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Approaching dangerous impacts of global climate change
Ač, Alexander
Current global policy efforts are focused on limiting the global rise in mean temperature to well below a 2 K\nwarming compared to the pre-industrial temperature. It is questionable if achieving such goal is still feasible.\nHere, I review published works that suggesting that to keep global warming below or at a 2 K level cannot\nbe considered as safe, as is often assumed. A large body of studies have emerged recently investigating\nthe impacts of global climate change (GCC) at a 1.5 K or 2 K warming. The impacts range from changes in\nthe hydrological cycle, increasing frequency and intensity of extreme weather events, triggering of change\nfeedback processes at various spatio-temporal scales, affecting biological processes from the molecular to\necosystem levels, and to disrupting socio-economic conditions. In this short review, I present the latest scientific\nknowledge regarding some of the most important impacts of GCC on natural ecosystems, humanmade\nsystems, and societies.
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Forest regeneration within the treeline ecotone in the Giant Mountains under climate change
Cudlín, Ondřej ; Chumanová-Vávrová, Eva ; Edwards-Jonášová, Magda ; Heřman, Michal ; Štěpánek, Petr ; Cudlín, Pavel
Natural regeneration of mountain spruce forests began in the Giant Mountains 25 years ago after a reduction\nof severe and long-enduring air pollution. This process has been influenced by climatic change.\nThe aim of our contribution was to present background data for the potential elevational shift of spruce\nregeneration under conditions of climate change. These upslope shifts may also depend on constraints\nsuch as climate extremes, unfavourable soil conditions, absence of ectomycorrhizal symbionts, and lack of\nmicrosites suitable for seedlings. Since 2014, we have studied the main driving factors affecting Norway\nspruce regeneration, and in particular soil conditions, ectomycorrhizal symbionts, ground vegetation cover,\nand forest health, in six transects across the treeline ecotone located on a NW-to-NE transect through\nthe Giant Mountains. Microclimatic measurements showed that the mean difference in growing season\ntemperature between the montane spruce forests and forests at the treeline was −0.54°C. The model\nHADGEM2 predicted that in 20 years the temperature at the treeline will be similar to the current one at\nmontane elevations. The difference in prevailing soil types between the montane spruce forests and forests\nat the current treeline (i.e. podzol vs. ranker type) could be an important factor limiting success of the\nupslope spreading of spruce. Furthermore, areas covered by microsites favourable for natural spruce regeneration,\nespecially spruce litter patches, decaying wood, mosses, and Avenella flexuosa stands, were\nshown to decrease with increasing elevation. It is likely that spruce will move upslope in response to climate\nchange, but the process is likely to be slow or even blocked for some periods, especially by unfavourable\nsoil conditions and climatic extremes.
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Towards a combining of remote sensing and in situ evapotranspiration measurements
Fischer, Milan ; Jurečka, František ; Anderson, M. ; Hain, C. ; Pozníková, Gabriela ; Hlavinka, Petr ; Orság, Matěj ; Lukas, V. ; Žalud, Z. ; Trnka, Miroslav
This study provides preliminary results from combining in situ Bowen ratio energy balance (BREB) and\nevapotranspiration (ET) measurements techniques with physically based remote sensing ET estimates determined\nby the Atmosphere-Land Exchange Inverse (ALEXI) model. Evapotranspiration measurements\nand ALEXI estimates were analysed in an agricultural area close to Polkovice, Czech Republic during 2015,\nwhen a drought spell and intensive heatwaves appeared in the country. The BREB system was monitoring a\nwinter wheat (Triticum aestivum L.) field (~26 ha) while the ALEXI pixel (~5 km resolution) covered a wide\nrange of crops, including mainly winter wheat, spring barley, and winter rape. The study results showed that,\nalthough the applied methods work at different spatial scales (field vs. landscape), their combination can provide\nfurther insights into ET at both scales. For instance, such approach can be used to identify whether a specific\necosystem investigated in situ contributes to cooling or warming of the landscape.
