A techno-functional approach applied to the lithics of the Late Upper Palaeolithic Shizitan 29 site allows the identification of previously unrecognized technical features of microblade pressure ...production and new behavioral understanding of its evolution beginning ca. 26,000 cal b.p. These technical features may relate to the evolution of so-called boat-shaped cores, including the development of two blade scar sequences and the 8-like contour of the striking platform (likely related to fixing cores in a holding device). Counter to traditional typological lithic analyses centered on final core morphologies, we seek to identify technical objectives related to the required pressure production. In doing so, we argue that earlier semi-conical cores may have maximized the exploitation of the core volume, while subsequent boat-shaped cores developed to maximize the efficiency of the production of straight profile, regular blades. This allowed microblades to become a critical adaptation for final Pleistocene hunter-gatherers in northern East Asia.
•Water use differed between Larix principis-rupprechtii and Picea meyeri.•Larch relied upon winter snowmelt water for tree growth onset more than spruce did.•Both larch and spruce mainly used water ...from 10 to 20 cm soil layer in growing season.•There was inter-specific competition for water due to weak water source partitioning.•Spruce showed greater plasticity in soil water uptake than larch during drought.
Understanding interspecific differences in tree water use will aid in the assessment of both tree-level ecophysiological adaptation to climate change and forecasts of forest dynamics. We investigated the seasonal variation of water sources between two co-occurring trees species with contrasting leaf phenology and rooting traits: the deciduous Larix principis-rupprechtii Mayr. and the evergreen Picea meyeri Rehd. et Wils. At weekly/biweekly intervals from September 2013 to October 2014 in the Luya Mountains in North-Central China, we collected and analyzed a total of approximately 2400 samples of δD and δ18O in tree xylem water, potential water sources for all study trees, and the contribution of water at different soil depths. Concurrently, we monitored leaf phenology by direct observation and wood phenology with the microcore method. Microcoring allowed us to trace intra-annual dynamics of word formation (i.e., onset, end, and maximum growth rate). These results, including a seasonal origin index, indicated that winter snowmelt water is sourced for growth initiation for both larch and spruce, although larch relies on it more than spruce. Larch and spruce mainly absorbed water from the same soil layer of 10–20 cm during the growing season (circa 38.9% and 37.5% of total water uptake, respectively). However, this potential inter-specific water competition did not increase until growth rates reached the maximum for the year; larch used more water from deeper soil layers while spruce used water generally equally from each soil layer. Unlike deeper-rooting larch, the more shallow-rooted spruce showed a greater ability to shift water uptake among various soil layers. This plasticity in water uptake was accompanied by tighter stomatal regulation, suggesting spruce growth is generally more tightly coupled to water availability. Such diverging species-specific water use strategies improve our knowledge on tree-level ecophysiological mechanisms, with implications for understanding ecosystem-level forest dynamics and potential resilience to environmental stress.
Monitoring cambial phenology and intra-annual growth dynamics is a useful approach for characterizing the tree growth response to climate change. However, there have been few reports concerning ...intra-annual wood formation in lowland temperate forests with high time resolution, especially for the comparison between deciduous and coniferous species. The main objective of this study was to determine how the timing, duration and rate of radial growth change between species as related to leaf phenology and the dynamics of non-structural carbohydrates (NSC) under the same climatic conditions. We studied two deciduous species, Fagus sylvatica L. and Quercus petraea (Matt.) Liebl., and an evergreen conifer, Pinus sylvestris L. During the 2009 growing season, we weekly monitored (i) the stem radial increment using dendrometers, (ii) the xylem growth using microcoring and (iii) the leaf phenology from direct observations of the tree crowns. The NSC content was also measured in the eight last rings of the stem cores in April, June and August 2009. The leaf phenology, NSC storage and intra-annual growth were clearly different between species, highlighting their contrasting carbon allocation. Beech growth began just after budburst, with a maximal growth rate when the leaves were mature and variations in the NSC content were low. Thus, beech radial growth seemed highly dependent on leaf photosynthesis. For oak, earlywood quickly developed before budburst, which probably led to the starch decrease quantified in the stem from April to June. For pine, growth began before the needles unfolding and the lack of NSC decrease during the growing season suggested that the substrates for radial growth were new assimilates of the needles from the previous year. Only for oak, the pattern determined from the intra-annual growth measured using microcoring differed from the pattern determined from dendrometer data. For all species, the ring width was significantly influenced by growth duration and not by growth rate, which differs from previous studies. The observed between-species difference at the intra-annual scale is key information for anticipating suitability of future species in temperate forests.
