21. Growth-limiting factors and climate response variability in Norway spruce (Picea abies L.) along an elevation and precipitation gradients in SloveniaJernej Jevšenak, Ivan Tychkov, Jožica Gričar, Tom Levanič, Jan Tumajer, Peter Prislan, Domen Arnič, Margarita Popkova, Vladimir V. Shishov, 2020, izvirni znanstveni članek Povzetek: Norway spruce (Picea abies L.) is among the most sensitive coniferous species to ongoing climate change. However, previous studies on its growth response to increasing temperatures have yielded contrasting results (from stimulation to suppression), suggesting highly site-specific responses. Here, we present the first study that applies two independent approaches, i.e. the nonlinear, process-based Vaganov-Shashkin (VS) model and linear daily response functions. Data were collected at twelve sites in Slovenia differing in climate regimes and ranging elevation between 170 and 1300 m a.s.l. VS model results revealed that drier Norway spruce sites at lower elevations are mostly moisture limited, while moist high-elevation sites are generally more temperature limited. Daily response functions match well the pattern of growth-limiting factors from the VS model and further explain the effect of climate on radial growth: prevailing growth-limiting factors correspond to the climate variable with higher correlations. Radial growth correlates negatively with rising summer temperature and positively with higher spring precipitation. The opposite response was observed for the wettest site at the highest elevation, which positively reacts to increased summer temperature and will most likely benefit from a warming climate. For all other sites, the future radial growth of Norway spruce largely depends on the balance between spring precipitation and summer temperature.
Ključne besede: Vaganov-Shashkin model, climate-growth correlations, tree rings, process-based modelling, dendroTools, dendroclimatology
Objavljeno v DiRROS: 21.10.2020; Ogledov: 1261; Prenosov: 1006
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22. The effect of harvesting on national forest carbon sinks up to 2050 simulated by the CBM-CFS3 model : a case study from SloveniaJernej Jevšenak, Matija Klopčič, Boštjan Mali, 2020, izvirni znanstveni članek Ključne besede: carbon, forest reference levels, forest management, harvesting scenarios, yield curves, UNFCCC, prirastne krivulje, UNFCCC
Objavljeno v DiRROS: 19.10.2020; Ogledov: 1283; Prenosov: 901
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23. New features in the dendroTools R package : bootstrapped and partial correlation coefficients for monthly and daily climate dataJernej Jevšenak, 2020, izvirni znanstveni članek Povzetek: Climate-growth relationships are usually analysed using monthly climate data. The dendroTools R package also provides methodological approaches that enable climate-growth analysis for daily climate data. Such analysis reveals more complete climate signal patterns. In this article, new functions of the dendroTools R package are presented. Partial correlation coefficients are now implemented and can be used to calculate the strength of a linear relationship between two variables, while controlling for a third variable. Bootstrapped correlations can then be used to provide insights into the confidence intervals of statistical estimates. The calculation of partial and bootstrapped correlations is available for daily and monthly data. Finally, data transformation, S3 generic plotting and summary functions are also presented here.
