Dendroclimatic signals deduced from riparian versus upland forest interior pines in North Karelia, Finland

Spatiotemporal patterns of standing and fallen dead trees were examined in two protected Scots pine ( Pinus sylvestris L.)-Norway spruce ( Picea abies (L.) Karst.) forests in eastern Finland (Pahkavaara and Pönttövaara). In Pahkavaara the volume of standing dead trees was 10 m 3 ha -1 and the volume of fallen logs was 66 m 3 ha -1 , and in Pönttövaara the values were 48 m 3 ha -1 and 107 m 3 ha -1 , respectively. The areas differed with respect to the tree species composition, whereas the proportion of different decay stages was similar. Decay stage and dendrochronological analyses revealed the continuity of dead wood formation. The spatial pattern of standing dead trees was usually towards clustered. The volumes of fallen logs showed a spatial autocorrelation up to distances of 10-20 m. The results also suggest that the current amount and diversity of dead wood is rather high, but that forest succession is likely to lead to a less diverse state in the future.

Coastal sand dunes near the Baltic Sea are a dynamic environment marking the boundary between land and sea and oftentimes covered by Scots pine (Pinus sylvestris L.) forests. Complex climate-environmental interactions characterize these ecosystems and largely determine the productivity and state of these coastal forests. In the face of future climate change, understanding interactions between coastal tree growth and climate variability is important to promote sustainable coastal forests. In this study, we assessed the effect of microsite conditions on tree growth and the temporal and spatial variability of the relationship between climate and Scots pine growth at nine coastal sand dune sites located around the south Baltic Sea. At each site, we studied the growth of Scots pine growing at microsites located at the ridge and bottom of a dune and built a network of 18 ring width and 18 latewood blue intensity tree-ring chronologies. Across this network, we found that microsite has a minor influence on ring width variability, basal area increment, latewood blue intensity, and climate sensitivity. However, at the local scale, microsite effects turned out to be important for growth and climate sensitivity in some sites. Correlation analysis indicated that. the strength and direction of climate-growth responses for the ring width and blue intensity chronologies were similar for climate variables over the 1903-2016 period. A strong and positive relationship between ring width and latewood blue intensity chronologies with winter-spring temperature was detected at local and regional scales. We identified a relatively strong, positive influence of winter-spring/summer moisture availability on both tree-ring proxies. When climate-growth responses between two intervals (1903-1959, 1960-2016) were compared, the strength of growth responses to temperature and moisture availability for both proxies varied. More specifically for the ring-width network, we identified decreasing temperature-growth responses, which is in contrast to the latewood blue intensity network, where we documented decreasing and increasing temperature-growth relationships in the north and south respectively. We conclude coastal Scots pine forests are primarily limited by winter or winter-spring temperatures and drought despite differing microsite conditions. We detected some spatial and temporal variability in climate-growth relationships that warrant further investigation.

We studied the spatial evenness of nitrogen (N) fertilizer and the effects of fertilization intensity on the short-term volume growth responses in two ground-fertilized Scots pine and two airborne-fertilized Norway spruce study sites on mesic (Myrtillus-type) upland forests in Eastern Finland. We also studied the relationships between measured fertilizer dose, N concentrations in the needles and soil organic (humus) layer, and volume growth of the trees. In each study site, we established three replicate 1 ha blocks for each fertilization treatment (0, 150 and 200 kg N ha–1). Each block contained three 200 m2 circular plots. The spatial evenness of the fertilizer was measured using textile funnels. The height, breast height diameter and vitality of the trees were measured annually. The nutrient concentrations in the needles and humus layer were measured once. Differences between the target and measured fertilizer doses were 3–10% for Scots pine and 11–22% for Norway spruce. At the Scots pine and Norway spruce sites, the volume growth was 0.4–2.1 and 1.8–2.6 m3 ha–1 a–1 higher with fertilization, respectively. The fertilizer dose correlated with the N concentrations in the needles and humus layer, and volume growth. Significant volume growth responses to the fertilization (p < 0.05) were found only in the Scots pine at Ilomantsi, possibly due to variations in the initial volume and the fertilizer dose realized between and within treatments. We expect that the differences in volume growth responses between fertilization treatments will increase over time.

