首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 191 毫秒
1.
We aimed to study tree effects on the chemical properties of forest soils. We compared soil features of three types of forest ecosystems, each with four stands (replicates): beech forests (Fagus sylvatica), oak forests (dominated by Quercus pyrenaica) and pine plantations (Pinus sylvestris). Five samples from the top 10 cm of soil were taken per stand, from which pH, organic matter content (O.M.), total nitrogen (N) and available calcium (Ca2+), magnesium (Mg2+), potassium (K+) and sodium (Na+) were determined. Litter layer depth was measured at each soil sampling point. We also measured tree density and crown diameters at each stand. Our results indicated that soil samples from the four pine plantation stands were more similar while oak and beech stands were characterised by great variability in terms of soil properties and leaf litter depth. Although the identity of the dominant tree species significantly influenced several topsoil chemical properties (increase in pH and available cations in oak forests and higher organic matter and total nitrogen in beech and pine ecosystems), there were other important factors affecting soil features that may be taken under consideration. Differences between soil properties of the three types of forest ecosystems were mainly related to the characteristics of the litter layer and less related to the tree layer structure. Finally, the establishment of pine plantations in naturally deciduous tree areas made the topsoil features more homogeneous.  相似文献   

2.
The influence of stand composition and age on forest floor chemical properties, nitrogen availability, and microbial activity was examined in mixed and pure stands of Douglas-fir (Pseudotsuga menziesii) and paper birch (Betula papyrifera). Decomposition of Douglas-fir and birch litter over two years as well as annual litter input was also measured. Mixed and pure stands of each species aged 10–25, 50–65 and >85 years old were selected in the Interior Cedar Hemlock (ICH) zone of southern interior British Columbia. Significantly more total N was mineralized in the forest floor of pure birch compare to that of pure Douglas-fir stands while forest floor of mixed species stands had intermediate N mineralization values. When sampling times were pooled forest floor N mineralization was lowest in the young stands compared to the older stands. Stand composition did not significantly affect litter decomposition were found in litter decomposition, microbial respiration and biomass. Stand age, however, did affect these parameters significantly. More birch litter mass was lost in young stands than in their older counterparts while the opposite trend was observed for fir litter. Generally, lower basal respiration, microbial biomass and Cmic/Corg was found in young compared to older stands. Concentrations and contents of forest floor total N and exchangeable K and Mg, and pH under pure birch were consistently higher compared to pure Douglas-fir. While forest floor total C, available P contents, exchangeable K and Mg concentrations were lowest in young stands, no differences were observed for total N and exchangeable Ca. All litter nutrient concentrations and contents were highest in pure birch stands. No clear trends could be discerned in litter nutrient concentration data among stand ages, although when converted to nutrient contents, there was a general increase with stand age. Both stand type and age had significant effects on forest floor properties and processes suggesting that stand age is another factor to evaluate when assessing the influence of forest composition on forest floor processes and chemistry. In terms of the effect of mixture, the data indicated that the maintenance of paper birch in mixed stands in these forest may have some effect on nutrient availability and status.  相似文献   

3.
Spiders (Araneae) and ground beetles (Coleoptera, Carabidae) were studied in a woodland of the Northwest German lowland. An ancient oak–beech stand (170 years old) growing on mineral soil as well as a 110-year-old Scots pine (Pinus sylvestris) and a 55-year-old spruce (Picea spp.) forest growing on peat were investigated by pitfall trapping. A total of 155 species (39 carabids, 116 spiders) and 16,887 individuals (5269 carabids, 11,618 spiders) was recorded. Beetle diversity was high in the oak–beech stand and the spruce forest, but significantly lower in the pine forest. In both conifer plantations the activity density of carabids was considerably lower. Spider diversity was significantly higher in the spruce forest when compared to the beech and pine stand, respectively. Analyses of assemblage similarity distinguished clearly the fauna of all three stands. For each forest type, indicator species were detected. Although both conifer plantations were planted on former bogs, spider species typical of bogs were present only in the pine stand, not in the spruce stand. In both animal taxa, species typical of deciduous forests were more numerous and abundant in the oak–beech stand when compared to the conifer plantations. Although they were in direct contact, the conifer stands on peat only to a very low extent serve as secondary habitats for the epigeic fauna of the autochthonous deciduous woodland. During the 1990s, various agricultural programmes in Central Europe promoted such conifer plantations – in contrast, such afforestation measures on extensively used or fallow land of former bogs are not supported by the results of this study.  相似文献   

