关。利用DNA混池测序共...     

Comparing automatically generated and manually measured tree-ring transects of growth trends with Hawaiian sandalwood as an example species

Tree-ring measurements are a primary quantitative tool used in numerous scientific disciplines. Some species, however, exhibit morphological complexities leading to significant uncertainty in these measurements. Hawaiian Sandalwood (Santalum paniculatum) stems, for example, often develop asymmetric growth features that hinder tree-ring measurements. These features include faint-ring boundaries and wedging rings which disappear in portions of the cross-section. In this work we a use a novel two-dimensional transect methodology and our own open-source software, svg-dendro, to analyze particularly difficult cross-sections. Our method accomplishes this by first tracing all rings by hand and automatically generating a user-specified number of transects. On average, these traced measurements had more sensitivity to tree-ring variability without losing important equivalencies with the traditional binocular stereomicroscope technique (e.g., radii, skewness) as indicated by greater mean variance for ring number, mean tree-ring width, and standard deviation. All S. paniculatum samples had ring wedging, where certain sides of the stem had many locally absent tree rings but to different intensities. The new technique allows us to analyze the shift from complete rings with little to no wedging to rings with more wedging starting between the 19th and 40th ring, where deep stem lobes begin forming. The new method also reveals the difficulty in measuring these trees, as the wedging creates multiple lobes with different visible ring counts. This research suggests that this two-dimensional methodology would be best applied to non-circular trees with fewer incomplete rings, supporting the importance of species and population selection. Overall, we have developed an efficient and flexible means to measure otherwise unmeasurable growth features in tree samples through representing tree-ring boundaries as curves and developing software to sort and map transects.     

Negative-stain electron microscopy of inside-out FtsZ rings reconstituted on artificial membrane tubules show ribbons of protofilaments

FtsZ, the primary cytoskeletal element of the Z ring, which constricts to divide bacteria, assembles into short, one-stranded filaments in vitro. These must be further assembled to make the Z ring in bacteria. Conventional electron microscopy (EM) has failed to image the Z ring or resolve its substructure. Here we describe a procedure that enabled us to image reconstructed, inside-out FtsZ rings by negative-stain EM, revealing the arrangement of filaments. We took advantage of a unique lipid that spontaneously forms 500 nm diameter tubules in solution. We optimized conditions for Z-ring assembly with fluorescence light microscopy and then prepared specimens for negative-stain EM. Reconstituted FtsZ rings, encircling the tubules, were clearly resolved. The rings appeared as ribbons of filaments packed side by side with virtually no space between neighboring filaments. The rings were separated by variable expanses of empty tubule as seen by light microscopy or EM. The width varied considerably from one ring to another, but each ring maintained a constant width around its circumference. The inside-out FtsZ rings moved back and forth along the tubules and exchanged subunits with solution, similarly to Z rings reconstituted outside or inside tubular liposomes. FtsZ from Escherichia coli and Mycobacterium tuberculosis assembled rings of similar structure, suggesting a universal structure across bacterial species. Previous models for the Z ring in bacteria have favored a structure of widely scattered filaments that are not in contact. The ribbon structure that we discovered here for reconstituted inside-out FtsZ rings provides what to our knowledge is new evidence that the Z ring in bacteria may involve lateral association of protofilaments.     

SPACING OF PARENCHYMA BANDS IN WOOD OF CARYA GLABRA (MILL.) SWEET,PIGNUT HICKORY,AS AN INDICATOR OF GROWTH RATE AND CLIMATIC FACTORS

