This technical note highlights a minor mistake in the calculation of Gleichläufigkeit (glk) suggested by Schweingruber (1983). Namely, if two series that are compared with each other show a ...synchronous lack of growth change this will not be treated accurately. We present an accurate way of glk calculation based on Gegenläufigkeit (Huber, 1943) as in Eckstein and Bauch (1969) and suggest that software-tools and methodological approaches which make use of glk should be tested for the way they compute glk.
Averaging tree-ring measurements from multiple individuals is one of the most common procedures in dendrochronology. It serves to filter out noise from individual differences between trees, such as ...competition, height, and micro-site effects, which ideally results in a site chronology sensitive to regional scale factors such as climate. However, the climate sensitivity of individual trees can be modulated by factors like competition, height, and nitrogen deposition, calling attention to whether average chronologies adequately assess climatic growth-control. In this study, we demonstrate four simple but effective methods to visually assess differences between individual trees. Using individual tree climate-correlations we: (1) employed jitter plots with superimposed metadata to assess potential causes for these differences; (2) plotted the frequency distributions of climate correlations over time as heat maps; (3) mapped the spatial distribution of climate sensitivity over time to assess spatio-temporal dynamics; and (4) used t-distributed Stochastic Neighborhood Embedding (t-SNE) to assess which trees were generally more similar in terms of their tree-ring pattern and their correlation with climate variables. This suite of exploratory methods can indicate if individuals in tree-ring datasets respond differently to climate variability, and therefore, should not solely be explored with climate correlations of the mean population chronology.
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.
► We develop mathematical relationships between Haloxylon-morphology and biomass. ► We apply these allometric formulas on transect data across Central Asia. ► Haloxylon aphyllum exhibits higher shrub ...biomass values compared to Haloxylon persicum. ► Environmental conditions and human impact cause the observed biomass variations.
The Haloxylon vegetation in Central Asia has undergone vast changes throughout the last century, which has lead to a strong degradation and desertification of the desert ecosystems in Kazakhstan, Uzbekistan, and Turkmenistan. In terms of combating desertification and restoration of ecosystems, two pilot-projects recently are aiming at the reforestation of Haloxylon ecosystems. Hereby, two of the internationally discussed climate change mitigation activities may be of higher relevance: (I) to sequester CO2 through afforestation and reforestation and (II) to substitute fossil fuels by sustainable utilization of regenerative bio-fuels. With particular focus on Central Asian desert ecosystems, the questions arose: (I) to which extent Haloxylon species – the dominant shrub species – sequester CO2, (II) what the recent carbon pool related to Haloxylon ecosystems is, and (III) in which magnitude the existing and/or reforested ecosystems could be utilized for bio-fuels sustainably. Therefore, this study aims at the derivation of allometric models including carbon contents for the two Haloxylon species in Central Asian desert ecosystems. A first application to measured transect data across Central Asia is carried out to reflect the recent biomass variability of the two study species. We found, that above- and below-ground biomass for both species is best modeled when taking growth height, basal area, and canopy area of shrubs into account (0.87<r2<0.97 for the top-models). Regarding the transect data, Haloxylon aphyllum showed a significantly higher variability of measured and modeled variables as well as higher maximum and average biomass estimates when compared to Haloxylon persicum. As our study sites partly include regions with moderate to strong human impact, the observed biomass variability represents differing ecological conditions as well as anthropogenic effects, with the latter also being reflected in the observed shrub species compositions.
Tree growth at northern boreal treelines is generally limited by summer temperature, hence tree rings serve as natural archives of past climatic conditions. However, there is increasing evidence that ...a changing summer climate as well as certain micro-site conditions can lead to a weakening or loss of the summer temperature signal in trees growing in treeline environments. This phenomenon poses a challenge to all applications relying on stable temperature-growth relationships such as temperature reconstructions and dynamic vegetation models. We tested the effect of differing ecological and climatological conditions on the summer temperature signal of Scots pine at its northern distribution limits by analyzing twelve sites distributed along a 2200 km gradient from Finland to Western Siberia (Russia). Two frequently used proxies in dendroclimatology, ring width and maximum latewood density, were correlated with summer temperature for the period 1901-2013 separately for (i) dry vs. wet micro-sites and (ii) years with dry/warm vs. wet/cold climate regimes prevailing during the growing season. Differing climate regimes significantly affected the temperature signal of Scots pine at about half of our sites: While correlations were stronger in wet/cold than in dry/warm years at most sites located in Russia, differing climate regimes had only little effect at Finnish sites. Both tree-ring proxies were affected in a similar way. Interestingly, micro-site differences significantly affected absolute tree growth, but had only minor effects on the climatic signal at our sites. We conclude that, despite the treeline-proximal location, growth-limiting conditions seem to be exceeded in dry/warm years at most Russian sites, leading to a weakening or loss of the summer temperature signal in Scots pine here. With projected temperature increase, unstable summer temperature signals in Scots pine tree rings might become more frequent, possibly affecting dendroclimatological applications and related fields.
