Severe droughts have the potential to reduce forest productivity and trigger tree mortality. Most trees face several drought events during their life and therefore resilience to dry conditions may be ...crucial to long-term survival. We assessed how growth resilience to severe droughts, including its components resistance and recovery, is related to the ability to survive future droughts by using a tree-ring database of surviving and now-dead trees from 118 sites (22 species, >3,500 trees). We found that, across the variety of regions and species sampled, trees that died during water shortages were less resilient to previous non-lethal droughts, relative to coexisting surviving trees of the same species. In angiosperms, drought-related mortality risk is associated with lower resistance (low capacity to reduce impact of the initial drought), while it is related to reduced recovery (low capacity to attain pre-drought growth rates) in gymnosperms. The different resilience strategies in these two taxonomic groups open new avenues to improve our understanding and prediction of drought-induced mortality.
Na Savski cesti 10 v Kranju so arheološka izkopavanja leta 2010 razkrila tri gradbene faze prazgodovinske poselitve. Ob bogatih keramičnih najdbah so bili iz vsake faze ohranjeni tudi ostanki ...lesenih stavb. V štirih jamah za sohe, ki pripadajo dvema stavbama, so bili najdeni kosi lesenih brun, ki so omogočili dendrokronološke analize in radiokarbonsko datiranje. Osrednji del prispevka obsega tipološko študijo keramičnega posodja. Ta je na podlagi primerjav z najdbami z drugih najdišč pokazala, da ima območje ob Savski cesti, podobno kot druge lokacije v Kranju, največ vzporednic med gradivom iz časa stopenj Ljubljana II in IIIa oz. Ha B3 in Ha C0 (v srednjeevropskem smislu). Opredelitev je nadgrajena z absolutno datacijo ostankov brun. Ta kaže, da je stavba 1A iz prve faze nastala v prvi polovici 8. st. pr. n. št. in stavba 2 druge faze najverjetneje na začetku druge polovice 8. st. pr. n. št.
Tree rings are natural archives of climate and environmental information with a yearly resolution. Indeed, wood anatomical, chemical, and other properties of tree rings are a synthesis of several ...intrinsic and external factors, and their interaction during tree growth. In particular, Intra-Annual Density Fluctuations (IADFs) can be considered as tree-ring anomalies that can be used to better understand tree growth and to reconstruct past climate conditions with intra-annual resolution. However, the ecophysiological processes behind IADF formation, as well as their functional impact, remain unclear. Are IADFs resulting from a prompt adjustment to fluctuations in environmental conditions to avoid stressful conditions and/or to take advantage from favorable conditions? In this paper we discuss: (1) the influence of climatic factors on the formation of IADFs; (2) the occurrence of IADFs in different species and environments; (3) the potential of new approaches to study IADFs and identify their triggering factors. Our final aim is to underscore the advantages offered by network analyses of data and the importance of high-resolution measurements to gain insight into IADFs formation processes and their relations with climatic conditions, including extreme weather events.
Physiological and ecological mechanisms that define treelines are still debated. It has been suggested that the absence of trees above the treeline is caused by low temperatures that limit growth. ...Thus, we hypothesized that there is a critical minimum temperature （CTmin） preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir （Abies georgei var. srnithii） treeline sites on the southeastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature （CTmin） for the onset and end of xylogenesis occurred at 0.7 ±0.4 ℃. A process-based modelling chronology of tree-ring formation using this CTmin was consistent with actual tree-ring data. This extremely low CTmin permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation.
