Spruce Forest Sites Research Articles

Simulated mechanisms of soil N feedback on the forest CO2 response

AbstractAn improved understanding of the response of forest ecosystems to elevated levels of CO2 in the atmosphere is crucial because atmospheric CO2 concentration continues to increase at an accelerating rate and forests are an important sink in the global carbon cycle. Several CO2‐enrichment experiments have now been running for more than 10 years, with highly variable short‐term results after the first decade. Responses to rising [CO2] over the next few decades will depend on several plant and ecosystem feedbacks that are inadequately understood. In this study, we conduct a sensitivity analysis, within the context of the simulated CO2 response, using a new version of the G'DAY ecosystem model, with an improved decomposition submodel, applied to a nitrogen‐limited Norway spruce forest site in the north of Sweden. The new decomposition model incorporates important modifications to soil processes, including some that constitute negative feedbacks on an ecosystem's growth response to elevated [CO2]. The sensitivity analysis reveals key parameters and processes that are important for the simulated CO2 response on the short term and others that are more important on the long term. A process that has a strong impact on the short‐term response is a change in decomposer composition, potentially in response to altered litter quality. Parameters that become increasingly important in the long term are carbon allocation to root exudates that are directly or indirectly associated with atmospheric N2 fixation, and the rate of humification of soil organic matter. We identify factors intrinsic to species and site (microbes and resources) and ecosystem nutrient supply that determine the duration of the enhanced simulated growth response to elevated [CO2].

Multivariate Patterns of Antioxidative and Photoprotective Defence Compounds in Spruce Needles at Two Central European Forest Sites of Different Elevation

In this work we measured a set of antioxidative and photoprotective compounds (chlorophylls, carotenoids, tocopherol, ascorbate and glutathione), which were suggested previously as stress markers in conifer needles, at two spruce forest sites at different elevation in Saxony, Germany. Most variables differed significantly between current and 1-year-old needles, but only the content of the xanthophyll cycle per mg total chlorophyll and the oxidation state of glutathione were significantly different between the sites. We applied principal component analysis (PCA) to address the question if underlying accumulated variables are similar to the ones found in spruce needles across Alpine elevation profiles and/or for pines in Mediterranean ecosystems. Four principal components (accumulated variables, PC) representing 68% of the total variance of the dataset were extracted. PC 1 encompassed total chlorophyll, lutein, and beta-carotene contents, PC 2 combined the epoxidation state of xanthophylls, ascorbate content and redox state, and glutathione content, PC 3 represented the content of xanthophylls and the redox state of glutathione, and PC 4 encompassed the content of alpha-carotene and the epoxidation state of xanthophylls. Only PC 3 was significantly different between sites. The PCA structure shows many similarities to corresponding findings in studies on spruce in mountain forests in the Alps and pines in Mediterranean systems. This corroborates the interpretation of PCs as indicative for underlying physiological processes. However, separation of the two investigated sites by PCs was in the present case study not superior to the separation by single input variables.

Spatial distribution of fine roots at ploughed Norway spruce forest sites

We examined the spatial distribution of fine roots at two forest sites that were ploughed 20 (site K1) and 33 years (site K2) before sampling and planted with Norway spruce (Picea abies (L.) Karst.) seedlings. Soil core samples were taken from the tilt and beneath the tilt, the furrow and the intermediate undisturbed soil to a depth of 0.4 m for fine root biomass, length and necromass determinations. Norway spruce fine roots were found throughout the ploughed forest sites. The fine roots were, however, unevenly distributed: the fine root biomass was highest in the tilt (624 and 452 g m at sites K1 and K2, respectively) and lowest in the undisturbed soil at site K1 (79 g m) and in the furrow at site K2 (145 g m). The estimated average fine root biomass at the ploughed forest sites (268 and 248 g m at sites K1 and K2, respectively) was, however, similar to those presented in other studies concerning sites that had not been ploughed. In the tilt, a substantial proportion of the fine roots was in the inverted mineral soil horizons and in the new organic horizon above the tilt. Consistent with the fine root biomass findings, the Norway spruce necromass was highest in the tilt but the vertical distribution of the dead roots was different: the necromass was highest in the buried O horizon. The results of this study suggest that at the ploughed forest sites, a substantial part of Norway spruce nutrient and water uptake occured in the tilt during the first 20 or 33 years after plantation.–2–2–2–2BT

