Litter Thickness Research Articles

Effects of sawdust thickness on the growth performance, environmental condition, and welfare quality of yellow broilers

An experiment was conducted to evaluate the effect of litter thickness on growth performance, immune status, environmental condition, and welfare quality in yellow broilers. In total, 1,800 one-day-old Suqin yellow broilers were raised for 21 d. On d 22, 1,600 birds of similar BW (404 ± 12 g) were randomly selected and placed into 20 indoor pens (8 birds/m2, 10 m2/pen). These birds were assigned to a litter treatment of 4, 8, 12, and 16 cm. Each treatment was repeated in five pens. The results showed that a thicker litter was related to increased BW, daily weight gain, and daily feed intake (P < 0.001). Feed conversion ratio and mortality were unaffected by litter thickness (P = 0.320, P = 0.353, respectively). Absolute and relative liver weights showed a significant linear response to increasing litter thickness (P = 0.01, P = 0.001, respectively). The litter moisture content, air ammonia, and CO2 content decreased, whereas the air dust content increased with increasing litter thickness (P < 0.001, P = 0.017, P = 0.033, P < 0.001, respectively). Litter thickness had no effect on gait, plumage damage, hock burn or breast skin crusting (P = 0.076, P = 0.964, P = 0.131, P = 0.401, respectively). Plumage cleanliness, foot pad dermatitis, hock swelling and breast blister varied significantly with litter thickness (P = 0.027, P = 0.011, P = 0.014, P = 0.042, respectively). The results of this study suggest that an increasing litter thickness has a beneficial effect on the growth performance, environmental condition and welfare of birds.

Aménagement des logettes et confort des vaches laitières

Réalisant un bon compromis entre les besoins des animaux et ceux des éleveurs, la stabulation libre à logettes s’est imposée comme une des principales modalités d’hébergement des vaches laitières. Les recommandations relatives à sa mise en place et à sa gestion font cependant toujours l’objet de révisions. Une attention particulière est actuellement accordée à l’amélioration des conditions de confort de la vache. Le confort de la vache couchée peut être évalué par le temps passé en position couchée, la fréquence des changements de position et la facilité avec laquelle les vaches se couchent et se lèvent. Le confort de couchage est principalement lié à la souplesse du sol, aux dimensions des logettes et à la façon de les délimiter tant latéralement qu’à l’avant. Un sol suffisamment souple peut être assuré soit par des matelas multicouches, soit par des litières épaisses. Les matelas doivent être recouverts d’un matériau de litière absorbant l’humidité en surface et contribuant à garantir la propreté du sol et de la mamelle. Pour atteindre ces objectifs, la nature du matériau (paille, sciure, sable, chaux…) apparaît moins importante que la fréquence de renouvellement. Les logettes « creuses », dont le sol est recouvert d’une couche épaisse (± 20 cm) de litière, semblent globalement mieux appréciées par les vaches que celles équipées de matelas et leur utilisation est associée à une moindre fréquence de lésions au niveau des membres ainsi que de boiteries. Le sable apparaît comme un matériau de premier choix pour assurer le confort des animaux. Néanmoins, l’entretien des logettes creuses demande un surcroît de travail et la manutention de sable comme matériau de litière nécessite des équipements spécifiques. Les recommandations relatives aux dimensions des logettes entrent dans une fourchette de valeurs assez étendue car devant être adaptées au gabarit des animaux et intégrer la recherche de conditions optimisant la propreté du bâti. Les modèles de séparations latérales sont à évaluer quant à leur efficacité à contraindre l’animal à ne pas déborder sur les emplacements voisins tout en évitant qu’il ne se blesse ou ne soit gêné lors du lever et du coucher. Enfin, le dispositif limitant l’avancement dans la logette sera jugé sur son efficacité à dégager l’espace nécessaire pour permettre à l’animal de projeter sans contrainte la tête vers l’avant lors du relevé.

Factors of spatiotemporal variability of CO2 fluxes from soils of southern taiga spruce forests of Valdai

Factors determining the spatiotemporal variability of carbon dioxide emission from soil on various scales (from hours and days to seasons of the year and multiple years, and from microbiotopes to mesobiotopes) were identified using the results of a five-year study in the southern taiga spruce forest at Valdai highlands (Novgorod oblast). The air temperature close to the soil and that of the top layer of the soil, the humidity of the top layer of the soil, the precipitation during the preceding period, the litter thickness, the minimal distance to the trunks of dead standing and fallen spruce trees, and the coefficient of enhancement of microbial respiration were among the most significant factors. The soil temperature at a depth of 1 cm was the only variable of significance for both spatial and temporal distribution. The necessity of taking both spatial and temporal factors into account upon the prediction of the estimated value of CO2 emission by the soil has been demonstrated.

