Effects of experimental stem burial on radial growth and wood anatomy of pedunculate oak

In dendrogeomorphology, abrupt changes in wood anatomy are frequently used to date the exact year of burial and exposure events. However, few studies have addressed the precision and underlying mechanisms of these changes. In a field experiment, performed in a drift-sand area in the Netherlands, we buried the stems of mature pedunculate oak trees (Quercus robur L.) up to a height of 50 cm and analysed the responses in ring width and earlywood-vessel characteristics, while monitoring the course of temperature above and below the soil surface.After 3 years of stem burial, we found no significant differences in ring width and earlywood-vessel characteristics between control and buried trees both above and below the burial level. Burial however strongly reduced temperature amplitude and the occurrence of sub-zero temperatures around the buried stems. All buried trees formed epitropic roots that grew upward into the new sediment layer, but no adventitious roots were formed on the buried stems. Irrespective of the burial treatments, we found that the mean ring width was largest at the original stem base and lowest at breast height. In contrast, vessel sizes were significantly larger at breast height compared with the stem base. Differences in vessel density barely differed between years and heights.In our field experiment on mature pedunculate oak trees, the burial of stems by 50 cm of drift sand did not induce any local growth suppression or detectable changes in wood anatomy. As wood-anatomical changes in response to burial have previously been reported for trees that had formed adventitious roots, we stress the role of adventitious-root formation as a possible trigger behind the local changes in wood anatomy, reflecting a functional change of a buried stem towards a root. Based on our field experiment, it seems unlikely that years of shallow or moderate burial events (≤50 cm) can be reconstructed using the wood structure of buried stems. As epitropic roots develop quickly after burial, dating such roots may potentially yield better estimates of burial events. Further research on the relation between adventitious root and changes in stem anatomy is needed to ascertain the precision of dating sand-burial events using tree rings.     

Tree rings as an early warning against catastrophic landslides: Assessing the potential of dendrochronology for determining slope stability

We investigated three slopes (in southern Poland, the Carpathian Mts, and the Sudeten Mts) subject to catastrophic, sudden landslides. To reconstruct past landslide activity, we analysed the eccentricity of tree rings in the stems of Norway spruce (Picea abies) using a per cent eccentricity index method. We obtained data on year-by-year changes in eccentricity patterns of single specimens, as well as data on landslide events dated from the whole population of trees sampled on each slope (13–30 spruce trees). These data supplied indirect information on the temporal variability of landslide activity on the three slopes revealing that all three slopes were subject to frequent landslide activity (recurrence intervals 2.0–2.7 years) well before catastrophic events that occurred in 1997 and 2010. The study also showed that 3–5 years before a catastrophic event the sample trees started to record increasing ground instability demonstrated as an uninterrupted, sudden increase in the eccentricity of single trees. Our results suggest that the application of dendrochronological methods can reveal slopes at an increased risk of catastrophic landsliding well in advance. The methods we applied show great promise for forecasting catastrophic landslides and assessing landslide hazard, slope stability and the effectiveness of engineering works undertaken to stabilise landslides.     

The potential of intra-annual density information for crossdating of short tree-ring series

The crossdating of tree-ring series is typically based on tree-ring width sequences, which is a crude abstraction of the growth signal stored in tree rings. In contrast, intra-annual wood density data allows a much more detailed comparison of wood growth processes and new measurement techniques scale well to measure large amounts of samples. Thus, chronologies of intra-annual densitometric curves can be built. Here, we investigate to what extent intra-annual wood density information can improve crossdating. We evaluate different approaches on a data set of Norway spruce trees (Picea abies) and compare the results to standard methods that are based on ring width or maximum density. Our results show that intra-annual densitometric data indeed increases crossdating success rate notably for short tree ring series that cover less than 25 years.     

