Increase In Radial Growth Research Articles

Modelling metabolic fluxes of tomato stems reveals that nitrogen shapes central metabolism for defence against Botrytis cinerea.

Among plant pathogens, the necrotrophic fungus Botrytis cinerea is one of the most prevalent, leading to severe crop damage. Studies related to its colonization of different plant species have reported variable host metabolic responses to infection. In tomato, high N availability leads to decreased susceptibility. Metabolic flux analysis can be used as an integrated method to better understand which metabolic adaptations lead to effective host defence and resistance. Here, we investigated the metabolic response of tomato infected by B. cinerea in symptomless stem tissues proximal to the lesions for 7 d post-inoculation, using a reconstructed metabolic model constrained by a large and consistent metabolic dataset acquired under four different N supplies. An overall comparison of 48 flux solution vectors of Botrytis- and mock-inoculated plants showed that fluxes were higher in Botrytis-inoculated plants, and the difference increased with a reduction in available N, accompanying an unexpected increase in radial growth. Despite higher fluxes, such as those involved in cell wall synthesis and other pathways, fluxes related to glycolysis, the tricarboxylic acid cycle, and amino acid and protein synthesis were limited under very low N, which might explain the enhanced susceptibility. Limiting starch synthesis and enhancing fluxes towards redox and specialized metabolism also contributed to defence independent of N supply.

Solar and Climatic Factors Affecting Tree-Ring Growth of Mountain Birch (Betula pubescens) beyond the Northern Timberline on Kola Peninsula, Northwestern Russia

A 105-year chronology (AD 1917–2021) was developed from mountain birch (Betula pubescens Ehrh.) from beyond the coniferous treeline on the Kola Peninsula in Northwestern Russia (68.86 N, 34.69 E). A total of 22 trees were cored, including the oldest living mountain birch of 105 years old. The highest correlations occurred for the May temperature (r = 0.39, p < 0.01) and July sunshine duration (r = −0.39, p < 0.05). The increase in radial growth in May seemed to be caused by snowmelt giving rise to soil temperature, which can lead to a resumption in radial growth after winter dormancy. The negative correlation with the July sunshine duration seemed to be connected to changes in the spectral composition of solar radiation in the red to far-red ratio in the end of the polar day in July. The application of wavelet coherency revealed a significant (>95%) connection between the radial growth of B. pubescens, and solar activity in frequency bands encompassed the main solar cycles: 5.5 years (the second harmonic of the Schwabe cycle), 11 years (the Schwabe cycle) and 22 years (the Hale cycle). The results show that the northernmost birch trees in Europe are suited for tree-ring research. This allows us to expand the area of dendrochronological research further beyond the conifer treeline above the Polar Circle.

TOR Signaling Tightly Regulated Vegetative Growth, Conidiation, Oxidative Stress Tolerance and Entomopathogenicity in the Fungus Beauveria bassiana.

Beauveria bassiana degenerates after repeated subcultures, demonstrating declined conidiation and insect virulence. The target of rapamycin (TOR) kinase conserved among eukaryotes is the master regulator of cellular physiology and is likely involved in culture degeneration. Indeed, the levels of TOR-associated proteins increase over successive subcultures. Here, CRISPR/Cas9 locus engineering introduced the inducible Tet-On promoter upstream of the TOR kinase 2 gene tor2 in B. bassiana. The mutant PTet-Ontor2 'T41' was verified for the Tet-On integration via PCR analyses and provided a model for evaluating the fungal phenotypes according to the tor2 expression levels, induced by doxycycline (Dox) concentrations. At 0 µg·mL-1 of Dox, T41 had 68% of the wild type's (WT) tor2 expression level, hampered radial growth and relatively lower levels of oxidative stress tolerance, conidiation and virulence against Spodoptera exigua, compared to those under the presence of Dox. A low dose of Dox at 0.1-1 µg·mL-1 induced tor2 upregulation in T41 by up to 91% compared to 0 µg·mL-1 of Dox, resulting in significant increases in radial growth by 8-10% and conidiation by 8-27%. At 20 µg·mL-1 of Dox, which is 132% higher than T41's tor2 expression level at 0 µg·mL-1 of Dox, T41 showed an increased oxidative stress tolerance and a decrease in growth inhibition under iron replete by 62%, but its conidiation significantly dropped by 47% compared to 0 µg·mL-1 of Dox. T41 at 20 µg·mL-1 of Dox had a strikingly increased virulence (1.2 day lower LT50) against S. exigua. The results reflect the crucial roles of TOR kinase in the vegetative growth, conidiation, pathogenicity and oxidative stress tolerance in B. bassiana. Since TOR upregulation is correlated with culture degeneration in multiple subcultures, our data suggest that TOR signaling at relatively low levels plays an important role in growth and development, but at moderate to high levels could contribute to some degenerated phenotypes, e.g., those found in successive subcultures.

