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Growth response of different tree species (oaks, beech and pine) from SE Europe to precipitation over time
Saša Orlović, Stefan Stjepanović, Bratislav Matović, Tom Levanič, Dejan Stojanović

Abstract: Changing climatic conditions can have various consequences for forest ecosystems, from increasing frequencies of forest fires, ice and windstorm events to pathogen outbreaks and mass mortalities. The Standardized Precipitation Index (SPI) was chosen for the evaluation of drought impact on the radial growth of trees after extensive preliminary testing of various calculated monthly climate parameters from the CARPATCLIM database. SPI was calculated for periods between 3 and 36 months for different sites (lowland and mountainous parts of Serbia, Southeast Europe), from which Quercus robur, Q. cerris, Fagus sylvatica and Pinus sylvestris samples were acquired. Bootstrapped Pearson%s correlations between SPI monthly indices and radial growth of tree species were calculated. We found that 12-month SPI for summer months may be a good predictor of positive and negative growth of different species at different sites. The strongest positive correlations for five of six tree-ring width chronologies were between 12-month June and 14-month September SPI, which implies that high growth rates can be expected when the autumn of the previous year, and winter, spring and summer of the current year, are well supplied with precipitation, and vice versa (low precipitation in given period/low growth rates).
Keywords: standardized precipitation index, SPI, climate change, tree mortality, Quercus sp., Fagus sylvatica, Pinus sylvestris
DiRROS - Published: 18.04.2018; Views: 1264; Downloads: 434
.pdf Fulltext (2,91 MB)

Effect of spatial scale and harvest on heterogeneity of forest floor CO2 efflux in a sessile oak forest
Eva Dařenová, Matjaž Čater, 2020

Abstract: Soil respiration is the second largest flux of carbon between terrestrial ecosystems and the atmosphere and it is substantially sensitive to climate change. Monitoring CO2 efflux and its upscaling from field measurements to the ecosystem level is a complex task, due to the high spatial and temporal variability of the fluxes. Human intervention, e.g. through forest harvest, may change both CO2 efflux and its spatial heterogeneity. The objective of our study was to quantify spatial heterogeneity of soil CO2 efflux within and among plots distributed within a topographically variable sessile oak forest stand before and after harvesting. Forest floor CO2 efflux, soil temperature and soil water content were measured monthly in a sessile oak forest during two growing seasons: one before and one after harvesting. Stand structure characteristics (gap fraction, leaf area index, tree number and size) and the amount of understory also were determined. Relationships between individual variables and spatial heterogeneity were analyzed. The small-scale spatial heterogeneity (expresses as the coefficient of variation) of forest floor CO2 efflux and soil water content (SWC) in the undisturbed forest was low, at maximum 0.22 and 0.13, respectively. Studied variables had no effect on spatial heterogeneity of forest floor CO2 efflux except for the amount of understorey vegetation which positively correlated with forest floor CO2 efflux. Although the studied forest was situated in topographically variable terrain, we observed that inter-plot heterogeneity of forest floor CO2 efflux was lower than that within plots. Stand harvest increased the intra-plot heterogeneity of forest floor CO2 efflux but did not affect the inter-plot heterogeneity. This leads to the conclusion that the number of positions within an individual plot should increase after harvest but the number of plots may remain unchanged to determine adequately ecosystem forest floor CO2 efflux.
Keywords: gap fraction, LAI, Quercus petraea, soil respiration, soil water content
DiRROS - Published: 20.02.2020; Views: 130; Downloads: 69
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Spread and potential host range of the invasive oak lace bug [Corythucha arcuata (Say, 1832) - Heteroptera: Tingidae] in Eurasia
György Csóka, Anikó Hirka, Serap Mutun, Milka Glavendekić, Ágnes Mikó, Levente Szőcs, Márton Paulin, Eötvös Csaba Béla, Gáspár Csaba, Mariann Csepelényi, Maja Jurc, Dušan Jurc, 2020

