Humus Profiles Research Articles

The heterogeneity of humus components in a virgin beech forest

A non-random sampling design allowed to distinguish within a virgin beech ecosystem two main components of humus profile heterogeneity. The stratification of the profile into horizons reflects changes in the composition of the soil/litter matrix occurring under the influence of the anisotropic deposition of leaf and wood litter and the stratified occurrence of soil organisms (roots, microbes, animals). The horizontal heterogeneity is mainly influenced by changes in vegetation, in particular the decreasing influence of beech (and the increasing influence of ground vegetation) when passing from the tree trunk base, where the influence of the tree reaches a maximum, to the centre of adjacent gaps where the influence of beech is replaced by that of another vegetation. The use of multivariate methods, used for description rather than for modelling, is suggested to be the best procedure for understanding patterns underlying heterogeneity without a priori assumptions.

Differential responses of freshwater wetland soils to sulphate pollution

Sulphate (SO4 2-)reduction rates are generally low in freshwater wetlands and are regulated by the scarce availability of the ion. Increased concentrations of this electron acceptor due to sulphur (S) pollution of groundwater and surface water may, however, lead to high SO4 2- reduction rates now regulated by the availability of appropriate electron donors. Due to variations in this availability,the response to S pollution (e.g. from surface water or groundwater) is expected to differ between soils. This hypothesis was tested inlaboratory mesocosm experiments by comparing two wetland soil types with distinctly different humus profiles: a Hydromoder and a Rhizomull type. In the first type, expected to have a higher availability of degradable soil organic matter (SOM), SO4 2-availability appeared to be rate limiting for SO4 2- reduction. In the Rhizomullsoils, in contrast, the electron acceptor did not limit SO4 2- reduction rates at higher concentrations. These differences in response could not, however, be attributed to differences in the various SOM fractions or in SOM densities. Eutrophication and free sulphide accumulation, two major biogeochemical problems caused by SO4 2- pollution, occurred in both types. The absolute extent of phosphorus mobilisation was determined by the concentration of this element in the soil (C/Pratio), while the level of sulphide accumulation was governed by the concentration of dissolved iron in the pore water. It was therefore concluded that neither the humus profile nor the concentrations of different SOM fractions in the soils are reliable indicators for the sensitivity of wetland types to S pollution.

Changes in the composition of humus profiles near the trunk base of an oak tree ( Quercus petraea (Mattus.) Liebl.)

Humus profiles were sampled under the crown of a mature oak tree in a coppice with standards (Senart forest, 30 km south of Paris). The sampling design compared the composition of humus profiles at three distances of the trunk base (40, 140 and 240 cm) and in the four cardinal directions. An increase in the development of the OF layer (strongly decayed litter and faeces of epigeic fauna) was observed at 40 cm from the trunk base, paralleling an increase in soil titratable acidity. Since no significant change in litter composition occurred with distance to the trunk base and in the absence of stemflow reaching the ground during showers, diffusion of bark tannins from buried parts of the trunk and main lateral roots were suspected to negatively influence soil biological activity, particularly earthworm activity.

Changes in the earthworm community of an acidophilous lowland beech forest during a stand rotation

The study examines humus profile development during a chronosequence consisting of four beech forest growth stages, and particularly the role of some components of soil fauna (lumbricid oligochaetes) on humus morphogenesis. An experimental site was set up in a lowland beech forest (Fougères state forest, eastern Brittany, France) to carry out a chronosequence analysis. This lowland beech forest is acidophilous, managed as an even-aged beech stand. The dominant tree species is beech ( Fagus sylvatica L.). Samples were taken twice a year, from autumn 1997 to spring 2000 inclusive. Earthworms were caught after watering with formalin solutions. Only five species were found: three epigeic (litter-dwellers): Dendrobaena octaedra, D. rubida tenuis, Eisenia eiseni; one epi-anecic (litter/soil-dweller): Lumbricus rubellus; one endogeic (soil-dweller): Allolobophora caliginosa. D. octaedra is dominant in the four plots at densities ranging from 41 ind·m –2 (88 % of total earthworm population) to 12.4 ind·m –2 (99 % of total). Species richness and abundance are low in accordance with a moder humus form typical of acid soil conditions. Results are discussed according to plot heterogeneity, stand age, seasonal variations and functional diversity.

