In this study, we explore the potential to reconstruct lake-level (and groundwater) fluctuations from tree-ring chronologies of black alder (Alnus glutinosa L.) for three study lakes in the ...Mecklenburg Lake District, northeastern Germany. As gauging records for lakes in this region are generally short, long-term reconstructions of lake-level fluctuations could provide valuable information on past hydrological conditions, which, in turn, are useful to assess dynamics of climate and landscape evolution. We selected black alder as our study species as alder typically thrives as riparian vegetation along lakeshores. For the study lakes, we tested whether a regional signal in lake-level fluctuations and in the growth of alder exists that could be used for long-term regional hydrological reconstructions, but found that local (i.e. site-specific) signals in lake level and tree-ring chronologies prevailed. Hence, we built lake/groundwater-level reconstruction models for the three study lakes individually. Two sets of models were considered based on (1) local tree-ring series of black alder, and (2) site-specific Standardized Precipitation Evapotranspiration Indices (SPEI). Although the SPEI-based models performed statistically well, we critically reflect on the reliability of these reconstructions, as SPEI cannot account for human influence. Tree-ring based reconstruction models, on the other hand, performed poor. Combined, our results suggest that, for our study area, long-term regional reconstructions of lake-level fluctuations that consider both recent and ancient (e.g., archaeological) wood of black alder seem extremely challenging, if not impossible.
Dendrometers offer a useful tool for long-term, high-resolution monitoring of tree responses to environmental fluctuations and climate change. Here, we analyze a 4-year dendrometer dataset (2014-17) ...on European beech (Fagus sylvatica L.), common hornbeam (Carpinus betulus L.) and pedunculate oak (Quercus robur L.), co-occuring in a mixed broadleaved forest in northeastern Germany. In our analyses, we focus both on seasonal growth dynamics as well as on the environmental forcing of daily stem-size variations. Over the study period with contrasting weather conditions, we observed species- and year-specific differences in growth phenology (i.e., growth onset, cessation and duration). Oak was characterized by early growth onset and long growth duration in all years as compared with beech and hornbeam. The analysis on the environmental forcing of daily stem dynamics revealed, however, highly similar responses for the studied species, with current-day vapor pressure deficit and sunshine duration negatively, and relative humidity and precipitation positively affecting stem size. When considering lagged effects, environmental conditions often oppositely affected stem-size changes. No consistent seasonality in environmental responses was detected, though specific weather conditions were found to affect temporal patterns in individual years. We suggest that the high similarity in environmental forcing observed between tree species can be explained by daily stem-size changes mainly reflecting tree water status rather than tree growth. Our results stress that correcting dendrometer series for reversible stem hydrological changes is of utmost importance to better quantify tree growth from dendrometers in future.
Scots pine (Pinus sylvestris L.) is a widely used tree species in European dendroclimatology studies due to its common distribution across much of the continent. Almost all studies find radial growth ...strongly related to summer temperature, a result reflecting site selection at high elevation/latitude environments where trees grow at their ecophysiological limits. Due to the amount of attention spent on these sites there is a geographical and seasonal bias in temperature reconstructions based upon tree‐ring proxies in Europe. To overcome the limited availability of tree‐ring data in temperate lowlands, we present a northern Poland ring‐width chronology developed from living and historic Scots pine material with a strong common growth signal going back to AD 1200. Investigations into climate‐growth relationships found year‐to‐year ring‐width variability to be more strongly correlated to cold season temperature (November to April) prior to the growing season than summer temperatures during tree‐ring formation. Based on this relationship it was possible to reconstruct cold season temperature conditions for the last 810 years. Spatial field correlations with gridded instrumental records indicated that the reconstruction provides relevant cold season temperature information across the land regions bordering the North Atlantic Ocean and Baltic Sea, lowlands and uplands of western and central Europe, and the eastern and central interior of Russia. Despite an unsuccessful attempt to find a stationary relationship with the North Atlantic Oscillation, comparisons with several cold season temperature reconstructions confirmed the long‐term connection between our reconstructed temperature series for northern Poland and the wider area.