Variations in the spacing of concentric, tangential bands of apotracheal axial wood parenchyma cells in the annual growth rings of Carya glabra (Mill.) Sweet constitute a record of changes in radial growth rate and of fluctuations in climatic factors. This relationship was determined from trees that were growing under moisture stress and consequently had highly consistent ring-width patterns from tree to tree. Band spacing decreased across a growth ring and was generally greater in wide than in narrow rings. Thus, the proportion of xylem cross-sectional area occupied by axial parenchyma tissue was inversely related to ring width. Average numbers of bands in each of 67 years were analyzed relative to ring widths. Years in which bands were unusually numerous relative to ring width were years of low April-May precipitation, leading to slow spring growth and closely spaced bands early in the growing season. Years in which band numbers were unusually low relative to ring width were years of high April-May precipitation, leading to rapid growth and widely spaced bands early in the season; low July precipitation in these years apparently curtailed growth before much of the typical late-season wood, with its closely spaced bands, could form. Parenchyma bands were aggregated within some rings, suggesting that a slowing of growth had been followed by a growth spurt. Evidence for a late-season spurt was that rings with aggregations were significantly wider than rings formed the same year and not having aggregations of bands. The number of vessels per unit of cross-sectional area was inversely related to ring width.     

Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) wood properties in an alkaline air pollution environment

This paper examines the long-term influence on pine (Pinus sylvestris L.) wood properties of alkaline dust pollution (pH 12.3–12.7) emitted over 135 years from a cement plant in Estonia. A study of stemwood physical and mechanical properties in 70–80-year-old Scots pines growing in three zones of different air pollution levels showed serious deviations in comparison with a relatively healthy forest in an unpolluted area. Specimens from polluted trees evidenced smaller sapwood annual ring widths than those from the control trees. At the same time, the number of growth rings in sapwood at breast height increased under pollution. In the polluted areas, percentage of latewood in the annual ring widths was higher than in the unpolluted area. Small amounts of cement dust, which contains elements essential for the mineral nutrition of the trees, might have acted as fertilizer. Pine wood in the polluted stands exhibited increased density, bending strength across the grain, compression strength along the grain and, in some instances, hardness along the grain.     

Seasonal and perennial changes in the distribution of water in the sapwood of conifers in a sub-frigid zone

An analysis was made of progressive changes in patterns of cavitation in the sapwood of three species of conifer (Larix kaempferi, Abies sachalinensis, and Picea jezoensis) that were growing in a sub-frigid zone. In all three conifers, all tracheids of the newly forming outermost annual ring were filled with water or cytoplasm during the period from May to August. However, many tracheids in the transition zone from earlywood to latewood lost water in September, presumably through drought-induced cavitation. Cavitated tracheids tended to be continuously distributed in a tangential direction. Subsequently, some earlywood tracheids of the outermost annual ring lost water during the period from January to March. This was associated with freeze-thaw cycles. In the second and third annual rings from the cambium of all three conifers, the lumina of most tracheids in the transition zone from earlywood to latewood contained no water. In contrast, some latewood tracheids near the annual ring boundary and many earlywood tracheids retained water in their lumina. The third annual ring had more cavitated tracheids than the second annual ring. Our observations indicated that cavitation progressed gradually in the tracheids of the conifers and that they were never refilled once cavitation had occurred. The region involved in water transport in conifers did not include the entire sapwood and differed among annual rings.     

Frequency of partial and missing rings in Acer saccharum in relation to canopy position and growth rate

Locally absent growth rings are known to occur in trees during periods of environmental stress, but little evidence has been available on their frequency in moist temperate forests or on their potential for causing problems in dendroecological studies. In this study, 95 stem disks of Acer saccharum cut from trees representing a wide range of size and age were examined for ring anomalies using three techniques – inspection of disks for partial rings, crossdating of each tree against regional master chronologies, and use of stand history evidence. The number of ring anomalies in Acer saccharum was inversely related to growth rate and vigor. Mean percentage of ring anomalies was 1.3% in dominant canopy trees, 4.6% in trees of the intermediate crown class, and 16.2% in overtopped trees. All of the overtopped trees had partial or missing rings, with a mean of 10 per tree and a range of 2 to 20. Use of crossdating to correct for ring anomalies appeared to be successful in 88% of the canopy trees. However, crossdating results were inconclusive in 32% of the overtopped trees because of low ring width variability, multiple missing rings, and short duration of trouble-free segments. Because overtopped trees are of limited value in reconstructing disturbance history and often cannot be crossdated reliably, we suggest that they normally be excluded from disturbance chronologies.