Modelling and analyzing the surface fire behaviour in Hyrcanian forest of Iran

The purpose of this study was to assess the forest fire behaviour and investigate the impact of different parameters on the spread of surface fire in the Hyrcanian forest of Iran. Surface fire was simulated using mathematical models in Microsoft Visual Basic 6.0 environment during a 30-minute time period. Several parameters that contributed to the speed of surface fire such as slope, wind velocity and litter thickness in the forest floor and various types of forest litter associated with hornbeam (Carpinus betulus L.), Persian ironwood (Parrotia persica C.A.M), beech (Fagus orientalis L.) and maple (Acer velutinum L.) were investigated. The results indicated that the maximum burned area was associated with beech litter. Forest surface fire demonstrated similar behaviour for the litter types of beech and Ironwood, whereas in the case of maple and hornbeam litters, the fire spread parallelly and perpendicularly to contour lines, respectively. The burned area increased in an irregular pattern as the forest floor slope gradient was increased. Moreover, the skewed pattern of the burned area for the forest floor composed of maple, beech, ironwood andhornbeam litter was described as high, low, moderate and low, respectively. The fire spread angle in forest floor associated with maple and beech litters changed with litter thickness. Finally, litter thickness had a significant effect on the direction of fire spread and this was more prominent with hornbeam litter. &amp;nbsp;

Effects of Historical Selective Logging on Anuran Communities in a Wet Evergreen Forest, South India

AbstractVast areas of tropical evergreen forests have been selectively logged in the past, and many areas continue to be logged. The impacts of such logging on amphibians are poorly understood. I examined the response of anuran communities to historical selective logging in a wet evergreen forest in south India. Anuran assemblages in unlogged forest were compared with assemblages in selectively logged forest. Forty 10 m × 10 m quadrats in forest, riparian zones, and streams of unlogged and selectively logged forests were searched at night for anurans. Species richness did not appear to be affected by logging. However, anuran density varied significantly and was 42 percent lower in selectively logged forests compared to unlogged forests. Anuran densities also varied significantly across microhabitats, with highest densities in streams of both selectively logged and unlogged forests. Patterns of niche overlap varied with selective logging as niche breadth either expanded, contracted, or remained neutral for different species. Ordination analysis explained 95 percent of the variation in species assemblage across selectively logged and unlogged forests. The assemblage in selectively logged forest was nested within unlogged forest. Among the habitat characteristics, litter thickness and water depth had the highest influence on the assemblage. This was followed by litter/water temperature, air temperature, and lastly relative humidity. It appears that species richness and composition of anurans in selectively logged forests is converging with unlogged forests, but the effects of historical logging seem to persist on anuran densities and their niche characteristics even ca 40 yr since logging ceased.

Does ant richness and composition respond to phytophysiognomical complexity and seasonality in xeric environments?

This study aims to analyze how the vegetation structure (physiognomy) and seasonal changes between seasons (wet and dry) influence richness, diversity and composition of ant species of arboreal and shrubby Caatinga environments. The vegetation structure was significantly different among the three strata for all parameters (mean diameter of vegetation, level of herbaceous cover, degree of coverage and thickness of litter and percentage of canopy cover). We collected 127 ant species. The mean number of species was approximately two times higher in the rainy season than in the dry season. There was no difference in species richness between the arboreal and shrubby Caatinga physiognomies nor interaction between season and physiognomy. Despite the similarity in richness, species composition differed between physiognomies, however we found no difference in composition between seasons. The seasonal differentiation may be mainly related to the variation in the overall numbers of individuals circulating in the environment, since the enhancement of resource availability during rainy season allows the colony to grow or expand foraging activities, which increases local diversity. Water restriction explains the limited diversity in both environments, while the occurrence of species with greater resource specificity may determine differences in ant composition. Differences in composition of each of Caatinga's physiognomy enhance beta diversity, therefore, raising the overall diversity in the Caatinga Domain.

