Scots Pine Forest (scots + pine_forest)

Distribution by Scientific Domains

Selected Abstracts

Holocene solifluction, climate variation and fire in a subarctic landscape at Pippokangas, Finnish Lapland, based on radiocarbon-dated buried charcoal,

John A. Matthews
Abstract A large number of radiocarbon dates from charcoal layers buried beneath stacked solifluction lobes at Pippokangas, in the northern boreal zone of Finnish Lapland, are used to reconstruct a Holocene history of solifluction. Although the site is surrounded by Scots pine forest, the solifluction lobes occur on the lower slopes of a kettle hole, the microclimate of which prevents the growth of trees. Samples from the upslope end of charcoal layers have enabled the recognition of four synchronous phases of solifluction lobe initiation: 7400,6700, 4200,3400, 2600,2100 and 1500,500,cal.,yr,BP. Rates of lobe advance are shown to be lobe-dependent and age-dependent: initially, average rates were commonly 0.14,0.19,cm yr,1, later falling to 0.02,0.07,cm,yr,1 or less as the lobes approached the bottom of the slope. The absence of charcoal prior to 8000,cal.,yr,BP, together with single IRSL and TL dates, indicate a relatively stable early Holocene landscape. The onset of solifluction around 7400,cal.,yr,BP. appears to have followed the immigration of pine around the site, which increased the frequency of forest fires. Phases of solifluction activity seem to have been triggered by millennial-scale variations in effective moisture (the climatic hypothesis), rather than episodic burning of the surface vegetation cover (the geoecological hypothesis), although climate may also have affected fire frequency and severity. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Tree root and soil heterotrophic respiration as revealed by girdling of boreal Scots pine forest: extending observations beyond the first year

ABSTRACT Limitations in available techniques to separate autotrophic (root) and soil heterotrophic respiration have hampered the understanding of forest C cycling. The former is here defined as respiration by roots, their associated mycorrhizal fungi and other micro-organisms in the rhizosphere directly dependent on labile C compounds leaked from roots. In order to separate the autotrophic and heterotrophic components of soil respiration, all Scots pine trees in 900 m2 plots were girdled to instantaneously terminate the supply of current photosynthates from the tree canopy to roots. Högberg et al. (Nature 411, 789,792, 2001) reported that autotrophic activity contributed up to 56% of total soil respiration during the first summer of this experiment. They also found that mobilization of stored starch (and likely also sugars) in roots after girdling caused an increased apparent heterotrophic respiration on girdled plots. Herein a transient increase in the ,13C of soil CO2 efflux after girdling, thought to be due to decomposition of 13C-enriched ectomycorrhizal mycelium and root starch and sugar reserves, is reported. In the second year after girdling, when starch reserves of girdled tree roots were exhausted, calculated root respiration increased up to 65% of total soil CO2 efflux. It is suggested that this estimate of its contribution to soil respiration is more precise than the previous based on one year of observation. Heterotrophic respiration declined in response to a 20-day-long 6 °C decline in soil temperature during the second summer, whereas root respiration did not decline. This did not support the idea that root respiration should be more sensitive to variations in soil temperature. It is suggested that above-ground photosynthetic activity and allocation patterns of recent photosynthates to roots should be considered in models of responses of forest C balances to global climate change. [source]

Modelling sources and sinks of CO2, H2O and heat within a Siberian pine forest using three inverse methods

M. Siqueira
Abstract Source/sink distributions of heat, CO2 and water vapour in a Siberian Scots pine forest were estimated from measured concentration and temperature profiles using three inverse analysis methods. These methods include: a Eulerian second-order closure model (EUL); a localized near-field Lagrangian dispersion model (LNF); and a hybrid model (HEL) which uses the Eulerian second-order turbulence model to calculate the flow statistics combined with the regression analysis used with the Lagrangian model. Model predictions were compared to heat flux profiles measured at five levels in the canopy, and to CO2 and water-vapour fluxes measured close to the ground and above the forest. Predictions of sensible-heat flux profiles by the LNF and HEL schemes were systematically better than results from the EUL analysis. This improvement was attributed to the redundancy in the measured profile (scalar concentration and temperature) data for LNF and HEL and to the imposed smoothness condition used in the regression analyses, whereas the EUL approach calculates a source for each level without any redundancy. The LNF and HEL schemes were also better than EUL in predicting source distributions for CO2 and water vapour, although errors were larger than for sensible heat. The main novelty in our study is the use of EUL to decompose the vertical variability in scalar (or heat) sources into variability produced by the inhomogeneity in flow statistics and variability inferred from the measured mean scalar concentration (or temperature) profile. Hence, it is possible with this analysis to assess how much ,new information' about the source variability is attributed to vertical variation in the measured mean scalar concentration (or temperature) profiles. The analysis shows that measured water vapour concentration profiles provide little information on the inferred source distribution, whereas the CO2 profiles contain more information. Monte Carlo simulations show that computed sources from all three inverse methods have similar sensitivities to errors in measured temperatures. Errors are reduced when the reference temperature above the canopy is held fixed, implying that errors in this temperature propagate throughout the entire domain. When information content and error estimations are combined, a valuable tool to assess the quality of source prediction by inverse methods can be generated. Copyright © 2003 Royal Meteorological Society [source]

Effects of increasing fire frequency on black carbon and organic matter in Podzols of Siberian Scots pine forests

C. I. Czimczik
Summary Fires in boreal forests frequently convert organic matter in the organic layer to black carbon, but we know little of how changing fire frequency alters the amount, composition and distribution of black carbon and organic matter within soils, or affects podzolization. We compared black carbon and organic matter (organic carbon and nitrogen) in soils of three Siberian Scots pine forests with frequent, moderately frequent and infrequent fires. Black carbon did not significantly contribute to the storage of organic matter, most likely because it is consumed by intense fires. We found 99% of black carbon in the organic layer; maximum stocks were 72 g m,2. Less intense fires consumed only parts of the organic layer and converted some organic matter to black carbon (> 5 g m,2), whereas more intense fires consumed almost the entire organic layer. In the upper 0.25 m of the mineral soil, black carbon stocks were 0.1 g m,2 in the infrequent fire regime. After fire, organic carbon and nitrogen in the organic layer accumulated with an estimated rate of 14.4 g C m,2 year,1 or 0.241 g N m,2 year,1. Maximum stocks 140 years after fire were 2190 g organic C m,2 and 40 g N m,2, with no differences among fire regimes. With increasing fire frequency, stocks of organic carbon increased from 600 to 1100 g m,2 (0,0.25 m). Stocks of nitrogen in the mineral soil were similar among the regimes (0.04 g m,2). We found that greater intensities of fire reduce amounts of organic matter in the organic layer but that the greater frequencies may slightly increase amounts in the mineral soil. [source]