To assess past climate variability in west-central Scandinavia, a new 972-year-long temperature reconstruction, based on adjusted delta blue intensity (ΔBIadj), was created. Presently, it is the longest blue intensity chronology in Fennoscandia and the third longest in the northern hemisphere. Measurements were obtained from 119 tree line Scots pine ( Pinus sylvestris L.) samples from Rogen, in the central Scandinavian Mountains, Sweden. Early and latewood blue intensity absorption data were used to create ΔBIadj. The data were detrended using a signal-free regional curve standardization method (RSFi) to minimize biological noise and maximize low-frequency climate information. The Rogen ΔBIadj chronology has a substantially stronger temperature signal at inter-annual timescales than the corresponding tree-ring width (RW) chronology, and it displays good spatial representation for the south-central parts of Scandinavia. The ΔBIadj summer (June through August) temperature reconstruction, extending back to 1038 CE, exhibits three warm periods in 1040–1190 CE, 1370–1570 CE and the 20th century and one extended cold period between 1570 and 1920 CE. Regional summer temperature anomalies are associated with a Scandinavian–Greenland dipole sea-level pressure pattern, which has been stable for the past several centuries. Major volcanic eruptions produce distinct anomalies of ΔBIadj indices indicating cooling of summer temperatures in the subsequent years. Our results show that ΔBIadj from Pinus sylvestris in Scandinavia is a suitable proxy providing opportunities to explore past temperature variability at various frequencies, atmospheric dynamics and variability in external forcing. Nevertheless, long-term trend differences with RW imply that further research is needed to fully understand the application of this technique in dendroclimatology.

The peculiarities of the radial growth of pine in the conditions of air pollution in the Arctic zone are considered. The results of measurements of the width of annual rings of pine growing at different distances from the emission source are presented. The variability of annual radial growth of pine trees varies in a wide range: from moderate to very high. Age changes in the width of annual rings of pine are corresponding to the regularities of the curve of the “large growth”. The average annual radial growth begins to decrease in plants older than 70 years. The dependence of the average annual radial growth of pine on age is approximated by an exponential equation. The accuracy of the approximation (coefficient of determination) is very high. Comparative analysis of the width of the annual rings and the value of gross emissions of the APPM in the year of formation of the annual layer did not show a clear synchronicity or asynchrony in the dynamics of these indicators for all plots. In most cases, the relationship between the total annual emissions of the APPM into the atmosphere and the width of the annual rings of pine was insignificant. The analysis of dendrochronology did not reveal a significant influence of atmospheric emissions of the Arkhangelsk pulp and paper mill on the growth of pine. The correlation coefficients between total annual atmospheric emissions and radial annual increments did not show a relationship between them, both when comparing these parameters year-on-year and with a delay of one year. For the period from 2001 to 2018 significant direct or delayed negative effect of emissions from Arkhangelsk pulp and paper mill in the atmosphere in the investigated areas of pine forests have not been identified.

Influence of Climatic Factors on the Annual Radial Growth of Scots Pine (Pinus sylvestris L.) in Western Latvia Dendroclimatological research has been perfomed in Latvia after a break of about 25 years. The growth pattern of Scots pine (Pinus sylvestris L.) in six districts of western Latvia is analysed in relation to climatic factors (monthly and seasonal mean air temperature and precipitation). Applying various statistical techniques, it was observed that in this area the growth of pine on mineral soils with normal moisture conditions has been affected most significantly by the mean air temperature during the period from the second half of January to the first half of April of the same year. Thus, the period when mean air temperature is the most significant influence is similar across an area at least from Lithuania (inclusive) to southern Scandinavia, while further north it is mean summer air temperature that gradually becomes the determining factor in the radial growth of pine. Also the quality of the dendrochronological signal in tree-ring chronologies of pine growing in the environmental conditions of Latvia was determined and signature years during the 20th century were identified, when the majority of pines throughout the territory of the Baltic States exhibit a similar change in annual radial growth.

