► Dendrochronological investigations of beech and oak along precipitation gradient. ► Growth strongly depends on water availability especially during June and July. ► Sensitivity of tree growth and ...correlations to climate increase along gradient. ► Numbers of pointer years increase, changes more pronounced for beech. ► oak might gain competitive advantages under the projected drier climate.
For north-eastern Germany regional climate models project rising temperatures in combination with decreasing summer and increasing winter precipitation. The resulting overall drier conditions during the growing season will considerably impact forest growth there. We evaluate the consequences of increasing drought on the growth of the two locally most important broadleaf tree species common beech (
Fagus sylvatica L.) and pedunculate oak (
Quercus robur L.). Three mixed forests of beech and oak were sampled along a west-east gradient of declining precipitation. In total we used 257 ring-width samples from 133 trees to build six species and site specific chronologies. Additionally, we modelled the soil water budget for each site. We performed continuous and discontinuous (pointer year) analysis of climate-tree-growth relationships with particular emphasis on inter-annual-variations and their dependence upon climatic factors (temperature, precipitation, soil moisture) and on the stability of the obtained relationships. Results of climate-growth correlations together with pointer year analysis indicate a strong dependency of growth of both species from water availability, especially during early summer (June and July). General correlation pattern between growth and climate are similar for both species, but climate sensitivity of beech is generally higher. We identified drought as the main driver of negative growth depressions in both species. Increasing drought stress along the gradient is expressed in higher correlations to climatic variables, higher sensitivity (variance) of growth, and a higher number of negative pointer years for both species. For beech we also found a significant trend of decreasing average growth rates along the gradient. Growth superiority of beech compared to oak declines with decreasing precipitation. The relationships were generally stable throughout the 20th century. A rise of sensitivity together with a higher frequency of negative pointer years during the last decades suggests that increasing climatic variability together with rising temperatures might be influencing growth of
Fagus at the more humid sites. If we substitute space by time it seems that already small changes in precipitation regime can have considerable impact, especially on the growth of beech. Other, more drought tolerant species like oak might gain competitive advantages under the projected climatic changes.
Maximum latewood density and delta 13C discrimination of Interior Alaska white spruce were used to reconstruct summer (May through August) temperature at Fairbanks for the period 1800-1996, one of ...the first high-resolution reconstructions for this region. This combination of latewood density and delta 13C discrimination explains 59.9% of the variance in summer temperature during the period of record 1906-1996. The 200-yr. reconstruction is characterized by 7 decadal-scale regimes. Regime changes are indicated at 1816, 1834, 1879, 1916, 1937, and 1974, are abrupt, and appear to be the result of synoptic scale climate changes. The mean of summer temperature for the period of reconstruction (1800-1996) was 13.49 degrees C. During the period of instrument record (1903-1996) the mean of summer temperature was 13.31 degrees C for both the reconstruction and the recorded data. The coldest interval was 1916-1937 (12.62 degrees C) and the warmest was 1974-1996 (14.23 degrees C) for the recorded data. The reconstruction differs from records of northern hemisphere temperatures over this period, especially because of Interior Alaska warm periods reconstructed from 1834 to 1851 (14.24 degrees C) and from 1862 to 1879 (14.19 degrees C) and because of the cool period in the early part of the 20th century (1917-1974). We show additional tree ring data that support our reconstruction of these warm periods. Alternate hypotheses involving autogenic effect of tree growth on the site, altered tree sensitivity, or novel combinations of temperature and precipitation were explored and while they cannot be ruled out as contributors to the anomalously warm 19th century reconstruction, they were not supported by available data. White spruce radial growth is highly correlated with reconstructed summer temperature, and temperature appears to be a reliable index of carbon uptake in this system.
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▶ Trees from upper treeline were mainly limited by temperature and trees from lower treeline were mainly limited by precipitation at the northeast Tibet Plateau. ▶ Trees from higher ...elevations show divergent growth trends over time and two responses to climate (increasing positive and increasing negative responses to growing season temperature) during the last decades. ▶ Trees from lower treeline show a strengthening drought stress signal over time and no divergent growth trends within sites.
