<Emphasis Type="Italic">Araucaria araucana</Emphasis> tree-ring chronologies in Argentina: spatial growth variations and climate influences

Seventeen tree-ring chronologies from the conifer Araucaria araucana (Molina) K. Koch have been analyzed across its range of distribution in Argentina. We studied the growth patterns and determined the main climatic factors influencing A. araucana radial growth. All the chronologies show a strong common signal observed by the high amount of variance explained by the first principal component (PC1) and the high mean correlation (r = 0.597) between the chronologies over the 1676–1974 interval. On this basis, we developed a regional chronology that is 866 years long (A.D. 1140–2006) and includes 621 tree-ring series. Based on the PC2 scores, chronologies were clearly separated by elevation in high- and low-elevation records. Regional tree growth is strongly negatively related to temperatures during summer and fall in the previous-growing season and spring in the current-growing season, respectively. A positive association of tree growth with precipitation is recorded during spring in the current growing season. These results suggest a close relationship between A. araucana tree growth and water availability on a regional scale. This observation is also consistent with a positive and significant correlation between our A. araucana regional record and a reconstruction of November–December rainfall for northern Patagonia inferred from the xeric Austrocedrus chilensis during the past 400 years. Negative correlations between A. araucana regional growth and the sea surface temperature in the Niño 3.4 region reflect the occurrence of above-mean summer temperatures in the region during positive tropical Pacific SST anomalies. The negative relationship with the Antarctic Oscillation (AAO) results from reduced precipitation in our study region during the positive phase of the AAO. The effect of elevation on water availability is consistent with significant correlations between ring-width variations at lower elevations and the Palmer Drought Severity Index during spring and summer in the current growing season. Our study emphasizes the high dendroclimatological potential of A. araucana chronologies for reconstructing past climate variations in northern Patagonia during the past millennium.     

Periphyton growth and diatom community structure in a cooling water pond

Periphyton (Aufwuchs) accumulation was measured on artificial substrates in a pond in central Finland which receives warm cooling-water effluent from a power plant. The growth of periphyton was generally more rapid on the substrates during the first two weeks of colonization near the inflow of the warm water effluent than in the middle of the pond. The maximum accumulation of periphyton was in spring and autumn (dry weight maximum at warm effluent was in spring 3.5 mg DW cm⁻²,2.65 mg AFDW cm⁻²; chlorophyll a maximum 3.96 μg cm⁻² was found in autumn at pond-middle station). During mid-winter months the growth was strongly limited by solar radiation, but the growth was also slow at both stations in the summer months, when the power plant was out of operation. The periphyton accumulation rate was fastest near the water surface and decreased rapidly with increasing depth. A total of 167 diatom species were found in periphyton samples. However, most species were rare; many of the dominants were common to both plankton and periphyton. Species similarity analyses (Jaccard's similarity) between 10 different diatom communities (including periphyton from 9 different types of substrates and phytoplankton) indicated low similarity index values although differences between communities were not significant.     

Dendroclimatic regions of pedunculate oak (Quercus robur L.) in Belarus

In this study, we present the boundaries of five dendrochronologically homogeneous regions of pedunculate oak (Quercus robur L.) and the master chronologies for them for the period 1703–2018 based on 27 tree-ring chronologies from different locations around Belarus. The average length of the master chronologies ranges from 70 to 310 years. Our research shows that the radial increment of a pedunculate oak in Belarus is primarily limited by the previous year’s August-September temperature, by the current year’s May temperature and by June precipitation. Oak growth in northern Belarus is mostly limited by air temperature, whereas precipitation plays more significant role in central and southern parts of the country. The most unfavorable years for oak growth in Belarus were 1940 and 1952, both of which were years when a very frosty winter was followed by a droughty summer. The results provide an important achievement in Belarusian dendrochronology, since they represent a significant breakthrough for Eastern Europe, where there is a considerable lack of dendroclimatic researches of broadleaved species.     