Wood formation in European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) was intra-annually monitored to examine plastic responses of the xylem phenology according to altitude in ...one of the southernmost areas of their distribution range, i.e., in the Moncayo Natural Park, Spain. The monitoring was done from 2011 to 2013 at 1180 and 1580 m a.s.l., corresponding to the lower and upper limits of European beech forest in this region. Microcores containing phloem, cambium and xylem were collected biweekly from twenty-four trees from the beginning of March to the end of November to assess the different phases of wood formation. The samples were prepared for light microscopy to observe the following phenological phases: onset and end of cell production, onset and end of secondary wall formation in xylem cells and onset of cell maturation. The temporal dynamics of wood formation widely differed among years, altitudes and tree species. For Fagus sylvatica, the onset of cambial activity varied between the first week of May and the third week of June. Cambial activity then slowed down and stopped in summer, resulting in a length of growing season of 48-75 days. In contrast, the growing season for P. sylvestris started earlier and cambium remained active in autumn, leading to a period of activity varying from 139-170 days. The intra-annual wood-formation pattern is site and species-specific. Comparison with other studies shows a clear latitudinal trend in the duration of wood formation, positive for Fagus sylvatica and negative for P. sylvestris.
Dendrometer measurements are a frequently used alternative to the laborious and time consuming microcoring to investigate intra-annual growth dynamics of trees. However, since dendrometer data not ...only comprise cambial growth, but also hydrological fluctuations, both signals need to be disentangled to derive critical dates of xylem phenology from dendrometer data. For this purpose, various approaches can be found in the literature, however a systematic comparison of the different options is still missing. In this study we present a methodological framework to evaluate the accuracy of different mathematical fittings to derive tree-ring phenology from dendrometer data and apply this approach to a data set comprised of three conifer species where high-resolution band dendrometer measurements and microcore sampling have been done in parallel. Based on our study we provide evidence that the most common approaches to derive onset and cessation of xylem cell enlargement from dendrometer data, i.e. applying absolute and relative thresholds to deterministic models fitted to dendrometer data, caused systematic deviations from the reference of xylogenesis observations, but could be improved by small adaptations. The most precise and unbiased predictions of xylem growth phenology were obtained by fitting the three-parameter Gompertz model to the dendrometer data and applying a relative threshold of 3.5% of annual increment to the model predictions for growth onset and an absolute threshold of 4.5 µm day-1 based on the first model derivative for growth cessation. Our framework enables an improved usage of dendrometer data for the prediction of the onset and cessation of xylem cell enlargement, which are important ecological indicators to quantify the effects environmental changes on forest growth and the terrestrial carbon cycle.
Dendrometers offer valuable insights into how tree growth responds to climatic variables and physiological processes over the course of a year. Yet, their applicability to extremely slow-growing ...trees, such as those in peatlands, has been limited due to the intricate and slow nature of growth, therefore rendering interpretation of results complex. In this study, we conducted a comprehensive monitoring of tree wood formation in both peatland and mineral soil ecosystems in southern Sweden (58.37 N, 12.17 E, 75 m asl) in 2021 and 2022, using both band and point dendrometers. To verify and validate the dendrometer data, we also sampled microcores every two weeks during both growing seasons. We find that peatland trees grow at approximately 30 % the rate of their neighbors on mineral soils. The onset of growth among peatland trees typically occurs between mid-May and early June, consistently lagging the start of the growing season in trees on mineral soils by one to three weeks. Notably, growth peaks are synchronized across peatland trees and coincide with the summer solstice. Both types of dendrometers exhibit varying degrees of accuracy depending on the phenological stages measured. They perform well in identifying growth onset and peak but are less effective at detecting growth cessation. Point dendrometers demonstrate superior accuracy as they better capture daily irreversible growth increments. In the case of band dendrometers, growth increments are obscured by greater reversible fluctuations in dead bark tissues. However, they remain valuable for tracking the wood phenology of trees with growth rates exceeding 2 mm/year. Based on our results, for an effective tree monitoring in peatlands, we strongly recommend (1) using point dendrometers and (2) removing the dead bark tissues on monitored trees.