21st Century Warming, Site Aspect, and Reversal of Age-Related Growth Decline in Shortleaf Pine (Pinus echinata) in North Carolina, USA

We examined the influence of significant 21st century warming on the radial growth patterns of shortleaf pine growing on adjacent north/northeast- and south/southwest-facing slopes (hereafter NS and SS), in the Uwharrie Mountains of North Carolina, USA. Using two chronologies developed from old-growth trees dating to the 1700s, we compared raw radial growth rates (hereafter radial growth) associated with earlywood, latewood, and totalwood during 1935–2020. Both chronologies exhibited similar (r = 0.951, p < 0.001) age-related growth decreases through the 20th century. However, both chronologies experienced abrupt increases in radial growth with less fidelity (r = 0.86, p < 0.001), correlating with the onset of warming mean annual temperatures (r = 0.58, p < 0.01) and warming winter temperatures (r = 0.55, p < 0.05) in 2002. These results show that shortleaf pine growing on both NS and SS have experienced significant radial growth increases since the early 21st century, but that aspect affected growth rates. During 2002–2020, NS radial growth increased significantly (p < 0.05) more than SS earlywood, latewood, and totalwood, indicating that the effects of warming were greater for NS trees. We conclude that old-growth shortleaf pine trees retain climatic sensitivity to significant environmental changes associated with a warming climate and can reverse age-related growth declines.

Whether increased water‐use efficiency of Picea crassifolia promotes radial growth of trees in the eastern Qilian Mountains

AbstractGlobal change, characterized by elevated atmospheric CO2 concentrations and warming, is profoundly affecting terrestrial forests. However, whether the increasing atmospheric CO2 concentration has a fertilizer effect on tree growth and whether intrinsic water use efficiency (iWUE) promotes tree growth in semi‐arid regions is not entirely clear. In this study, we evaluated the relationships between tree‐ring widths, δ13C values and iWUE of Qinghai Spruce (Picea crassifolia Kom.) in the eastern Qilian Mountains, northwestern China. We found that the iWUE is significantly consistent with the δ13C of rings in the high‐frequency signal, and the relationship between iWUE and tree‐ring width is unstable. The first‐order difference correlation analysis with meteorological data showed that both the iWUE and tree‐ring width were drought‐limited. The radial growth was mainly regulated by water availability in current April and July, while annual variation of iWUE was primarily controlled by that in current July. In the early stage of trees growth, there was a positive relationship between iWUE and radial growth due to the CO2 fertilization. During the 1970s–2000s, the effect of water availability in July on radial growth increases because of the decreased precipitation in July. This has decreased stomatal conductance, intercellular CO2 concentration, carbon uptake and growth, contributing to the negatively significant correlation between tree‐ring widths and iWUE (p < .05). Since the year of 2010, the relationship between the radial growth and iWUE shifted because of the increased precipitation in July. This study provided new insights for whether increased water‐use efficiency enhances tree growth under semixeric conditions.