Vessel features of Quercus ilex L. growing under Mediterranean climate have a better climatic signal than tree-ring width

We investigated whether vessel time series of Holm oak (Quercus ilex L.), a diffuse to semi-ring-porous species, can record a climatic signal which differs from the signal encoded in tree-ring width (TRW). The study was conducted in ten Q. ilex trees from a coppice stand in northeast Spain. Chronologies of TRW, mean vessel area (MVA) and maximum vessel area (MAX) were developed and correlated with climate data, for the period 1985–2004 (20 years). Our results indicate that vessel features contain environmental information that is different from that stored in TRW. MAX chronologies correlate better to early spring precipitation (April–May) than TRW chronologies, and so does MVA of the largest 20–25 vessels from the first third of the ring with late spring precipitation (May–June). Also, the combination of MVA and TRW is a better predictor of summer precipitation. This explorative study clearly shows that vessel features can complement the climatic signal of TRW increasing the resolution of the climate reconstructions for the Mediterranean region.     

Precision dating of Cook’s Mill,a Civil War era structure in West Virginia

Dendroarchaeology can provide critical understanding of a structure built during key historic periods, such as the American Civil War (1861–1865), when historical documentation is likely to be sparse or incomplete. Cook’s Mill is located in Greenville, West Virginia and extensive information derived from deeds, court records, wills, and oral history places the present mill’s original construction in 1857. The American Civil War began shortly after its construction and military conflict in the area led to the burning of several key structures, one of which was an unknown mill in Greenville (formerly Centerville). Written history suggests the mill is original and survived the American Civil War, however we used dendroarchaeology to confirm its precise date of construction. We collected 46 samples from the mill and 6 cross sections from a nearby exhumed bridge for dendrochronological dating. The mill was constructed with white oak (Quercus alba) and tulip poplar (Liriodendron tulipifera) logs and the bridge samples were white oak. We visually and statistically crossdated 32 white oak samples from the mill and bridge by comparing them to a local chronology developed for this study and two regional oak chronologies from the International Tree-Ring Data Bank. Based on terminal ring attributes and cutting date years we were able to provide a suggested construction date of the spring or early summer of 1868. This date suggests Cook’s Mill was the mill burned during military conflict in the area and that the current structure was subsequently rebuilt following the conclusion of the war.     

On the palaeoclimatic potential of a millennium-long oak ring width chronology from Slovakia

Although Slovakia is largely forested and rich in historical buildings, it is one of the few European countries without a millennium-long tree-ring chronology. In this study, we gather all available oak ring width data from Slovakia, establish a new composite chronology and assess its climate sensitivity. The nation-wide oak network includes 276 samples from historical buildings and 1028 modern series from material that was randomly collected at sawmills and wood submission sites across Slovakia. The final composite oak record covers the period from CE 967–2013, reflects a distinct hydroclimatic signal from late spring to early summer, and is highly correlated with other oak chronologies from surrounding countries. Although this study reveals a high degree of growth coherency and climate sensitivity inherent to the new Slovakian oak ring width chronology, changes in sample size at the transition from modern to relict material and further back in time limit any applicability to palaeoclimatic analysis.     

Seasonal changes in the content of lipids and photosynthetic pigments in a brown alga Saccharina cichorioides

Seasonal changes in the contents of lipids and photosynthetic pigments (PSP) were investigated in a brown alga Saccharina cichorioides Miyabe (Phaeophyceae, the family Laminariaceae). The content of lipids varied from 0.27 to 0.60% of the algal fresh weight. The content of glyceroglycolipids (GL) was much greater in the time of spore formation (June–July and September–October), phospholipids — in the spring and in September–October, and the content of neutral lipids — in the spring and in November. In the period of spore release (August and October), the level of GL and polyunsaturated fatty acids (PUFA) sharply decreased. A high level of PUFA was observed from March to July and in November. In August and October, the same as in the spring, the proportion of saturated fatty acids (FA) was great. The content of chlorophylls from March to November varied from 20.3 to 26.9%, and the level of carotenoids — from 10.7 to 16.1%. Total content of PSP was relatively high in March and in August–September. Free sterols accounted for 3.4–7.3% of total lipids; their proportion was greater in spring than in summer and autumn.     

