排序方式： 共有11条查询结果，搜索用时 15 毫秒
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Kristina Sohar Alar Läänelaid Dieter Eckstein Samuli Helama Jaak Jaagus 《European Journal of Forest Research》2014,133(3):535-549
This study investigates the climate impact on the radial increment of pedunculate oak (Quercus robur L.) in Estonia at the species’ northern distribution limit. Tree-ring width series of 162 living oaks were compiled into three regional chronologies—western (1646–2008), northeastern (1736–2011), and southeastern Estonia (1912–2011). Although these regional growth patterns are similar to each other and even to the growth patterns in adjacent regions, spatial differences in growth responses to climate were established. Thus, oaks growing on shallow soil in western Estonia are positively influenced by summer (June–August) precipitation, and oaks on the deeper soil in northeastern Estonia are favoured by June temperature, while oaks in the southeastern part of the country depend on both July precipitation and temperature. These relationships are pronounced especially in pointer years. However, due to the impact of regional weather fluctuations on tree growth, there is a lack of correspondence between the local and the pan-European pointer years. In addition, our research presents the first tree-ring-based palaeoclimatic reconstruction for the country. Although the created model has relatively low predictive skill describing less than a quarter of the variance in actual summer precipitation in western Estonia, it has passable capacity of detecting past rainfall extremes. 相似文献
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Mari Lappalainen Marjo Palviainen Jussi V.K. Kukkonen Heikki Setälä Sirpa Piirainen Tytti Sarjala Harri Koivusalo Leena Finér Samuli Launiainen Ari Laurén 《Water, air, and soil pollution》2018,229(7):240
Terrestrial export of dissolved organic carbon (DOC) to watercourses has increased in boreal zone. Effect of decomposing material and soil food webs on the release rate and quality of DOC are poorly known. We quantified carbon (C) release in CO2, and DOC in different molecular weights from the most common organic soils in boreal zone; and explored the effect of soil type and enchytraeid worms on the release rates. Two types of mor and four types of peat were incubated in laboratory with and without enchytraeid worms for 154 days at +?15 °C. Carbon was mostly released as CO2; DOC contributed to 2–9% of C release. The share of DOC was higher in peat than in mor. The release rate of CO2 was three times higher in mor than in highly decomposed peat. Enchytraeids enhanced the release of CO2 by 31–43% and of DOC by 46–77% in mor. High molecular weight fraction dominated the DOC release. Upscaling the laboratory results into catchment level allowed us to conclude that peatlands are the main source of DOC, low molecular weight DOC originates close to watercourse, and that enchytraeids substantially influence DOC leaching to watercourse and ultimately to aquatic CO2 emissions. 相似文献
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Samuli Junttila Mikko Vastaranta Jarno Hämäläinen Petri Latva-käyrä Markus Holopainen Rocío Hernández Clemente 《Scandinavian Journal of Forest Research》2017,32(2):154-165
The effect of forest structure and health on the relative surface temperature captured by airborne thermal imagery was investigated in Norway Spruce-dominated stands in Southern Finland. Airborne thermal imagery, airborne scanning light detection and ranging (LiDAR) data and 92 field-measured sample plots were acquired at the area of interest. The surface temperature correlated most negatively with the logarithm of stem volume, Lorey’s height and the logarithm of basal area at a resolution of 254?m2 (9?m radius). LiDAR-derived metrics: the standard deviations of the canopy heights, canopy height (upper percentiles and maximum height) and canopy cover percentage were most strongly negatively correlated with the surface temperature. Although forest structure has an effect on the detected surface temperature, higher temperatures were detected in severely defoliated canopies and the difference was statistically significant. We also found that the surface temperature differences between the segmented canopy and the entire plot were greater in the defoliated plots, indicating that thermal images may also provide some additional information for classifying forests health status. Based on our results, the effects of forest structure on the surface temperature captured by airborne thermal imagery should be taken into account when developing forest health mapping applications using thermal imagery. 相似文献
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Samuli Launiainen Gabriel G. KatulPasi Kolari Timo VesalaPertti Hari 《Agricultural and Forest Meteorology》2011,151(12):1672-1689