Simulation and scaling of temporal variation in gross primary production for coniferous and deciduous temperate forests

AbstractObservations of ecosystem net carbon dioxide exchange obtained with eddy covariance techniques over a 4‐year period at spruce, beech and pine forest sites were used to derive time series data for gross primary production (GPP) and ecosystem respiration (Reco). A detailed canopy gas exchange model (PROXELNEE) was inverted at half‐hour time step to estimate seasonal changes in carboxylation capacity and light utilization efficiency of the forest canopies. The parameter estimates were then used further to develop a time‐dependent modifier of physiological activity in the daily time step gas exchange model of Chen et al. (1999), previously used for regional simulations in BOREAS. The daily model was run under a variety of assumptions and the results emphasize the need in future analyses: (1) to focus on time‐dependent seasonal changes in canopy physiology as well as in leaf area index, (2) to compare time courses of physiological change in different habitats in terms of recognizable cardinal points in the seasonal course, and (3) to develop methods for utilizing information on seasonal changes in physiology in regional and continental carbon budget simulations. The results suggest that the daily model with appropriate seasonal adjustments for physiological process regulation should be an efficient tool for use in conjunction with remote sensing for regional evaluation of global change scenarios.

Modelling the production and transport of dissolved organic carbon in forest soils

DyDOC describes soil carbon dynamics, with a focus on dissolved organic carbon (DOC). The model treats the soil as a three-horizon profile, and simulates metabolic carbon transformations, sorption reactions and water transport. Humic substances are partitioned into three fractions, one of which is immobile, while the other two (hydrophilic and hydrophobic) can pass into solution as DOC. DyDOC requires site-specific soil characteristics, and is driven by inputs of litter and water, and air and soil temperatures. The model operates on hourly and daily time steps, and can simulate carbon cycling over both long (hundreds-to-thousands of years) and short (daily) time scales. An important feature of DyDOC is the tracking of 14C, from its entry in litter to its loss as DO14C in drainage water, enabling information about C dynamics to be obtained from both long-term radioactive decay, and the characteristic 14C pulse caused by thermonuclear weapon testing during the 1960s ("bomb carbon"). Parameterisation is performed by assuming a current steady state. Values of a range of variables, including C pools, annual DOC fluxes, and 14C signals, are combined into objective functions for least-squares minimisation. DyDOC has been applied successfully to spruce forest sites at Birkenes (Norway) and Waldstein (Germany), and most of the parameters have similar values at the two sites. The results indicate that the supply of DOC from the surface soil horizon to percolating water depends upon the continual metabolic production of easily leached humic material. In contrast, concentrations and fluxes of DOC in the deeper soil horizons are controlled by sorption processes, involving comparatively large pools of leachable organic matter. Times to reach steady state are calculated to be several hundred years in the organic layer, and hundreds-to-thousands of years in the deeper mineral layers. It is estimated that DOC supplies 89% of the mineral soil carbon at Birkenes, and 73% at Waldstein. The model, parameterised with "steady state" data, simulates short-term variations in DOC concentrations and fluxes, and in DO14C, which are in approximate agreement with observations.

Effects of liming and ash application on below ground ectomycorrhizal community structure in two Norway spruce forests

The effect of lime and ash additions upon the below ground ectomycorrhizal communities was studied at two spruce forest sites, Horrod and Hasslov, in Southern Sweden. At Hasslov, fifteen years after the addition of 8.75 ton ha-1 of dolomite, the species richness of the mycorrhizal community was unchanged. However, the liming resulted in an almost total replacement of species normally found under the site conditions, with only three morphotypes from a total of 24 distinguished being common to both the control and limed plots. At Horrod, four years after the application of 3.25 ton ha-1 crushed lime, there was a significant reduction in the number of species recorded. This was not a result of a reduction in root tips sampled, since there was no significant treatment effect upon root tip abundance. Instead, it appeared that the less common species present in the control plots had been lost following liming. At the same site, the addition of 4.28 ton ha-1 of wood ash had little effect upon the mycorrhizal community as a whole, with only small changes recorded in the abundance of a small number of species. This study highlights the urgent need for additional data on the temporal and load response of ectomycorrhizal fungi to the addition of lime. This information is vital in view of the proposed widespread use of lime as a counter measure to soil acidification.