The geography of white oak's (Quercus alba L.) response to climatic variables in North America and speculation on its sensitivity to climate change across its range

Dendrochronological analysis is used to determine white oak's (Quercus alba L.) sensitivity to mean monthly temperature and monthly precipitation for the entirety of its range in the United States. Throughout much of its range, white oak is sensitive to summer precipitation (positive), summer temperature (negative), and previous season late-summer and fall precipitation (positive). Spatially, populations of white oak in the western and central portion of its range are most highly correlated with these variables, while Appalachian and eastern populations show little sensitivity to monthly climate variables. White oak's radial growth rate in light of anthropogenic climate change (based on regional and downscaled climate models) may be most reduced in the far western portion of its range (Illinois and Missouri), whereas eastern populations are less likely to be adversely affected.     

Occurrence of Phytophthora plurivora and other Phytophthora species in oak forests of southern Poland and their association with site conditions and the health status of trees

Phytophthora plurivora and other Phytophthora species are known to be serious pathogens of forest trees. Little is known, however, about the presence of P. plurivora in Polish oak forests and their role in oak decline. The aims of this study were to identify P. plurivora in healthy and declining Quercus robur stands in southern Poland and to demonstrate the relationship between different site factors and the occurrence of P. plurivora. In addition, the virulence of P. plurivora and other Phytophthora species was evaluated through inoculations using 2-year-old oak seedlings. Rhizosphere soil was investigated from 39 oak stands representing different healthy tree statuses. The morphology and DNA sequences of the internal transcribed spacer regions (ITS) of the ribosomal DNA and the mitochondrial cox1 gene were used for identifications. P. plurivora, an oak fine root pathogen, was isolated from rhizosphere soil samples in 6 out of 39 stands. Additionally, Phytophthora cambivora, Phytophthora polonica and Phytophthora rosacearum-like were also obtained from several stands. The results showed a significant association between the presence of P. plurivora and the health status of oak trees. Similar relationships were also observed for all identified Phytophthora species. In addition, there was evidence for a connection between the presence of all identified Phytophthora species and some site conditions. Phytophthora spp. occurred more frequently in declining stands and in silt loam and sandy loam soils with pH?≥?3.66. P. plurivora and P. cambivora were the only species capable of killing whole plants, producing extensive necrosis on seedling stems.     

Effect of ecological factors on intra-annual stem girth increment of holm oak

Key message

The intra-annual stem girth increment of Quercus ilex is mainly driven by water availability and secondly by temperature. Tree size and competition modulate the growth response to climate.

Abstract

Holm oak (Quercus ilex ssp. ballota [Desf.] Samp.) is the most widespread species in the Iberian peninsula, being one of the most representative trees in forests and open woodlands. The analysis of stem girth increment of holm oak may provide valuable information about how Mediterranean ecosystems will respond to the forecasted climate changes. However, due to the variability of the Mediterranean climate, the knowledge of intra-annual patterns of growth is needed for a better understanding of the influence of the climatic variables at this scale. To this end, we used band dendrometers to measure monthly stem girth increments of 96 holm oak trees from 2003 to 2010, located in open woodlands and dense Mediterranean forests in southwestern Spain. We assessed the effects of climate, competition, topography, and initial stem diameter on stem girth increment. The major stem increment periods were in spring and autumn whereas increment rates were very low or even negative in winter and summer. Spring was not every year the season with the higher stem increments, but autumn when spring was very dry. Higher precipitation, soil moisture, and relative humidity had significant positive effects on stem increment, whereas higher temperature, reference evapotranspiration, and solar radiation had significant negative effects. Initial tree diameter and competition from nearby trees partly explained significant differences in stem increment of individual trees. Therefore, the forecasted climatic changes, in which decreased rainfall in spring and increased summer drought are expected in the Mediterranean region, may be a significant threat to the Q. ilex ecosystems.     