Nurse plant effect of Solanum lycocarpum A. St.-Hil. in area of Brazilian Savanna undergoing a process of restoration

The use of nurse plants in ecological restoration aims to reactivate succession processes to improve environmental quality and biodiversity. This study targets Solanum lycocarpum as a nurse species to promote different plant species beneath its crown by microenvironmental changes in a disturbed area in Brazilian Savanna undergoing a process of restoration. The hypothesis is that S. lycocarpum modifies the microenvironment beneath its crown and influence in order to facilitate the density and richness of different plant species. Biotic parameter as density and species-rich biota, dispersal syndromes and habit were sampled. Additionally abiotic parameters were evaluated: litter thickness, light interception, penetration resistance, moisture, soil bulk density, saturated hydraulic conductivity of soil, nutrient content, acidity and soil structure. These parameters were evaluated in ten sampling units beneath S. lycocarpum, called the area of direct influence, ten around the nurse species crown, in the area of indirect influence and ten in open fields nearby without the influence of other trees, in the control area. For the biotic factors, density and species richness were higher beneath the crown of S. lycocarpum than in other treatments, mainly due to more litter accumulation, light interception, higher nutrient content (potassium, calcium and magnesium), more moisture and lower penetration resistance. Results showed the importance of S. lycocarpum as a nurse species in a Brazilian Savanna area, because of their role in local microenvironmental changes to facilitate other plant species and promote succession processes.

Factors influencing humus forms and forest litter properties in the mid-mountains under temperate climate of southwestern Poland

The conversion of spruce monocultures towards mixed and deciduous tree stands has been undertaken in central European countries, including south-western Poland. There is, however, still insufficient knowledge on the results of this transformation on the soil organic matter pools and humus forms. Thus, this study was focused on the relationship between altitude (a climatic factor), bedrock and soil type (trophic factors) and tree stand composition (a biotic factor steered by humans), and humus form, taking into account the forest litter and (mineral) humus horizon characteristics. The research was conducted as a part of environmental monitoring program in the Stolowe Mountains National Park (south-western Poland). Five aeromorphic humus forms (mull, moder–mull, moder, moder–mor, and mor) were noted in the soils of the Stolowe Mountains, and among them the mull, moder–mull and mor were distinctly correlated to specified sets of environmental factors. Litter thickness, SOC pools, and the concentrations of Pb and Cu increased with altitude and were higher on less fertile soils (Podzols developed from sandstone) under Norway spruce stands. Litter pH, in turn, decreased with altitude and was significantly higher on Eutric Cambisols and Luvisols under European beech stands. Among the compared environmental factors, bedrock geology was the least influencing factor, both on humus forms and forest litter characteristics, possibly due to the relatively small differences between the bedrocks (more or less acid regoliths, carbonate-free). Replacement of the Norway spruce by European beech will change the composition of forest litters and may transform the present-day moder and moder–mor humus forms into moder–mull and moder in those environments where spruce has previously been introduced in place of beech, against native soil trophic status. This transformation will restore natural ecological relationships in the forest ecosystems in south Poland and other Central European countries; however, it may reduce the topsoil organic carbon pools in the converted forest stands.

CO2 efflux from leaf litter focused on spatial and temporal heterogeneity of moisture

Leaf litter respiration (RLL) was directly measured in situ to evaluate relationships with the water content in leaf litter (WC), which is distributed heterogeneously under natural conditions. To do so, we developed a small, closed static chamber system using an infrared gas analyzer, which can measure instantaneous RLL. This study focuses on the measurement of CO2 effluxes from leaf litter using the chamber system in the field and examines the relationship between RLL and WC among seven broadleaf species in a temperate forest. The measurements focused on the position of leaves within the litter layer, finding that both RLL and WC were significantly higher in the lower layer. The value of RLL increased with increasing WC, and the response of RLL to WC was similar among all seven species. Moreover, the temporal variation in WC differed among three species and was associated with leaf litter thickness. The observed heterogeneity in WC induced by the physical environment (e.g., position and thickness of leaf litter) affects the variation in WC and, therefore, both RLL and the decomposition rates of organic matter in the litter layer.

Features of the moisture regime of a model sod-podzolic soil when mulching with spruce litter

During the dry growing seasons of 2011 and 2012, mulching of a sod-podzolic soil with coniferous litter maintained the moisture of the upper soil layer at high and fairly stable levels. By varying the spruce litter thickness, it is possible to maintain optimum conditions for acidophilic plants characterized by varying responses to the soil moisture content. In dry years (PER 0.5–0.8), the degree of influence of the mulch layer on the soil moisture content is closely related to the magnitude of the moisture deficit calculated for a warm season.