Linkage between the leaf-level stomatal conductance (gs) response to environmental stimuli and canopy-level mass exchange processes remains an important research problem to be confronted. How various formulations of gs influence canopy-scale mean scalar concentration and flux profiles of CO2 and H2O within the canopy and how to derive ‘effective’ properties of a ‘big-leaf’ that represents the eco-system mass exchange rates starting from leaf-level parameters were explored. Four widely used formulations for leaf-level gs were combined with a leaf-level photosynthetic demand function, a layer-resolving light attenuation model, and a turbulent closure scheme for scalar fluxes within the canopy air space. The four gs models were the widely used semi-empirical Ball-Berry approach, and its modification, and two solutions to the stomatal optimization theory for autonomous leaves. One of the two solutions to the optimization theory is based on a linearized CO2-demand function while the other does not invoke such simplification. The four stomatal control models were then parameterized against the same shoot-scale gas exchange data collected in a Scots pine forest located at the SMEAR II-station in Hyytiälä, Southern Finland. The predicted CO2 (Fc) and H2O fluxes (Fe) and mean concentration profiles were compared against multi-level eddy-covariance measurements and mean scalar concentration data within and above the canopy. It was shown that Fc comparisons agreed to within 10% and Fe comparisons to within 25%. The optimality approach derived from a linearized photosynthetic demand function predicted the largest CO2 uptake and transpiration rates when compared to eddy-covariance measurements and the other three models. Moreover, within each gs model, the CO2 fluxes were insensitive to gs model parameter variability whereas the transpiration rate estimates were notably more affected. Vertical integration of the layer-averaged results as derived from each gs model was carried out. The sensitivities of the up-scaled bulk canopy conductances were compared against the eddy-covariance derived canopy conductance counterpart. It was shown that canopy level gs appear more sensitive to vapor-pressure deficit than shoot-level gs. 相似文献
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Samuli Helama Matti Vartiainen Taneli Kolström Jouko Meriläinen 《Wood Science and Technology》2010,44(2):335-351
X-ray microdensitometry was applied to a set of Scots pinewood (i.e. low extractive content). Earlywood and latewood properties
were determined as minimum and maximum densities of each tree ring and the potential influence of acetone-soluble extractives
(i.e. non-structural and secondary constituents of wood) was estimated using tree-ring statistics. The occurrence of extractives
in different portions of wood was determined using dendrochronological methods, by comparing the densities of unextracted
and extracted wood. It was not only found that unextracted samples exhibited inflated earlywood and latewood density values,
but the growth trends were also altered. Extractives flattened the inter-annual growth variability, both in earlywood and
latewood, and influenced the estimation of intra-annual radial growth variations. Characterizing the varying amount of extractives
is of inter-disciplinary importance. The results in this study describe their occurrence and show that the radial variations
in extractives could be highly detailed by simply using densitometry-based dendrochronology. 相似文献
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Radial growth was examined in two Scots pine stands that were seeded during the 1920s and 1930s due to reforestation and afforestation
activity on the timberline of northern Finnish Lapland. Tree-rings of seeded pines were calibrated against the instrumental
records of local weather and large-scale atmospheric patterns and further compared to pines of natural origin on the timberline.
The studied stands were shown to contain common growth variability that differed from the variability of natural pines. Deviating
growth of seeded pines was attributed to their only moderate growth dependence on mid-summer (July) temperatures and, likewise,
their strong dependence on the autumn climate in the previous year, and linked to the different genetic origin of artificial
stands due to southern seeds. Stands were thinned for different densities in 1985 and 1986. The growth response to thinning
was markedly better than could be expected according to previous studies. We found that the positive growth reaction conceivably
benefited from the ameliorated winter conditions, expressed as warmed (March) temperatures and the prolonged positive phase
of the Arctic Oscillation (February). The results emphasize the determining influence of climatic fluctuations on reforestation
and afforestation near the distributional limits of tree species. 相似文献
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Matti Sirén Aura Salmivaara Jari Ala-Ilomäki Samuli Launiainen Harri Lindeman Jori Uusitalo 《Scandinavian Journal of Forest Research》2019,34(2):145-154
Predictive factors for forwarder rut formation were studied on fine-grained mineral soils. The study was carried out in southern Finland in mid-May, when the soil water contents were high after snowmelt. A total of 7 study tracks of 20?m were cut with a harvester. After removing the logging residues, a loaded forwarder made 3–4 passes on each track. The forwarder rut depth was related to the total overdriven mass driven over the measurement line, volumetric water content, cone penetration resistance and the harvester rut depth. A total of five mixed-effects models are presented to predict the rut depth. The first model includes the overdriven cumulative mass, volumetric water content of the soil and the cone penetration resistance. As a penetrometer is more of a research tool, the second model includes only the overdriven cumulative mass and water content, factors that can be used in practical planning operations. The remaining three models all include the rut depth after the harvester pass and the overdriven cumulative mass and also include volumetric water content and cone penetration resistance. The model including the rut depth after a harvester pass and the overdriven cumulative mass is a good predictor of the rut depth and supports earlier findings on the connection between harvester and forwarder rut formations. 相似文献