Risto Jalkanen

• D. Sc. (For.), PhD (Bot.)
• Researcher at Silva Lapponica

The vapor pressure deficit reflects the difference between how much moisture the atmosphere could and actually does hold, a factor that fundamentally affects evapotranspiration, ecosystem functioning, and vegetation carbon uptake. Its spatial variability and long-term trends under natural versus human-influenced climate are poorly known despite bei...

Aspen mosaic-associated virus (AsMaV) is a newly identified Emaravirus, in the family Fimoviridae, Bunyavirales, associated with mosaic symptoms in aspen trees (Populus tremula). Aspen trees are widely distributed in Europe and understanding the population structure of AsMaV may aid in the development of better management strategies. The virus geno...

Fifteen proxy records of summer temperature in Fennoscandia, Northern Europe and in Yamal and Taymir Peninsulas (Western Siberia) were analyzed for the AD 1700–2000 period. Century-long (70–100 year) and quasi bi-decadal periodicities were found from proxy records representing different parts of Fennoscandia. Decadal variation was revealed in a sma...

In March 2021, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. The phylum was expanded by four families (Aliusviridae, Crepuscuviridae, Myriaviridae, and Natareviridae), three subfamilies (Alpharhabdovirinae, Betarhabdovirinae, a...

In March 2021, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. The phylum was expanded by four families (Aliusviridae, Crepuscuviridae, Myriaviridae, and Natareviridae), three subfamilies (Alpharhabdovirinae, Betarhabdovirinae, a...

Highlights • Sphaeropsis sapinea was found for the first time as an endophyte in healthy Scots pine in Finland. • This finding confirms that S. sapinea can proliferate in a symptomless stage in Scots pine in Finland. Abstract The aim of this study was to determine if the ascomycete fungus Sphaeropsis sapinea (Fr.) Dyko & B. Sutton (syn. Diplodia sa...

Eleven proxy records of Northern Fennoscandia and North Atlantic climate variability were analyzed. Correlation of climatic records with (a) a quasi 11-year solar cycle of Schwabe, (b) a quasi 22-year solar cycle of Heil, (c) a quasi 20-year planetary-tidal cycle, related to wobbling of the Sun around the baricenter of the solar system, has been st...

Eight proxy records of Northern Fennoscandian summer temperature variability were analyzed for the AD 1700–2000 period. Stable and statistically significant correlation between the summer temperature reconstructions and a quasi 22-year Hale solar cycle was found to be present through the entire study period. The revealed solar–climatic link is a re...

Since Emaraviruses have been discovered in 2007 several new species were detected in a range of host plants. Five genome segments of a novel Emaravirus from mosaic‐diseased Eurasian aspen (Populus tremula) have been completely determined. The monocistronic, segmented ssRNA genome of the virus shows a genome organisation typical for Emaraviruses enc...

Since Emaraviruses have been discovered in 2007 several new species were detected in a range of host plants. Five genome segments of a novel Emaravirus from mosaic‐diseased Eurasian aspen (Populus tremula) have been completely determined. The monocistronic, segmented ssRNA genome of the virus shows a genome organisation typical for Emaraviruses enc...

Plain Language Summary Temperatures have increased globally over recent decades, strongly linked to increases in greenhouse gases. However, over Northern Fennoscandia summer temperatures have increased little over this period, although this region should be strongly affected by global warming. We suggest that changes in summer cloud cover, driven b...

Tree growth at northern boreal treelines is generally limited by summer temperature, hence tree rings serve as natural archives of past climatic conditions. However, there is increasing evidence that a changing summer climate as well as certain micro-site conditions can lead to a weakening or loss of the summer temperature signal in trees growing i...

In declining birches (Betula sp.) from different European stands affected by the “birch leaf-roll disease” (BLRD) a novel virus is identified by means of RNA-Seq virome analysis. The virus represents a new member in the genus Badnavirus, family Caulimoviridae, tentatively named Birch leaf roll-associated virus (BLRaV) and it is the first badnavirus...