Growth response of Abies georgei to climate increases with elevation in the central Hengduan Mountains,southwestern China

Climatic harshness is expected to increase at higher elevations; however, elevational trends of tree radial growth response of high-elevation forests to climate change need to be investigated at different locations because of existing local variability in site-specific climatic conditions. We developed tree-ring width chronologies of Yunnan fir (Abies georgei) along elevation gradients at two sites in the central Hengduan Mountains (HM). High-elevation forests of A. georgei showed growth synchronicity and common growth signals along elevation gradients, indicating a common climatic forcing, although tree radial growth rates decreased with increasing elevation. Radial growth of Yunnan fir showed positive correlations with summer temperatures and February precipitation and moisture availability, but were negatively correlated with spring temperatures. The strongest positive relationship indicated summer (July) mean and minimum temperatures are the most important growth determining climatic factors for tree radial growth in the cold environment of HM, and this relationship revealed a clear elevational trend with stronger correlations at higher altitudes. In contrast, tree radial growth was negatively correlated with June precipitation and moisture availability. The whole study period 1954–2015 was split in two sub-periods of equal length. Comparing the early sub-period (1954–1984) to the later sub-period (1985–2015), tree growth response to the summer temperatures strongly increased, while it became weaker to June precipitation and moisture availability. High-elevation Yunnan fir forests in the HM currently benefit from elevated growing season temperatures under humid summer conditions. However, increasing temperatures may induce drought stress on tree radial growth if the observed decreasing trend in humidity and precipitation continues.     

Long-term radial growth and climate-growth relationships of Quercus petraea (Matt.) Liebl. and Quercus cerris L. in a xeric low elevation site from Hungary

Sessile oak (Quercus petraea [Matt.] Liebl.) and Turkey oak (Quercus cerris L.) dominated mixed forests are common in low montane and hilly regions in Hungary. Here, we aimed to describe the long-term pattern and climatic responses of the radial growth of Q. petraea and Q. cerris in a xeric low-elevation forest, using retrospective tree-ring analysis for the period 1910–2019. We performed separate analyses with time series of full tree-ring (TRW), earlywood (EW) and latewood (LW) widths. Our results showed that the radial growth of the two species was largely synchronous over time, but became transiently divergent for a 20-year period after a drought in 1968, due to the greater-than-expected growth of Q. cerris and the supressed growth of Q. petraea. Precipitation was the major growth-limiting factor for both species, with a strong positive influence on LW particularly during the current early growing season (March-June), on EW in the previous late summer (August-September) and in the current early spring (March), and on all tree-ring traits in the previous December. The radial growth of both species was negatively related to temperature in the spring (May) and late summer (August) of both current and previous years. The climate-growth relationships showed general instability over time: the most striking temporal change was a gradual shift of positive correlations with precipitation and SPEI during the growing season from spring (March-May) to summer (June-August) since the 1980s over the analysed period. The two species had similarly low growth resistance to droughts in four studied pointer years (1968, 1993, 2002 and 2012), but Q. cerris exhibited a greater capacity to recover over the four post-drought years, and thus higher growth resilience, particularly after the drought of 1968. Our results contribute to the better understanding of the role of climate variability and droughts in the growth of the two co-existing species in transitional locations between closed forests and forest-steppes.     

Size-dependent responses to summer drought in Scots pine, Norway spruce and common oak

In this study, we provide a detailed analysis of tree growth and water status in relation to climate of three major species of forest trees in lower regions of Bavaria, Southern Germany: Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and common oak (Quercus robur). Tree-ring chronologies and latewood δ¹³C were used to derive measures for drought reaction across trees of different dimensions: growth reduction associated with drought years, long-term growth/climate relations and stomatal control on photosynthesis. For Scots pine, growth/climate relations indicated a stronger limitation of radial growth by high summer temperatures and low summer precipitation in smaller trees in contrast to larger trees. This is corroborated by a stronger stomatal control on photosynthesis for smaller pine trees under average conditions. In dry years, however, larger pine trees exhibited stronger growth reductions. For Norway spruce, a significantly stronger correlation of tree-ring width with summer temperatures and summer precipitation was found for larger trees. Additionally, for Norway spruce there is evidence for a change in competition mode from size-asymmetric competition under conditions with sufficient soil water supply to a more size-symmetric competition under dry conditions. Smaller oak trees showed a weaker stomatal control on photosynthesis under both dry and average conditions, which is also reflected by a significantly faster recovery of tree-ring growth after extreme drought events in smaller oak trees. The observed patterns are discussed in the context of the limitation-caused matter partitioning hypothesis and possible species-specific ontogenetic modifications.     