4.
Effects of forest management and soil acidity on herb layer vegetation were studied after 10 years on 190 permanent plots in south Swedish beech (Fagus sylvatica) and oak (Quercus robur) forests. Species richness generally increased with management intensity, mainly due to establishment of ruderal species from the seed bank. Species richness of the typical forest flora was unaffected by management. Moderate management of oak stands favoured several species which are commonly found in semi-natural pastures. Classification and ordination of the data showed that the main floristic gradient within Swedish beech and oak forest vegetation is related to soil acidity. Species richness of the typical forest flora was strongly positively correlated with soil pH in beech forests, but this correlation was weaker in oak forests. The number of herbaceous plants with a broader habitat range increased with pH only in the oak forest plots. Long term changes in the forest environment, which may affect the vegetation, are the decline of grazing 150-50 years ago and soil acidification mainly caused by atmospheric pollutants during the last 50 years. In the one-decade perspective of this study, however, we did not find a general trend towards a more acid-tolerant flora. Neither could we find a general decrease of pasture species in currently ungrazed oak stands. The results indicate that most typical forest plants are well adapted to and partly depend on occurrence of canopy gaps and soil disturbance. If canopy thinning is followed by periods of canopy closure the characteristic shade tolerant flora of Swedish beech and oak forests may be able to persist as long as soil chemical limits of existence are not exceeded.  相似文献   

5.
Monitoring of soil nitrogen (N) cycling is useful to assess soil quality and to gauge the sustainability of management practices. We studied net N mineralization, nitrification, and soil N availability in the 0 10 cm and 11 30 cm soil horizons in east China during 2006 2007 using an in situ incubation method in four subtropical evergreen broad-leaved forest stands aged 18-, 36-, 48-, and 65-years. The proper- ties of surface soil and forest floor varied between stand age classes. C:N ratios of surface soil and forest floor decreased, whereas soil total N and total organic C, available P, and soil microbial biomass N increased with stand age. The mineral N pool was small for the young stand and large for the older stands. NO 3 - -N was less than 30% in all stands. Net rates of N mineralization and nitrification were higher in old stands than in younger stands, and higher in the 0 10 cm than in the 11 30 cm horizon. The differences were significant between old and young stands (p < 0.031) and between soil horizons (p < 0.005). Relative nitrification was somewhat low in all forest stands and declined with stand age. N trans- formation seemed to be controlled by soil moisture, soil microbial bio- mass N, and forest floor C:N ratio. Our results demonstrate that analyses of N cycling can provide insight into the effects of management distur- bances on forest ecosystems.  相似文献   

6.
The aim of this study was to develop statistical models for first order branchiness in young planted forest stands of pedunculate oak (Quercus robur L.) and European beech (Fagus sylvatica L.), and to give an ecological and silvicultural interpretation to these models. The reported models focus on the lower most-valuable stem part (i.e. until 6 m height), and cover different tree development classes to capture the development of branchiness over time. For each species 30 study plots were selected spread over two nearby forests in Flanders (northern Belgium), minimising site and genetic variability. Branches were counted on a total of 399 oak and 376 beech trees. On a subsample of 30 trees per species (one tree per plot), detailed non-destructive branch measurements were performed, yielding data for 555 oak and 438 beech branches. For both species, models for tree self-pruning (i.e. total branch number and dead branch portion), branch mortality and branch architecture (i.e. branch diameter and branch insertion angle) were built. A generalised linear mixed modelling approach was adopted. The models for total branch number and dead branch portion may be interpreted in terms of four processes contributing to self-pruning: (1) stand and tree development, (2) tree competitive status, (3) stand density and (4) site humidity. The reported models reveal similar self-pruning rates in oak and beech, but with different driving factors: early branch dying and slow shedding for oak and the other way around for beech. Mortality of individual branches is further determined by branch position and branch dimension. Branch diameter and branch insertion angle of both species are mainly related to branch cord length and relative branch position. All modelled effects are consistent with known ecological and ecophysiological processes. Silvicultural implications for stand establishment and early tree selection are discussed. The reported models can be used to fine-tune operational silvicultural choices for quality timber production. This is a first step towards the integration of branchiness models for oak and beech into forest growth simulators.  相似文献   