Long-term fire frequency in the spruce-dominated forests of the Ulvinsalo strict nature reserve, Finland

The long-term fire history of the spruce-dominated forests of the Ulvinsalo strict nature reserve in Kuhmo, eastern Finland (63°58′N, 30°22′E), was studied by means of charcoal particle layer records and macroscopic charcoal particles in peat and by pollen analysis. The data suggest that spruce forest sites in the area burned at a mean interval of a few centuries over a period of almost 6000 years prior to the beginning of slash-and-burn cultivation in the area. This low forest fire frequency can be attributed to the fragmented landscape pattern, which restricted the spread of fires ignited by lightning. Because a similar landscape pattern predominates over large areas of boreal Fennoscandia, it is possible that natural fire frequencies may also have been considerably lower than expected in these areas. It may well have been the case that, at least in spruce forests located in fragmented landscapes, small-scale disturbances were more important for the forest dynamics than fires.

Soil water-retention characteristics of Scots pine and Norway spruce forest sites in Finnish Lapland

Scots pine and Norway spruce forests, which differ from each other ecologically and economically, dominate in Finnish Lapland. The need to investigate the soil properties of these forests has increased due to the problems found in forest reforestation. The present paper examines soil water-retention characteristics (WRC), hydraulic conductivity ( K), texture and organic matter content (OMC) in 10 Scots pine ( Pinus sylvestris L.) and 10 Norway spruce ( Picea abies L. Karst.) dominated forest sites in Finnish Lapland (North Finland). In general, the studied soil properties were comparable to those reported earlier for till soils in Lapland and Fennoscandia. However, according to semivariogram analysis, the properties showed spatial dependence within sites that was most commonly below 60 m. Moreover, the properties differed significantly between the pine and spruce sites ( P<0.05). The most significant differences were in the water content (WC, vol.%) at −5 and −10 kPa matric potentials ( ψ) (i.e. near field capacity) and in the sum of the OMC and fine particle fraction (<0.06 mm). Compared with the spruce sites, the pine sites had thinner genetic soil horizons and lower OMC, less fine particles and a lower WRC. The air-filled porosity (AFP) and saturated K were higher on the pine sites. The most significant vertical differences in AFP and WRC between the pine and spruce soils were found at depths of 3 and 50 cm below the organic horizon. The proportion of pine (of basal area) in the tree stands showed a significant positive correlation with AFP at −5 and −10 kPa ψ. The mean WC content and AFP at −10 kPa ψ were <30 and >20 vol.%, respectively, at about 80% of the sampling points on the pine sites, while on the spruce sites the values of >30 and <20% occurred at a corresponding number of points. The results showed that pine and spruce sites in Lapland differ significantly in their soil physical properties. The sites where pine is naturally dominant tend to have a lower soil WC especially near field capacity (c. −10 kPa ψ) than spruce sites, which suggests that Scots pine requires drier soil for optimal growth and regeneration than Norway spruce.

The Enchytraeidae of spruce forest plots of different exposure and acid deposition in a German mountain range

Enchytraeidae were studied at spruce forest sites (Harz, Germany) differing in their exposure and soil acidity affected by acid deposition. Total density ranged between 38 000 and 59 000 ind. m –2 and biomass between 0.5 and 1 g m –2 d.m. (annual means). Of the seven species recorded, Cognettia sphagnetorum, Marionina clavata, and Achaeta camerani were dominant. The site affected most by acidification had the highest densities and lowest species number. Population dynamics and vertical distributions were affected by climate. Field and laboratory data provide evidence for sexual reproduction in C. sphagnetorum. Substrate preference experiments showed this species to prefer spruce litter from the O L-Horizon to that from the O H-Horizon, and spruce litter to beech litter.