Abstract: The North American oak lace bug feeds on leaves of 'white oaks' in its native range. In Europe, it was first discovered in northern Italy in 2000. In recent years, it has subsequently spread rapidly and population outbreaks have been observed in several European countries. In the present study, we summarize the steps of its expansion. To predict its potential host range, we checked 48 oak species in 20 sentinel gardens in seven countries between 2013 and 2018. In total, 27 oak species were recorded as suitable hosts; 13 of them are globally new ones, 23 out of the 29 in section Quercus (white oaks, an intrageneric taxonomic unit within genus Quercus), including Asian oaks, native to Japan, Korea and China, and four out of five in section Cerris (another intrageneric unit of the same genus), were accepted as hosts. None of the species in section Lobatae (red oaks) or in the Ilex group was accepted. Host records were also collected in forest stands of 10 countries. We found 11 oak species that were infested. Outbreak populations were most commonly found on Quercus robur, Quercus frainetto, Quercus petraea and Quercus cerris, comprising widespread and outstandingly important oaks species in Europe. Based on our findings, we conclude that suitable hosts for oak lace bug are present in most of Europe and Asia. This means that a lack of hosts will likely not restrict further range expansion.
Keywords: Corythucha arcuata, host plants, non-native species, Quercus spp, sentinel gardens
DiRROS - Published: 20.02.2020; Views: 169; Downloads: 104
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Sapwood characteristics of Quercus robur species from the south-western part of the Pannonian Basin
Jernej Jevšenak, Ernest Goršić, Dejan Stojanović, Bratislav Matović, Tom Levanič, 2019

Abstract: We analysed sapwood characteristics in 344 pedunculate oak (Quercus robur L.) samples from the south-western part of the Pannonian Basin. The samples came from 13 sites, located in Slovenia, Croatia and Serbia. The trees had an average of 13.3 sapwood rings, with a minimum of 5 and maximum of 32. Fifteen log-log linear regression models were employed to assess the statistical relationship between sapwood and heartwood variables. The number of sapwood rings (NSW), which is usually needed in dendroarchaeological dating, is significantly related to the number of heartwood rings (NHW), heartwood width (WHW) and heartwood growth rate (GHW). Older and more slowly growing trees had a higher average number of sapwood rings. Using NHW and WHW, we employed an additional multiple regression model and calculated coefficients for NSW predictions for real-world dendroarchaeological dating from the south-western part of the Pannonian Basin.
Keywords: sapwood, archaeology, tree-ring dating, Quercus robur, Pannonian Basin
DiRROS - Published: 20.02.2020; Views: 179; Downloads: 85
URL Fulltext (0,00 KB)

Different structure of sessile oak stands affects soil moisture and soil CO2 efflux
Eva Dařenová, Matjaž Čater, 2018

Abstract: Soil moisture, soil CO2 efflux (RS), and isotopic composition of RS (%R) were studied in three sessile oak forest stands with different management practice: a high forest (HF), a high forest converted from coppice stand (CHF), and a coppice forest (CF). Measurements were taken monthly, with each position described by light parameters. RS was driven by temperature and moisture. RS increased dramatically with moisture in relatively dry soil, while they remained on the same level when moisture exceeded 13%. Differences in mean soil moisture and RS normalized for 10 °C (R10) among the stands usually followed the pattern HF > CF > CHF. The %R was highest in CHF, but during drought the pattern was HF > CHF > CF. To test the effect of stand structure on soil moisture and R10, we analyzed relationship of these variables to light parameters calculated for the angles of 60° and 180°. Subsequently, we analyzed data from all measured positions divided according to gap fraction into six groups. The results showed that forest floor shading by the canopy decreases moisture regardless of stand type, but no significant relationship was found between the light parameters and R10. We may conclude that soil moisture is affected by canopy structure and RS by stand type.
Keywords: gap fraction, LAI, light parameters, Quercus petraea, soil respiration
DiRROS - Published: 20.02.2020; Views: 145; Downloads: 130
URL Fulltext (0,00 KB)

Predicting the vessel lumen area tree-ring parameter of Quercus robur with linear and nonlinear machine learning algorithms
Jernej Jevšenak, Sašo Džeroski, Tom Levanič, 2018

Abstract: Climate-growth relationships in Quercus robur chronologies for vessel lumen area (VLA) from two oak stands (QURO-1 and QURO-2) showed a consistent temperature signal: VLA is highly correlated with mean April temperature and the temperature at the end of the previous growing season. QURO-1 showed significant negative correlations with winter sums of precipitation. Selected climate variables were used as predictors of VLA in a comparison of various linear and nonlinear machine learning methods: Artificial Neural Networks (ANN), Multiple Linear Regression (MLR), Model Trees (MT), Bagging of Model Trees (BMT) and Random Forests of Regression Trees (RF). ANN outperformed all the other regression algorithms at both sites. Good performance also characterised RF and BMT, while MLR, and especially MT, displayed weaker performance. Based on our results, advanced machine learning algorithms should be seriously considered in future climate reconstructions
Keywords: dendroclimatology, artificial neural networks, multiple linear regression, machine learning, vessel lumen area, Quercus robur
DiRROS - Published: 20.02.2020; Views: 181; Downloads: 102
URL Fulltext (0,00 KB)

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