Species richness and meta-community structure of land snails along an altitudinal gradient on Bioko Island, Equatorial Guinea

We investigated the land-snail fauna of rain forests on the eastern slopes of Pico Biao on Bioko Island in the Gulf of Guinea. Thirty-seven plots were studied along an altitudinal transect reaching from sea level (lowland rain forest) to an altitude of 1,830 m (mossy forest). A total of 1,755 specimens were collected and were assigned to 68 land-snail species. Eleven species were new records for Bioko. At least 15 of the recorded species are endemic to Bioko. The degree of endemism was high in mossy forest (23%) and in lowland rain forest (20%), but lower in montane forest (8%). Species richness showed a hump-shaped distribution along the altitudinal gradient with a maximum at 500 m a.s.l. Species richness peaked in forests in which there had been selective logging more than 50 years ago, indicating that some disturbance may have beneficial effects on biodiversity. Species richness was correlated with the thickness of leaf litter. The availability and quality of suitable microhabitats is more important for the occurrence of snail species than gradients of otherwise often decisive environmental parameters like temperature, which are strongly correlated with altitude. A lack of clustering of the occurrences of different snail species along the altitudinal gradient indicated a Gleasonian meta-community structure with individualistic responses of the various species to environmental parameters. No negative co-occurrence patterns that might provide evidence for interspecific competition could be detected. The frequent coexistence of morphologically similar, and presumably ecologically equivalent, congeneric species may indicate that such equivalents do not exclude each other as predicted by the neutral theory of biodiversity. However, current knowledge about individual snail species is too scanty to exclude the possibility that niches of congeneric species differ in some details.

Canada bluejoint foliar δ15N and δ13C indicate changed soil N availability by litter removal and N fertilization in a 13-year-old boreal plantation

Canada bluejoint grass [Calamagrostis canadensis (Michx.) P. Beauv., hereafter referred to as bluejoint] outcompetes overstory tree species such as white spruce [Picea glauca (Moench) Voss] by creating a thick litter layer and competing for the available nitrogen (N). This study was conducted to investigate the effects of bluejoint litter layer (with or without litter removal) and N fertilization on soil water and N availabilities using principal component analysis (PCA) and foliar δ15N and δ13C of bluejoint in a plantation in north-central Alberta, Canada. PCA using soil properties and understory growth data demonstrated that N fertilization was more effective in changing the soil environment and resource availabilities for bluejoint growth than litter layer removal. The increase in soil N availability by N fertilization was linked with increased bluejoint foliar δ15N (by around 3‰) in fertilized plots, as a result of greater N isotopic fractionation in the fertilized plots. The more negative δ13C (by around 1‰) of bluejoint in litter layer-removed plots suggested that litter layer removal increased soil water availability, indicating that the litter layer reduced soil water availability on the site. Therefore, results from this and previous studies showed that the litter layer decreased both soil water and N availabilities. Although the exact mechanisms of the benefit of the litter layer for bluejoint remains unknown, bluejoint likely adversely impacted tree growth by competing for N due to its strong N acquisition ability under soil resource-limiting conditions.

Assessment of 80 years of ancient‐badlands restoration in Saldaña, Spain

ABSTRACTThis paper presents the history of badland generated in the Saldaña region, Spain; as well as the main responses eight decades after the start of restoration – in terms of vegetation, soil and erosive processes. The restoration consisted of intense reforestation and construction of more than 100 check dams and numerous wattle fences. Presently, the dense vegetation (87% cover) contrasts markedly with the degraded landscape from the early 20th century (5% cover). The thickness of litter and the natural presence of some species (Quercus pyrenaica, Paeonia broteroi and Lactarius deliciosus) clearly indicate the recovery of the site. The development of the forest cover shows that the intervention has the potential to recover almost 90% of the area. There is also evidence of soil regeneration, although some properties (erodibility, resistance to penetration and shear‐strength resistance) are not that different between the forested and degraded areas. In the restored zones, runoff is negligible, since a thick layer of moss covers the spillways of all the check dams. Erosion has almost been stopped by the effects of vegetation cover, litter and higher infiltration rates (infiltration rate in forested slopes is 43.4 times greater than in bare slopes). Sediment detachment, such as landslides, mudflows and piping, still occur, but are restricted to the degraded zones. Furthermore, even when sediments are mobilized from the upper degraded hillslopes during the larger storms events (2000–2010), check dams and the lower elevation restored forest‐buffers effectively work to reduce the sediment yield into the Carrión River by almost three orders of magnitude (&lt;102 mg L‐1), compared with data from the 1930s and 1940s (&gt;105 mg L‐1). Copyright © 2014 John Wiley &amp; Sons, Ltd.