The use of ground vegetation and humus type as indicators of soil nutrient regime for an ecological site classification of British forests

In many countries ground vegetation and humus type are used as indicators of forest soil quality, especially nutrient regime. This paper reports the development of such methods for use in British forests, within a new Ecological Site Classification combining climate, soil moisture regime and soil nutrient regime. To develop a field assessment method for soil nutrient regime, a study was made of soil chemistry, humus type and ground vegetation in British forests. Sites were selected in both mature plantations and semi-natural woodlands. Soil and humus profiles were described and the soil was sampled volumetrically for later chemical analysis. Vascular ground vegetation was recorded in quadrats by species cover fraction, and classified according to the existing British National Vegetation Classification. Soils were analyzed for a number of chemical variables. Vegetation data were treated by application of the species indicator values for soil reaction ( R) and soil nitrogen ( N), as proposed by Ellenberg [Vegetation Ecology of Central Europe, 4th Edition. Cambridge University Press, Cambridge]. Site mean indicator values mR and mN (weighted by species cover fraction) were then calculated. Multivariate statistical analysis techniques were applied to both the soil chemical and the vegetation sample data. Soil nutrient regime was shown to be a composite gradient of several soil chemical variables, of which the pH value and the availability of mineral (especially nitrate) nitrogen, and of calcium, were of particular importance. The species composition of the ground vegetation was related to position on this soil nutrient gradient. The vegetation: soil nutrient correlation using the site mean Ellenberg values was satisfactory ( r=0.89), but was improved by using indicator values generated from within the present data. The occurrence of the major humus types (mor, moder and mull) is broadly related to soil nutrient regime defined in this way. Both ground vegetation and humus type can therefore be used as soil nutrient indicators in British forests. A division of the soil nutrient gradient into five classes (Very Poor, Poor, Medium, Rich and Very Rich) is proposed. Future sampling work may lead to the definition of an additional class of soils with carbonate nutrient regimes. The Ecological Site Classification will provide forest managers in Great Britain with an improved basis for the selection of tree species for planting, and the adoption of silvicultural methods best suited to the site.

Effect of land use on forest floor and soil of aQuercus suber L. forest in Gallura (Sardinia, Italy)

In order to determine the effect of land use on forest floor and soil, two adjacent sites with different land use were investigated in Gallura (northern Sardinia, Italy). One site is a Quercus suber L. forest mainly used for cork production and the other is an open Quercus suber L. forest where livestock is put out to graze. In each site one soil profile was studied to characterize the mineral soil, and five humus profiles were opened along a vegetation transect, were studied to characterize the forest floor. Samples of L, F and H horizons of the forest floor and of the A mineral horizons were collected and analysed for each profile. In the site mainly used for cork production well-developed ectorganic (L, F and H) horizons are always present, with a total thickness ranging from 5·2 to 9·5 cm. Humus profile is of the Moder type, while mineral soils have an A–C profile, generally 50 cm deep. Organic matter content in the forest floor ranges from 1·76–3·72 kg m−2 and nutrients content in the mineral soil is high. In the site used chiefly for grazing the ectorganic horizons are very poorly developed, with a total thickness ranging from 1–3 cm, except for some islands under the Quercus suber L. canopy where the total thickness may reach 5·3 cm. Humus profile is of the Mull type, but the used classification system seems not appropriate when the tree density is below a critical limit. Mineral soils have an A–C profile 20–25 cm deep. The organic matter content in the forest floor ranges from 0·45 to 1·84 kg m−2, while nutrient content in the mineral soil maintains at high level, even higher than in the former case for C, N and Ca, probably in relation with higher supply of cattle excreta. Sheet erosion is evident in the site. It is concluded that cork production will maintain a sustainable forest floor development in cork–oak forest ecosystem, whereas cattle grazing, fires and ploughing in cork–oak forests may be considered to trigger off severe soil degradation processes. Copyright © 2000 John Wiley & Sons, Ltd.

