Structure and function of intra–annual density fluctuations: Mind the gaps

Tree rings are natural archives of climate and environmental information with a yearly resolution. Indeed, wood anatomical, chemical, and other properties of tree rings are a synthesis of several intrinsic and external factors, and their interaction during tree growth. In particular, Intra-Annual Density Fluctuations (IADFs) can be considered as tree-ring anomalies that can be used to better understand tree growth and to reconstruct past climate conditions with intra-annual resolution. However, the ecophysiological processes behind IADF formation, as well as their functional impact, remain unclear. Are IADFs resulting from a prompt adjustment to fluctuations in environmental conditions to avoid stressful conditions and/or to take advantage from favorable conditions? In this paper we discuss: (1) the influence of climatic factors on the formation of IADFs; (2) the occurrence of IADFs in different species and environments; (3) the potential of new approaches to study IADFs and identify their triggering factors. Our final aim is to underscore the advantages offered by network analyses of data and the importance of high-resolution measurements to gain insight into IADFs formation processes and their relations with climatic conditions, including extreme weather events

Comparing Forest Measurements from Tree Rings and a Space-Based Index of Vegetation Activity in Siberia

Different methods have been developed for measuring carbon stocks and fluxes in the northern high latitudes, ranging from intensively measured small plots to space-based methods that use reflectance data to drive production efficiency models. The field of dendroecology has used samples of tree growth from radial increments to quantify long-term variability in ecosystem productivity, but these have very limited spatial domains. Since the cambium material in tree cores is itself a product of photosynthesis in the canopy, it would be ideal to link these two approaches. We examine the associations between the normalized differenced vegetationindex (NDVI) and tree growth using 19 pairs of tree-ring widths (TRW) and maximum latewood density (MXD) across much ofSiberia. We find consistent correlations between NDVI and both measures of tree growth and no systematic difference between MXD and TRW. At the regional level we note strong correspondence between the first principal component of tree growth and NDVI for MXD and TRW in a temperature-limited bioregion, indicating that canopy reflectance and cambial production are broadly linked. Using a network of 21 TRW chronologies from south of Lake Baikal, we find a similarly strong regional correspondence with NDVI in a markedly drier region. We show that tree growth is dominated by variation at decadal and multidecadal time periods, which the satellite record is incapable of recording given its relatively short record

Author Correction: Limited capacity of tree growth to mitigate the global greenhouse effect under predicted warming.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Contribution of xylem anatomy to tree-ring width of two larch species in permafrost and non-permafrost zones of Siberia

Plants exhibit morphological and anatomical adaptations to cope the environmental constraints of their habitat. How can mechanisms for adapting to contrasting environmental conditions change the patterns of tree rings formation? In this study, we explored differences in climatic conditions of permafrost and non-permafrost zones and assessed their influence on radial growth and wood traits of Larix gmelinii Rupr (Rupr) and Larix sibirica L., respectively. We quantified the contribution of xylem cell anatomy to the tree-ring width variability. Comparison of the anatomical tree-ring parameters over the period 1963–2011 was tested based on non-parametric Mann-Whitney U test. The generalized linear modeling shows the common dependence between TRW and the cell structure characteristics in contrasting environments, which can be defined as non-specific to external conditions. Thus, the relationship between the tree-ring width and the cell production in early- and latewood are assessed as linear, whereas the dependence between the radial cell size in early- and latewood and the tree-ring width becomes significantly non-linear for both habitats. Moreover, contribution of earlywood (EW) and latewood (LW) cells to the variation of TRW (in average 56.8% and 24.4% respectively) was significantly higher than the effect of cell diameters (3.3% (EW) and 17.4% (LW)) for the environments. The results show that different larch species from sites with diverging climatic conditions converge towards similar xylem cell structures and relationships between xylem production and cell traits. The work makes a link between climate and tree-ring structure, and promotes a better understanding the anatomical adaptation of larch species to local environment conditions

Permafrost regime affects the nutritional status and productivity of larches in Central Siberia

Вечная мерзлота оказывает сильное влияние на развитие лесов благодаря доступности питательных веществ. Основные вопросы этого исследования касались влияния условий площадки на концентрацию макроэлементов в массе и стабильную изотопную (13C и 15N) динамику в течение вегетационного периода, а также стехиометрию питательных веществ и эффективность резорбции в листве двух общих видов лиственницы в Сибири. Концентрация личинок, выращенных на многолетнемерзлых почвах лиственных пород (N, P и K), была чрезвычайно высокой в юных иглах по сравнению с концентрациями в зоне без вечной мерзлоты, но была в 2 раза ниже с созреванием игл. В пределах вечной мерзлоты деревья с участков с более теплым и более глубоким почвенным активным слоем имели концентрацию питательных веществ на 15-60% и более высокую 15N в их иглах по сравнению с более слабыми, более холодными почвами. Лиственница без вечной мерзлоты демонстрировала обогащение листвой в 15N (от +1,4 до +2,4 ‰) по сравнению с вечной мерзлотой (от -2,0 до -6,9 ‰). Сезонная динамика листьев d13C, как правило, снижалась с июня по август на всех участках, положительно коррелируя с массовыми концентрациями N (r = 0,69, p <0,05) и отрицательно с отношением C: N (r = -0,79, p <0,05) , При старении концентрация питательных веществ в иглах лиственницы значительно уменьшилась на 60-90%. Эта сильная способность лиственницы сохранять питательные вещества посредством резорбции является важным механизмом, который поддерживает рост деревьев в начале вегетационного периода, когда почва остается замороженной. Высокая резорбтивная эффективность, обнаруженная для K и P для лиственниц, установленных на вечной мерзлоте, указывает на ограничение питательных веществ роста деревьев в Центрально-Сибирском плато не только по N, как сообщалось ранее, но и по P и K. Наряду с увеличением биомассы (до 50 раз ), более высокие концентрации питательных веществ и обогащение листьев 15N в более теплых местах указывают на сильную реакцию производительности лиственницы на углубление активного слоя почвы