Formation of Chloroform in Soil. A Year-round Study at a Danish Spruce Forest Site

Soil air from top soil of a Danish spruce forest was investigatedmonthly from December 1997 to December 1998 for the occurrence ofchloroform, 1,1,1-trichloroethane, tetrachloromethane, trichloroethene and tetrachloroethene. Within the monitoring period, three different patterns of soil air concentrations wereidentified. For chloroform, concentrations peaked in spring and autumn while 1,1,1-trichloroethane and tetrachloromethane peakedduring mid winter. Trichloroethene and tetrachloroethene, concentrations remained constant throughout the year. The relative ratios of soil air concentrations to ambient air concentrations indicated a natural production of chloroform, while the other chlorinated compounds investigated probably originated from non-point source pollution. The seasonal variation of the chloroform concentration suggested a productionby microorganisms, as high chloroform concentrations were found in the soil in warm and humid periods of the year (spring and autumn) with high microbial activity.

Organic halogens in spruce forest throughfall

Deposition of dissolved organic halogens by throughfall was determined in a small spruce forest site in Denmark (56°28'N, 8°24'E). The mean annual deposition of dissolved organic halogens was 377 g ha −1yr −1, and larger than the general deposition by precipitation. No relationship between the position of the collectors and the forest edge or dominating wind-direction was found, suggesting that dry deposition was not a major source. The concentration of organic halogens was related to that of organic carbon and decreased from the tree-trunk and outwards. In addition, the concentrations were higher during the growing season than during the dormant season. This indicates that the major part of the organic carbon and organic halogens in spruce forest throughfall originates from canopy leachates or other internal sources.

Impact of N-input by wet deposition on N-trace gas fluxes and CH 4-oxidation in spruce forest ecosystems of the temperate zone in Europe

In an effort to elucidate the impact of N-deposition from the atmosphere on trace gas fluxes (N 2O, NO, CH 4) from soils of temperate coniferous forests, two spruce forest sites in Germany and Ireland with comparable edaphic and climatic conditions, but with pronounced differences in the amounts of N-input from the atmosphere were compared at different seasons. At the site in Germany trace gas fluxes as well as wet deposition of NH + 4 and NO - 3 were recorded continuously over the entire year 1994. Correlation analysis between fluxes and N-input data were performed, in order to elucidate if a direct effect between flux and N-deposition could be demonstrated. At all sampling dates N 2O fluxes at the site receiving high atmospheric N-input (Höglwald, Germany) were significantly 1.5–5 fold higher than N 2O emission rates at the site receiving low N-input by wet deposition from the atmosphere (Ballyhooly, Ireland). In contrast to the Höglwald site, at which only emission of N 2O to the atmosphere was observed, at certain periods the Ballyhooly soil functioned as a sink for atmospheric N 2O. Methane oxidation rates were significantly lower at the Höglwald site compared to the Ballyhooly site. At the Höglwald site it could be demonstrated by correlation analysis that the input of NH + 4 and NO - 3 by wet deposition significantly altered emissions of N 2O and NO (stimulation) and of CH 4 oxidation (reduction). The coefficient of determination was better for NH + 4 than for NO - 3 for all trace gases studied and was best for the relation between NO emission rates and NH + 4-input.

Fluxes of NO and N2O from temperate forest soils: impact of forest type, N deposition and of liming on the NO and N2O emissions