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Application of multispectral remote sensing indices for sensing indices for estimating crop yields at field level
Jurečka, František ; Lukas, Vojtěch ; Hlavinka, Petr ; Semerádová, Daniela ; Fischer, Milan ; Žalud, Zdeněk ; Trnka, Miroslav
Remote sensing can be used for yield estimation prior to harvest and can replace or complement classical\nways of estimating crop yields. This study was undertaken in Polkovice, located in the Czech Republic’s\nHaná region. For 2015 and 2016, two data sets of satellite imagery were used: the Moderate Resolution\nImaging Spectroradiometer and the Landsat 8. Vegetation indices from satellites were compared with crop\nyields at the level of land blocks. Winter wheat and spring barley yield data, representing crops planted\nover the analysed period, were used for the comparison. The results of the index–yield comparison showed\nthat vegetation indices from remote sensing data provide reliable information for yield estimation prior to\nharvest. Indices are also able to evaluate the spatial variability of a crop within the field. The results showed\nthat remote sensing data need to have detailed spatial resolution in order to provide reasonable information\nabout yield at such a detailed level.
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Predicting light use efficiency using optical vegetation indices at various time scales and environmental conditions
Kováč, Daniel ; Ač, Alexander ; Veselovská, Petra ; Dreveňáková, Petra ; Rapantová, Barbora ; Klem, Karel
This study presents data points acquired during 2 years of measuring optical properties and gas-exchange\ncharacteristics of European beech (Fagus sylvatica) and Norway spruce (Picea abies) tree species in controlled\nenvironments. The observed statistical relationships between 105 pairs of selected optical parameters\n(i.e. photochemical reflectance index [PRI], ΔPRI, and normalized difference between wavebands R690\nand R630 [where R is a reflectance at a subscripted wavelength]) and light use efficiency (LUE) were considered\nat assumed different canopy leaf area index, changing pigments stoichiometrics, and daily changing\ndynamics of environmental conditions. Our measurements suggested that consistency of the LUE estimation\nusing PRI may be disrupted by acclimation responses of plants that reduce energetic carriers for\nuse in photosynthetic CO2 uptake and the xanthophyll cycle. Also, a changing chlorophylls-to-carotenoids\nratio tends to interrupt the PRI–LUE relationship. ΔPRI showed sensitivity to leaf area index of the measured\ntrees that complicated leaf-level estimation of LUE. The most consistent assessment of LUE was\nachieved using the chlorophyll fluorescence detecting ratio (R690 – R630)/(R690 + R630).
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Influence of the chlorophylls-to-carotenoids ratio on light use efficiency estimation by optical parameters
Ač, Alexander ; Kováč, Daniel ; Veselovská, Petra ; Večeřová, Kristýna ; Klem, Karel
The influence is examined of changing leaf photosynthetic pigments concentrations on sensitivity of the\nphotochemical reflectance index (PRI) and ΔPRI optical parameters in relation to light use efficiency\n(LUE). Photosynthetic and leaf chlorophylls-to-carotenoids (Chl/Car) ratio changes during the growth of\nEuropean Beech (Fagus sylvatica) and Norway spruce (Picea abies) saplings were induced by altering the\nliving environment inside growth chambers. Point reflectance measurements of each individual tree were\nrecording changes in optical properties while measurements were being taken simultaneously of altering\nphotosynthesis. Based on the evaluation of 45 pairs of measurements conducted on six individual saplings,\nthe observed variability in the strength of the PRI and ΔPRI versus LUE relationships was compared to the\nresulting leaf Chl/Car ratio of each tree. Data were used to explain the influence of changing pigments on\nthe sensitivity of each individual optical parameter with regards to the LUE estimation.
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Potential of flux-variance and surface renewal methods for sensible heat flux measurements at agricultural and forest surfaces
Fischer, Milan ; Katul, G. ; Pozníková, Gabriela ; Noormets, A. ; Domec, J.-C. ; Trnka, Miroslav ; King, J.