Ključne besede: dendroTools, daily climate data, partial correlations, bootstrap, dendroclimatology
Objavljeno v DiRROS: 24.09.2020; Ogledov: 1268; Prenosov: 573
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24. Obvladovanje tveganj pri gospodarjenju s smreko v gozdovih Slovenije : zaključno poročilo projekta V4-1614Tom Levanič, Lado Kutnar, Andrej Kobler, Aleksander Marinšek, Matjaž Čater, Gregor Božič, Marjana Westergren, Maarten De Groot, Jernej Jevšenak, Samo Stopar, 2020, končno poročilo o rezultatih raziskav Ključne besede: gospodarjenje z gozdovi, smreka, Slovenija, smrekovi gozdovi
Objavljeno v DiRROS: 27.05.2020; Ogledov: 1723; Prenosov: 711
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25. Seasonal radial growth of Black pine (Pinus nigra Arnold) from Bosnia and Herzegovina, monitored by the pinning method and manual band dendrometersSimon Poljanšek, Jernej Jevšenak, Jožica Gričar, Tom Levanič, 2019, izvirni znanstveni članek Povzetek: Despite numerous dendroclimatological investigations into different tree species from Bosnia and Herzegovina, information is lacking on intra-annual wood formation patterns, which would help us to interpret the climate signal in tree rings better. Using the pinning method and manual band dendrometers, we investigated the seasonal dynamics of radial growth of black pine (Pinus nigra Arnold) trees in two successive growing seasons: 2011 and 2012. The up to 60-year-old trees grew in a stand at the base of a hill in the western, mountainous part of the Balkan Peninsula. The seasonal dynamics of wood formation and final number of cells differed between the studied years. Wood formation started in both years in early to mid-March. Differences were noticed in the wood production culmination; in 2011 it occurred at the end of May and beginning of June in 2012 and 2011, respectively. Xylem growth finished in 2012 in the middle of August and in 2011 in the middle of September. Based on the first derivative of the Gompertz function calculated rate of xylem growth was lowest in 2011. The dendrometers recorded a slow increment rate in spring, higher in summer and a decreasing rate again in the late summer in both growing seasons. In comparison with pinning, dendrometers showed a delay in the start of radial growth of up to 20 days in 2012. Additionally, dendrometers showed an increase in stem girth after the end of both growing seasons, when wood formation was already completed. Deviations between the two methods could be ascribed to the influence of water storage dynamics in the main stem and numerous structural processes in bark tissue, which are captured in dendrometer data. The influence of weather conditions on xylem phenology is also indicated by differences between the two studied years, although it is difficult to identify the influence of particular short-term weather events.
Ključne besede: pinning, manual dendrometers, radial growth, Pinus nigra, cambium, Balkan Peninsula
Objavljeno v DiRROS: 11.09.2019; Ogledov: 4760; Prenosov: 3875
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26. Daily climate data reveal stronger climate-growth relationships for an extended European tree-ring networkJernej Jevšenak, 2019, izvirni znanstveni članek Povzetek: An extended European tree-ring network was compiled from various sources of tree-ring data from Europe, northern Africa and western Asia. A total of 1860 tree-ring chronologies were used to compare correlation coefficients calculated with aggregated day-wise and month-wise mean temperature, sums of precipitation and standardised precipitation-evapotranspiration index (SPEI). For the daily approach, climate data were aggregated over periods ranging from 21 to 365 days. Absolute correlations calculated with day-wise aggregated climate data were on average higher by 0.060 (temperature data), 0.076 (precipitation data) and 0.075 (SPEI data). Bootstrapped correlations are computationally expensive and were therefore calculated on a 69.4% subset of the data. Bootstrapped correlations indicated statistically significant differences between the daily and monthly approach in approximately 1% of examples. A comparison of time windows used for calculations of correlations revealed slightly later onset and earlier ending day of the year for the daily approach, while the largest differences between the two approaches arise from window lengths: Correlations calculated with day-wise aggregated climate data were calculated using fewer days than the monthly approach. Differences in the onset and ending dates of periods for the daily and monthly approaches were greater for precipitation and SPEI data than for temperature data.
Ključne besede: tree rings, dendroclimatology, tree-ring network, daily climate data, climate-growth relationships, dendroTools
Objavljeno v DiRROS: 21.08.2019; Ogledov: 2287; Prenosov: 1058
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27. Dendrokronološka analiza debelinskega priraščanja smreke (Picea abies (L.) Karst.) na območju njene naravne in umetne razširjenosti v SlovenijiSamo Stopar, Jernej Jevšenak, Andrej Kobler, Tom Levanič, 2018, izvirni znanstveni članek Povzetek: Z dendrokronološkimi metodami smo analizirali debelinsko priraščanje smreke na osmih lokacijah v Sloveniji. Med njimi je bilo pet naravnih smrekovih združb, v druge je bila smreka umetno vnesena v preteklosti, oziroma je bil povečan njen naravni delež. Na vsaki ploskvi smo s prirastoslovnim svedrom odvzeli izvrtke najmanj 20 dreves. V dendrokronološkem laboratoriju smo jih posušili in zbrusili do visokega sijaja, nato pa skenirali s pomočjo sistema ATRICS ter izmerili širine branik v programih CooRecorder in CDendro. Ugotovili smo, da med naravnimi in antropogenimi rastišči ni značilnih razlik v debelinskem priraščanju. Na lokacijah Sorško polje, Ravnik in Mašun smo opazili spremembe v debelinskem priraščanju, ki kažejo, da se vpliv temperature zraka (toplejša poletja) in padavin (pogostejši pojav suše) na rast povečuje. Analiza značilnih let je pokazala, da so le-ta v zadnjih 30 letih pogostejša in da se pojavljajo na več lokacijah hkrati, predvsem pa se je povečalo število negativnih značilnih let, t.j. nadpovprečno toplih in suhih let.