Divergent responses between tree growth and climate factors have been widely reported at high latitudes in the northern hemisphere. Here we show variable climate-growth relationships and divergent growth responses of Qinghai spruce (
Picea crassfolia) along an elevation gradient at a mid-latitude site at the northeastern Tibetan Plateau, China. Trees from higher elevations, limited mainly by temperature, show divergent growth trends over time and two responses to climate. Some trees show increasing positive and some increasing negative responses to growing season temperature during the last decades. Trees from lower treeline show a strengthening drought stress signal over time and no divergent growth trends within sites. Our results indicate that single tree analysis might be a worthwhile tool to (1) uncover spatial–temporal changes in climate-growth relationships of trees, (2) better understand future growth performance and (3) help overcome current limitations of tree ring based climatic reconstructions.
Peatlands are effective carbon sinks as more biomass is produced than decomposed under the prevalent anoxic conditions. Draining peatlands coupled with warming releases stored carbon, and subsequent ...rewetting may or may not restore the original carbon sink. Yet, patterns of plant production and decomposition in rewetted peatlands and how they compare to drained conditions remain largely unexplored. Here, we measured annual above- and belowground biomass production and decomposition in three different drained and rewetted peatland types: alder forest, percolation fen and coastal fen during an exceptionally dry year. We also used standard plant material to compare decomposition between the sites, regardless of the decomposability of the local plant material. Rewetted sites showed higher root and shoot production in the percolation fen and higher root production in the coastal fen, but similar root and leaf production in the alder forest. Decomposition rates were generally similar in drained and rewetted sites, only in the percolation fen and alder forest did aboveground litter decompose faster in the drained sites. The rewetted percolation fen and the two coastal sites had the highest projected potential for organic matter accumulation. Roots accounted for 23–66% of total biomass production, and belowground biomass, rather than aboveground biomass, was particularly important for organic matter accumulation in the coastal fens. This highlights the significance of roots as main peat-forming element in these graminoid-dominated fen peatlands and their crucial role in carbon cycling, and shows that high biomass production supported the peatlands’ function as carbon sink even during a dry year.
Shrub dendrochronological investigations are recently gaining more and more importance within the dendro-scientific community. As being a rather young discipline, many means of shrub dendrochronology ...lean on established methods that have been developed for trees. Although shrubs as trees are woody plants, it seems likely that they express differing growth characteristics due to their often multi-stemmed and prostrate stature. Yet, the majority of shrub dendrochronological investigations have measured shrub ring widths along two radii within one (sometimes several) stem disk(s) per individual. To our knowledge only one study so far has undertaken the approach to measure complete area increments (e.g. basal area increments, if applied to the basal stem disk of a shrub), however not focusing in detail on a comparative evaluation of this new approach with respect to radial measurements. To fill this knowledge gap our study focuses on the comparison of stem disk area increment measurements with radial measurements in the context of shrub growth representation and response- and transfer-function analyses. Our results indicate that for eccentric shrubs a minimum of four radial measurements per stem disk should be obtained for a good representation of the average stem disk growth. Inter-stem-disk comparisons showed that growth differences between individuals were often misestimated when only based on one or two radial measurements per stem disk. Response- and transfer-function analyses suggested, that the investigated shrubs reflect different environmental signals within different sectors of stem discs. This implies to carefully select radial measurements and individuals to increase the strength of environmental signals within transfer functions.
Tree‐ring records provide global high‐resolution information on tree‐species responses to global change, forest carbon and water dynamics, and past climate variability and extremes. The underlying ...assumption is a stationary (time‐stable), quasi‐linear relationship between tree growth and environment, which however conflicts with basic ecological and evolutionary theory. Indeed, our global assessment of the relevant tree‐ring literature demonstrates non‐stationarity in the majority of tested cases, not limited to specific proxies, environmental parameters, regions or species. Non‐stationarity likely represents the general nature of the relationship between tree‐growth proxies and environment. Studies assuming stationarity however score two times more citations influencing other fields of science and the science–policy interface. To reconcile ecological reality with the application of tree‐ring proxies for climate or environmental estimates, we provide a clarification of the stationarity concept, propose a simple confidence framework for the re‐evaluation of existing studies and recommend the use of a new statistical tool to detect non‐stationarity in tree‐ring proxies. Our contribution is meant to stimulate and facilitate discussion in light of our results to help increase confidence in tree‐ring‐based climate and environmental estimates for science, the public and policymakers.