List of samples used for the BLRaV variability analysis. Samples correspond to partial ORF3 sequences and represent BLRaV variants detected in symptomatic trees in Berlin (Germany) and Rovaniemi (Finland). (PDF)

A number of numerical experiments with artificial random signals (the second order autoregressive processes), which have important statistical properties similar to that of the observed instrumental temperature (1850-2015), were carried out. The results show that in frame of the selected mathematical model the return period of climatic events, anal...

The stable carbon isotopic analysis of tree-rings for environmental, plant physiological and archaeological applications using conventional methods is occasionally limited by physical constraints (narrow rings) or administrative concerns (requirement for non-destructive sampling) that prevent researcher access to scientifically valuable wood sample...

Plant viral diseases are currently a major economic problem in agriculture throughout the world. The objective of the COST Action is to coordinate and raise the European capacity to apply Next Generation Sequencing (NGS) technologies for the study and diagnosis of viral diseases in vegetatively propagated plants, seeds and seedlings. NGS enables ra...

The vascular cambium of trees is a secondary meristem and is responsible for the formation of the xylem and phloem. The main focus of this chapter is on the xylem, specifically on the following three topics, demonstrating that the cambium is not only responsible for the quantitative side of xylem formation, but also for the expression of stable ana...

Seven proxies of summer temperature in Northern Fennoscandia, sea surface temperature in the North Atlantic and solar activity were analyzed over AD 1567–1986. A stable and significant positive correlation between summer temperatures in Northern Fennoscandia and sea surface temperature in the North Atlantic is shown to exist during the entire time...

Currently available proxies were studied as networks for building reconstruction models of the Atlantic Multidecadal Oscillation (AMO). Only proxies that would double the current record length (backwards in time from AD 1564) were included. We present two proxy networks and corresponding reconstruction (transfer) models, one for tree-growth based p...

Northern treelines are expected to reflect a strong summer temperature signal as they are generally cold-limited. Ring width data from northern treelines, and in particular Scots pine (Pinus sylvestris L.) from Fennoscandia, have thus frequently been used to build long chronologies in order to reconstruct climatic conditions of the past centuries (...

A viral epidemic associated with the Cherry leaf roll virus (CLRV) has emerged in Betula species in Fennoscandia, exhibiting quick and effective spread during the last 15 years. A population genetics approach is chosen in order to characterise the virus diversity and the sources of genetic variation aiming to investigate the epidemiology of the pat...

Needle pathogens of larch (Larix spp.) in the Nordic countries are under-studied. Their incidence in Finland tends to be low and local, and this may be a function of enemy release, since species of larch were introduced to the region. Here, the ecology and incidence of larch needle pathogens and the abiotic factors that also affect larch in norther...

Five proxy temperature time series based on tree-rings and varves from middle and high latitudes (φ>500) of North America, which cover the last 3–5 centuries, were analyzed. It was shown that reconstructions from Canadian Rockies (52.150 N, 117.150 W) and northeast Alaska (68.80 N, 142.30 W) correlate appreciably with Wolf number and 10Be concentra...

We analyzed a number of Antarctic climatic proxies including: 1) an annual proxy covering the time interval 1800-2003, 2) four low-resolution (tens to hundreds of years) ice core records covering the last 242,000 years. The main goal of the work was to search for traces of solar influence on Antarctic climate. Both Fourier and wavelet approaches we...

Key message Pine species differ in needle proxies but have similar growth, climate sensitivity and response to wildfires. The latter was recorded as an abrupt reduction of needles and a major growth decline. Abstract Black pine (Pinus nigra Arnold) and Scots pine (P. sylvestris L.) form mixed stands on one of the ridges of Šator Mountain in Bosn...

The pine shoot beetle, Tomicus piniperda, is a secondary colonizer of pines and other conifers. Although it is necessary to understand interactions of this insect with other organisms, few studies have focused on its fungal associates. This study focused on the effect of geographical distance on the occurrence of fungi carried by the beetle. Adult...

A viral epidemic associated with the Cherry leaf roll virus has emerged in Betula species in Fennoscandia exhibiting quick and effective dispersal. A population genetics approach is chosen in order to characterize the virus´s diversity and the sources of genetic variation aiming to investigate factors that may affect this disease´s emergence. Two C...

The ability to provide a fast, inexpensive and reliable diagnostic for any given viral infection is a key parameter in efforts to fight and control these ubiquitous pathogens. The recent developments of high-throughput sequencing (also called Next Generation Sequencing - NGS) technologies and bioinformatics have drastically changed the research on...