Identifying signatures of natural selection in cork oak (Quercus suber L.) genes through SNP analysis

Cork oak (Quercus suber L.) is an evergreen tree species endemic to the western Mediterranean Basin with a major economical, social and ecological relevance, associated with cork extraction and exploitation. In the last years, cork oak stands have been facing a significant decline, which may be aggravated by the climate changes that are predicted to occur within cork oak distribution range during this century. Under this scenario, the assessment of adaptive genetic variation is essential to understand how cork oak may cope with these threats and to delineate strategies for the management of its genetic resources. In this study, six candidate genes possibly significant for environmental adaptation were analysed in cork oak populations from its entire distribution range. Signatures of natural selection were investigated using population genetic statistics and environmental association tests under alternative scenarios of population genetic structure. Signals of balancing selection were detected in the putative non-expressor of pathogenesis-related gene 1 (NPR1), involved in plant defence response against pathogens, in auxin response factor 16 (ARF16), a gene implicated in root development, in RAN3, also involved in developmental processes, and in glutamine synthetase nodule isozyme (GS), involved in nitrogen fixation. Furthermore, for ARF16, a class I heat shock protein (sHSP) and GS, associations were found between SNP allele and haplotype frequencies and several spatial and climatic variables, suggesting that these genes may have a role on cork oak local adaptation. In this study, the first steps were taken into gathering information on cork oak adaptation to environmental conditions.     

Shifts in the height‐related competitiveness of tree species following recent climate warming and implications for tree community composition: the case of common beech and sessile oak as predominant broadleaved species in Europe

Height growth is a trait that contributes to tree species fitness. How height growth responds to environmental changes may therefore provide indications on species ability to compete and maintain, and on changes in tree community composition. Common beech Fagus sylvatica and sessile oak Quercus petraea are the predominant late‐successional broadleaved species in Europe, and they differ in their shade‐tolerance. On common beech (a shade tolerant species), recent observations across Europe have shown a growth decline during recent climate warming. Because sessile oak is a warmth‐ and light‐demanding species, we therefore hypothesised that it may gain in competitiveness relative to common beech. We conducted analyses of historical height growth in several regions spanning the distributional range of the two species across a temperate‐continental gradient in France. Common beech and sessile oak were sampled in two and four regions, respectively, and were compared in two neighbouring regions. We documented the climatic and nutritional conditions of regional samples. Height growth of 408 trees of various ages was reconstituted from stem analyses. We estimated 20th‐century regional chronologies of height growth using a statistical modelling approach that filtered out the effects of ontogeny and site fertility. In regions where both species were sampled, modelled height trajectories were compared at different periods over the 20th century. Growth chronologies revealed 1) long‐term growth rate increases of a magnitude of 50–100% over 100 years in both species, more acute in the continental domain, 2) recurrent historical inversions in growth fluctuations between species, 3) a recent divergence, with growth decline in common beech versus a dramatic growth increase in sessile oak, more acute in colder regions. The analysis of height trajectories indicated a recent reduction in common beech competitiveness relative to sessile oak. In the face of future climate warming, we conclude that increased prevalence of beech–oak mixtures may arise.     

Photosynthesis,stomatal conductance and terpene emission response to water availability in dry and mesic Mediterranean forests

Key message

Warmer summer conditions result in increased terpene emissions except under severe drought, in which case they strongly decrease.

Abstract

Water stress results in a reduction of the metabolism of plants and in a reorganization of their use of resources geared to survival. In the Mediterranean region, periods of drought accompanied by high temperatures and high irradiance occur in summer. Plants have developed various mechanisms to survive in these conditions by resisting, tolerating or preventing stress. We used three typical Mediterranean tree species in Israel, Pinus halepensis L., Quercus calliprinos and Quercus ithaburensis Webb, as models for studying some of these adaptive mechanisms. We measured their photosynthetic rates (A), stomatal conductance (g _s), and terpene emission rates during spring and summer in a geophysical gradient from extremely dry to mesic from Yatir (south, arid) to Birya (north, moist) with intermediate conditions in Solelim. A and g _s of P. halepensis were threefold higher in Birya than in Yatir where they remained very low both seasons. Quercus species presented 2–3-fold higher A and g _s but with much more variability between seasons, especially for Q. ithaburensis with A and g _s that decreased 10–30-fold from spring to summer. Terpene emission rates for pine were not different regionally in spring but they were 5–8-fold higher in Birya than in Yatir in summer (P < 0.05). Higher emissions were also observed in Solelim for the drought resistant Q. ithaburensis (P < 0.001) but not for Q. calliprinos. α-Pinene followed by limonene and 3-carene were the dominant terpenes. Warmer summer conditions result in increased Terpene emission rates except under severe drought, in which case they strongly decrease.