Natural regeneration potential of the degraded Krkono?e forests

Self-regulating mechanisms and natural regeneration capacities still exist in the Krkonosˇe National Park, although the magnitude of these varies with altitude. A study of changes after forest decline and clear-cut with respect to the establishment of pioneer trees, changes in the herb layer, changes in humus profile characteristics and soil base status was conducted in the Krkonosˇe Mountains National Park in order to evaluate potentials for natural regeneration in forests affected by severe atmospheric deposition. Pioneer trees establish in both the upper and the lower supramontane zones. Even lowland species such as Fagus sylvatica appear to rejuvenate at high altitude, although in low numbers. Cover values of Betula pendula increase during clear-cut development, partly because they are avoided by deer; those of Sorbus aucuparia remain low due to browsing. In the upper supramontane zone changes in the herb layer are not significant: Calamagrostis villosa is dominant in (already declined) forests and remains so in clear-cut areas. In the lower supramontane zone Vaccinium myrtillus has its optimum in forests, while Deschampsia flexuosa strongly increases in clear-cut areas. Pioneer herbs establish after clear-cut. During clear-cut development, LF horizons decrease, due to a shift in input from low-decomposable spruce needles to easily decomposable grass (and later pioneer) litter. H horizons increase because of continuing decomposition and organic matter transfer from F to H horizons. At higher altitude, these processes occur at a lower rate. Pioneer trees have ameliorating effects on the soil via an increase in base elements and pH compared to spruce forests. There are only few indications that pioneer trees are severely hampered by dense grass carpets, which may occur in particular microhabitats escaping attention in the larger plot descriptions. High grass covers instead seem to have stimulating effects on seedling establishment via the improvement of the humus profile, which continues after pioneer trees grow up. Copyright © 2000 John Wiley & Sons, Ltd.

Humus profile degradation as influenced by decreasing earthworm activity

Humus profile degradation as influenced by decreasing earthworm activity

Earthworm distribution and humus forms in the development of a semi-natural alpine spruce forest

Abstract The relationship between earthworm population, soil humus and forest development were studied along a 200-m transect of an alpine Norway spruce ( Picea abies Karst.) forest in the Sixt-Fer-à-Cheval nature reserve near Samoëns in Haute-Savoie in the North Alps. Four developmental stages in the spruce forest were included in this transect ranging from early colonization by trees to degradation. Observations were made both at the scale of these developmental stages and at the scale of individual trees. Fifteen plots were sampled along the transect and the humus profile in each plot was described. Earthworms were collected by spraying formaldehyde onto 1-m 2 plots for three repetitions. Earthworm distribution was strongly correlated with the age of individual trees, but not with the developmental stages of the forest. The greatest density and biomass of earthworms were associated with mull and dysmull humus.

Interactions between earthworms, litter and trees in an old-growth beech forest

Forty plots were selected in an old-growth beech forest (Biological Reserve of La Tillaie, Fontainebleau State Forest, France), to embrace the whole range of site conditions and phases of vegetation dynamics. Soils are sandy, thus the nutrient status of the topsoil is very poor except when trees have access to an underlying limestone layer. The study was focused on the role of calcium in the sustainability of the beech ecosystem. Calcium is mostly redistributed through leaf litter accretion and the activity of litter-consuming organisms, but other sources are fallen wood and uprooted mounds. In each of the 40 plots, earthworm species were sampled, and measurements were taken in order to describe humus profiles, growth of adult trees, litter quantity and quality, and access to lime. Densities of soil-dwelling earthworms, calcium content of beech leaf litter, height of tallest trees and depth of the limestone layer were correlated, indicating a gradient of soil fertility which mainly results from long-term interactions between soil organisms and trees in varying geological conditions. Possible causal relationships and implications of calcium turnover for nature conservation were discussed in the light of existing knowledge.