Biases in RCS tree ring chronologies due to sampling heights of trees

The Regional Curve Standardization (RCS) is one of the most employed standardization methods to remove biological signals in long tree ring chronologies. The approach assumes that an overall age-related growth trend typify all tree ring series to be included in a standardized tree ring chronology. Although several potential problems of the method have been examined, the influence of varying the sampling height along tree stems has not been evaluated. Considering that age-related growth trends may vary with stem height, biases may arise when combining samples from unknown or variable sampling heights, a frequent situation with subfossil logs. In this study we perform a detailed stem analysis of 15 lakeshore black spruce (Picea mariana Mill. B.S.P.) trees in the taiga of eastern Canada to describe how the age-related growth trend varies with stem height and evaluate associated biases in RCS chronologies built from living and subfossil trees. Results show that the age-related growth trends vary markedly and systematically along stems, potentially generating large methodological biases in RCS chronologies, especially near the recent chronology end. These biases may lead to erroneous reconstructions of recent climatic trends and cause false divergence between tree ring and climate series. We have developed a correction procedure that appears efficient in removing these biases from chronologies built with the lakeshore trees and associated subfossil logs.     

Estimation of stem and tree level biomass models for Prosopis juliflora/pallida applicable to multi-stemmed tree species

The aim of this paper is to develop biomass models for commonly multi-stemmed Prosopis juliflora/pallida trees. The data were collected on three of the Cape Verde islands (Maio, Santiago and Santo Antao). The dataset covers 240 trees containing 1,882 stems with stem diameter at breast height over 2 cm; of that 255 individual tree stems were sampled destructively. These calibration data were used to construct stem and tree-level models for estimation of total aboveground biomass and its fine and course fractions with diameter threshold of 5 cm. A set of parameterized biomass models for multi-stemmed Prosopis spp. trees suited for biomass estimation at tree and stem levels using appropriate set of independent variables, commonly available in forest inventory programs, was created. The effect of site (island) on tree allometry was not detected. The two-phase construction of tree biomass models based on destructive sampling limited to individual stems combined with a routine field measurement of entire multi-stemmed tree specimen represents a practicable approach leading to biomass and carbon assessment that may be generally suited for tree species with complex multi-stemmed growth form similar to that of Prosopis spp.     

BAI BAI bias – An evaluation of uncertainties in calculating basal area increments from cores

Basal area increment (BAI) is increasingly used in tree-ring based studies as it provides a direct measure of wood production and thus allows for the interpretation of growth trends. BAIs from increment cores are generally calculated while assuming circular growth patterns. However, observation of stem discs shows that many ring shapes are characterized by some form of eccentricity, not only characterized by deviations from circular ring shapes but also by piths not being centrally located. This observation poses to the question with what accuracy BAIs are calculated from increment cores. To quantify the estimation bias in BAI, we have developed a method that mimics eccentric tree growth by simulation. Various aspects of eccentricity are incorporated to created ‘stem discs’ with realistic appearances. Since BAI time series for our simulated discs are known, we can evaluate the accuracy of BAI calculation methods from cores. The ‘coring’ is simulated by taking cores at the thickest and thinnest sides of the simulated discs, whereby the number of cores is varied from one to four. In our simulations, we choose two calculation methods, namely the traditional circular approach and one that is based on the assumption of elliptical growth shapes. We find that bias in calculated BAI values is highly influenced by the number of cores taken, with a dramatic decrease from one to four cores. Furthermore, trend patterns in BAI series might be misleading in case of highly eccentric growth patterns. Based on these findings, we discuss the consequences for the interpretation of existing literature, where BAI analyses are based on one or two cores (along with the assumption of circular ring shapes). Such consequences are, however, difficult to quantify since we have no eccentricity statistics of tree growth within a forest stand. Therefore, we do not know the randomness of eccentricity within a stand, and thus to what extent chronology building (i.e. averaging BAI estimates over multiple trees) may reduce estimation bias. To lower BAI bias, we recommend to base BAI calculations on as many cores as possible. For individual trees with high levels of eccentricity, taking four increment cores seems necessary to reasonably estimate their basal area increments.     

3D analysis of anatomical reactions in conifers after mechanical wounding: first qualitative insights from X-ray computed tomography

The ability of trees to recover from damage beyond the last-formed periderm as well as the drivers and nature of associated wound reactions have been studied for more than two centuries using macroscopic (desiccation, aeration or discoloration of wood) and microscopic approaches (anatomical and chemical reactions). However, no studies currently exist which address large-scale macroscopic and microscopic reactions surrounding wounds in the tangential, axial, and radial directions over continuous segments of tree stems. This note explores the potential of 3D X-ray computed tomography in assessing effects of wounding under natural conditions in European conifers (Abies alba, Larix decidua, Picea abies). We present results from a pilot study and qualitatively evaluate the potential of the approach used in assessing and illustrating the formation and spread of de-differentiated xylem parenchyma cells, xylem decay compartmentalization, resin ducts, and stabilizing compression wood cells.     