Pattern of functional diversity along an altitudinal gradient in the Baihua Mountain Reserve of Beijing, China

Environmental gradients have been shown to be important to functional diversity of communities. The variation pattern of functional diversity of plant communities along an elevation gradient in the Baihua Mountain Reserve was tested. Sixty-one quadrats of 10 m × 20 m of plant communities were established along an altitudinal gradient and species composition, traits, and environmental variables were measured and recorded. Six functional diversity indices based on functional distances were used to calculate functional diversity. The results showed that functional diversity in communities varied greatly; functional diversity showed a “humped” pattern, with peak diversity appearing at middle elevation; functional diversity was significantly correlated with elevation, slope, aspect, litter thickness, and disturbance; functional diversity was significantly correlated with species diversity and evenness; environmental filtering was important to functional diversity pattern; the six indices were all successful in the analysis of functional diversity in plant community with different effectiveness and were significantly correlated with each other, and functional divergence, modified functional attribute diversity, and functional attribute diversity performed better than the other three indices in this study.

Diversity of Soil Arthropods in Teak Forest Plantation Forests at Cepu, Blora, Central Java

Insects are the main group of soil arthropod and the most dominant animals in the terrestrial ecosystems. The aims of this study were to get information about soil arthropod diversity in relation to environmental influence at teak plantations at Cepu, Central Java. The sampling plot design was based on forest health monitoring design method. Pitfall trap and Berlese-Tullgren funnel were employed to collect the soil arthropods. The trapped specimens were sorted in the laboratory and then identified up to family or genus. The result of the study revealed that young-age plantation has higher abundance and diversity of arthropod than old-age plantation. Totally we found 3 classes, 11 orders, 29 families, and 714 individuals from young teak plantation, and 3 classes, 11 orders, 25 families, and 397 individuals from the old one. The dominant class was insect and the dominant order of the insects was Hymenoptera. The thickness of the teak litter was the most important factor to the abundance of soil arthropods (R2 = 0.891).

Leaf decomposition and fine fuels in floodplain forests of the Rio Negro in the Brazilian Amazon

Abstract:Despite being inundated for up to 9 mo of the year, black-water floodplain forests in the Brazilian Amazon are susceptible to fire. Post-fire tree mortality is higher and fire spreads further in the floodplain, compared with adjacent upland forest. To understand these differences between the two forest types, we compared how leaf decomposition and fine-fuel loads change with inundation and soil texture. Litterbags containing leaves of Clitoria fairchildiana were placed on upland forest floor and submerged at two depths in a backwater of the Rio Negro. We used 80 bags per treatment and retrieved subsets every ~16 d from which the contents were cleaned, dried, weighed and discarded. Over the 81-d experiment, upland leaves decomposed two to three times faster than submerged leaves. Fine-fuel biomass (litter + root mat) was measured at 28 upland forest sites and 29 floodplain forest sites of the middle Rio Negro. Floodplain forests held about twice the fine fuel (25.9 ± 10.6 Mg ha−1) of uplands (10.9 ± 2.3 Mg ha−1). Upland soils had more sand but a carpet of fine apogeotropic tree roots was more common and thicker in floodplains. We infer that slow decomposition of submerged leaves leads to high tree mortality from fire in black-water floodplains by (1) increasing fire intensity due to high fine-litter fuel load and (2) making tree roots more vulnerable to burning because they form a peat-like mat to absorb nutrients from the thick litter.

Leaf litter depth as an important factor inhibiting seedling establishment of an exotic palm in tropical secondary forest patches

Intact tropical rainforests on continents and continental islands are considered to be relatively resistant to invasions by introduced plant species, but fragmentation and degradation may render them susceptible, especially to species from predominantly shade-tolerant families with centres of diversity in the tropics, such as palms. We investigated the seedling establishment patterns of the most common exotic palm species in Singapore’s secondary forest patches, the Macarthur palm (Ptychosperma macarthurii), in relation to landscape-level planting intensity, abiotic conditions, and recipient community composition. We first used conditional inference forests to narrow down the set of possible explanatory variables, followed by fitting generalised linear models with the forest patch and individual plots as random intercepts, to account for the nesting of plots within patches and overdispersion, respectively. The number of cultivated adults in the vicinity was not an important variable. Instead, leaf litter was the most important predictor of seedling density. Thick leaf litter in the disturbed and younger secondary forest matrix that surrounds old growth forest patches may therefore serve as a buffer against invasions, especially by small-seeded exotics. However, if adults of exotic species are allowed to establish unchecked, for example along forest trails that lead into the interior of the forested landscape, the seed rain may eventually reach old growth forest where leaf litter is typically thin. Further studies are required to determine if second-generation adults within invaded habitats contribute disproportionately more to propagule pressure than first-generation cultivated plants outside the invaded habitat.

