Key message
Effect of drought during 2017 and 2018 resulted in radial stem increment reduction to 78% and 61%, respectively, of the levels occurring in normal year 2016 in Central Europe.
Norway ...spruce (
Picea abies
(L.) Karst.) is currently the most threatened commercial tree species in Central Europe. This is due to increased drought stress from advancing climate change as well as the species’ distribution outside its natural range. Tree water status and water movement through a tree are key parameters influencing tree growth and vitality. This study is focused on the growth and stress reaction of spruce to climatic conditions, analysing stem diameter variation along an elevation gradient (381–995 m a.s.l.) in the Czech Republic. Tree water deficit based on the zero-growth concept (TWD), calculated from high-frequency dendrometer records and the temporal dynamics of radial growth, was studied for 3 years (2016–2018). Two of these 3 years were affected by severe drought during the growing season. Contrary to our expectations, the observed TWD showed no clear linear decline with rising elevation. The most severe tree desiccation was observed in experimental sites at middle elevations of about 600 m a.s.l. Here, we show that both the timing and level of tree water deficit had an impact on annual stem radial increment (SRI
annual
). Severe drought had a substantial negative impact on SRI
annual
of Norway spruce in both 2017 and 2018. Drought conditions in 2017 and 2018 resulted in reduction of SRI
annual
relative to measurements for the wetter year in 2016 to 78% and 61%, respectively. We report the evidence that the current climatic conditions in the Central European region are not suitable for growing Norway spruce at lower and middle elevations and that forest management needs to react immediately to this situation.
Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial ...scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.
Atmospheric carbon dioxide (CO2) has increased substantially since the industrial revolution began, and physiological responses to elevated atmospheric CO2 concentrations reportedly alter the ...biometry and wood structure of trees. Additionally, soil nutrient availability may play an important role in regulating these responses. Therefore, in this study, we grew 288 two-year-old saplings of sessile oak (Quercus petraea (Matt.) Liebl.) in lamellar glass domes for three years to evaluate the effects of CO2 concentrations and nutrient supply on above- and belowground biomass, wood density, and wood structure. Elevated CO2 increased above- and belowground biomass by 44.3% and 46.9%, respectively. However, under elevated CO2 treatment, sapling wood density was markedly lower (approximately 1.7%), and notably wider growth rings-and larger, more efficient conduits leading to increased hydraulic conductance-were observed. Moreover, despite the vessels being larger in saplings under elevated CO2, the vessels were significantly fewer (p = 0.023). No direct effects of nutrient supply were observed on biomass growth, wood density, or wood structure, except for a notable decrease in specific leaf area. These results suggest that, although fewer and larger conduits may render the xylem more vulnerable to embolism formation under drought conditions, the high growth rate in sessile oak saplings under elevated CO2 is supported by an efficient vascular system and may increase biomass production in this tree species. Nevertheless, the decreased mechanical strength, indicated by low density and xylem vulnerability to drought, may lead to earlier mortality, offsetting the positive effects of elevated CO2 levels in the future.
Tree growth depends on many factors such as microsite conditions, vitality, and variations in climate and genetics. It is generally accepted that higher growth indicates both an economic benefit and ...better vitality of any tree. Here we use a modified approach of evaluating tree social area to study mutual tree competition based on the orientation and shape of trees social area. The investigation was performed in nine Norway spruce stands in the Czech Republic. The objective of this study performed from 2008 to 2012 was to quantify relative tree radial increments with respect to the lowest and highest competition found in specific sectors of tree social area (AS). Specific groups of trees (tree classes) were evaluated according to their classes (dominant, co-dominant and sub-dominant) and their composition status in ninety-degree sectors of AS using established classifying rules. The results showed that a spatially-available area (AA) is an inappropriate parameter for predicting tree growth, whereas AS provided robust explanatory power to predict relative radial growth. Tree size was observed as an important indicator of relative radial increments. A significantly positive correlation was found for a radial increment of sub-dominant trees with the lowest competition from western directions; whereas a negative correlation was observed when the lowest competition was observed from eastern directions. For dominant trees, there was an evident growth reaction only when more than 50% of the AS was oriented towards one of the cardinal points. Individual differences in the orientation of tree AS may be important parameters with regard to competition and its spatial variability within an area surrounding a particular tree and deserve more detailed attention in tree growth models and practice.
•4 years of species-oriented phenocamera and ground-based phenological observations.•Confirmed prolongation of growing season length due to a warmer climate.•Phenocamera-derived phenophases ...corresponded closely with field observations.•Greenup was advanced by above-average warm days, but leaf maturation was delayed.•Cold spell in 2017 showed marked effect on phenological shifts.