Prominent role of volcanism in Common Era climate variability and human history

Climate reconstructions for the Common Era are compromised by the paucity of annually-resolved and absolutely-dated proxy records prior to medieval times. Where reconstructions are based on combinations of different climate archive types (of varying spatiotemporal resolution, dating uncertainty, record length and predictive skill), it is challenging to estimate past amplitude ranges, disentangle the relative roles of natural and anthropogenic forcing, or probe deeper interrelationships between climate variability and human history. Here, we compile and analyse updated versions of all the existing summer temperature sensitive tree-ring width chronologies from the Northern Hemisphere that span the entire Common Era. We apply a novel ensemble approach to reconstruct extra-tropical summer temperatures from 1 to 2010 CE, and calculate uncertainties at continental to hemispheric scales. Peak warming in the 280s, 990s and 1020s, when volcanic forcing was low, was comparable to modern conditions until 2010 CE. The lowest June–August temperature anomaly in 536 not only marks the beginning of the coldest decade, but also defines the onset of the Late Antique Little Ice Age (LALIA). While prolonged warmth during Roman and medieval times roughly coincides with the tendency towards societal prosperity across much of the North Atlantic/European sector and East Asia, major episodes of volcanically-forced summer cooling often presaged widespread famines, plague outbreaks and political upheavals. Our study reveals a larger amplitude of spatially synchronized summer temperature variation during the first millennium of the Common Era than previously recognised

A New Approach to Measuring Tree-Ring Density Parameters

Древесные кольца являются одними из наиболее достоверных источников информации об условиях окружающей среды и климата в прошлом. Рентгеновская денситометрия как один из важнейших инструментов дендроэкологии и дендроклиматологии существенно расширяет возможности исследований по реконструкции различных природных процессов. Классический рентгеновский денситометрический комплекс DENDRO 2003, обладая общепризнанными достоинствами, тем не менее имеет ряд существенных недостатков, таких как высокая стоимость, громоздкость, использование рентгеновских плёнок и т.д., что вынуждает искать альтернативные пути развития денситометрии годичных колец. В работе представлен новый методический подход к измерению профиля плотности годичных колец деревьев и построению хронологий параметров плотности древесных колец, основанный на разделении точек изображения клеточной структуры колец по их контрастности, получивший название пиксель-контрастной денситометрии (Pixel Contrast Densitometry, PiC densitometry). Проведена экспериментальная апробация разработанных методов PiC денситометрии при помощи демонстратора, реализованного в виде программного обеспечения, позволяющего выполнять измерения профиля плотности годичных колец и получать хронологии различных его параметров. Сравнительный анализ результатов измерений и функциональных характеристик рентгеновской и PiC денситометрии показал, что денситометрический комплекс, построенный на базе разработанных методов и программного обеспечения PiC денситометрии, позволяет получать результаты, идентичные результатам рентгеновской денситометрии, обладает большей функциональностью, меньшей стоимостью и способен полностью заменить собой рентгеновский денситометрический комплекс DENDRO 2003 в широком спектре дендроэкологических и дендроклиматических исследованийTree rings are the most reliable high-resolution proxy archive for past climate and environmental changes, and X‑ray densitometry is an important tool, which significantly expands the possibilities of dendroecology and dendroclimatology. The classic X‑ray densitometric laboratory DENDRO 2003 with all its advantages, however, has a number of drawbacks, such as its high price, installation size, requirement of X‑ray films and experienced technical staff, etc., which forces one to look for alternatives. The paper presents a new methodological approach to measuring wood density, developing tree-ring density profiles, and constructing tree- ring density chronologies. The proposed method – contrast densitometry (PiC densitometry) – is based on the pixel contrast in a high- resolution image of ring structures. Initial experimental tests using a specially developed demonstrator showed the strength and functionality of our approach, which produced results comparable to those derived by the traditional X‑ray DENDRO 2003 technique. This new methodology is capable of replacing traditional DENDRO 2003 applications in a wide range of dendroecological and dendroclimatic studie