Radial growth of trees can result in opposite wood (OW) and compression wood (CW) due to the varying impact of stem mechanical stress, such as that caused by gravity or wind. Previous research has ...identified higher xylem production in CW compared to OW. Yet, it remains unclear whether the difference in the number of xylem cells between OW and CW results from differences in growth rate or the duration of xylem cells. In this study, we collected wood microcores on a weekly basis from March 2019 to January 2020 in
Pinus massoniana
Lamb. located on a steep slope. Our objective was to compare the dynamic of cambial activity and resulting cellular anatomical parameters between OW and CW in a humid subtropical environment. Our results showed that the xylem phenology of OW and CW was generally consistent with the xylem cell division process beginning in early March and ceasing in November. The last latewood cell completed its differentiation at the end of December. The response of wood formation dynamics to climate was consistent in both OW and CW. Moreover, both wood types exhibited a limited development of the enlargement phase due to the heat and drought during the summer. The rate of cell division was responsible for 90.7% of the variability in the number of xylem cells. The CW xylem obtained a larger number of cells by increasing the rate of cell division and displayed thinner earlywood cells with larger lumens than OW cells. Our findings showed that the xylem of conifer species responds to mechanical stress by accelerating the cell division rate. As a result, we suggest calculating the ratio between OW and CW widths to reconstruct wind stress changes rather than calculating the residuals used in the current study.
Determining the effect of a changing climate on tree growth will ultimately depend on our understanding of wood formation processes and how they can be affected by environmental conditions. In this ...context, monitoring intra-annual radial growth with high temporal resolution through point dendrometers has often been used. Another widespread approach is the microcoring method to follow xylem and phloem formation at the cellular level. Although both register the same biological process (secondary growth), given the limitations of each method, each delivers specific insights that can be combined to obtain a better picture of the process as a whole. To explore the potential of visualizing combined dendrometer and histological monitoring data and scrutinize intra-annual growth data on both dimensions (dendrometer → continuous; microcoring → discrete), we developed DevX (Dendrometer vs. Xylogenesis), a visualization application using the “Shiny” package in the R programming language. The interactive visualization allows the display of dendrometer curves and the overlay of commonly used growth model fits (Gompertz and Weibull) as well as the calculation of wood phenology estimates based on these fits (growth onset, growth cessation, and duration). Furthermore, the growth curves have interactive points to show the corresponding histological section, where the amount and development stage of the tissues at that particular time point can be observed. This allows to see the agreement of dendrometer derived phenology and the development status at the cellular level, and by this help disentangle shrinkage and swelling due to water uptake from actual radial growth. We present a case study with monitoring data for Acer pseudoplatanus L., Fagus sylvatica L., and Quercus robur L. trees growing in a mixed stand in northeastern Germany. The presented application is an example of the innovative and easy to access use of programming languages as basis for data visualization, and can be further used as a learning tool in the topic of wood formation and its ecology. Combining continuous dendrometer data with the discrete information from histological-sections provides a tool to identify active periods of wood formation from dendrometer series (calibrate) and explore monitoring datasets.
Key message
A technique whereby whole mounts of delicate tissues of differentiating xylem are imaged directly by polishing and block-face imaging of embedded microcores. Autofluorescence and image ...analysis aids identifying the stages of xylogenesis.
Stem microcores from fast-growing trees, such as
Pinus radiata
(D. Don) with wide zones of cambium and differentiating xylem and very wide growth rings, pose a challenge for microscopy, as they are difficult to handle and easily damaged compared to slower growing species. A novel procedure has been developed which captures high-resolution images directly from the block face of large samples embedded in plastic resin without the need for sectioning or staining. Microcores of differentiating xylem of
P. radiata
growing in the central North Island of New Zealand were embedded in a low viscosity acrylic resin. The surface of the entire resin block was abraded and polished to expose cross sections of the wide zone of wood formation in these fast-growing trees without damage or distortion. Autofluorescence imaging was performed using a confocal laser scanning microscope. This avoided the need for staining and allowed the determination of the beginning of lignification based on lignin autofluorescence. Image analysis was used to determine the widths of: (a) the cambium, cell expansion, and wall-thickening zone (CET) and (b) the wall lignification zone (LT). A fast-growing tree had wider CET and LT zones than a slow-growing tree. This was due to the fast-growing tree producing more tracheids than the slow-growing tree, rather than by the production of larger tracheids.
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