Two alternative micrometeorological methods, flux-variance (FV) and surface renewal (SR), based on\nmeasurements of high-frequency temperature fluctuation and Obukhov length stability parameter, were\ntested against eddy covariance (EC) sensible heat flux (H) measurements. The study was conducted at\nthree sites representing agricultural, forestry, and agroforestry systems. In terms of measurement setup,\nthese sites represented surface, roughness, and canopy top layer, respectively. As expected, the best match\nof all the methods was in the surface layer, whilst it was poorer in the roughness and canopy sublayers.\nSystematic deviation from EC across all three investigated surfaces was within 16% and 8% for FV and SR,\nrespectively. While FV resulted in higher correlation with EC measurements (0.93–0.98 vs. 0.89–0.97),\nSR provided less systematic biases (1.02–1.08 vs. 0.94–1.16). In general, both FV and SR provided slightly\nhigher H as compared to EC. We suggest that parallel deployment of FV and SR is useful, as both methods\nrequire the same instrumentation yet they are based on sufficiently different theories. Therefore, the agreement\nbetween FV and SR increases confidence in the results obtained and vice versa.
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Modulation of ozone flux in a mountain spruce forest under different cloud cover
Juráň, Stanislav ; Fares, S. ; Urban, Otmar
Ozone (O3) fluxes were modelled from a concentration gradient in a Norway spruce forest at the Bílý Kříž experimental station for years 2012–2016. Daily and seasonal O3 depositions were calculated separately for days with cloudy, partly cloudy, and clear sky conditions. The hypothesis that overcast conditions modulate O3 flux in the forest ecosystem via controlled stomatal conductance is tested. Indeed, the highest stomatal conductance followed by the highest O3 deposition was found during partly cloudy and cloudy sky conditions in all seasons.
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Stem emissions from poplar hybrids grown in a shortrotation plantation contribute to ecosystem balance of nitrous oxide and methane
Macháčová, Kateřina ; Kreuzwieser, J. ; Rennenberg, H.
The expansion of short-rotation coppices (SRCs) of fast-growing trees can affect the global balance of greenhouse\ngases (GHGs). These include not only carbon dioxide (CO2) but also methane (CH4) and nitrous oxide\n(N2O), both naturally produced by soil microorganisms. Trees are known to exchange CH4 and N2O with\nthe atmosphere. To date, however, the fluxes of these gases from fast-growing trees have been excluded from\nestimation of the GHGs balance for SRCs. Our objectives were to quantify and scale up CH4 and N2O fluxes\nfrom stems of the fast-growing poplar hybrids Max4 and Monviso at an SRC in southwest Germany. Our\ncase study shows that the stems of both hybrids were sources of N2O and CH4, even though consumption of\nCH4 was also observed. The hybrids did not differ in their exchange capacity. Nitrogen fertilization resulted in\nhigher stem N2O emissions compared to non-fertilized trees. The emissions of N2O and CH4 from stems contributed\nas much as 1.5% and 1.2% of soil N2O emission and soil CH4 uptake, respectively.
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Effect of elevated CO2 on morphological and photosynthetic parameters in two understory grass species in Beskydy Mountains
Holub, Petr ; Klem, Karel ; Urban, Otmar
We transplanted two grass species, Calamagrostis arundinacea and Luzula sylvatica, to the understory of\na 10-year-old experimental mixed forest exposed to ambient (385 μmol CO2 mol–1, AC) and elevated (700\nμmol CO2 mol–1, EC) atmospheric CO2 concentration using a glass dome facility. Effects of EC on plant\nmorphology and photosynthesis were examined after three years of treatment. We tested the hypotheses\nthat shade-tolerant species can profit from EC even at low light conditions and that relatively low accumulation\nof assimilates at such light conditions will not cause CO2-induced down-regulation of photosynthesis.\nWe expected that EC can substitute insufficient light intensities under the tree canopy and lead to both\nhigher biomass production and survival of plants in deep forest understories. The typical shade-tolerant\nspecies L. sylvatica exhibited positive acclimation under EC allowing higher light use efficiency under subsaturating\nlight intensities as compared to plants grown under AC. In contrast, C. arundinacea showed\nhigher stimulation of growth and photosynthetic rates by EC mainly under saturating light intensities at\nthe beginning of the growing season, when the forest leaf area is not fully developed and the open canopy\nallows a greater proportion of incident light to reach the understory. Our data indicate that growth and\nphysiological responses of EC plants in forest understories are species specific, differ from responses of\nsun-exposed plants, and depend on degree of shading.
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