Tree‐ring records provide global high‐resolution information on tree‐species responses to global change, forest carbon and water dynamics, and past climate variability and extremes. The underlying assumption is a stationary (time‐stable), quasi‐linear relationship between tree growth and environment. Our results show that this assumption might be too simplistic. Non‐stationarity between tree growth and climatic or environmental drivers is evident at global scale.
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.
Climate warming is expected to enhance productivity and growth of woody plants, particularly in temperature‐limited environments at the northernmost or uppermost limits of their distribution. ...However, this warming is spatially uneven and temporally variable, and the rise in temperatures differently affects biomes and growth forms. Here, applying a dendroecological approach with generalized additive mixed models, we analysed how the growth of shrubby junipers and coexisting trees (larch and pine species) responds to rising temperatures along a 5000‐km latitudinal range including sites from the Polar, Alpine to the Mediterranean biomes. We hypothesize that, being more coupled to ground microclimate, junipers will be less influenced by atmospheric conditions and will less respond to the post‐1950 climate warming than coexisting standing trees. Unexpectedly, shrub and tree growth forms revealed divergent growth trends in all the three biomes, with juniper performing better than trees at Mediterranean than at Polar and Alpine sites. The post‐1980s decline of tree growth in Mediterranean sites might be induced by drought stress amplified by climate warming and did not affect junipers. We conclude that different but coexisting long‐living growth forms can respond differently to the same climate factor and that, even in temperature‐limited area, other drivers like the duration of snow cover might locally play a fundamental role on woody plants growth across Europe.
Climate warming is expected to increase plant productivity and growth especially in temperature‐limited environments; however, vegetation dynamics considering concurrently both shrubs and trees are still not well explored. We investigated, with a dendroecological approach, the growth trends and climate sensitivity of Juniperus communis L. and coexisting trees to better understand their responses to recent climate in three contrasting biomes, Polar, Alpine and Mediterranean, across the European continent. Shrub and tree growth forms revealed divergent growth trends in all biomes, with juniper performing better than trees at Mediterranean than at Polar and Alpine sites. The post‐1980s decline of tree growth in Mediterranean sites might be induced by drought stress amplified by climate warming and did not affect junipers. This study emphasizes that other climatic drivers, as drought or snow cover, in addition to temperature could play a fundamental role in defining future woody plant growth under the pressure of climate changes.
Purpose
Nowadays, several higher education institutions around the world are integrating sustainability topics into their daily operations, functionality and education systems. This paper presents a ...case study from a pilot project implemented by the Ernst-Moritz-Arndt-Universität Greifswald (hereafter, Greifswald University), Germany on its way towards a “carbon-neutral university”. The purpose of this paper is to share an institutional process targeting a gradual transformation towards achieving carbon neutrality. This might be relevant to other higher education institutions striving for a systematic and progressive change from a traditional system to a low emission or carbon-neutral pathway.
Design/methodology/approach
To achieve carbon neutrality, three major transformative strategies were adopted: carbon reduction, carbon offsetting and mainstreaming sustainable actions via teaching and research.
Findings
A locally adaptable institutional framework on sustainability was successfully developed to: promote changes in daily operations, implement interdisciplinary research, incorporate sustainability into teaching and education and enhance outreach programs. Strong commitment from all stakeholders resulted in reduction of the university’s carbon footprint from 8,985 to 4,167 tCO2e year−1. Further, the unavoidable emissions could be locally offset through enhanced carbon sequestration on the university-owned forests.
Originality/value
Based on the experiences of Greifswald University, this paper presents major challenges and success lessons learned during the process of gradual institutional transformation to achieve the target of carbon neutrality.
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