Effects of environmental factors and management on dynamics of mixed calcareous forests under climate change in Central European lowlands

Mixed lowland forests reserved for natural succession are sparse in the Czech Republic. However, their development provides essential insights into the natural processes of these forests and recommendations for forest management in a changing climate. The research describes the dynamics, productivity, structure, diversity, dead wood, and radial growth of hornbeam-oak groves and calcareous beech-dominated forests in the Karlštejn National Nature Reserve (Czechia) based on inventory in 2002, 2008, 2014 and 2020. The objective was to evaluate changes in differently managed stands (high forest, coppice with standards, and coppice) after leaving the stands to spontaneous development in 2004. The tree density increased by 2–10% from 2002 to 2014 and decreased by 6–18% in 2020. In the high forest, an increase in the stand volume was observed during the whole period, while in the coppice with standards and coppice, only until 2014. The stand volume ranged from 190 (coppice) to 630 (high forest) m³ ha−1 in 2020 and increased by an average of 28% over 18 years. Overall diversity of tree layer showed an uneven structure in the high forest and a substantially diverse structure in the other variants. The deadwood volume has been steadily increasing (18–35 m³ ha−1 in 2020), accumulating an average of 1 m³ ha−1 yr−1. A lack of precipitation and high temperatures from June to August were the main limiting factors of the radial growth of tree species, while the number of negative pointer years has increased in the last decade. European beech (Fagus sylvatica L.) was the most sensitive tree species to climate compared to the resilient European ash (Fraxinus excelsior L.). The lowest fluctuations in the diameter increment were recorded in Norway maple (Acer platanoides L.) and the highest in beech in the temperature cycles of 7–15 years. Over the last 20 years, sessile oak [Quercus petraea (Matt.) Liebl.] showed an increase in radial growth by 7%, while other tree species reported a decrease with a maximum in beech (by −38%). The forest stands managed as high forest, characterized by a higher production potential and lower diversity, had slower dynamics when compared to coppice with standards and coppice.

Оценка эффективности рубок ухода в сухих сосняках Казахского мелкосопочника

According to the current Forest Code of the Republic of Kazakhstan, in the forest plantations of specially protected natural areas, the main forestry measures aimed at the conservation and enhancement of the protective functions of forests are intermediate felling, that is, thinning. Pinus sylvestris L. is one of the main forest-forming species in Kazakhstan. Increasing the stability of forest plantations and the possibility of forming recreationally attractive landscapes through thinning is an urgent problem for plantations growing in arid conditions. The research purpose is to analyze the effectiveness of thinning of high intensity in dry pine forests of the Kazakh Uplands for a 70-year period, using dendrochronological methods. It was proved that in dense pine forests growing in dry conditions, there is an increase in radial growth in each subsequent 10-year period after thinning. It was found with statistical certainty that the greatest response to changes caused by thinning of high intensity was observed between 1949 and 1960. Analysis of indexed tree-ring chronologies using regional curves (indexed average tree-ring chronologies of pine) using a cubic spline function revealed differences in pine radial growth indices from the site where thinning of high intensity were carried out and from the control site (time periods: 1947–1955, 1961–1970, 1981–1990, and 1995–2015). The data obtained show a positive effect of thinning of high intensity on the radial growth of trees in the considered pine forests. In dense pine forests of dry growing conditions of the Kazakh Uplands it is recommended to make 1 or 2 cuttings with thinning intensity of 25–35 % at the age of 20–25 and 40–50, respectively, with subsequent increment thinning.

Sensitivity of recruitment and growth of alpine treeline birch to elevated temperature

Trees at temperature-limited alpine treeline are highly sensitive to temperature fluctuations. However, few studies have directly linked the recruitment and growth of juvenile trees to climate warming to investigate the processes underlying climate-induced alpine treeline shift. On the cold-humid Changbai Mountain of northeastern China, almost no tree recruitment occurred above the current treeline on the west side before 1985, whereas considerable recruitment has occurred since 1985. To investigate whether this recent recruitment was caused by warming temperatures, we established a 450 m × 50 m permanent plot above the current alpine treeline. We used dendrochronology to reconstruct the time series of recruitment of Betula ermanii juveniles. In addition, we used open top chambers (OTCs) to increase the growing season day-time temperature by c. 2.8°C and thereby to study the growth responses of juvenile trees to future warmer conditions beyond the current treeline. We found that tree recruitment increased substantially during a period of warmer summer temperatures since 1985, showing a high sensitivity of tree recruitment to temperature above the alpine treeline. The daily stem radial increment recorded by dendrometers was significantly (p ≤ 0.05) positively correlated with temperature but negatively correlated with soil water content, indicating no water limitation. Correspondingly, the increase in radial growth in OTCs was primarily a consequence of higher temperatures, especially in July. The regression slope between stem radial growth and temperature in the OTCs did not differ from that in ambient controls, indicating that the sensitivity of stem radial growth to temperature was not altered by warming. These suggest that future climate warming will induce increases in tree recruitment and growth above the alpine treeline. Our results revealed a direct link between temperature and recruitment and growth of juvenile trees, and that climate warming will likely cause forests to advance beyond the alpine treeline.