Annual cycles of NO, NO2 and N2O emission rates from soil were determined with high temporal resolution at a spruce (control and limed plot) and beech forest site (“Hoglwald”) in Southern Germany (Bavaria) by use of fully automated measuring systems. The fully automated measuring system used for the determination of NO and NO2 flux rates is described in detail. In addition, NO, NO2 and N2O emission rates from soils of different pine forest ecosystems of Northeastern Germany (Brandenburg) were determined during 2 measuring campaigns in 1995. Mean monthly NO and N2O emission rates (July 1994–June 1995) of the untreated spruce plot at the Hoglwald site were in the range of 20–130 µg NO-N m-2 h-1 and 3.5–16.4 µg N2O-N m-2 h-1, respectively. Generally, NO emission exceeded N2O emission. Liming of a spruce plot resulted in a reduction of NO emission rates (monthly means: 15–140 µg NO-N m-2 h-1) by 25-30% as compared to the control spruce plot. On the other hand, liming of a spruce plot significantly enhanced over the entire observation period N2O emission rates (monthly means: 6.2–22.1 µg N2O-N m-2 h-1). Contrary to the spruce stand, mean monthly N2O emission rates from soil of the beech plot (range: 7.9–102 µg N2O-N m-2 h-1) were generally significantly higher than NO emission rates (range: 6.1–47.0 µg NO-N m-2 h-1). Results obtained from measuring campaigns in three different pine forest ecosystems revealed mean N2O emission rates between 6.0 and 53.0 µg N2O-N m-2 h-1 and mean NO emission rates between 2.6 and 31.1 µg NO-N m-2 h-1. The NO and N2O flux rates reported here for the different measuring sites are high compared to other reported fluxes from temperate forests. Ratios of NO/N2O emission rates were >> 1 for the spruce control and limed plot of the Hoglwald site and << 1 for the beech plot. The pine forest ecosystems showed ratios of NO/N2O emission rates of 0.9 ± 0.4. These results indicate a strong differentiating impact of tree species on the ratio of NO to N2O emitted from soil.

Describing anthropogenic impacts on stream water quality: the problem of integrating soil water chemistry variability

Problems encountered when (a) lumped soil water information is used to assess the relevance of cation exchange equations in the soil and (b) lumped mathematical models are used to describe the hydrochemical behaviour of catchments, are discussed. To highlight the difficulties and to focus the discussion, an example is provided using synthetic data. This data is generated using a mathematical model employing simple cation exchange reactions to describe water chemistry within the microporous regions of the soil. The proportion of the individual cations is assessed by varying the strong anion content within the micropore. These solutions are then mixed and the resultant chemistries are compared with the cation exchange formulations. It is taken that, on transfer from the micropore to the soil water sampler, the mixed solutions do not participate in cation exchange reactions: the chemical speciation programme ALCHEMI is used to characterise the chemical speciation changes occurring after mixing. The model is calibrated on the basis of average soil water data from two acidified spruce forest sites. The results show that by lumping the soil chemistry data, the averaged values for the chemical constituents systematically deviate away from the underlying theoretical cation exchange equations when differing cation charges are involved: no deviations occur when the charges are the same. The findings are extended to suggest that, for the chemically heterogeneous catchments being studied, the use of lumped mathematical models, which smooth out and ignore this variability, nullifies the theoretical equations on which the models are based. An appeal is made for (a) more detailed field studies to determine the degree of catchment inhomogeneity for soil properties and chemistry and (b) an assessment of the importance of catchment heterogeneity within a modelling framework.

Inferring cloud deposition to a forest canopy using a passive cloudwater collector

A widely used passive cloudwater collector was operated continuously along with an automated canopy water throughfall measurement system at a high elevation spruce forest site. Cloudwater collection rate (Rc) and throughfall (TF) rate were examined to determine their interrelationship. In addition, the use of the cloudwater collector for inferring cloud liquid water content was examined. The degree of direct hourly correlation was fairly good between Rc and canopy TF rate for non‐rain periods when the canopy was saturated (the former explained 58% of the variance in the latter). The correlation was even better (R² = 0.84) when TF rate was time‐lagged one hour. Estimated liquid water content, using collector data, was characterized by a large degree of uncertainty. This uncertainty appears to be caused, to a large extent, by the inability of the estimation method to account for the variation in cloudwater collection efficiency as a function of wind speed and droplet size.

Ethylene formation in some coniferous forest soils

SEthylene formation in different litter components and soil layers from a Scots pine forest (site 1) and a mixed Scots pine and Norway spruce forest (site 2) is reported. The effects of temperature. moisture, length of incubation and anaerobic incubation on C 2H 4 formation in humus are also reported. The highest concentrations of C 2H 4 that accumulated in 24 h under ambient conditions in the laboratory were 3 and 17 parts/10 6 in humus from sites 1 and 2 respectively and 153 parts/10 6 in pine-needle litter. The most frequent microfungi from site I were tested for C 2H 4 formation on different media. A Mucor silvaticus isolate was found to form C 2H 4in the presence of methionine. The origin and significance of the C 2H 4 formed is discussed.