Effective fire suppression in combination with intensive forestry has caused a large number of dead wood‐dependent (saproxylic) species to become threatened in Fennoscandia. In order to return the fire disturbance dynamics and to increase the amount of dead wood, restoration actions are urgently needed. We studied the effects of restoring young (under 30 years old) pine‐dominated (Pinus sylvestris L.) forest stands on saproxylic beetle assemblages in eastern Finland, focusing especially on rare, red‐listed, and pyrophilous (RRLP) species. Our experiment included a restoration treatment including two tree felling levels for fuel load (10 or 20 m3/ha) followed by burning, and an untreated control. We sampled beetles before restoration in 2005, during the year of restoration in 2006, and in two post‐treatment years in 2007 and 2011. Both restoration treatments increased the number of saproxylic and RRLP species. The species richness increased most in the year of restoration in 2006 and this trend continued in the following year 2007, but no differences in species assemblages were detected between the two fuel load levels. By 2011, however, the species richness and abundance had declined back to the pre‐treatment level. We suggest that restoration burning can also be directed to young forests where biodiversity values are initially low. On the basis of the observed decline in the species richness, we suggest that fire could be introduced in neighboring areas in approximately 5‐year intervals to maintain populations of the most demanding pyrophilous species.

The aim of this study was to compare the understory vegetation in chronosequences representing seminatural and managed Scots pine (Pinus sylvestris L.) forests on dryish heaths of the Vaccinium type. The data represent the middle boreal vegetation zone and were collected in eastern Finland and the Dvina area of Karelia, on both sides of the border between Finland and the Russian Federation. Species diversity and the coverage of the various life-form groups (ground lichens, mosses, liverworts, grasses, herbs, dwarf shrubs, and tree seedlings) were used to analyse the properties of the ground vegetation over the succession from open forest land to closed forest communities. The clearest differences in diversity between the seminatural forests mainly influenced by fire and managed forests occurred in the early stages of succession. Forest management appeared to increase the species richness at the beginning of succession. The seminatural stands were rich in Cladonia lichens and dwarf shrubs up until tree canopy closure; however, the abundance of mosses was lower in the seminatural stands. Forest management favoured an abundance of grasses, notably Deschampsia flexuosa, which was common after clear-cutting. The use of prescribed burning in silviculture could result in more natural vegetation succession dynamics in managed stands.

The static bending properties of Scots pine (Pinus sylvestris L.) clear wood were studied using a material collected from commercial thinning forests in eastern Finland. In Myrtillus type, the modulus of elasticity and bending strength of the first thinning wood were 7.8 GPa and 66.0 MPa, respectively, whereas for more mature wood from the second thinnings, the modulus of elasticity and bending strength were 10.0 GPa and 80.3 MPa. The results were compared with final fellings, which resulted in the modulus of elasticity of 10.1 GPa and bending strength of 81.8 MPa. The bending properties of the first thinning material were low, and thus they did not indicate any potential for applications requiring high strength or stiffness and material homogeneity. On the contrary, the properties of Scots pine wood from the second commercial thinnings may be comparable with or sometimes even better than those of the final-felling wood. The results can be utilised in wood marketing, procurement, sorting, allocation to different industries and end-uses, as well as in wood processing, product sales, and branding.