7.
How to quantify forest management intensity in Central European forests   总被引：1，自引：0，他引：1  
Existing approaches for the assessment of forest management intensity lack a widely accepted, purely quantitative measure for ranking a set of forest stands along a gradient of management intensity. We have developed a silvicultural management intensity indicator (SMI) which combines three main characteristics of a given stand: tree species, stand age and aboveground, living and dead wooden biomass. Data on these three factors are used as input to represent the risk of stand loss, which is a function of tree species and stand age, and stand density, which is a function of the silvicultural regime, stand age and tree species. Consequently, the indicator consists of a risk component (SMIr) and a density component (SMId). We used SMI to rank traditional management of the main Central European tree species: Norway spruce (Picea abies [Karst.] L.), European beech (Fagus sylvatica L.), Scots pine (Pinus sylvestris L.), and oak (Quercus robur L. and Quercus petraea L.). By analysing SMI over their whole rotation period, we found the following ranking of management intensity: oak<beech<pine?spruce. Additionally, we quantified the SMI of actual research plots of the German Biodiversity exploratories, which represent unmanaged and managed forest stands including conifer forests cultivated outside their natural range. SMI not only successfully separate managed from unmanaged forests, but also reflected the variability of forest management and stand properties across the entire sample and within the different management groups. We suggest using SMI to quantify silvicultual management intensity of stands differing in species composition, age, silvicultural system (even-aged vs. uneven-aged), thinning grade and stages of stand conversion from one stand type into another. Using SMI may facilitate the assessment of the impact of forest management intensity on biodiversity in temperate forests.  相似文献   

8.
We compared soil organic carbon (SOC) stocks and stability under two widely distributed tree species in the Mediterranean region: Scots pine (Pinus sylvestris L.) and Pyrenean oak (Quercus pyrenaica Willd.) at their ecotone. We hypothesised that soils under Scots pine store more SOC and that tree species composition controls the amount and biochemical composition of organic matter inputs, but does not influence physico-chemical stabilization of SOC. At three locations in Central Spain, we assessed SOC stocks in the forest floor and down to 50 cm in the mineral in pure and mixed stands of Pyrenean oak and Scots pine, as well as litterfall inputs over approximately 3 years at two sites. The relative SOC stability in the topsoil (0-10 cm) was determined through size-fractionation (53 μm) into mineral-associated and particulate organic matter and through KMnO4-reactive C and soil C:N ratio.Scots pine soils stored 95-140 Mg ha−1 of C (forest floor plus 50 cm mineral soil), roughly the double than Pyrenean oak soils (40-80 Mg ha−1 of C), with stocks closely correlated to litterfall rates. Differences were most pronounced in the forest floor and uppermost 10 cm of the mineral soil, but remained evident in the deeper layers. Biochemical indicators of soil organic matter suggested that biochemical recalcitrance of soil organic matter was higher under pine than under oak, contributing as well to a greater SOC storage under pine. Differences in SOC stocks between tree species were mainly due to the particulate organic matter (not associated to mineral particles). Forest conversion from Pyrenean oak to Scots pine may contribute to enhance soil C sequestration, but only in form of mineral-unprotected soil organic matter.  相似文献   

9.
Trees on sand dunes are more sensitive to environmental changes because sandy soils have extremely low water holding capacity and nutrient availability. We investigated the dynamics of soil respiration(Rs) for secondary natural Litsea forest and plantations of casuarina,pine, acacia and eucalyptus. Results show that significant diurnal variations of Rsoccurred in autumn for the eucalyptus species and in summer for the pine species, with higher mean soil respiration at night. However, significant seasonal variations of Rswere found in all five forest stands. Rschanged exponentially with soil temperatures at the 10-cm depth; the models explain 43.3–77.0% of Rs variations. Positive relationships between seasonal Rsand soil moisture varied with stands. The correlations were significant only in the secondary forest, and the eucalyptus and pine plantations. The temperature sensitivity parameter(Q10 value) of Rsranged from 1.64 in casuarina plantation to 2.32 the in secondary forest; annual Rswas highest in the secondary forest and lowest in the pine plantation. The results indicate that soil temperatures and moisture are the primary environmental controls of soil respiration and mainly act through a direct influence on roots and microbial activity. Differences in root biomass, quality of litter,and soil properties(pH, total N, available P, and exchangeable Mg) were also significant factors.  相似文献   

