Abstract. Tree-rings tell of past climates. To do so, tree-ring chronologies comprising numerous climate-sensitive livingtree and subfossil time-series need to be "transferred" into palaeoclimate estimates using transfer functions. The purpose of this study is to compare different types of transfer functions, especially linear and nonlinear algorithms. Accordingly, multiple linear regression (MLR), linear scaling (LSC) and artificial neural networks (ANN, nonlinear algorithm) were compared. Transfer functions were built using a regional tree-ring chronology and instrumental temperature observations from Lapland (northern Finland and Sweden). In addition, conventional MLR was compared with a hybrid model whereby climate was reconstructed separately for short-and long-period timescales prior to combining the bands of timescales into a single hybrid model. The fidelity of the different reconstructions was validated against instrumental climate data. The reconstructions by MLR and ANN showed reliable reconstruction capabilities over the instrumental period (AD 1802(AD -1998. LCS failed to reach reasonable verification statistics and did not qualify as a reliable reconstruction: this was due mainly to exaggeration of the low-frequency climatic variance. Over this instrumental period, the reconstructed low-frequency amplitudes of climate variability were rather similar by MLR and ANN. Notably greater differences between the models were found over the actual reconstruction period (AD 802-1801). A marked temperature decline, as reconstructed by MLR, from the MeCorrespondence to: S. Helama (samuli.helama@helsinki.fi) dieval Warm Period (AD 931-1180) to the Little Ice Age (AD 1601-1850), was evident in all the models. This decline was approx. 0.5 • C as reconstructed by MLR. Different ANN based palaeotemperatures showed simultaneous cooling of 0.2 to 0.5 • C, depending on algorithm. The hybrid MLR did not seem to provide further benefit above conventional MLR in our sample. The robustness of the conventional MLR over the calibration, verification and reconstruction periods qualified it as a reasonable transfer function for our forest-limit (i.e., timberline) dataset. ANN appears a potential tool for other environments and/or proxies having more complex and noisier climatic relationships.

Nowadays, there is a large number of time series of natural data to study geophysical and astrophysical phenomena and their characteristics. However, short length and data gaps pose a substantial problem for obtaining results on properties of the underlying physical phenomena with existing algorithms. Using only an equidistant subset of the data with coarse steps leads to loss of information. We present a method to recover missing data in time series. The approach is based on modeling the time series with manifolds of small dimension, and it is implemented with the help of neural networks. We applied this approach to real data on cosmogenic isotopes, demonstrating that it could successfully repair gaps where data was purposely left out. Multi-fractal analysis was applied to a true radiocarbon time series after recovering missing data.

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Heluta V.P., Makarenko N.V., Al-Maali G. A. 2019. First records of Erysiphe corylacearum (Erysiphales, Ascomycota) on Corylus avellana in Ukraine. Ukrainian Botanical Journal, 76(3): 252-259. Abstract. Information on the records of a new adventive powdery mildew fungus Erysiphe corylacearum (Erysiphales, Ascomycota) in Ukraine is provided. The fungus was found on Corylus avellana (Betulaceae) in Kyiv, as well as in Crimea. Current distribution of this species outside its primary range is analyzed. It has been shown that the fungus came to Ukraine from the East through the Caucasus. Ukrainian specimens were compared with samples collected in the Far East of Russia. It was found that Ukrainian specimens have slightly larger chasmothecia, somewhat more numerous asci, which are slightly more elongated and often short stalked. It is noted that the fungus has a great invasive potential and in the future can cause considerable damage to the forestry of European countries. The article is illustrated with micrographs obtained under light and scanning electron microscopes. на Corylus avellana в Україні. Український ботанічний журнал, 76(3): 252-259. 1 Інститут ботаніки ім. М.Г. Холодного НАН України вул. Терещенківська 2, Київ 01004, Україна 2 Національний ботанічний сад ім. М.М. Гришка НАН України вул. Тимірязєвська 1, Київ 01014, Україна Реферат. Наводиться інформація про знахідки в Україні нового адвентивного борошнисторосяного гриба Erysiphe corylacearum (Erysiphales, Ascomycota). Гриб виявлено на Corylus avellana (Betulaceae) у м. Києві, а також в Криму. Аналізується новітнє поширення цього виду поза межами його первинного ареалу. Показано, що гриб потрапив в Україну зі Сходу через Кавказ. Порівнюються українські матеріали зі зразками, зібраними на Далекому Сході Росії. Встановлено, що вони мають дещо більші хазмотеції, більшу кількість сумок, останні більш витягнуті, частіше на маленькій ніжці. Зазначається, що гриб має значний інвазійний потенціал і в майбутньому може завдавати помітної шкоди лісовому господарству європейських країн. Стаття проілюстрована зображеннями, отриманими за допомогою світлового та скануючого електронного мікроскопів. Ключові слова: адвентивний вид, борошниста роса, інвазія, ліщина, Erysiphe corylicola