To study growth responses of trees to extreme events, analyses of so-called ‘pointer years’ are often performed. Thereby, the term pointer year refers to years in which a majority of trees shows ...extraordinary growth responses, like very narrow (or wide) ring widths. A wide variety of methods has been used to analyze pointer years, hampering comparisons between studies. The latter illustrates that there is a strong need to harmonize pointer year detection methods. This review contributes to that by describing and comparing the main methods (and variants thereof) found in the literature for the last two decades, both in a qualitative and quantitative way. We discuss methodological considerations and provide recommendations how to proceed with pointer year detection in future. Given that the individual methods for pointer year detection were found to highlight different aspects of extraordinary growth, the one method cannot completely substitute the other. Hence, we suggest to use multiple methods in a harmonized way to get the deepest insight into the nature of pointer years.
•After the 2018–2020 drought, crown condition differed strongly within beech stands.•Growth dynamics and tree genetics of non–/vital individuals were compared.•Long-term growth decline was widespread ...in both groups.•Climate sensitivity and individual heterozygosity did not consistently differ.•Crown condition after drought is a poorer indicator of tree vitality than ring width.
Global warming poses a major threat to forest ecosystems around the world. In Central Europe, vitality losses and tree mortality have already been observed in various regions, especially after extreme drought episodes such as the 2018–2020 drought. European beech (Fagus sylvatica L.), which is the dominating deciduous tree species in large parts of temperate Europe, also suffered from the recent drought. In Germany, for example, losses in crown condition were observed. Within individual stands, however, the crown condition of beech differed strongly from non–/weakly damaged trees (hereafter referred to as vital trees) to severely damaged/dead trees (non-vital trees). Tree characteristics and micro-site conditions were apparently similar. Hence, we checked whether differences in growth behavior exist and (or) developed over time and assessed if observed differences between the non–/vital individuals might be genetically driven. We found that the climate sensitivity as well as the drought resistance of tree growth did not consistently differ between non–/vital trees. In both groups, a growing importance of water availability for tree growth was apparent. Further, long-term growth decline was widespread in both vital and non-vital trees, suggesting severe stress and future risks of tree mortality irrespective of crown condition. Only at one out of nine sites, we found significant differences in individual heterozygosity, signaling potential differences in the adaptation of trees to environmental stress. As a consequence, our study highlights that crown condition after an extreme drought is a poorer indicator of tree vitality than ring width in beech stands in Germany.
Kyrgyzstan features the largest naturally occurring walnut forests in the world. Their high plant biodiversity, including wild relatives to modern-day fruit species such as apple and pear, make them ...a valuable guardian of genetic diversity. Further, walnut forests have a high economic importance for the country. Climate change, however, poses a major threat to these ecosystems, in particular since rises in temperature are projected that are well above global average. As studies on effects of changing environmental conditions on the growth of walnut are missing, we investigate the climate sensitivity and temporal stability thereof as well as extreme growth responses of walnut along its full elevational gradient in Kyrgyzstan. Whereas we expected to find a shift from water- to temperature-limitation over the elevational gradient, which may move upwards with recent warming, we found walnut growth to be temperature-limited along the entire elevational gradient. In recent decades, negative correlations between the drought index SPEI and tree growth, however, weakened. An up until now low importance of drought stress for walnut growth is also substantiated by a pointer-year analysis. Overall, our results show that walnut growth is already affected by climate change, though imminent risks of drought-induced vitality loss seem still low. With ongoing climate change, this may, however, rapidly change.
After being proposed by Lloret et al. in 2011, the resilience components resistance, recovery, resilience and relative resilience became highly popular for studying tree growth responses to ...disturbances and extreme weather events. As the ‘Lloret indices’, however, have conceptual limitations, various additional indices to characterize tree resilience have been discussed since then, namely: recovery period, total growth reduction, average recovery rate, and average growth reduction. In pointRes 2.0, a major update of the R-package pointRes, these new indices have now been implemented. Besides convenient functions for calculating and plotting resilience indices, two new functions for calculating pointer years using (i) the interval trend method, and (ii) a 'z-transformation of site chronology'-approach have been included as well. This technical note illustrates pointRes' new functionalities.
Key message
European beech showed low resistance but high resilience in radial growth after an extreme late frost event. Site-specific growth reductions correlated with absolute minimum temperature ...in May
.