Mechanosensing and Plant Growth Regulators Elicited During the Thigmomorphogenetic Response

The influence of mechanical bending or flexing of trees, due primarily to wind, on tree growth and development has been observed and reported for hundreds of years. This response was defined as the thigmomorphogenetic response in 1973. In general, the response of trees and other plants to bending is a reduction in extension/height growth, increase in radial growth, and increased allocation from above-ground to below-ground tissues accompanied by changes in biomechanical properties of the xylem. Within the last 50 years, significant advancements have been reported in characterizing the response of trees to this mechanical perturbation. Current research has advanced the understanding of how plants respond after mechanopreception via molecular signaling and physiological changes in growth regulation. This review provides insight into these subcellular reactions of thigmomorphogenesis and a summary of recent advances.

Linking radial growth patterns and moderate-severity disturbance dynamics in boreal old-growth forests driven by recurrent insect outbreaks: A tale of opportunities, successes, and failures.

In boreal landscapes, emphasis is currently placed on close‐to‐nature management strategies, which aim to maintain the biodiversity and ecosystem services related to old‐growth forests. The success of these strategies, however, depends on an accurate understanding of the dynamics within these forests. While moderate‐severity disturbances have recently been recognized as important drivers of boreal forests, little is known about their effects on stand structure and growth. This study therefore aimed to reconstruct the disturbance and postdisturbance dynamics in boreal old‐growth forests that are driven by recurrent moderate‐severity disturbances. We studied eight primary old‐growth forests in Québec, Canada, that have recorded recurrent and moderately severe spruce budworm (Choristoneura fumiferana [Clem.]) outbreaks over the 20th century. We applied an innovative dendrochronological approach based on the combined study of growth patterns and releases to reconstruct stand disturbance and postdisturbance dynamics. We identified nine growth patterns; they represented trees differing in age, size, and canopy layer. These patterns highlighted the ability of suppressed trees to rapidly fill gaps created by moderate‐severity disturbances through a single and significant increase in radial growth and height. Trees that are unable to attain the canopy following the disturbance tend to remain in the lower canopy layers, even if subsequent disturbances create new gaps. This combination of a low stand height typical of boreal forests, periodic disturbances, and rapid canopy closure often resulted in stands constituted mainly of dominant and codominant trees, similar to even‐aged forests. Overall, this study underscored the resistance of boreal old‐growth forests owing to their capacity to withstand repeated moderate‐severity disturbances. Moreover, the combined study of growth patterns and growth release demonstrated the efficacy of such an approach for improving the understanding of the fine‐scale dynamics of natural forests. The results of this research will thus help develop silvicultural practices that approximate the moderate‐severity disturbance dynamics observed in primary and old‐growth boreal forests.

Divergence of Arctic shrub growth associated with sea ice decline

Arctic sea ice extent (SIE) is declining at an accelerating rate with a wide range of ecological consequences. However, determining sea ice effects on tundra vegetation remains a challenge. In this study, we examined the universality or lack thereof in tundra shrub growth responses to changes in SIE and summer climate across the Pan-Arctic, taking advantage of 23 tundra shrub-ring chronologies from 19 widely distributed sites (56°N to 83°N). We show a clear divergence in shrub growth responses to SIE that began in the mid-1990s, with 39% of the chronologies showing declines and 57% showing increases in radial growth (decreasers and increasers, respectively). Structural equation models revealed that declining SIE was associated with rising air temperature and precipitation for increasers and with increasingly dry conditions for decreasers. Decreasers tended to be from areas of the Arctic with lower summer precipitation and their growth decline was related to decreases in the standardized precipitation evapotranspiration index. Our findings suggest that moisture limitation, associated with declining SIE, might inhibit the positive effects of warming on shrub growth over a considerable part of the terrestrial Arctic, thereby complicating predictions of vegetation change and future tundra productivity.