The ability to provide a fast, inexpensive and reliable diagnostic for any given viral infection is a key parameter in efforts to fight and control these ubiquitous pathogens. The recent developments of high-throughput sequencing (also called Next Generation Sequencing - NGS) technologies and bioinformatics have drastically changed the research on...

A viral epidemic associated with the Cherry leaf roll virus has emerged in Betula species in Fennoscandia exhibiting quick and effective dispersal. A population genetics approach is chosen in order to characterize the virus´s diversity and the sources of genetic variation aiming to investigate factors that may affect this disease´s emergence. Two C...

Bud break and height-growth of Scots pine (Pinus sylvestris L.) in the northern boreal zone in Lapland, Finland, was followed through the entire growing seasons in the periods 2001–2003 and 2008–2010 in sapling stands in two different locations in northern Finland set some 250 km apart along a latitudinal transect. Field measurements continued at t...

Time evolution of growing season temperatures in the Northern Hemisphere was analyzed using both wavelet and Fourier approaches. A century-scale (60–140 year) cyclicity was found in the summer temperature reconstruction from the Taymir peninsula (�72� N, �105� E) and other high-latitude (60–70� N) regions during the time interval AD 1576–1970. This...

Proxies of solar activity, based on radiocarbon and beryllium, covering most of the Holocene were statistically analysed using both wavelet and Fourier approaches. It was shown that a significant tri-centennial (300–400 yr) cyclicity is present in the both series. Evidence for the same kind of variation was found in data on flux of 10Be in Dye-3 (S...

Solar activity is a phenomenon very important for the mankind existence. Presence of link between Sun’s activity, galactic cosmic ray (GCR), effectively modulated by Sun, and terrestrial climate has been claimed by many authors and possible solar contribution to the global warming of the last century is actively debated. Clarification of the nature...

Cherry leaf roll virus (CLRV) is a nepovirus, classified to subgroup C within the newly established family Secoviridae. CLRV has been reported worldwide revealing its wide natural host range which comprises at least 24 genera of broad-leaved trees and shrubs as well as a variety of herbaceous plants. The complete nucleotide sequence of both genomic...

Cherry leaf roll virus (CLRV) is a nepovirus, classified to subgroup C within the newly established family Secoviridae. CLRV has been reported worldwide revealing its wide natural host range which comprises at least 24 genera of broad-leaved trees and shrubs as well as a variety of herbaceous plants. The complete nucleotide sequence of both genomic...

The increasing carbon dioxide (CO2) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores. However, the magnitude and spatial patterns of such changes in natural fore...

Six chronologies based on the growth of Scots pine from the inland of Northern Fennoscandia were built to separately enhance low, medium, and high frequencies in 1000–2002. Several periodicities of growth were found in common in these data. Five of the low-frequency series have a significant oscillatory mode at 200–250 years of cycle length and mos...

Tämän työraportin artikkelit ovat kooste Metsäntutkimuslaitoksen Rovaniemen tutkimusyksikön järjestämän tutkimuspäivän esitelmistä. Tutkimuspäivä pidettiin Lapin ammattikorkeakoulun tiloissa Rovaniemellä 11.12.2014. Kaikki artikkelit ovat tulosta tiiviistä ja tuloksellisesta yhteistyöstä tutkimuksen ja käytännön metsätalouden välillä. Toimijoina ja...

ttp://www.metla.fi/julkaisut/workingpapers/2014/mwp321.htm

A new summer temperature proxy was built for northern Fennoscandia in AD 1000-2004 using parameters of tree growth from a large region, extending from the Swedish Scandes to the Kola Peninsula. It was found that century-scale (55-140 year) cyclicity is present in this series during the entire time interval. This periodicity is highly significant an...

Cherry leaf roll virus in the birch forests in northern Finland has expanded widely during the last decade and rapidly turned to a severe epidemic. To investigate the genetic variability of the virus, 14 birch trees exhibiting strong symptoms (leaf discoloration and deformation as well as tree decline) were selected in Rovaniemi. After total RNA-is...