Late spring frost events occurring after the early leaf unfolding (“false spring”) can result in severe leaf damages in deciduous trees. With climate warming, such damages may occur more frequently due to an earlier start of the growing season. While affected, mature trees usually survive, but radial and height growth after the late frost has rarely been quantified in relation to the magnitude of the frost events. The effects of a severe late frost event in the early May 2011, following a warm spring and early bud break, was quantified for European beech (
Fagus sylvatica
L.) at 7 forest stands in Bavaria, Germany. Resistance and resilience of tree growth were quantified based on tree-ring widths of 135 trees. Resistance to the late frost event (comparing tree-ring width in the frost year with the previous 5 years) was on average reduced by 46%. Resistance was positively correlated with May minimum temperature at the study sites, indicating a relationship between growth reduction and frost severity. Partial least-square linear models based on monthly climate data (precipitation, temperature, potential evapotranspiration, and the Standardized Precipitation Evapotranspiration Index) could not explain the growth reduction in 2011, thereby providing evidence for the importance of frost damages on annual growth.
F. sylvatica
showed high resilience after the frost year, with tree-ring widths in the subsequent years being comparable to the previous years. This study suggests that frost events may strongly reduce growth of
F. sylvatica
in the event year, but that carry-over effects on the radial growth of subsequent years are not likely.
Element composition of annually resolved tree-rings constitutes a promising biological proxy for reconstructions of environmental conditions and pollution history. However, several methodological and ...physiological issues have to be addressed before sound conclusions can be drawn from dendrochemical time series. For example, radial and vertical translocation processes of elements in the wood might blur or obscure any dendrochemical signal. In this study, we tested the degree of synchronism of elemental time series within and between trees of one coniferous (Pinus sylvestris L.) and one broadleaf (Castanea sativa Mill.) species growing in conventionally managed forests without direct pollution sources in their surroundings. Micro X-ray fluorescence (μXRF) analysis was used to establish time series of relative concentrations of multiple elements (Mg, Al, P, Cl, K, Ca, Cr, Mn, Fe and Ni) for different stem heights and stem exposures. We found a common long-term (decadal) trend for most elements in both species, but only little coherence in the high frequency domain (inter-annual variations). Aligning the element curves by cambial age instead of year of ring formation reduced the standard deviations between the single measurements. This points at an influence of age on longer term trends and would require a detrending in order to extract any environmental signal from dendrochemical time series. The common signal was stronger for pine than for chestnut. In pine, many elements show a concentration gradient with higher values towards the tree crown. Mobility of elements in the stem leading to high within- and between-tree variability, as well as a potential age-trend apparently complicate the establishment of reliable dendrochemical chronologies. For future wood-chemical studies, we recommend to work with element ratios instead of single element time series, to consider potential age trends and to analyze more than one sample per tree to account for internal variability.
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•Element translocation in tree stems constitutes a major problem in dendrochemistry.•Multi-element time series for two species were established with X-ray fluorescence.•Synchronicity was compared between different stem heights and expositions.•Common long term trends but low inter-annual coherence were detected.•High within- and between-tree variability plus age trends need to be considered.
The forests along the southern Baltic Sea coast harbour some stands of the rare and endangered European yew (
Taxus baccata
L.), which are hypothesised to be autochthonous. Using the example of an ...occurrence on the Darss-Zingst peninsula, the population dynamics of the yew since the late Holocene are interdisciplinarily investigated and linked to the forest history of this area. Pollen analysis shows that yew has been present in the study area for at least 2600 years and thus indeed represents an autochthonous tree species in the area. The yew was probably originally part of a second tree storey and of forest margins within a mixed forest mainly consisting of several deciduous tree species and Scots pine. Historical evidence reveals that yew was still occurring in the forest in the middle of the eighteenth century, but then had nearly disappeared by the end of the nineteenth century. This was caused by several factors including forest grazing by livestock, high game populations and clear-cutting. First replanting of yew took place in the 1930s/1940s and 1950s/1960s, followed by planting campaigns in the 1990s and 2000s. Planting material from local and regional autochthonous relict populations was used, at least in part. The current yew population mainly comprises young individuals with a total number of ca. 1300 trees. It has thus been possible here to re-establish an autochthonous yew occurrence that was nearly extinct in historical times. This local example of targeted re-enrichment of native tree diversity may also encourage further measures to give this species a new chance again elsewhere in the wider region.
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