Adventitious roots as a source of information in reconstructing the activity of modern aeolian processes in the temperate climate zone: A case study from the Kozłów sandy area (SW Poland)

This paper presents a spatial-temporal reconstruction of inland dune movements at an anthropogenic active sandy area known as the Kozłów Desert, SW Poland. This unique sandy area, with assemblages of aeolian forms typical of “true” deserts, is an inactive military training ground (decommissioned in 1992) where military activity led to the initiation of geomorphic processes. The reconstruction was carried out based on the growth reaction characteristics of Scots pine (Pinus sylvestris L.) and downy birch (Betula pubescens L.) trees. 14 increment cores were collected from 12 trees and analysed with standard dendrochronological techniques. Samples of adventitious roots from all the trees examined were collected and prepared to extend the analyses and check their usefulness in dating modern geomorphic processes. The adventitious roots of pine and birch were found to react differently to burial, in terms of both reaction time and the shape of the root system. Growth-ring widths and wood anatomy were indicative of sudden or multi-stage sand movement, thus confirming the usefulness of adventitious roots as an additional source of information about aeolian process activity. More broadly, the study shows that the dynamics of landforming processes can be assessed more accurately and reliably by using such a combination of methods, comparing data from roots to data from tree trunks.     

Exploring the growth response of Norway spruce (Picea abies) along a small-scale gradient of soil water supply

The climate-growth response of specific sites and species is one of the main research subjects in classic tree ring studies. Traditional sampling approaches therefore aim at maximizing the climate signal of the analyzed tree ring series, which is typically achieved by focusing on dominant trees or on sites located in particularly temperature or moisture limited environments. However, there is increasing evidence that these selective sampling strategies cannot yield chronologies that are representative for entire populations. One promising approach to gain a deeper understanding of forest dynamics and climate-growth responsiveness is the analysis of climate signal ranges among trees. This individualistic approach requires random sampling and the integration of information on small-scale heterogeneities in site and tree characteristics. Here, we analyze the climate-growth response of 144 Norway spruce trees (Picea abies Karst.) on difference levels of data aggregation. The aim of our study is to investigate the relevance of small-scale heterogeneities in site conditions, particularly in soil water supply, for the detected climate-growth signal. We identify soil water supply and site characteristics, which indirectly modify the water availability for trees, as dominating growth factors across scales. The driest sites show the strongest climate-growth reaction, while the growth response of wetter sites is weak or even insignificant. Therefore, we conclude that integrating small-scale information on site characteristics, particularly on soil water supply, can help to gain a deeper understanding of species specific growth limitations.     

Optimization of sampling procedures for DNA‐based diagnosis of wood decay fungi in standing trees

Aims: To develop fast and reliable sampling procedures for DNA‐based diagnosis of wood decay fungi in standing trees. Methods and Results: A total of 250 trees were tested for the presence of a suite of wood decay fungi by collecting wood frass obtained by drilling each tree once with a 4‐mm‐diameter, 43‐cm‐long bit. We identified at least one of 11 target wood decay fungi in 56 trees through multiplex PCR assays. The presence of target wood decay taxa was further investigated in these 56 trees, by analysing independently wood from each of six drillings. Results were then compared with those obtained using sampling schemes differing in terms of number and position of drillings. Samples of 1–4 drillings were either analysed separately, and the results were combined, or pooled together before analysis was performed. In comparison with taxa identified by the analysis of six drillings, diagnostic efficiency ranged from 56·6% for the scheme based on a single drill to 96·8% for the scheme based on four drillings analysed separately. Both schemes significantly differ (P < 0·05) from those based on two and three drillings, whose efficiency was 72·6% and 83·9%, respectively. Diagnostic efficiency of pooled samples was comparable to that of samples analysed separately. Conclusions: Highest diagnostic efficiency was obtained by analysing wood from four drillings. It is advisable to pool samples deriving from different drillings to reduce laboratory costs. Significance and Impact of the Study: Fast and reliable sampling procedures make DNA‐based diagnosis more suitable for tree inspection procedures.     