Virus-related symptoms such as vein banding, leaf roll, chlorosis, and subsequent necrosis (Fig. 2) were found on birch leaves throughout Finland, northern Norway and Sweden. Disease symptoms occurring on downy birch, silver birch, dwarf birch, Kiilopää birch, mountain birch and curly birch could be associated with an infection of Cherry leaf roll...

Virus-related symptoms such as vein banding, leaf roll, chlorosis, and subsequent necrosis (Fig. 2) were found on birch leaves throughout Finland, northern Norway and Sweden. Disease symptoms occurring on downy birch, silver birch, dwarf birch, Kiilopää birch, mountain birch and curly birch could be associated with an infection of Cherry leaf roll...

Tree-ring stable carbon isotope ratios (δ13C) often display a decline over the industrial period (post-AD1850) that is only partly explained by changes in the isotopic ratio of carbon dioxide (CO2) and may represent a response to increased atmospheric concentrations of CO2 (ca). If this is not addressed, reconstructions using long tree-ring stable...

We used needle trace method (Kurkela and Jalkanen, 1990) to acquire additional information aboutthe dendrochronologically dated extreme event in the year 1929 in Bosnia and Herzegovina (BiH) (Poljanšek et al., 2012), during which Black pine (Pinus nigra Arnold) radial increment declinedmassively. Extreme event was initially noticed, when analyzing...

The growth of trees is a spectacular and exposed process based on a highly interlinked complex of hidden and cryptic metabolic and signaling pathways not yet fully understood. In this chapter, we focus on a sequence of studies on Scots pine as an example tree species during the past 10 years in the north of Finland. We particularly compare annual h...

European mountain ash ringspot-associated virus (EMARaV) is a plant virus inducing characteristic ringspots and mottling in Sorbus aucuparia L. For the first time, EMARaV was detected in mountain ash in Sweden. All four genomic segments of the virus were detectable by RT-PCR after total RNA extraction from leaves showing chlorotic ringspots, mottli...

Recently, Abdussamatov (2012) claimed that a period of deep (>1.0 oC) global cooling–a new Little Ice Age–will begin soon. The question of future climate variability is not merely of scientific interest but of huge significance for the wellbeing of mankind. We examine here in detail the statements of Abdussamatov (2012), which have received appreci...

Combining nine tree growth proxies from four sites, from the west coast of Norway to the Kola Peninsula of NW Russia, provides a well replicated (> 100 annual measurements per year) mean index of tree growth over the last 1200 years that represents the growth of much of the northern pine timberline forests of northern Fennoscandia. The simple mean...

Accurate modelling of long-term changes in plant stomatal functioning is vital to global climate change studies because changes in evapotranspiration influence temperature via physiological forcing of the climate. Various stomatal models are included in land surface schemes, but their robustness over longer timescales is difficult to validate. We c...

This exploratory study on Scots pine in subarctic Finland was aimed at identifying the climatic signal(s) ‘archived’ in cellular anatomy and tree-ring variables, such as diameter and wall thickness of tracheids, or early- and latewood width, respectively. For this purpose, these variables were measured in increment cores year by year from 1961–2008...

Four Nordic temperature proxies based on tree growth at the northern timberline – ring-width from Sweden and Finland, maximum latewood density from Sweden, and height increment from Finland – were compared. Three indexing methods were used to enhance the low (centennial and above), medium (decadal-to-multidecadal) and high (decadal-to-interannual)...

Height-increment and tree-ring width data of Scots pine from northern Fennoscandia were updated and their sample replication increased considerably. Standard chronologies as well as low-frequency chronologies were built and compared during their common period in ad 745–2007. The two chronologies correlate significantly (r = 0.58) with each other an...

Needle retention (number of needle sets), needle density, height increment and radial increment were surveyed on seven Japanese black pines (Pinus thunbergii Parl.) and seven Japanese red pines (Pinus densiflora Sieb. et Zucc.) growing on the same site. Number of needle sets on branches with respect to whorl position was estimated visually. In 1999...

Metoda preučevanja sledi iglic terminalnega poganjka, ali krajše metoda sledi iglic (ang.: needle trace method), retrospektivno beleži starost iglice v trenutku, ko odpade, ter preučuje vpliv okoljskih in biotskih dejavnikov na številne izpeljane podatke, ki temeljijo na ugotovljeni življenjski dobi iglice. Z izvedbo metode pridobimo podatke o dolž...