Phenological observations are important as indicators of global warming and as estimation tools for the terrestrial carbon balance in vulnerable ecosystems, such as the last fragments of floodplain forests in the Czechia. The aim of this paper was to compare ground-based phenological observations of three dominant species (European hornbeam, English oak and narrow-leaved ash) in this ecosystem, with the seasonal trajectory of the greenness index (Gcc) and thresholds extracted from images taken by phenocameras located on a meteorological mast. The average annual air temperature in the studied years 2014–2017 was 1 °C higher than the long-term average, and the precipitation deficit reached ⅓ of annual rainfall. We found a high proportion of above-average warm days in the warmest part of the growing season. Above-average air temperatures significantly accelerated the onset of budbreak in ash. Yet a higher proportion of above-average air temperatures prolonged the period between budbreak to fully developed leaf area, especially in ash and oak. In 2017, rapid cooling after exceptionally warm temperatures at the onset of spring had a detrimental effect on the stand productivity and showed a marked effect on the phenological shifts. The period when leaf area developed was in the range of DOY 66-286 for hornbeam, DOY 79-329 for oak and DOY 88-321 for ash in 2014–2017. The seasonal trajectory of Gcc showed differences between tree species that corresponded to the dynamics of the onset of phenophases observed in the field. According to image analyses, the phenophase of greenup and maturity for hornbeam and ash had minimal uncertainty. In contrast, the uncertainty was high in the determination of phenophases for oak. Our observations show that the modern method of phenological observation by phenocameras is suitable for mixed forests, but classical ground-based observations by a phenologist are still crucial in order to verify the results.
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The vulnerability of floodplain forests, a critically sensitive global ecosystem, is exacerbated by both hydrological management practices and the escalating frequency and severity of drought events ...caused by climate change. This issue is particularly acute in Central European floodplain forests, where river regulation and reduced groundwater levels have markedly contributed to increased water deficits and intensified drought conditions, causing forest growth decline, species dieback and shifts in forest composition. In this study, we utilized tree-ring measurements from pedunculate oak (Quercus robur L.) and narrow-leaved ash (Fraxinus angustifolia Vahl.) across four sites with varying groundwater levels. This approach allowed us to assess the impact of artificial groundwater modifications and drought conditions in their growth, providing valuable insights into the resilience and adaptation of these species. Our study indicates that the most determining drivers of tree-growth are hydrological parameters such as groundwater levels and drought indices while temperature alone was less important for tree growth. However, we observed species-specific growth responses to these environmental drivers. In particular, Q. robur exhibited a greater adaptability to climatic variables, with a weaker relationship of tree-ring width to climate compared to F. angustifolia, which demonstrated a stronger dependence on hydroclimatic variables and appeared to feature a higher drought susceptibility. Our findings also reveal that radial growth during the vegetation period relies on different water sources; in spring, growth is primarily driven by precipitation, while groundwater levels become more critical in summer and autumn. Overall, our study underscores the significant threat posed to floodplain forests by both groundwater modifications and the escalating frequency of drought events. However, not all floodplain species are equally adaptable to these environmental changes, exhibiting varied responses and vulnerability.
•Ring-widths of ring-porous oak and ash were analysed in floodplain forest.•Four sites with comparable climate but varying groundwater levels were evaluated.•Dependence on spring rainfall and groundwater increased over time for both species.•Ash's growth dependence on hydroclimatic factors was more consistent and pronounced.•Oak demonstrated higher drought resilience in its growth patterns.
Norway spruce is one of the most economically important coniferous species in Europe, but it has faced high mortality rates in the last few decades due to the increasing frequency of extreme weather ...events. Primary and secondary growth development may be affected by these non-optimal conditions. In this study, we aimed to analyze the timing, possible asynchrony and time-lag between the growth processes of Norway spruce. We used a novel methodological approach of primary (based on phenocamera picture evaluation) and secondary (dendrometers) growth detection. The combination of these novel approaches allowed us to compare these growth process in high temporal resolution. Measurements were performed in two experimental plots with contrasting climatic conditions (middle and higher elevations) in the years 2016–2019, during the presence of extreme climatic conditions. We demonstrated a significant elongation of the growing season, with a more pronounced effect at higher elevation. Compared to the long-term mean, we observed an additional 50 days with a temperature above 15 °C at the higher elevation plot. There were no found patterns in the time-shift of both growth processes between plots. On the other hand we observed asynchrony of radial growth and meristems growth. Radial growth began earlier than the phenology of apical meristems growth. The onset, end and duration of meristem growth differed between studied plots and years as well. The onset of radial growth did not follow the gradient of microclimatic parameters; however, the differences in climatic conditions between plots did cause a shift in the onset of meristem growth. The process of the radial growth was twice as long as for apical meristem development. On average, radial growth requires 71 days more than meristem phenology to reach full process completion. Our data confirmed that these growth processes are strongly affected by external weather conditions and the duration of the growing season. More advanced and detailed monitoring of these processes can provide more accurate data of the health status of trees in the forest.