Effect of elevated [CO2] on stem wood properties of mature Norway spruce grown at different soil nutrient availability

The objective of the present study was to investigate the interactive effects of elevated [CO₂] and soil nutrient availability on secondary xylem structure and chemical composition of 41‐year‐old Norway spruce (Picea abies (L.) Karst.) trees. The nonfertilized and irrigated‐fertilized trees were, for 3 years, continuously exposed to elevated [CO₂] in whole‐tree chambers. Elevated [CO₂] decreased concentrations of soluble sugars, acid‐soluble lignin and nitrogen in stem wood, but the effects were not consistent between sampling height and/or fertilization. The effect of 2*ambient [CO₂] on wood structure depended on the exposure year and/or fertilization. Radial lumen diameter decreased and annual ring width increased in the second year of exposure (1999) in elevated [CO₂]. In the latter, the CO₂ effect was significant only in the nonfertilized trees. Stem wood chemistry and structure were significantly affected by fertilization. Fertilization increased the concentrations of nitrogen and gravimetric lignin, annual ring width, and radial lumen diameter. Fertilization decreased C/N ratio, mean ring density, earlywood density, latewood density, cell wall thickness, cell wall index, and latewood percentage. We conclude that elevated [CO₂] had only minor effects on wood properties while fertilization had more marked effects and thus may affect ecosystem processes and suitability of wood for different end‐use purposes.     

African Baobabs with False Inner Cavities: The Radiocarbon Investigation of the Lebombo Eco Trail Baobab

The article reports the radiocarbon investigation results of the Lebombo Eco Trail tree, a representative African baobab from Mozambique. Several wood samples collected from the large inner cavity and from the outer part of the tree were investigated by AMS radiocarbon dating. According to dating results, the age values of all samples increase from the sampling point with the distance into the wood. For samples collected from the cavity walls, the increase of age values with the distance into the wood (up to a point of maximum age) represents a major anomaly. The only realistic explanation for this anomaly is that such inner cavities are, in fact, natural empty spaces between several fused stems disposed in a ring-shaped structure. We named them false cavities. Several important differences between normal cavities and false cavities are presented. Eventually, we dated other African baobabs with false inner cavities. We found that this new architecture enables baobabs to reach large sizes and old ages. The radiocarbon date of the oldest sample was 1425 ± 24 BP, which corresponds to a calibrated age of 1355 ± 15 yr. The dating results also show that the Lebombo baobab consists of five fused stems, with ages between 900 and 1400 years; these five stems build the complete ring. The ring and the false cavity closed 800–900 years ago. The results also indicate that the stems stopped growing toward the false cavity over the past 500 years.     

Cross-sectional compression wood distribution and its relation to eccentric radial growth in Picea abies [L.] Karst

The formations of compression wood and eccentric radial increment are two phenomena that are so closely associated that they cannot be readily discussed separately. However, various studies suggest that their formation is stimulated by different mechanisms and that there is no functional relationship. While the formation of compression wood is a reaction of coniferous trees to negative gravitroptic scenarios which enables the trees to recover from displacement, one-sided radial growth promotion is stimulated by unilateral mechanical strain on the cambium for lowering stress peaks. This study offers an approach to quantify the relation of both phenomena in stem cross-sections and single growth rings.Samples of 56 Norway spruces (Picea abies [L.] Karst.) from sites differing in slope and exposure to the prevailing wind direction were examined for their cross-sectional compression wood distribution and eccentricity in radial increment. The assessment of both phenomena on stem cross-sections was based on their spectral properties in reflected light. Hyperspectral image analysis allowed detection of compression wood distribution as well as measurement of annual radial increment along eight radii, oriented by compass direction.Since the distributions of both phenomena comprise both a directional component as well as amplitude in annual reference, these data were handled as vectors. Circular statistics were applied to describe and quantify their relationship and to test both phenomena for the inducing environmental factor that stressed the tree.The direction of compression wood formation and eccentric growth is significantly positively correlated. In the majority of observations a unimodal distribution of both phenomena is given. Mostly strong one-sided compression wood formation is associated with a coincident direction of eccentric radial increment. However, stem cross-sections with a distinct direction of compression wood were observed without a dominating direction of eccentric growth, and vice versa.Bivariate statistics that consider vector direction as well as vector length have proved to be very helpful in retrospectively identifying possible initiating environmental factors for both phenomena at a given site. The location of standard and confidence ellipses in relation to the assumed direction of action is a strong indication for or against an assumed environmental factor.     