Potassium (K), calcium (Ca), iron (Fe) and aluminium (Al) release from Norway spruce (Picea abies Karsten), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) logging residues (fine roots, foliage and small branches) were studied by means of litterbags over a period of three years in clear-cut area and adjacent uncut Norway spruce dominated mixed boreal forest in eastern Finland (63°51′ N, 28°58′ E, 220 m a.s.l) to determine the amounts and rates of release for these elements and to evaluate whether clear-cutting accelerates mineralization. Almost all K was released from logging residues already during the first year. Calcium was released from foliage and roots but accumulated in branches. Most of the roots Fe and Al content were released during three years while the absolute amounts of Fe and Al in branches and foliage generally increased with decomposition. The results indicate that mineralization is slightly accelerated as a result of clear-cutting since K from foliage and branches of all studied tree species and Ca from pine and spruce roots was released significantly faster at the clear-cut plot than at the forest plot. In three years the initial K pool in the logging residues declined by 90%, Ca by 8%, Fe by 55% and Al by 61% in the clear-cut area. These results indicate that Ca is retained a long time; but Fe, Al and in particular, K are soon released from logging residues. Fine roots of the logged trees release large amounts of Fe and Al and can significantly affect Fe and Al fluxes.

Forest management affects soil carbon (C) storage through forest composition, microclimate and litter inputs. How two major forest management systems, continuous-cover forestry (CCF) and clear-cut-based rotation forest management (RFM), differ in their impact on soil C in boreal forests is still poorly understood, however. We compared their effects on soil organic carbon (SOC) storage and quality in boreal Scots pine (Pinus sylvestris L.) dominated forests in eastern Finland. We tested the hypotheses that (1) colder microclimates and continuous litter inputs will lead to higher SOC stocks in CCF plots than in clear-cuts and (2) the more labile litter in clear-cuts with varying ground vegetation will enhance SOC decomposition rates. We sampled uncut mature forests, clear-cuts, retention-cuts and gap-cuts, in which we analysed SOC concentrations and calculated the stocks. We measured stand characteristics such as diameter-at-breast height, basal area, dominant tree height, and understorey species coverage of the various treatments and modelled the above- and belowground litter inputs based on these parameters. We used laboratory incubation and sequential fractionation of SOC to assess its degradability under standardized conditions. To estimate the decomposition rate in the various environments we incubated cellulose bags in situ. We assessed the impact of microclimate on SOC decomposition, using data from soil-temperature and soil-moisture field measurements. We quantified the microbial biomass C pool, using chloroform fumigation extraction to gain insight on the impact of forest management practice on soil microbes. The SOC concentrations and SOC stocks did not differ significantly between the treatments, despite the presence of a warmer microclimate and lower litter inputs in the clear-cut plots. However, we found differences in the quality of the SOC. Soils in clear-cut sites showed lower proportions of labile SOC compounds than did the other treatments. As hypothesized, the decomposition rates were elevated in clear-cuts, but were equally as high within the canopy gaps on gap-cut stands. Our work highlights that forest management affects the quality, degradability, long-term accumulation and storage of SOC. We conclude that the accumulation of labile compounds in uncut forests and retention-cuts, combined with the decreased decomposition rates, indicate a higher potential for future C accumulation in the soil than in clear-cuts.

Elevated dissolved carbon (C), nitrogen (N) and phosphorus (P) concentrations are frequently observed in surface water soon after clear-cutting of boreal coniferous forests. It has been suggested that they originate from the fine logging residues whose decomposition may be accelerated as a result of changes in soil temperature and moisture conditions. In the present study, the decomposition rate and release of C, N, and P from Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karsten) and silver birch (Betula pendula Roth.) logging residues (fine roots ∅≤2 mm, branches ∅≤10 mm and foliage) were investigated during three years with the litterbag method in a clear-cut area and in an adjacent Norway spruce dominated, mixed boreal forest in eastern Finland (63°51′ N, 28°58′ E, 220 m asl). The mass loss of the logging residues decreased in the order: foliage > roots > branches. Birch leaves were the only fraction that showed significantly higher losses of mass and C at the clear-cut plot than at the forest plot; otherwise there was no tendency for accelerated decomposition or mineralization at the clear-cut plot. After three years the initial C pool in the logging residues had declined by 33% and that of P by 49% but there was no net release of N as more N accumulated in roots and branches than was released from foliage. The results indicate that 1) logging residues release relatively large and rapid fluxes of CO2 to the atmosphere 2) are potential source of elevated P in surface waters soon after clear-cutting 3) are not a net source of N immediately after clear-cutting.