We developed a millennial length tree ring δ13C chronology from Pinus sylvestris at a site known as Laanila, in northern Finnish Lapland. In order to measure this series rapidly and with adequate replication, we adapted a multiple year pooling system. Using a combination of offset cut 5-year blocks, plus a novel method of joining tree cohorts toget...

The possible response of global climate to the changes of background radiation derived from satellite measurement during 1983-2001 is analyzed. Estimation is made by means of one-dimensional energy-balance climatic model. It is shown that the increase of the global surface radiation by 3 W × m –2 through 1983-2001 should result in a corresponding r...

The timing of phenophases of trees has increasingly been used as bio-indicator for climate change. Many studies, however, did not sufficiently consider an influence of tree age. According to our exploratory study, the phenophases at the tops of saplings and of pole-stage trees of Scots pine growing in an open canopy boreal forest coincided with eac...

Boreal forests are highly sensitive to climate and human impacts and therefore suitable as biological indicator for environmental changes. In this context, our study was aimed at getting deeper insight into the climate-dependence of the onset, intensity and end of wood formation of Scots pine during the growing season.We monitored the intra-annual...

A reconstruction of spring (April–May) temperature for northern Fennoscandia developed from the Tornionjoki (Tornio river) long cryophenological record of ice break-up dates, back to AD 1693, is presented. The record is strongly climatically sensitive and explains 67% of the variance in the instrumental data over the last 150 years. The record exhi...

The seasonal and latitudinal influences on the diversity and abundance of mycota of Pinus sylvestris needles were investigated. A sample of 1620 needles resulted in a total of 3868 fungal isolates, which were assigned to 68 operational taxonomic units (OTUs). The majority of these OTUs (65%) belong to Ascomycota and only 0.03% was grouped as Basidi...

Cloud cover is one of the most important factors controlling the radiation balance of the Earth. The response of cloud cover to increasing global temperatures represents the largest uncertainty in model estimates of future climate because the cloud response to temperature is not well-constrained. Here we present the first regional reconstruction of...

New data have allowed us to extend a previous height-increment chronology of Scots pine (Pinus sylvestris L.) at the northern Fennoscandian timberline 817 years backwards in time, from 1561 to 745. Our final transfer model accounts for 31% of the dependent instrumental (mean June—August) temperature variance between 1908 and 2007. According to the...

Fourteen Scots pines (Pinussylvestris L.) were felled in Thetford and Alice Holt forests, southern England, for needle retention studies. In the field, the main stem of each tree was divided into annual sections, with each section being reduced to 30 cm long bolts or less, omitting branch whorls and using the internodal part of each annual shoot. T...

Fifteen Scots pine (Pinussylvestris L.) trees that were slightly, moderately, or severely damaged by Gremmeniellaabietina (Lagerb.) Morelet were felled in northern Finland to determine the disease history of the stand. The annual level of damage was determined by counting the scars and cankers on all the first-order branches. Annual branch leader c...

The response of internal and external extracts of fresh arboreal lichens, Alectoria sarmentosa, Bryoria fuscescens and Bryoria fremontii, and commercial usnic acid extracted from Usnea spp. and Cladonia spp. on the growth of the Ascomycetous Gremmeniella abietina types was studied in vitro. Neither internal and external extracts of the three lichen...

Twentieth-century summer (July–August) temperatures in northern Finland are reconstructed using ring widths, maximum density and stable carbon isotope ratios (δ13C) of Scots pine tree rings, and using combinations of these proxies. Verification is based on the coefficient of determination (r2), reduction of error (RE) and coefficient of efficiency...

Investigating the many internal feedbacks within the climate system is a vital component of the effort to quantify the full effects of future anthropogenic climate change. The stomatal apertures of plants tend to close and decrease in number under elevated CO2 concentrations, increasing water-use efficiency (WUE) and reducing canopy evapotranspirat...

Investigating the many internal feedbacks within the climate system is a vital component of the effort to quantify the full effects of future anthropogenic climate change. The stomatal apertures of plants tend to close and decrease in number under elevated CO2 concentrations, increasing water-use efficiency (WUE) and reducing canopy evapotranspirat...