     

The autumn mesozooplankton community at South Georgia: biomass, population structure and vertical distribution

Mesozooplankton were sampled at shelf and oceanic stations close to South Georgia, South Atlantic during austral autumn 2004 with a Longhurst Hardy Plankton Recorder. Onshelf biomass ranged from 2.18 to 5.75 g DM m^?2 (0–200 m) and was dominated by the small euphausiid Thysanöessa spp. At the oceanic stations (10.57–14.71 g DM m^?2, 0–1,000 m) large calanoids, principally Rhincalanus gigas comprised ～47–52% of biomass. Here Calanus simillimus was still active and reproducing in surface waters (0–11.2 eggs fem day^?1) but R. gigas and Calanoides acutus were largely resident in the warm deep water and undergoing their seasonal descent. A comparison with spring and summer data indicated increased abundance and biomass from spring through to summer followed by a decline towards autumn particularly over the shelf. Autumn values in oceanic waters differed little from summer. Mesozooplankton biomass in the surface 200 m of the oceanic stations as a proportion of that found in the top 1,000 m ranged from 63 to 78% of the total in spring and 62–73% in summer, but was only 23–29% of the total in this study, following redistribution down the water column.     

Consequences of larch budmoth outbreaks on the climatic significance of ring width and stable isotopes of larch

Tree-ring widths and stable carbon and oxygen isotopes of five European larch trees from Lötschental, Switzerland were investigated for the period 1900–2004. The objective was to test the suitability of each of these parameters for high-frequency climate reconstructions. This is of special interest with regard to the problem of cyclic larch budmoth (LBM) infestations of alpine larch trees. The results clearly demonstrate that tree-ring width chronologies are not suitable for high-frequency reconstructions because infestations lead to variably reduced tree-ring increments, largely suppressing climate signals. On the other hand, the stable isotope chronologies proved less affected by larch budmoth outbreaks, independent of the strength of the infestations. The correlation of the carbon isotopes with summer temperatures was especially high (r = 0.73) and with precipitation lower but nevertheless significant (r = ?0.43). Oxygen isotopes were also correlated with summer temperature (r = 0.46); however, a certain perturbation of normal oxygen isotope signatures due to LBM outbreaks was evident. Contrary to tree-ring widths, none of the LBM outbreaks caused a significant disturbance of the current year’s isotopic climate signal and, most importantly, there were no delayed effects in the following years. Thus, stable carbon isotopes in tree-ring chronologies of the European larch provide an excellent opportunity for high-frequency temperature reconstructions.     

The climate to growth relationships of pedunculate oak in steppe

Pedunculate oak (Quercus robur L.) is a long-lived species that dominates the extra–zonal natural forests in the steppe landscape of southeastern Ukraine. Although Q. robur is considered to be one of the most important species in European dendrochronology, it has received little attention in the steppe zone because of its scarcity in the often-degraded steppe forests. Nevertheless, a small and unique patch of old-growth oak exists within the boundary of Donetsk, a large industrial center in Eastern Europe. This forest is a remnant of an ancient wood and includes several dozen old-age trees that can contribute to filling some of the spatial gaps in pedunculate oak dendrochronology in Eastern Europe. In this study, we aim to determine the effect of climatic variables on pedunculate oak growth in the steppe zone, and to estimate the longevity of this species in the heterogeneous conditions of an urban forest. A total of 20 trees were cored for this study, varying in age from 55 to 254. The resulting tree-ring chronology correlates strongly with local precipitation in spring and summer, and with local temperature in April, June and July. Moving correlation analysis indicates a shift over the last 80 years in the relationship between oak growth and late winter and early spring temperatures, as well as between oak growth and precipitation in February and August. These findings imply that warming has caused both an advance in oak phenology and changes in the climatic conditions in early spring.