Regional variability in the response of alpine treelines to climate change

The distributions of many high-elevation tree species have shifted as a result of recent climate change; however, there is substantial variability in the movement of alpine treelines at local to regional scales. In this study, we derive records of tree growth and establishment from nine alpine treeline ecotones in the Canadian Rocky Mountains, characterise the influence of seasonal climate variables on four tree species (Abies lasiocarpa, Larix lyallii, Picea engelmannii, Pinus albicaulis) and estimate the degree to which treeline movement in the twentieth century has lagged or exceeded the rate predicted by recent temperature warming. The growth and establishment records revealed a widespread increase in radial growth, establishment frequency and stand density beginning in the mid-twentieth century. Coinciding with a period of warming summer temperatures and favourable moisture availability, these changes appear to have supported upslope treeline advance at all sites (range, 0.23–2.00 m/year; mean, 0.83 + 0.67 m/year). However, relationships with seasonal climate variables varied between species, and the rates of treeline movement lagged those of temperature warming in most cases. These results indicate that future climate change impacts on treelines in the region are likely to be moderated by species composition and to occur more slowly than anticipated based on temperature warming alone.

Climate change evidence in tree growth and stand productivity at the upper treeline ecotone in the Polar Ural Mountains

BackgroundRecent warming is affecting species composition and species areal distribution of many regions. However, although most treeline studies have estimated the rates of forest expansion into tundra, still little is known about the long-term dynamic of stand productivity at the forest-tundra intersection. Here, we make use of tree-ring data from 350 larch (Larix sibirica Ledeb.) and spruce (Picea obovata Ledeb.) sampled along the singular altitudinal treeline ecotone at the Polar Urals to assess the dynamic of stand establishment and productivity, and link the results with meteorological observations to identify the main environmental drivers.ResultsThe analysis of stand instalment indicated that more than 90% of the living trees appeared after 1900. During this period, the stand became denser and moved 50 m upward, while in recent decades the trees of both species grew faster. The maximum afforestation occurred in the last decades of the twentieth century, and the large number of encountered saplings indicates that the forest is still expanding. The upward shift coincided with a slight increase of May–August and nearly doubling of September–April precipitation while the increase in growth matched with an early growth season warming (June + 0.27 °C per decade since 1901). This increase in radial growth combined with the stand densification led to a 6–90 times increase of biomass since 1950.ConclusionTree-ring based twentieth century reconstruction at the treeline ecotone shows an ongoing forest densification and expansion accompanied by an increased growth. These changes are driven by climate change mechanism, whereby the leading factors are the significant increase in May–June temperatures and precipitation during the dormant period. Exploring of phytomass accumulation mechanisms within treeline ecotone is valuable for improving our understanding of carbon dynamics and the overall climate balance in current treeline ecosystems and for predicting how these will be altered by global change.

Radial growth response of two oaks to climate at their disparate distribution limits in semiarid areas, Beijing, China

AbstractImpending climate warming is expected to influence plant growth and distribution, and the distribution range limit of tree species is extremely sensitive to climate change. However, synchronous comparisons of responses of different tree species with overlapping ecological niches to climate at their distribution range limit in the same region have received little attention. In the present study, we assessed the discrepancy in radial growth responses of two dominant oak species to climate at their distribution range limit (southern range limit forQuercus mongolica, northern range limit forQuercus variabilis) in Beijing, China. Furthermore, growth–climate relationships were examined using linear mixed‐effects models, and growth trends up to the year 2100 were forecast based on future climate scenarios (RCP2.6 and RCP8.5). Our results indicated that there were no significant differences in the growth response to climate betweenQ. variabilisat its northern limit andQ. mongolicaat its southern limit, and the growth of the two tree species was positively correlated with the minimum temperature and negatively correlated with the climatic moisture deficit of autumn. However, the growth response to climate variables varied at different sites. Additionally, the model forecast showed an increase in radial growth ofQ. variabilisat its northern limit andQ. mongolicaat its southern limit up to the end of the present century.