Key message
Complex overview of biomass structure for oak and ash tree species and wide range of allometric relationships for predicting above- and below-ground biomass components.
Due to changing ...climate conditions, trends in the proportion of the area of major tree species in Europe will tend to show a greater share of lowland tree species composition. The estimation of tree biomass and its components is needed to determine the amount of carbon held in trees and to plan forest resources. This study presents the biomass functions applicable for ash (
Fraxinus excelsior
L.) and oak (
Quercus robur
L.) trees growing in floodplain forest of the Czech Republic, which could subsequently be grouped into more efficient generic model for the particular tree species in the Central Europe. It is based on a detailed destructive analysis of six ash and seven oak trees. The range of the basic predictors of sampled trees included: diameter at breast height (DBH) from 21.3 to 69.7 cm, height (
H
) from 21.0 to 33.9 m, crown length (CL) from 7.6 to 16.3 m and width of crown (CW) from 3.8 to 14.3 m. The allometric relationships were constructed to derive leaf- (LB), shoot- (B
s
B), branch- (BB), stem- (SB) and root- (RB) biomass components and to derive aboveground- (TAB), which contains SB and BB, and total biomass (TB) comprising all biomass components. Equations for estimating stem volume were developed, which are required for forest management and it is necessary for planning the availability of commercially valuable wood. Finally, biomass expansion factors (BEFs) converting stem volume into biomass components were constructed. The BEFs were slightly positively linear DBH dependent for BsB, BB, TAB and TB, whereas for LB, SB and RB they were shown to be DBH independent across the diameter distribution of the sampled trees.
A novel Biginelli-like assembly of 3-amino-1,2,4-triazole with methyl acetoacetate and salicylaldehyde has been developed to enable easy access to spiro{1benzopyran-2,7′-1,2,4triazolo1,5-
...apyrimidine} compounds as representatives of a new class of spiro-fused heterocycles. A three-component condensation mechanism is proposed and discussed.
Top dieback in 40-60 years old forest stands of Norway spruce Picea abies (L.) Karst. in southern Norway is supposed to be associated with climatic extremes. Our intention was to learn more about the ...processes related to top dieback and in particular about the plasticity of possible predisposing factors. We aimed at (i) developing proxies for P 50 based on anatomical data assessed by SilviScan technology and (ii) testing these proxies for their plasticity regarding climate, in order to (iii) analyze annual variations of hydraulic proxies of healthy looking trees and trees with top dieback upon their impact on tree survival. At two sites we selected 10 tree pairs, i.e., one healthy looking tree and one tree with visual signs of dieback such as dry tops, needle shortening and needle yellowing (n = 40 trees). Vulnerability to cavitation (P 50) of the main trunk was assessed in a selected sample set (n = 19) and we thereafter applied SilviScan technology to measure cell dimensions (lumen (b) and cell wall thickness (t)) in these specimen and in all 40 trees in tree rings formed between 1990 and 2010. In a first analysis step, we searched for anatomical proxies for P 50. The set of potential proxies included hydraulic lumen diameters and wall reinforcement parameters based on mean, radial, and tangential tracheid diameters. The conduit wall reinforcement based on tangential hydraulic lumen diameters ((t/b ht)(2)) was the best estimate for P 50. It was thus possible to relate climatic extremes to the potential vulnerability of single annual rings. Trees with top dieback had significantly lower (t/b ht)(2) and wider tangential (hydraulic) lumen diameters some years before a period of water deficit (2005-2006). Radial (hydraulic) lumen diameters showed however no significant differences between both tree groups. (t/b ht)(2) was influenced by annual climate variability; strongest correlations were found with precipitation in September of the previous growing season: high precipitation in previous September resulted in more vulnerable annual rings in the next season. The results are discussed with respect to an "opportunistic behavior" and genetic predisposition to drought sensitivity.
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