10.
Published data on the quantities of organic matter in the forest floor (SOMfl) of European forest stands were collated. Studies of SOMfl were included if the total sampled surface was at least 0.15 m2, the surface of a single sample was at least 100 cm2, live material was sorted out, and ash or carbon content was determined. Data from 59 forest stands were compared with regard to stand characteristics and environment. Using a single variable, tree genus was most important for the amount of SOMfl (R 2 adj = 0.34). The amounts in spruce stands (41 × 103 kg ha?1) were significantly higher than those in larch, Douglas fir, oak and birch stands (4–11 × 103 kg ha?1). The best significant multiple model was genus combined with stand age and basal area (R 2 adj. = 0.72). The importance of litter quantity and quality for differentiating the tree genera is discussed.  相似文献   

11.
Understanding the spatial and temporal variation in soil respiration within small geographic areas is essential to accurately assess the carbon budget on a global scale. In this study, we investigated the factors controlling soil respiration in an altitudinal gradient in a southern Mediterranean mixed pine–oak forest ecosystem in the north face of the Sierra de Guadarrama in Spain. Soil respiration was measured in five Pinus sylvestris L. plots over a period of 1 year by means of a closed dynamic system (LI-COR 6400). Soil temperature and water content were measured at the same time as soil respiration. Other soil physico-chemical and microbiological properties were measured during the study. Measured soil respiration ranged from 6.8 to 1.4 μmol m?2 s?1, showing the highest values at plots situated at higher elevation. Q 10 values ranged between 1.30 and 2.04, while R 10 values ranged between 2.0 and 3.6. The results indicate that the seasonal variation of soil respiration was mainly controlled by soil temperature and moisture. Among sites, soil carbon and nitrogen stocks regulate soil respiration in addition to soil temperature and moisture. Our results suggest that application of standard models to estimate soil respiration for small geographic areas may not be adequate unless other factors are considered in addition to soil temperature.  相似文献   

12.
The effect of forest conservation on the organic carbon (C) stock of temperate forest soils is hardly investigated. Coarse woody debris (CWD) represents an important C reservoir in unmanaged forests and potential source of C input to soils. Here, we compared aboveground CWD and soil C stocks at the stand level of three unmanaged and three adjacent managed forests in different geological and climatic regions of Bavaria, Germany. CWD accumulated over 40–100 years and yielded C stocks of 11 Mg C ha?1 in the unmanaged spruce forest and 23 and 30 Mg C ha?1 in the two unmanaged beech–oak forests. C stocks of the organic layer were smaller in the beech–oak forests (8 and 19 Mg C ha?1) and greater in the spruce forest (36 Mg C ha?1) than the C stock of CWD. Elevated aboveground CWD stocks did not coincide with greater C stocks in the organic layers and the mineral soils of the unmanaged forests. However, radiocarbon signatures of the O e and O a horizons differed among unmanaged and managed beech–oak forests. We attributed these differences to partly faster turnover of organic C, stimulated by greater CWD input in the unmanaged forest. Alternatively, the slower turnover of organic C in the managed forests resulted from lower litter quality following thinning or different tree species composition. Radiocarbon signatures of water-extractable dissolved organic carbon (DOC) from the top mineral soils point to CWD as potent DOC source. Our results suggest that 40–100 years of forest protection is too short to generate significant changes in C stocks and radiocarbon signatures of forest soils at the stand level.  相似文献   