Ključne besede: klimatske spremembe, naravna smrekova rastišča, antropogeno spremenjena rastišča smreke, dendrokronologija, Slovenija, debelinski prirastek
Objavljeno v DiRROS: 04.02.2019; Ogledov: 5347; Prenosov: 3839
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28. DendroTools : R package for studying linear and nonlinear responses between tree-rings and daily environmental dataJernej Jevšenak, Tom Levanič, izvirni znanstveni članek Povzetek: We introduce in this paper the dendroTools R package for studying the statistical relationships between tree-ring parameters and daily environmental data. The core function of the package is daily_response(), which works by sliding a moving window through daily environmental data and calculating statistical metrics with one or more tree ring proxies. Possible metrics are correlation coefficient, coefficient of determination and adjusted coeffi- cient of determination. In addition to linear regression, it is possible to use a nonlinear artificial neural network with the Bayesian regularization training algorithm (brnn). dendroTools provides the opportunity to use daily climate data and robust nonlinear functions for the analysis of climate-growth relationships. Models should thus be better adapted to the real (continuous) growth of trees and should gain in predictive capabilities. The dendroTools R package is freely available in the CRAN repository. The functionality of the package is demonstrated on two examples, one using a mean vessel area (MVA) chronology and one a traditional tree-ring width (TRW).
Ključne besede: dendroclimatology, daily climate data, running window, nonlinear modelling, tree-ring proxies, climate reconstruction
Objavljeno v DiRROS: 16.04.2018; Ogledov: 3027; Prenosov: 1895
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29. Uporaba metod strojnega učenja za preučevanje odnosov med značilnostmi branik in okoljemJernej Jevšenak, Sašo Džeroski, Tom Levanič, 2017, izvirni znanstveni članek Povzetek: Različne študije so pokazale, da lahko z nelinearnimi metodami bolje opišemo (modeliramo) odnos med branikami in okoljem. V naši študiji smo primerjali (multiplo) linearno regresijo (MLR) in štiri nelinearne metode strojnega učenja: modelna drevesa (MT), ansambel bagging modelnih dreves (BMT), umetne nevronske mreže (ANN) in metodo naključnih gozdov (RF). Za primerjavo teh metod modeliranja smo uporabili štiri množice podatkov. Natančnost naučenih modelov smo ocenili z metodo 10-kratnega prečnega preverjanja (ang. 10-fold cross-validation) na naši množici in preverjanjem na dodatni testni množici. Na vseh množicah smo dobili boljše statistične kazalce za nelinearne metode s področja strojnega učenja, s katerimi lahko pojasnimo večji delež variance oz. dobimo manjšo napako. Nobena metoda se ni pokazala kot najboljša v vseh primerih, zato je smiselno predhodno primerjati več različnih metod in nato uporabiti najprimernejšo, npr. za rekonstrukcijo klime.
Ključne besede: strojno učenje, primerjava metod, dendroklimatologija, umetne nevronske mreže, modelna drevesa, ansambel modelnih dreves, naključni gozdovi, linearna regresija
Objavljeno v DiRROS: 21.02.2018; Ogledov: 5369; Prenosov: 3315
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30. Poročilo o spremljanju stanja gozdov za leto 2016 : vsebinsko poročilo o spremljanju stanja gozdov v l. 2016 v skladu s Pravilnikom o varstvu gozdov (2009)Mitja Ferlan, Andrej Grah, Jernej Jevšenak, Tom Levanič, Nikica Ogris, Špela Planinšek, Matej Rupel, Primož Simončič, Iztok Sinjur, Mitja Skudnik, Saša Vochl, Daniel Žlindra, Jure Žlogar, 2017, končno poročilo o rezultatih raziskav Ključne besede: varstvo gozdov, monitoring, meteorologija, letni prirastek, poročila
Objavljeno v DiRROS: 03.10.2017; Ogledov: 3241; Prenosov: 1063
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