Forest litter

Wildfires are an integral part of the Australian continent, and to estimate the rate of spread of wildfires using computational models, it is important to know the kinetic parameters of the materials that constitute the fuel load in forests. These kinetic parameters are utilised in pyrolysis and combustion sub-models of a computational model. In the present work, the kinetics of pyrolysis of timber and litter materials (consisting of bark, twig and leaf) from Pinus Radiata and Eucalyptus Obliqua sub. Messmate forests were estimated under nitrogen. The activation energy for the pyrolysis of timber was found to be independent of conversion, whereas it varied for the litter materials in the range of the pyrolysis temperatures employed. Furthermore, the parameters pertaining to a single equivalent reaction model were also identified. For the samples studied, the most suitable reaction model was identified as the Johnson-Mehl-Avarami model. The activation energy measurements reported here are consistent with measurements previously reported for other species within the Pinus and Eucalyptus genera.

The present study was an effort to understand the amount of litter fall and its subsequent decomposition and quantify the release of available nutrients and soil physic-ochemical characteristics in plantations of four forest tree species (Lagerstroemia parviflora, Tectona grandis, Shorea robusta and Michelia champaca) in the Chilapatta Reserve Forest of the Cooch Behar Wildlife Division in the Terai zone of West Bengal, India. The most litter (5.61 Mg ha-1) was produced by T. grandis plantation and the least (4.72 Mg ha-1) by L. parviflora. The material turnover rate to the soil through decomposition from total litter was fastest during the first quarter of the year and subsequently decreased during the next two quarters. The material turnover rate was only 1 year, which indicates that more than 90% of the total litter produced decomposed within a year. The available primary nutrient content in litter varied across the four plantations over the year. The plantations generally did not significantly influence the soil physical characteristics but did significantly influence the availability of primary nutrients and organic carbon at two depths (1–15 and 16–30 cm) over the year. The availability of soil primary nutrients in the four plantations also increased gradually from the first quarter of the year to the third quarter and then decreased during the last quarter to the same level as in the first quarter of the year at both depths. The availability for soil organic carbon in the plantations followed a similar trend. The amount of litter produced and the material turnover in the soil in the different plantations differed, influencing the nutrient availability and organic carbon at the plantations. The amount of soil organic carbon was highest for T. grandis (2.52 Mg ha-1) and lowest for L. parviflora (2.12 Mg ha-1). Litter is the source of soil organic matter, and more the litter that is produced by the plantations, the higher will be the content and amount of soil organic carbon in the plantation.

Decomposing litter accumulated on the soil surface in forests plays a major role in several ecosystem processes; its detailed characterization is therefore essential for thorough understanding of ecosystem functioning. In addition, litter is known to affect remote sensing radar data over forested areas and their proper processing requires accurate quantification of litter scattering properties. In the present study, ultrawideband (0.8–2.2 GHz) ground-penetrating radar (GPR) data were collected in situ for a wide range of litter types to investigate the potential of the technique to reconstruct litter horizons in undisturbed natural conditions. Radar data were processed resorting to full-wave inversion. Good agreement was generally found between estimated and measured litter layer thicknesses, with root-mean-square error values around 1 cm for recently fallen litter (OL layer) and around 2 cm for fragmented litter in partial decomposition (OF layer) and total litter (OL + OF). Nevertheless, significant correlations between estimated and measured thicknesses were found for total litter only. Inaccuracies in the reconstruction of the individual litter horizons were mainly attributed to weak dielectric contrasts amongst litter layers, with absolute differences in relative dielectric permittivity values often lower than 2 between humus horizons, and to uncertainties in the ground truth values. Radar signal inversions also provided reliable estimates of litter electromagnetic properties, with average relative dielectric permittivity values around 2.9 and 6.3 for OL and OF litters, respectively. These results are encouraging for the use of GPR for noninvasive characterization and mapping of forest litter. Perspectives for the application of the technique in biogeosciences are discussed.

The reactions and behaviours of the nematode fauna in an acid mull of a deciduous forest (State Forest of Orleans, France) have been monitored for four years in the course of an experimental deprivation and doubling of annual litter supplies as well as of a deprivation of litter and rain-leaching arrivals. The deprivation of litter rapidly entails, from the year following the withholding, a regression in the density of the populations, firstly at surface (0-3 cm) then at depth (-3-10 cm), as well as a modification in the intensity of the two seasonal activity peaks. In contrast to the other trophic groups, the density of the plant feeder nematodes increases during the two years after the litter withholding. Furthermore, a different behaviour in the animal activity at the surface and at depth occurs. As part of the two-fold litter supply, in addition to a decrease of the density of the nematode fauna, we have observed an enhancement of the dominance of fungal feeder nematodes compared to bacterial feeder nematodes, a particular trend of the level (-1-3 cm) that behaves, in the beginning of the experiment, as a surface level (0-1 cm) then evolves like a depth level (- 3-6 cm and - 6-10 cm), thus emphasizing the surface-depth imbalance in the vertical animal distribution. Also we have pointed out an increase of the density of Cephalobidae and Plectidae contrarily to the other bacterial feeder nematodes. The experiment of litter and rain-leaching arrival deprivation has allowed us to give some elements of comparison in situ on the nematode resistance to a deficient soil hydric regime but also on the aptitude and rapidity of some species to react when the environmental conditions become favourable again; then the ecological significance of the behaviour of the colonizing bacterial feeder species is discussed. Referring to a previous experiment of litter supply withholding and literature data (clear-cutting soil acidification, nematode behaviour in desert soils) the authors draw attention to the role of the litter and the underground vegetative system on the maintenance of the biological activity and on the organization of the nematode populations. Furthermore the role of these animals as potential indicators of the environmental conditions is emphasized.