Quantitative wood anatomy analyzes the variability of xylem anatomical features in trees, shrubs, and herbaceous species to address research questions related to plant functioning, growth, and ...environment. Among the more frequently considered anatomical features are lumen dimensions and wall thickness of conducting cells, fibers, and several ray properties. The structural properties of each xylem anatomical feature are mostly fixed once they are formed, and define to a large extent its functionality, including transport and storage of water, nutrients, sugars, and hormones, and providing mechanical support. The anatomical features can often be localized within an annual growth ring, which allows to establish intra-annual past and present structure-function relationships and its sensitivity to environmental variability. However, there are many methodological challenges to handle when aiming at producing (large) data sets of xylem anatomical data. Here we describe the different steps from wood sample collection to xylem anatomical data, provide guidance and identify pitfalls, and present different image-analysis tools for the quantification of anatomical features, in particular conducting cells. We show that each data production step from sample collection in the field, microslide preparation in the lab, image capturing through an optical microscope and image analysis with specific tools can readily introduce measurement errors between 5 and 30% and more, whereby the magnitude usually increases the smaller the anatomical features. Such measurement errors-if not avoided or corrected-may make it impossible to extract meaningful xylem anatomical data in light of the rather small range of variability in many anatomical features as observed, for example, within time series of individual plants. Following a rigid protocol and quality control as proposed in this paper is thus mandatory to use quantitative data of xylem anatomical features as a powerful source for many research topics.
Climate scenarios for Slovenia suggest an increase in the mean annual temperature by 2 °C over the next six decades, associated with changes in the seasonal distribution of precipitation. European ...beech is an ecologically and economically important forest species in Europe, so it is important to understand the influence of changing conditions on its phenology and productivity for the upcoming years. We hypothesise that the ongoing warming and reduction in precipitation during the growing season will shorten the period of xylem development, thus limiting beech growth in the next decades. Xylem formation was monitored weekly from 2008 to 2016 at two sites in Slovenia. Onset and cessation of cell enlargement and secondary wall formation, as well as xylem growth, are used to evaluate climate-growth relationships by means of partial least squares regression and to predict xylem formation phenology and annual xylem increments under climate change scenarios. A positive correlation of spring phenological phases with March–May temperatures is found. In contrast, autumn phenological phases show a negative correlation with August and September temperatures, while high temperatures at the beginning of the year delay growth cessation. According to the selected climate change scenarios, phenological phases may advance by 2 days decade-1 in spring and delay by 1.5 days decade-1 in autumn. The duration of the growing season may increase by 20 days over the next six decades, resulting in 38 to 83% wider xylem increments. The growth of beech is expected to increase under a warming climate in the sites characterised by abundant water availability.
•Xylem and phloem formation and leaf phenology in beech differed between the sites.•At the onset of growth phenological phases were positively related to temperature.•Between the sites, weather ...conditions before the occurrence of the observed phenological phases differed.•This difference may be the consequence of high intra-specific plasticity.•Phloem formation seems to be driven predominantly endogenously.
Xylem and phloem formation, as well as cambium and leaf phenology, and their relation to weather factors, were studied from 2008 to 2010 in beech (Fagus sylvatica L.) trees from two sites in Slovenia with different elevations and weather conditions: Panška reka (PA) (400m a.s.l.) and Menina planina (ME) (1200m a.s.l.). During the vegetation periods leaf phenology and dynamics of xylem as well as phloem formation were monitored. Leaf unfolding, onset of cambial cell production and increased number of active phloem cells occurred simultaneously for each site: in mid-April at PA and in the first week of May at ME; all three events were positively related to temperature in the first part of the growth season. Maximum rate of xylem cell production occurred at PA from 20 May until 9 June and about two weeks later at ME. Maximum phloem cell production occurred more than 1 month earlier at both sites. Cessation of xylem and phloem cell production was observed at PA around 19 August and around 10 days earlier at ME. Differentiation of the last-formed xylem cells was concluded by mid-September at both plots. The differences in xylem and phloem formation phases were smaller in the second part of the growth season and can be ascribed to similar temperatures at both plots. Year to year variability of the observed phases was not statistically significant but the differences between the sites were. Phloem formation seems to be less subjected to fluctuations in environmental conditions since the growth ring widths were comparable at both sites. Temperature and growing degree days before the occurrence of most of the observed phenological phases significantly differed between the sites. This demonstrates that the observed differences in xylem and phloem formation between the sites can be attributed to high intra-specific plasticity of beech.
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