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.

Large apparent growth increases in boreal forests inferred from tree-rings are an artefact of sampling biases

Tree rings are thought to be a powerful tool to reconstruct historical growth changes and have been widely used to assess tree responses to global warming. Demographic inferences suggest, however, that typical sampling procedures induce spurious trends in growth reconstructions. Here we use the world’s largest single tree-ring dataset (283,536 trees from 136,621 sites) from Quebec, Canada, to assess to what extent growth reconstructions based on these - and thus any similar - data might be affected by this problem. Indeed, straightforward growth rate reconstructions based on these data suggest a six-fold increase in radial growth of black spruce (Picea mariana) from ~0.5 mm yr−1 in 1800 to ~2.5 mm yr−1 in 1990. While the strong correlation (R2 = 0.98) between this increase and that of atmospheric CO2 could suggest a causal relationship, we here unambiguously demonstrate that this growth trend is an artefact of sampling biases caused by the absence of old, fast-growing trees (cf. “slow-grower survivorship bias”) and of young, slow-growing trees (cf. “big-tree selection bias”) in the dataset. At the moment, we cannot envision how to remedy the issue of incomplete representation of cohorts in existing large-scale tree-ring datasets. Thus, innovation will be needed before such datasets can be used for growth rate reconstructions.

Warmer Winter Ground Temperatures Trigger Rapid Growth of Dahurian Larch in the Permafrost Forests of Northeast China

AbstractPermafrost degradation due to rapid increase in ground surface temperature (GST) in recent years may strongly affect boreal forest ecosystems. However, comparatively few studies have explored how changes in permafrost affect tree growth dynamics in boreal forest. Here, we used a tree ring network of 12 Dahurian larch (Larix gmelinii) sites across permafrost regions in northeast China. We observed an increase in L. gmelinii growth over the past decade, seemingly linked to a shift in their climatic limitations, where winter GST has become the most strongly limiting factor for L. gmelinii growth. The recent increase in growth was particularly strong in older trees (>300 years), which could be related to older trees having a more developed root system. GST was the main limiting factor for tree growth. While summer GST had a somewhat consistently positive correlation with tree growth, winter GST has shifted from a negative to a strongly positive correlation with growth in the last decade, coincidental with a sharp increase in winter GST since 2004. Winter GST is also strongly correlated with the rapidly thawing permafrost dynamics. Overall, our results suggest a link between recent changes in the permafrost and shifts in climate‐growth correlations for one of the main boreal tree species. As a result, L. gmelinii has experienced an important increase in radial growth that may indicate that, unlike what has been reported for other boreal species, it may temporally benefit from warming climate in the continuous permafrost region of the Asian boreal forests.

A dendrochronological reconstruction of sugar maple growth and mortality dynamics in partially cut northern hardwood forests

We investigated the growth and mortality dynamics of 22 northern hardwood stands with well-known disturbance histories in southern Quebec, Canada. The main objective of this study was to evaluate the effect of short- and long-term growth trends on both the probability of mortality and the radial growth response of trees following partial cutting. This was first achieved by identifying growth release episodes and characterizing growth patterns prior to tree death from entire tree-ring series of 86 live and 26 dead sugar maple (Acer saccharum Marsh.) trees. Using mixed-effects logistic regression, we quantified the effects of short- and long-term growth trends, as well as external variables such as neighbourhood competition and tree vigour status on the probability of mortality and growth release events. Results showed that long periods of continuous growth decline or long periods of slow radial growth after a severe decrease occurred in 88% of dead trees. These growth patterns were associated with a progressive decline in tree vigour that was mostly initiated by drought and insect defoliations during the 1980s, thereby supporting the relevance of studying long-term tree-ring chronologies to deduce causes of post-harvest mortality. Our model showed that predictions of post-cut mortality events could be significantly improved by considering long-term radial growth trends (25 years before cutting) in individual trees. In terms of growth response, 24% of live trees had a release event occurring after the selection cut, which is slightly lower than the response induced by natural disturbance in previous decades. None of the tested long-term growth variables were significantly related to the occurrence of growth release events. Consequently, suppressed sugar maple trees appear to maintain their capacity to respond positively to gap creation, regardless of the length of the suppression period. We conclude that while decreasing trends in long-term radial growth increase mortality probabilities, the growth release potential of trees is negatively impacted by the presence of defects affecting tree vigour (e.g. fungal infections and cambial necroses) and positively related to the removal of neighbouring trees, rather than to prior growth trends.