The impact of grazing on spatial variability of humus profile properties in a grass-encroached Scots pine ecosystem

Grazing is often used in management of grass-encroached Scots pine ( Pinus sylvestris) forests in The Netherlands, because it is thought to increase diversity of vegetation and humus profiles. To test this hypothesis, two 1 ha plots in a primary pine stand on drift sand were grazed for 7 years at high and moderate intensities. The humus profiles of these two sites and of a control site were sampled at various scales to assess changes in grass biomass, thickness of ectorganic horizons, organic matter stocks, root stocks, and pH. Whether grazed or not, site factors such as slope angle and aspect, distance to trees and parent material did not explain the spatial variability of the plots. Spatial variability could be linked to the tussock structure of the grass layer. With continued grazing, ectorganic horizons became more compact (particularly the F horizon), stocks of organic matter increased, grass biomass decreased, variances tended to decrease and ranges tended to increase. These results suggest that at the landscape scale, where much variation in grazing intensity can be expected, spatial variability of humus profile properties and thus site diversity will increase. However, grazing intensities in the experiment were far greater than those normally employed in management of grass-encroached forests. Therefore grazing will scarcely affect site diversity, unless grazing variability is enhanced by special treatments, such as temporary fencing to create locally high grazing intensities.

Long-term effects of mineral amendments on soil fauna and humus in an acid beech forest floor

Mineral amendments (lime as CaCO3, N as ammonitrate and NPKCa) were applied in 1973 to the floor of some plots located in an acidic beech forest (Fougères state forest, eastern Brittany, France). Resulting modifications to humus structure and soil fauna composition were observed 22 years after amendment by comparison with control plots without amendment. Abundance and diversity of pedofauna (micro-, meso- and macrofauna) were estimated by Berlese funnel and formaldehyde methods. Micromorphological description of humus profiles and comparative quantification of their structure were achieved by digital image analysis. Humus structure in limed and NPKCa-treated plots had evolved from moder to mull-moder, whereas in N-treated plots it was unchanged and similar to the moder-type humus of control plots. Modifications in soil fauna were also observed, especially an increase in the lumbricid population. The observed changes in abundance and diversity differed between edaphic groups. Some effects of liming, like increase in numbers, were still present in NPKCa or limed plots, for example in pseudoscorpions (long-term effects). Lumbricid numbers (epigeic species) increased and remained higher in limed and NPKCa-treated plots than in N and control plots. Conversely, nitrogenous amendment did not induce similar changes, probably because of its soil acidifying effect. Nitrogenous amendment decreased numbers of oribatid mites and Collembola. These numbers are not different for limed and NPKCa plots in comparison with control ones.

Dynamics of temperate rainforest from fine resolution pollen analysis, Upper Ringarooma River, northeastern Tasmania

Abstract The relationship between sclerophyll forest and temperate rainforest in Tasmania is believed to be driven by climate, soils and fire regime; however, this has been tested infrequently on time frames relevant to the longevity of the major forest trees involved. This study uses sediments in four small hollows from within a rainforest stand in the Upper Ringarooma valley in northeastern Tasmania, Australia, to analyse vegetation dynamics and disturbance over the last 1000 years. Pollen‐vegetation relationships were investigated by comparing pollen rain and current vegetation, and the chronology was established by radiocarbon and lead‐210 dates. The lead‐210 data indicate that the two Sphagnum humus profiles were not always closed systems for inorganic inwash; however, the pollen and charcoal records are generally consistent indicating that a mixed Eucalyptus‐Nothofagus forest shifted to a Kothofagus dominated rainforest as fire became a less prominent component of the environment. About 400 years ago Leptospermum lanigerum invaded the community as canopy gaps developed, possibly as the older Nothofagus Cunninghamii trees died. There is no strong evidence of invasion by Atherosperma moschatum as suggested by some models of forest dynamics in these forests in Tasmania. In this stand of forest, fire and erosion following flooding have been the major causes of disturbance.