We examined the composition and spatial structure of the understorey vegetation at two sites with different fire histories in a mature Pinus sylvestris L. forest in eastern Finland. The entire study area had regenerated after a fire in the early 19 century. Besides, a part of the area was subsequently hit by a surface fire in 1906, which divided the study area into two parts. Vegetation and environmental variables measured from the these two parts, the 1800+ burn site and the 1906 burn site, have considerably different spatial pattern. Deciduous shrubs and ground layer, consisting primarily of bryophytes, had a more distinct patch structure at the 1800+burn site than at the 1906 burn site, while with lichens the situation was the reverse. Cover of the field layer, dominated by evergreen shrubs, was significantly higher at the 1800+burn site than at the 1906 burn site. At both sites, the spatial pattern of plant functional types was obviously strongly regulated by the spatial influence of living trees. Gradual formation of strong clonal patch structures of V. myrtillus, V. vitis-idaea and mosses, seems to be another important process affecting the properties of the understorey vegetation. The post-fire recovery of the understorey community was slow: in the 1906 burn site, the community composition and spatial structure were still in transition after almost 90 years since the last fire.

Forest wildfire and 12 years of post-disturbance succession of saprotrophic macrofungi (Basidiomycota, Ascomycota)

The tree species composition, vertical stratification and patterns of spatial autocorrelation at the tree and quadrate (25 × 25 m) scales were studied in a natural mature PinuS sylvestris dominated forest in eastern Finland. For the analyses we mapped the locations and dimensions of trees taller than 10 m in a 9 ha (300 × 300 m) area, and within this area we mapped all trees taller than 0.3 m on a core plot of 4 ha (200 × 200 m). The overall tree size distribution was bimodal. the dominant layer and the understory forming the peak frequencies. Pinus sylvestris dominated the main canopy, together with scattered Betula pendula and Picea abies. Alnus incana, Populus tremula, Salix caprea, Sorbus aucuparia and Juniperus communis occurred only in the under‐ and middlestories. Autocorrelation analysis (semivarianee) of tree size variation revealed spatial patterns, which were strongly dependent on the size of trees included in the analysis. When all living trees, including the understory regeneration, were taken into account, the autocorrelation pattern ranged up to 35 m inter‐tree distances, reflecting the spatial scale of understory regeneration patches. Competitive interaction among middle‐ and upperstory trees (height>10 m) had contrasting effects on autocorrelation pattern depending on spatial scale. At the fine scale, dominant trees suppressed their smaller close neighbors (asymmetric competition), which was shown as increased tree size variation at small inter‐tree distances (<2 m). At slightly larger inter‐tree distances, specifically among large trees of similar size, competition was more symmetrical, which resulted in decreased tree size variation at these inter‐tree distances (3–4 m). This effect was seen most clearly in the dominant trees, there being a clear autocorrelation pattern in tree size up to inter‐tree distances of ∼4 m. At the quadrate scale (25 × 25 m) the analysis revealed high local variation in structural characteristics such as tree height diversity (THD), tree species diversity (H) and autocorrelation of tree height. The analysis suggests that naturally developed P. sylvestris forests exhibit complex small‐scale patterns of structural heterogeneity and spatial autocorrelation in tree size. These patterns may be important for stand‐scale habitat diversity and can have aggregated effects on ecosystem dynamics at larger spatial scales though their influence on the spread of disturbance and regeneration after disturbance.