13.
The mixture of beech (Fagus sylvatica L.) and oak (sessile oak, Quercus petraea (Matt.) Liebl., and pedunculate oak, Q. robur L.) is of considerable importance in Europe and will probably become even more important under climate change. Therefore, the performance of oak and beech in mixture was compared with the species’ growth in pure stands. Data from 37 long-term mixing experiments in Poland, Germany and Switzerland were pooled for analysis of mixing effects on stand productivity and possible interrelationships with mixing portions or site conditions. We found that on average, mixed stands of oak and beech exceeded biomass productivity in pure stands by 30 % or 1.7 t ha?1 year?1, as the growth of both species was benefitted by the mixture. However, that the interaction actually ranged from facilitation and overyielding on poor sites to underyielding on fertile sites triggered by competition. An empirically derived interaction model showed volume and dry mass growth changing in mixed stands from gains of 50 % to losses of 10 % depending on site conditions. It is concluded that the analysed mixture grows in accordance with the stress-gradient hypothesis and that our results suggest a site-specific relationship between species mixture and biomass productivity. As a consequence, an adequate species mix should result in increased productivity under steady state as well as climate change.  相似文献   

14.
Carbon and nitrogen stocks and their medium-term and readily decomposable fractions in topsoils were compared in relation to soil microbial biomass and activity along sequences from coniferous to deciduous stands. The study was carried out in the Ore Mountains and the Saxonian lowland, representing two typical natural regions in Saxony, Germany. In accordance with current forest conversion practices, the investigation sites represent different stands: mature conifer stands of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) (type A); Norway Scots spruce and pine with advanced plantings of European beech (Fagus sylvatica L.) or European beech/Common oak (Quercus petreae Liebl.) (type B); and mature deciduous stands of European beech and European beech/Common oak (type C). The investigated forest sites can be grouped into three silvicultural situations according to the development from coniferous stands to advanced plantings and finally mature deciduous forests (chronosequence A–B–C). The organic layer (L, F and H horizons) and uppermost mineral soil (0–10 cm) were analysed for potential C mineralisation, microbial biomass, concentrations of total C and N (TOC and TN) and for medium-term and readily decomposable C and N fractions, obtained by hot- and cold-water extraction respectively. The results showed an increase in organic layer thickness and mass as well as TOC and TN stocks along the forest sequences in the lowland. Yet, underplanted sites with two storeys revealed higher organic layer mass as well as TOC and TN stocks as compared to coniferous and deciduous stands. Stocks of hot- and cold-water-extractable C and N in relation to microbial biomass and its activity revealed a high turnover activity in deeper organic horizons of deciduous forests compared to coniferous stands. The stand-specific differentiation is discussed in relation to microbial biomass, litter quantity and quality and forest structure, but also with respect to the site-specific climatic factors and water budget as well as liming and fly-ash impacts. Results indicate higher dynamics in deciduous stands in the lowland especially during the initial turnover phase. The elevated microbial activity in deeper organic horizons of deciduous litter-influenced sites in spring is discussed as a specific indicator for long-term C sequestration potential as besides C mineralisation organic compounds are humified and thus, can be stored in the organic layer or in deeper soil horizons. Due to liming activities, stand-specific effects on organic matter turnover dynamics have evened out today in the Ore mountain region, but will presumably occur again once base saturation decreases. Here, the stand-specific effect on microbial biomass can currently be seen again as Cmic in the L horizon increased from spruce to beech. Our study sites in the lowland revealed no significant fly-ash impact. Differences between sites were evaluated by calculating the discriminance function. TOC and TN as well as medium-term degradable C and N were defined in this study as indicators for turnover dynamics along forest conversion sites.  相似文献   