Biotic factors and increasing aridity shape the altitudinal shifts of marginal Pyrenean silver fir populations in Europe

Rear-edge tree populations are currently at the forefront of habitat conservation. Understanding the dynamics of such marginal and peripheral populations is necessary to improve their preservation in the face of global change. Focusing on the south-western rear edge populations of silver fir (Abies alba) in Europe (Spanish Pyrenees) and using 763 resampled plots from the Spanish National Forest Inventory (1989–2000 and 2001–2010), we analyzed temporal changes in demographic parameters such as regeneration, growth and mortality as well as changes in diameter distribution and vitality of silver fir to identify shifts in the distribution. For this purpose, montane (900–1600 m a.s.l.) and subalpine (1600–2000 m a.s.l.) silver fir populations were considered separately. We then assessed the relative effects of various biotic and abiotic factors on the observed changes and specifically on each of the studied demographic parameters. In montane forests, early recruitment and the proportion of trees exhibiting high vitality decreased, while the amount of dead trees increased. In subalpine forests, silver fir has become more abundant and displays the highest growth and recruitment rates as well as the lowest mortality rate. The increase in radial growth and saplings were positively related to elevation but negatively associated with warmer and drier conditions, coinciding with the intensified aridification observed in the study area over recent decades. Our findings point to the contraction of montane silver fir forests but also to an upward expansion of subalpine forests. The results also indicate that the dynamics of marginal tree populations are driven not only by climate warming, but particularly, by biotic factors, suggesting a positive impact of interspecific interactions with tree species displaying differentiated ecophysiological traits. Given the singularity of marginal Pyrenean silver fir populations, their importance as regards the conservation of forest biodiversity at European scale, and the demographic changes revealed in this study, an integral conservation strategy to ensure their long-term preservation is necessary.

Стан соснових насаджень на водно-льодовикових відкладах у Житомирському поліссі

Наведено результати досліджень стану лісових насаджень сосни звичайної різного віку на водно-льодовикових відкладах у Житомирському Поліссі. За фітоіндикаційним аналізом охарактеризовано типи лісорослинних умов як свіжі бори та свіжі субори. Встановлено, що у свіжих борах за І класом Крафта ростуть близько 40 % дерев, а у свіжих суборах – близько 50 %. До І класу товарності належить 30 % дерев у свіжих борах та 47 % дерев від загальної їх кількості у свіжих суборах. Частка ослаблих, всихаючих і відмерлих дерев у свіжих борах становить 35,5 %, а у свіжих суборах – 54,3 %. Виявлено, що абсолютні значення величин річних кілець дерев зменшуються із збільшенням віку сосни звичайної: у свіжих борах – на 28,0 %, у свіжих суборах – на 50,5 %. Встановлено, що найвужчі річні кільця характерні для насаджень свіжих борів, а найширші – для деревостанів, що ростуть у багатших умовах (свіжий субір). Максимальні значення приросту річних кілець зареєстровано для стиглих та перестійних деревостанів, незалежно від лісорослинних умов. Щорічний радіальний приріст сосни звичайної змінюється у межах 1,19–3,94 мм. За розрахунковими значеннями стандартного відхилення та коефіцієнта варіації можна стверджувати, що у свіжих борах фактично не формуються стійкі, внутрішньо збалансовані деревостани сосни звичайної, а у свіжих суборах соснові деревостани організовуються в єдину фітосистему лише після 60-ти років.