Palaeoclimate information from the annual rings of trees dominates research on climates of the last thousand years because the proxy is unrivalled through its combination of geographical coverage, absolute dating and depth of study. The stable isotope treering proxies (carbon hydrogen and oxygen isotopes measured in wood cellulose extracted from an...

The phenophases of Scots pine, from bud break up to the end of cambium activity, at two sites (approx. 80 and 300 km, respectively, south of the forest border) in the northern boreal zone of Finland were monitored with high time resolution during three growing seasons. Averaged over the study sites and years, bud break occurred in the first half of...

Annual height increments of 35 Scots pine (Pinus sylvestris L.) trees from the northern timberline (68°30′N, 27°30′E, 220ma.s.l., Laanila, North Finland) and monthly climate data from two meteorological stations, Sodankylä (from 1908 to present) and Ivalo (from 1958 to present) were used in climate and growth comparisons. The measured growth series...

• Radial and height growth chronologies from 150-year-old and 50-year old Scots pine stands, both located near to the northern timberline in Laanila, Finland (68° 30′ N, 27° 28′ E), were cross-correlated with each other and with mean temperatures of various temperature periods defined as months, days or growing-degree-days. • The height-growth chro...

Height increments of 60 Scots pine trees were used to reconstruct mean June—August temperature variability at interannual to decadal scales from 1561 to 2004. Three standardization methods (67%, 33% flexible splines, and a fixed 22 years spline) were compared in building chronologies in order to optimize the frequency response in relation to major...

In a 2007 paper (Gagen et al., 2007) we presented a stable carbon isotope tree ring archive covering the period AD 1640-2002. The stable carbon isotope series was constructed using trunk cellulose from the annual rings of Pinus sylvestris trees sampled from close to the northern limit for the species, in Finnish Lapland. This chronology was used to...

The spatial and temporal stability of the climatic signal in pine tree-ring width and maximum density is examined using data from four sites in northern Sweden and Finland. Moving-window multiple linear regression, using monthly and daily climate data, indicates that ring widths at all sites have been strongly controlled by July temperatures throug...

C. 2009. Cherry leaf roll virus – an emerging virus in Finland? Silva Fennica 43(5): 727–738. Cherry leaf roll virus, CLRV, is a plant pathogen that infects a variety of deciduous trees and shrubs in temperate regions. Little is known about its occurrence at high latitudes and especially in Finnish birch species. Still, symptoms that seemed to be a...

Both drought and fungal disease increase needle litterfall of Scots pine (Pinus sylvestris L.) trees, but most factors causing annual variation in needle litterfall are poorly understood. We hypothesized that radial growth and weather conditions favorable to growth correlate positively with needle litterfall with a lag equal to the number of needle...

Aim To identify temperatures at which cell division and differentiation are active in order to verify the existence of a common critical temperature determining growth in conifers of cold climates. Location Ten European and Canadian sites at different latitudes and altitudes. Methods The periods of cambial activity and cell differentiation were ass...

Non-climatic trends in tree ring δ13C series are investigated using highly replicated Pinus sylvestris δ13C series from Finnish Lapland. The declining trend in stable carbon isotopes over the industrial period, reflecting changes in the isotopic ratio of atmospheric CO2 is removed mathematically, without recourse to statistical de-trending. Regiona...

Three different methods were evaluated for analysing wood formation of Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) in Finland. During two growing seasons, wood formation dynamics were determined both by wounding the cambium with a needle followed by localisation of the wound-associated tissue modification after the...

To investigate the potential of Norway spruce (Picea abies L. Karst) as a palaeoclimate archive in the southeastern European Alps, tree ring chronologies were developed from trees growing at two sites in Slovenia which differed in their ecological and climatological characteristics. Ring width, maximum latewood density, annual height increment and...

We estimated the date of onset (Date(est)) of cambial activity by the pinning method in Scots pine (Pinus sylvestris L.) trees at Vanttauskoski (Site 1) and Laanila (Site 2) near the latitudinal limit of Scots pine in northern Finland. In each year and at each site, observations were made on a different set of five trees. The estimated dates of ons...