15.
The simulation of forest production until 2100 under different environmental scenarios and current management practices was performed using a process-based model BIOME-BGC previously parameterized for the main Central-European tree species: spruce, pine, beech and oak and adapted to include forest management practices. Climatic scenario HadCM3 used in the simulations was taken from the IPCC database created within the 3rd Assessment Report. It was combined with a scenario of CO2 concentration development and a scenario of N deposition. The control scenario considered no changes of climatic characteristics, CO2 concentration and N deposition. Simulation experiment was performed for the test region - South Bohemia - using a 1 km × 1 km grid. The actual data on the regional forest cover were aggregated for each grid cell in such a way that each cell represented an even-aged single-dominant species stand or non-forested area, and a standard management scenario depending on the stand age and species was applied to each cell. The effect of environmental variables was estimated as the difference of simulated carbon pools and fluxes in 2050 under environmental changes and under control scenario.The model simulation for the period to 2050 with only climate change under constant CO2 concentration and N deposition indicated a small decrease of NPP (median values by species reached −0.9 to −1.7% for different species), NBP (−0.3 to −1.7%) and vegetation carbon (−0.3 to −0.7%), whereas soil C slightly increased. Separate increase of N deposition gave small positive effect on carbon pools (0.8-2.9% for wood C and about 0.5% for soil C) and more expressed effect on carbon fluxes (1.8-4.3% for NPP and 1.0-9.7% for NBP). Separate increase of CO2 concentration lead to 0.6-2.4% increase of wood C pool and 0.1-0.5% increase of soil C. The positive effects of CO2 concentration and N deposition were more pronounced for coniferous than for deciduous stands.Replacement of 0.5% of coniferous plantations every year by natural broadleaved stands evoked 10.5% of increase of wood carbon pool due to higher wood density of beech and oak compared to spruce and pine, but slightly decreased soil and litter carbon pools.  相似文献   

16.
It was hypothesized that soil respiration can be affected by canopy composition. Hence, admixture of trees as a common forest management practice may cause significant change in the carbon cycling. This study was conducted in a mixed spruce-beech stand at Solling forest in central Germany to investigate the effect of canopy composition on soil respiration. The canopy cover was classified in four major canopy classes (pure beech, pure spruce, mixed and gap), and the area under each canopy class was identified as a sub-plot. Soil respiration in each sub-plot (n=4) was measured monthly from Jun 2005 to July 2006. Results show significant difference in annual soil respiration between the beech (359 g·m−2·a−1 C) and gap (211 g·m−2·a−1 C) sub-plots. The estimation of the total below-ground carbon allocation (TBCA) based on a model given by Raich and Nadelhoffer revealed considerably higher root CO2 production in the beech sub-plot (231 g·m−2·a−1 C) compare to the gap sub-plot (51 g·m−2·a−1 C). The contribution of the root respiration to the total soil respiration was higher in the soil under the beech canopy (59%) compared with the soil in the gap (29%). The findings suggested that the condition under the beech canopy may cause more desirable micro-site for autotrophic respiration and consequently higher CO2 release into the atmosphere.  相似文献   

17.
Based on data acquired from the spatial information system Silva-SI, the majority of the entire forest area in Slovenia (22,220 forest compartments with a total area of 7446 km2, classified into eight forest categories) was analysed for changes in the distribution of European beech (Fagus sylvatica L.) in the period 1975–2005 using a binary logistic regression model in terms of selected site, stand and management variables. Additionally, changes in the abundance of beech in forest stands in which beech was present at the beginning and the end of the analysed period were analysed. Beech expanded its area by more than 1200 ha per year on average, i.e. the annual expansion rate amounted to 0.24%. Among the 18 studied variables, three site, four stand and no management variables were included in the binary logistic regression model of beech expansion. Beech expansion was more pronounced at lower altitudes, on sites with steep topography, and on sites with a higher proportion of beech in potential natural vegetation. The probability of beech expansion reduced by a factor of 0.54 when the distance to the nearest compartment with beech increased by 1 km. Among other stand variables, the proportion of early successional phases and the proportion of silver fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) Karst.) also influenced the expansion of beech. During the observed period the growing stock of beech almost doubled, its proportion in total growing stock increasing from 27% to 32%. Significant differences were found in changes of beech proportion in the total growing stock among different forest categories; a decrease in the beech proportion was registered in alpine coniferous forests and thermophilous deciduous forests, while in other forest categories the proportion of beech increased. The recent development of forest stands and their current structure indicate a further expansion of beech and an increase in the proportion of beech in forest stands.  相似文献   