Accurate characterization of forest litter is of high interest for land surface modeling and for interpreting remote sensing observations over forested areas. Due to the large spatial heterogeneity of forest litter, scattering from litter layers has to be considered when sensed using microwave techniques. Here, we apply a full-waveform radar model combined with a surface roughness model to ultrawideband ground-penetrating radar (GPR) data acquired above forest litter during controlled and in situ experiments. For both experiments, the proposed modeling approach successfully described the radar data, with improvements compared to a previous study in which roughness was not directly accounted for. Inversion of the GPR data also provided reliable estimates of the relative dielectric permittivity of the recently fallen litter (OL layer) and of the fragmented litter in partial decomposition (OF layer) with, respectively, averaged values of 1.35 and 3.8 for the controlled experiment and of 3.9 and 7.5 for the in situ experiment. These results show the promising potentialities of GPR for efficient and non-invasive characterization of forest organic layers.

Observed on a 5 x 5 cm small surface of litter in a 35-years-old Scots pine stand with bracken and the moss Pseudoscleropodium purum, the Fl layer is extensively invaded by a mycelial mat made of several mycorrhizal fungi. Observations under a light microscope gave circumstantial evidence of the role of these fungi in advanced stages of decomposition: they seem to protect the partly decayed plant material and the faeces deposited by soil animaIs from subsequent attack by soil bacteria. Penetration of pine needles and cadavers of soil arthropods is prominent in so far as animaIs have previously made entries by tunnelling into the substrates. In addition the black mycorrhizal fungus Cenococcum geophilum was observed to penetrate bracken epidermal cells by its own means and to make lysis zones in dead arthropod cuticles. Consequences for forest soil ecology and tree nutrition are discussed in view of existing literature.

The fauna inhabiting a small area (ca. 5 cm x 5 cm) were investigated in a Scots pine stand. After microstratification of the litter layers in the field and fixation in 95% ethyl alcohol, invertebrates, mainly mesofauna, were sorted under a dissecting microscope and mounted or dissected in order to study their intestinal guts. Faeces were mounted or sectioned to obtain information about the activity of other invertebrate groups not represented in the sample and to follow the fate of plant and microbial material after defaecation occurred. Plant material, mainly from moss, bracken, pine needles and bark, was extensively consumed by enchytraeid and lumbricid worms, sciarid larvae and phthiracarid mites. Fungal material was ingested by all groups, either in combination with plant material or alone (camisiid and oppiid mites, some species of Collembola, sciarid and chironomid larvae). Isotomid springtails and chironomid larvae appeared to consume faecal material. The choice and the degree of comminution and digestion of the material differed greatly from one group to another, but without any indication of resource sharing.

Litter and soil communities of Collembola (Insecta, Apterygota) in a mixed deciduous forest in France were studied for four years after experimental litter removal and doubling. Total abundance was unaffected by these two treatments but substantial changes in species composition occurred at the soil surface. Epigeic groups (Entomobryoidea, Symphypleona) almost disappeared in the no-litter treatment, except for the genus Sminthurides whose abundance increased after litter disappearance. Doubling of litter had no significant effect on the Collembola abundance. Relative influences of shifts in habitat structure and food resources are discussed, together with a comparison between macrofaunal and mesofaunal responses to litter manipulations.

Micro-scale changes in earthworm communities and ground cover types were studied along five transect lines in an unmanaged beech forest (Fontainebleau forest, France). Spatial patterns were interpreted in the light of interactions between earthworm species and forest architecture, ground vegetation and quantity as well as quality of litter. The anecic Lumbricus terrestris was associated with patches of the grass Melica uniflora, with poor litter cover, while most epigeic species were favoured by accumulation of litter in the absence of grass vegetation. The endogeic Aporrectodea caliginosa avoided, at least in summer time, 4-year-old gaps opened by wind storms. Under the shade of beeches, the evergreen spiny shrub Ruscus aculeatus, and in opened areas the giant herb, Phytolacca decandra, seemed repellent to most earthworm species.