Bursts of CO2 released during freezing offer a new perspective on avoidance of winter embolism in trees

MethodsCO₂ efflux measurements were conducted during freezing experiments for saplings of three Scots pine (Pinus sylvestris) and three Norway spruce (Picea abies) trees under laboratory conditions, and the magnitudes of the freezing-related bursts of CO₂ released from the stems were analysed using a previously published mechanistic model of CO₂ production, storage, diffusion and efflux from a tree stem. The freezing-related bursts of CO₂ released from a mature Scots pine tree growing in field conditions were also measured and analysed.ConclusionsAll gases dissolved in the xylem sap are not trapped within the ice in the stem during freezing, as has previously been assumed, thus adding a new dimension to the understanding of winter embolism formation. The conduit water volume not only determines the volume of bubbles formed during freezing, but also the efficiency of gas efflux out of the conduit during the freezing process.     

Constructing tree stem form from digitized surface measurements by a programming approach within discrete mathematics

Key message

The main message of this work is the demonstration of possibility of creation of stem shape from digitized points using integer-programming approach. The points are digitized by magnetic motion tracker which in contrast to the laser scanning allows the reconstruction of complete cross-section of stem even in the “hidden (invisible)” part.

Abstract

Three-dimensional information on tree stem form plays an important role in understanding the structure and strength of a standing tree against the forces of wind, snow, and other natural pressure. It also contributes to precision in volume measurement compared to conventional two-dimensional measurement. We investigate approaches for obtaining three-dimensional information of tree stem form from partially organized surface measurements, acquired using a three-dimensional digitizing device (Polhemus FASTRAK^® motion tracking device). We then propose a new programming approach from discrete mathematics to construct tree stem form. Our method is based on an optimal connection of neighbor triangles for surface construction, which is created by locally possible combination of three digitized points on the stem surface. We compare the proposed method to the existing heuristic methods of contour tracing and region growing. Our analysis shows that the proposed method provides a consistent construction of tree stem form, for even stems with extremely irregular structure such as those from bent trees and mangrove trees with unique root spread, while the other methods are incapable for constructing such tree stems.     

Growth dynamics and potential for cross-dating and multi-century climate reconstruction of Podocarpus falcatus in Ethiopia

Podocarpus falcatus is an indigenous evergreen conifer species of tropical mountain forests in southeastern Ethiopia, showing potential tree ages of around 500 years. To study the influence of seasonal climate on the growth pattern of P. falcatus, we combined high-resolution electronic dendrometer measurements with wood anatomical investigations of microcores from the outermost stem parts collected in monthly intervals. At any time of the year sufficient rain events are able to cause cambial activity in P. falcatus. This permanent growing readiness leads to irregular wood formation with the formation of intra-annual density fluctuations and missing rings. Wood anatomical studies of microcores collected around the circumference of a mature P. falcatus revealed locally different activity status of the cambium on different lobes of the stem. Tree-ring width measurements of stem disks resulted in tentative tree ages that were confirmed by radiocarbon dating of selected wood samples. Although our efforts to cross-date ring-width series from several stem disks were not successful, further sampling in areas with different rainfall regimes, additional radiocarbon dating and measurements of stable isotopes hopefully would enable the establishment of a multi-century-long tree-ring series for climate reconstruction.     

When does dead wood turn into a substrate for spruce replacement?