18.
Klopatek JM 《Tree physiology》2002,22(2-3):197-204
Forest floor material and soil organic matter may act as both a source and a sink in global CO2 cycles. Thus, the ecosystem processes controlling these pools are central to understanding the transfers of carbon (C) between the atmosphere and terrestrial systems. To examine these ecosystem processes, the effect of stand age on temporal carbon source-sink relationships was examined in 20-year-old, 40-year-old and old-growth stands of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in the Cascade Mountains of south-central Washington State. Belowground C and nitrogen (N) storage and soil respiration were measured. In addition, nylon mesh bags containing homogenized soils from each site were buried at the respective sites to quantify root ingrowth and potential C sequestration and loss. The sites supporting the 20- and 40-year-old stands had soil C stores reflecting the C contributions from logging residue, coarse woody debris and stumps left after harvest. Because the N-fixer red alder (Alnus rubra Bong.) comprised 33% of the 40-year-old stand, this site had significantly greater concentrations and pools of N in the forest floor than sites without red alder. This N-rich site had consistently lower soil CO2 efflux rates during the growing season than the sites supporting the 20-year-old and old-growth stands. Estimated annual soil C efflux was 1367, 883 and 1194 g m-2 for the sites supporting the 20-, 40- and old-growth stands, respectively. These values are higher than previously reported values. Root ingrowth was significantly less in the 40-year-old stand than in the 20-year-old stand, and both young stands showed markedly less fine root growth than the old-growth stand. At the sites supporting the young stands, C and N were lost from the soil bags, whereas there was an increase in C and N in the soil bags at the site supporting the old-growth stand. The fine root growth and soil respiration data support the hypothesis that belowground C allocation decreases with increasing fertility. Quantification of the source-sink relationship of soil C at the three stands based on litterfall, relative root ingrowth and soil respiration measurements was compromised because of significant CO2 flux from decaying organic matter in the young stands.  相似文献   

19.
Different multiple linear regression models of maximum leaf area index (LAImax) based on stand characteristics, site quality, meteorological variables and their combinations were constructed and cross-validated for three economically important tree species in Flanders, Belgium: European beech (Fagus sylvatica L.), Pedunculate oak (Quercus robur L.) and Scots pine (Pinus sylvestris L.). The models were successfully tested on similar datasets of experimental sites across Europe. For each species, ten homogeneous and mature stands were selected, covering the species’ entire stand productivity range based on an a priori site index classification. LAImax was derived from measurements of leaf area index (LAI) made by means of hemispherical digital photography over the whole growing season (mid-April till end October 2008). Species-specific models of LAImax for beech and oak were mostly driven by management practice affecting stand characteristics and tree growth. Tree density and dominant height were main predictors for beech, while stand age and tree-ring growth were important in the oak models. Scots pine models were more affected by site quality and meteorological variables. The beech meteorological model showed very good agreement with LAI at several European sites. Scots pine’s stand model predicted well LAI across Europe. Since the species-specific models did not share common predictors, generic models of LAImax were developed for the 30 studied sites. Dominant height was found to be the best predictor in those generic models. As expected, they showed a lower predictive performance than species-specific ones.  相似文献   

20.
Soil hydrological properties like infiltration capacity and hydraulic conductivity have important consequences for hydrological properties of soils in river catchments and for flood risk prevention. They are dynamic properties due to varying land use management practices. The objective of this study was to characterize the variation of infiltration capacity, hydraulic conductivity and soil organoprofile development on forest sites with comparable geological substrate, soil type and climatic conditions, but different stand ages and tree species in terms of the effects of forest transformation upon soil hydrological properties. The Kahlenberg forest area (50 km northeast of Berlin in the German northeastern lowlands) under investigation contains stands of Scots pine (Pinus sylvestris) and European beech (Fagus sylvatica) of different age structures forming a transformation chronosequence from pure Scots pine stands towards pure European beech stands. The water infiltration capacity and hydraulic conductivity (K) of the investigated sandy-textured soils are low and very few macropores exist. Additionally these pores are marked by poor connectivity and therefore do not have any significant effect on water infiltration rate. Moreover, water infiltration in these soils is impeded by their hydrophobic properties. Along the experimental chronosequence of forest transformation, the thickness of the forest floor layer decreases due to enhanced decomposition and humification intensities. By contrast, the thickness of the humous topsoil increases. Presumably, changes in soil organic matter storage and quality caused by the management practice of forest transformation affect the persistence and degree of water repellency in the soil, which in turn influences the hydraulic properties of the experimental soils. The results indicate clearly that soils play a crucial role for water retention and therefore, in overland flow prevention. There is a need to have more awareness on the intimate link between the land use and soil properties and their possible effects on flooding.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号