Lumbricus terrestris L. distribution within an experimental humus mosaic in a mountain spruce forest

An experiment was designed at a mountain site to study the distribution of adult Lumbricus terrestris in relation to a small-scale mosaic of humus forms representative of different stages of a spruce forest ecosystem. Good agreement was found between distribution in the mosaic and that in the field. ANOVA tests demonstrated the strong influence of humus form on earthworm abundance when comparing a vermimull (high earthworm burrowing activity) taken from a spruce regeneration site (61.8 individuals m–2) with a leptomoder (no earthworm burrowing activity) taken from a 60-year-old spruce stand (6.2 individuals m–2). Other humus forms were intermediate (mean density 34.6 individuals m–2). The same pattern was found with individual biomass, but with lower significance. Main differences observed in the experimental design were attributed to the immediate carrying density of the humus forms. A distinction was made between humus profiles built up with or without spruce cover. In the latter case (regeneration site and bilberry heath), the immediate carrying capacity indicated by the experimental approach overestimated the field density by a factor of 4. Under spruce this overestimate was even higher (approximately 10 times too high in an adult spruce stand (160 years old) and 30 times too high under moss cover). The increase in density due to experimental conditions was not determined for leptomoder humus accumulated under the actively growing spruce stand (60 years old) since the earthworm density was near zero in both cases. Relationships between humus form and earthworm populations are discussed.

Diversity and dynamics of eco-units in the biological reserves of the Fontainebleau Forest (France): Contribution of soil biology to a functional approach

Beech integral biological reserves of the Fontainebleau forest (France) display varied site conditions due to geomorphological heterogeneity and to interactions between biological components of the ecosystem. Taking examples in shifts observed in plant communities following gap opening, the authors show that, as Oldeman viewed it, tree-fall gaps seem to be the driving force in sylvigenesis as well as a source of spatial biodiversity. Studies carried out on macromorphological features of humus profiles and on the behaviour of soil invertebrate communities (Lumbricidae and Nematoda) pointed out two key aspects of forest functioning. First, the renewal of the forest ecosystem is linked to the dynamics of humus forms and of soil animal functional groups, featuring the regeneration of trees. Second, tree-fall gaps are places where the forest ecosystem is destabilized and thereafter may renew itself or on the contrary may evolve towards another ecosystem, showing either a co-adaptation between the sylvigenetic and the edaphic cycle, or a discordance between these two cycles. These two aspects (co-adaptation and discordance), important from the point of view of fundamental ecology and forest management, suggest a need for further field research.

Characterisation of a humus profile under beech forest by using wet‐chemistry and CPMAS 13C NMR‐spectroscopy in consideration of spatial heterogeneity

AbstractThree of ten macromorphologically similar humus profiles of a Dystric Cambisol under a beech forest were randomly chosen and the litter and humus layers were characterized by wet‐chemistry and CPMAS 13C NMR‐spectroscopy. The spatial heterogeneity of the litter and humus layers was high for the bulk density and for the sugar and starch fraction; lowest coefficients of variation were obtained for the chemical shift range of O‐Alkyl‐C. The spatial heterogeneity of the layers did not differ by means of all chemical methods. Changes in the chemical composition at the beginning of humification were high from the fresh fallen litter (Ln‐layer) to the morphologically only slightly altered litter in the L‐layer, whereas the changes in the litter and humus layers from the L to the Ohf‐layer were minor. However, the organic matter of the first mineral horizon was characterized by a decrease in lignin and cellulose. With wet‐chemistry and 13C NMR‐spectroscopy similar results were obtained for polysaccharides whereas results which can be attributed to changes in lignin deduced by the methoxyl content differed from each other.