Question: How many years must elapse for freshly fallen Picea abies stems to be transformed into a substrate for P. abies recruitment? Location: Natural sub‐alpine spruce forest, 1200–1300 m a.s.l., western Carpathians, Poland. Methods: Coarse woody debris (CWD) was measured on nine plots with a total area of 4.3 ha. All individuals of P. abies regeneration growing on dead wood were counted and their age was estimated. Decay rate of logs was determined using dendrochronological cross‐dating of samples from logs in different decay stages. Results: Although CWD covered only 4% of the forest floor, 43% of the saplings were growing on decaying logs and stumps. The highest abundance of P. abies recruitment occurs on logs 30–60 years after tree death, when wood is in decay stages no. 4–7 (on an 8 degree decay scale). However, much earlier colonization is possible. The first seedlings may germinate on a log during the second decade after tree death and survive for decades. Their slow growth is possibly due to the gradual progressive decomposition of wood. Conclusions: This study confirms the importance of decaying wood for P. abies recruitment. The decaying logs exhibit continuous and favourable conditions for the germination of P. abies seeds throughout their decay process. Logs, irrespective of their decay stage and age, are colonized by young seedlings. This recruitment bank is constantly renewed.     

Effects of bending stress on taper and growth of stems of youngEucalyptus regnans trees

A glasshouse experiment investigated the effect of bending stress on stem radial and height growth and stem taper ofEucalyptus regnans seedlings. Eighteen-week-old, potted seedlings were bent continuously for 8 weeks with a static bending stress. The bending treatment was then removed and the seedlings grown for another 12 weeks. Other seedlings were stayed vertically throughout the experiment whilst control seedlings were neither bent nor stayed. Seedlings were rotated every 2 days to prevent reaction wood developing asymmetrically in the stems of bent trees. Bent trees had higher radial growth rates, developed more tapered stems and had higher safety factors (the ratio of stem radius to the minimum radius required to prevent the tree toppling over) than unbent seedlings. They produced a band of tension wood in their stems and ceased height growth whilst bent. When bending ceased, they resumed normal radial and height growth. Unbent trees developed more cylindrical stems. There were no differences in growth behaviour between stayed and control trees. Bent and unbent trees all developed a butt swell, the taper of which was not affected by treatment. It was concluded that bending stress has substantial effects on both the size and taper of tree stems. However, the development of butt swell is independent of the bending stress applied. The results were considered in relation to biomechanical theories of tree stem development.     

Mechanical properties of spruce and beech wood grown in elevated CO2

Biomechanical responses of stems of 6- to 7-year-old spruce [Picea abies (L.) Karst.] and beech (Fagus sylvatica L) trees were studied after 4 years of growth in elevated atmospheric CO₂ in combination with a nitrogen treatment and on two different soil types. At the end of the treatment, stems were harvested and tested in fresh and air-dried status. Bending characteristics of juvenile wood (modulus of elasticity, termed rigidity) were determined by bending tests. Fracture characteristics (termed toughness) were determined by stroke-pendulum tests. From the base disk of each stem densitometric data were obtained. In spruce, wood produced under elevated CO₂ was tougher on both soil types; enhanced N deposition made wood less rigid only on acidic soils. In contrast, beech wood samples showed no significant reaction to CO₂ but were significantly tougher under high nitrogen depositions on acidic soil. Effects on wood density of both CO₂ and N treatments were not significant, but wood density was higher on acidic soil and so were rigidity and toughness (soil effect). Different genotypes of spruce and beech reacted significantly differently to the treatments. Some genotypes reacted strongly to CO₂ or N, whereas others did not react or showed interactions between CO₂ and N. This underlines the importance of genetic diversity in tree communities.     

A power-driven increment borer for sampling high-density tropical wood

High-density hardwood trees with large diameters have been found to damage manually operated increment borers, thus limiting their use in the tropics. Therefore, we herein report a new, low-cost gasoline-powered sampling system for high-density tropical hardwood trees with large diameters. This system provides increment cores 15 mm in diameter and up to 1.35 m in length, allowing minimally invasive sampling of tropical hardwood tree species, which, up to the present, could not be collected by conventional 5 or 10 mm increment borers. This system provides a single core sample with ample amount of wood for multidisciplinary analyses, including ring width, stable isotope and wood anatomical measurements. The borer never gets stuck inside stems, even in hollowed trees, cores will never twist during coring, and the gasoline drill gives ample flexibility in the field. It is anticipated that the dendrochronological community will find our technique very useful in the pursuit of tropical tree ring research.