Dendroclimatological research is often based on the assumption that the relationship between tree growth and climate is not variable over time. Here we test this assumption by exploring if climate ...sensitivity of
Picea mariana (Mill.) trees growing in open-stand lowland forest and on top of a neighboring peatland in Interior Alaska is stable or changing over time. Climate–growth correlations at the study sites are strongly dependent on microtopography and vary substantially over time. Trees growing in the open forest site generally display stronger climate–growth correlations, especially significantly negative correlations with late summer temperatures (July, August) starting in the period 1920–1970. Trees growing on the peatland site are less climate sensitive, but display positive correlations between annual growth and temperature of October and December in the early 20th century, while in the late 20th century, significant negative correlations exist with January and February temperatures. This study, thus, demonstrates a transient climate–growth response for
P. mariana (Mill.) on two sites typical for lowland Interior Alaska. However, due to multiple possible explanations (e.g. changing climate, coupled with aging trees and a growing peatland surface) it is not possible at this time to pinpoint the exact cause for these changes in the climate–growth relationships.
Many dendroclimatic studies have been conducted in Alaska to understand recent climate changes, identify past and current warming trends, and determine how climate change may influence ecosystems. ...Four new white spruce (Picea glauca Moench Voss) ring‐width chronologies from four sites along a 30 kilometer north‐south transect in the Lake Clark National Park and Preserve on the Alaskan Peninsula span a common interval from AD 1769 to 2003. Two sites show an internally consistent positive growth response to increasing April–July temperatures after 1950. The two other sites each contain two subpopulations showing varying growth responses. One subpopulation diverges from historical temperature data after 1950 and one shows increased growth consistent with warming or exceeds expected growth increases. The growth decline may be due to temperature‐induced drought stress that acts on some trees. Unprecedented climatic changes are triggering diverse growth responses between and within study sites that may greatly complicate dendroclimatic reconstructions of past climate conditions.
Background： We compare the climate sensitivity of European beech （Fagus sylvatica L.） in two forest nature reserves in northeastern Germany. The one reserve, Schlossberg, is characterized by shallow ...chalk soils, whereas in the other reserve, EIdena, soils are deeper and more developed. Little is known about the drought sensitivity of beech on shallow chalk soils. Methods： We collected increment cores at both research sites and established climate-growth relationships. Inter- tree variability was assessed by employing linear mixed-effect models. Results： We expected to find distinctively higher drought sensitivity at Schlossberg due to limited water availability, but find only marginal differences in growth responses. At both sites, drought is the major climatic factor driving tree growth. Adaptations in tree architecture and an underestimation of the water holding capacity of shallow chalk soils are discussed as possible reasons for not finding more distinct climate responses. In analyzing climate-growth relationships, we specifically focused on growth responses of individual trees but observed only low inter-tree variability at both sites. Evident is a shift in climate response patterns from the first to the second half of the twentieth century with previous-year drought conditions becoming more important than current-year drought. This shift is discussed in relation to a warming trend over that same period, as well as possible trends in masting behavior of beech. Conclusion： The investigated beech trees on the shallow chalk soil are only slightly more drought sensitive than beech trees on the reference site with deeper and more developed soils.
Summary
Understanding the effects of temperature and moisture on radial growth is vital for assessing the impacts of climate change on carbon and water cycles. However, studies observing growth at ...sub‐daily temporal scales remain scarce.
We analysed sub‐daily growth dynamics and its climatic drivers recorded by point dendrometers for 35 trees of three temperate broadleaved species during the years 2015–2020. We isolated irreversible growth driven by cambial activity from the dendrometer records. Next, we compared the intra‐annual growth patterns among species and delimited their climatic optima.
The growth of all species peaked at air temperatures between 12 and 16°C and vapour pressure deficit (VPD) below 0.1 kPa. Acer pseudoplatanus and Fagus sylvatica, both diffuse‐porous, sustained growth under suboptimal VPD. Ring‐porous Quercus robur experienced a steep decline of growth rates with reduced air humidity. This resulted in multiple irregular growth peaks of Q. robur during the year. By contrast, the growth patterns of the diffuse‐porous species were always right‐skewed unimodal with a peak in June between day of the year 150–170.
Intra‐annual growth patterns are shaped more by VPD than temperature. The different sensitivity of radial growth to VPD is responsible for unimodal growth patterns in both diffuse‐porous species and multimodal growth pattern in Q. robur.
About 60% of the European wetlands are located in the European part of Russia. Nevertheless, data on methane emissions from wetlands of that area are absent. Here we present results of methane ...emission measurements for two climatically different years from a boreal peatland complex in European Russia. Winter fluxes were well within the range of what has been reported for the peatlands of other boreal regions before, but summer fluxes greatly exceeded the average range of 5-80 mg CH4 m−2 d−1 for the circumpolar boreal zone. Half of the measured fluxes ranged between 150 and 450 mg CH4 m−2 d−1. Extrapolation of our data to the whole boreal zone of European Russia shows that theses emissions could amount to up to 2.7 1.1 Tg CH4 a−1, corresponding to 69% of the annual emissions from European wetlands or 33% of the total annual natural European methane emission. In 2008, climatic conditions corresponded to the long term mean, whereas the summer of 2011 was warmer and noticeably drier. Counterintuitively, these conditions led to even higher CH4 emissions, with peaks up to two times higher than the values measured in 2008. As Russian peatlands dominate the areal extend of wetlands in Europe and are characterized by very high methane fluxes to the atmosphere, it is evident, that sound European methane budgeting will only be achieved with more insight into Russian peatlands.
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