A micromorphological study on the development of humus profiles in heavy metal polluted and non-polluted forest soils under Scots pine

To evaluate the influence of heavy metal pollution on the long term decomposition process of soil organic matter, the development of two humus profiles in the vicinity of a zinc smelter were compared to two reference humus profiles. Humus profiles reflect the relationships between vegetation type, biological activity and environmental conditions. All sites were located in Scots pine ( Pinus sylvestris) forest stands on nutrient poor driftsand deposits in the southeastern part of the Netherlands. The results of the chemical analysis showed that the concentrations of Cd, Zn and Pb in the polluted humus profiles were up to ten times that of the heavy metal concentrations in the non-polluted humus profiles. The development of the humus profiles was studied by micromorphological observations in thin sections and by field observations. All four humus profiles were characterized by an accumulation of soil organic matter on the mineral soil surface. These organic surface layers showed a similar development of distinct horizons, which represented proceeding stages in the decay continuum of soil organic matter. The increased decomposition of soil organic matter with depth in the humus profiles was supported by a relatively decrease of the amount of organic components and a simultaneous increase of excrements in thin sections. Micromorphological study of the excrements revealed that the decomposition of soil organic matter was mainly carried out by two groups of soil fauna: soil arthropods and macrofauna. The excrements of macrofauna were absent in the thin sections of the polluted humus profiles, probably as a result of pollution stress. The different types of soil fauna, however did not result in the development of different humus profiles. It is concluded that the decomposition of soil organic matter was not influenced by elevated heavy metal concentrations in the humus profiles studied, but was mainly determined by the chemical quality of Scots pine litter and the age of the forest stands.

Earthworm feeding activity and development of the humus profile

Earthworm casts and digestive tract contents were simultaneously examined, using the same methods, in a recently formed humus profile in a mountain spruce forest. Earthworm species had distinct diets and an earthworm foodweb could be distinguished. Lumbricus terrestris and Aporrectodea icterica were distinct from the other species examined: the former to some extent as a litter consumer, and both species because they excavated mineral material which was deposited within new top layers of the mull humus. Aporrectodea nocturna and Aporrectodea caliginosa both had a non-specific soil feeding mode. Most of the species enriched the humus profile with amorphous organic matter finely incorporated within a mineral matrix. Besides different food selection, a network of burrows was produced as a consequence of the different burrowing behaviour of each earthworm species.

Effects of minerals on the transformation of organic matter during simulated fire-induced pyrolysis

The effect of Fe(OH) 3, Al(OH) 3, birnessite, montmorillonite, and sea sand on changes in the composition of organic matter during heating was investigated. CO 2 was released in all treatments, although the experiments were conducted in the absence of oxygen. In the presence of Fe(OH) 3, Al(OH) 3, and birnessite, more CO 2 was evolved than in the other treatments. Birnessite and Fe(OH) 3 enhance the thermal decomposition of polysaccharides and lignin more than Al(OH) 3. Changes in the lignin signature resembled the alterations during aerobic litter decomposition and humification in humus profiles. DRIFT spectra indicate that the formation of aromatic compounds was favoured, especially in the presence of birnessite.

Soil organic matter composition in three humus profiles of the western Taurus, Turkey, as revealed by wet chemistry and CP/MAS 13C NMR spectroscopy

AbstractIn this study three soil profiles located in the Western Taurus (Turkey) at different altitudes (10, 1900, and 3080 m a.s.l.) were compared with respect to their soil organic matter characteristics. The soil samples were fractionated by density to plant residues, slightly altered plant material, organo‐mineral complexes, and organic‐free minerals. Bulk samples and fractions were analyzed for C and N, the bulk samples additionally for total sugars, lignin signature, and bulk soil organic matter composition by CP/MAS 13C NMR spectroscopy.The first step of litter decomposition and humification is a very strong degradation of polysaccharides without the loss of O‐alkyl structures. This process is slowing down very fast and the polysaccharides are stabilized. Lignin is decomposed as fast or even faster than polysaccharides. The data obtained by wet‐chemical analysis and by NMR spectroscopy are not or only weakly correlated to each other. This leads to the conclusion that the two types of methods give complementary rather than equivalent information. For the study of soil organic matter it is important to combine different methods and to draw the advantages of either type.