Vegetation Patterns and Species Diversity Along Elevational and Disturbance Gradients in the Baihua Mountain Reserve, Beijing, China

Vegetation and species diversity patterns in conservation areas near big cities are poorly known. These are important recreational areas used also for educational purposes. Therefore, investigations of local diversity patterns are urgently needed. The Baihua Mountain Reserve is close to the city of Beijing and is the northern end of the Taihang mountain range in north China. Sixty-one 10 × 20 m quadrats of plant communities were established along gradients for elevation (750–2043 masl) and disturbance (mainly due to tourism and agriculture). Data on species composition and environmental variables were measured and recorded in each quadrat. Two-way indicator species analysis and canonical correspondence analysis (CCA) were used to analyze the relationships between vegetation and environmental variables, while species diversity indices were used to analyze the pattern of species diversity. Twelve plant communities were found, mostly secondary forests with some plantations. These communities are representative of the vegetation in the mountains west of Beijing. Each community had a different composition, structure, and environment. The variation of plant communities was significantly related to elevation and disturbance and related to litter thickness, slope, and aspect. The cumulative percentage variance of species–environment relationships for the first 4 CCA axes was 89.6%. Elevation and disturbance intensity were revealed as the factors that most influenced community distribution and species diversity. Species richness, heterogeneity, and evenness all showed a “humped” pattern along elevational and disturbance gradients—the highest species diversity appeared in the middle elevation and under medium disturbance intensity. Recommendations regarding management measures are made.

Effects of retention site on breakdown of organic matter in a mountain stream

Summary Organic matter inputs to streams can be retained in contrasting sites, from small leaf packs on top of cobbles to thick organic deposits trapped by wood jams. Differences in environmental conditions and in stability among sites can affect the biological communities, the quality of organic matter and its use by consumers. We measured the accumulation and composition of coarse organic matter and the breakdown of alder leaves on the surface of the streambed, inside gravel bars and in thick litter deposits trapped by log jams. We also monitored fungal sporulation rates and macroinvertebrate diversity and density in these retention sites. The amount of organic matter in these locations differed significantly among sites and ranged from 118 g m−2 in gravel to 11 562 g m−2 in jams. The biomass of shredders also differed significantly among retention sites, being highest in jams (1440 mg m−2) and lowest in gravel (86 mg m−2). Breakdown of alder leaves in fine-mesh bags did not differ among retention sites. In coarse-mesh bags, leaf breakdown rate was significantly lower in gravel bars than in surface sites or jams. Despite large differences in amount and quality of organic matter between surface sites and jams, alder leaves broke down at the same rate. Density of invertebrates in bags and fungal sporulation rates tended to be highest in surface sites and lowest in gravel bars. The contribution of microbes to breakdown was 67% in gravel, 52% in surface and only 28% in jams. Overall, the differences among sites in leaf breakdown were correlated with invertebrate density. Our results showed large differences in the amount and quality of organic matter accumulated, in biological communities and in the use of organic matter among retention sites of a single stream reach. This spatial variability should be taken into account in studies of ecosystem functioning related to organic matter.

Unravelling the influence of light, litter and understorey vegetation on Pinus pinea natural regeneration

Pinus pinea (L.) is one of the most valuable species used in the Tunisian reforestation programme, with about 21 000 ha of plantations. In the coming decades the oldest of these stands will begin their regeneration stage. However, little is known about the factors that control the natural regeneration of this species. It is reputed to be a strict shade-intolerant species and so needs light to regenerate satisfactorily. Regeneration can also be influenced by understorey vegetation and litter, both correlated with light availability. The aim of this study was to quantify the respective importance of these three factors in P. pinea regeneration. Live seedlings were counted in 90 plots (500 m 2 each) in three forests of P. pinea located in the coastal dunes in north Tunisia, and related to light availability, biomass of understorey vegetation and litter. In addition, the influence of litter was experimentally manipulated by creating 1 m 2 regenerating areas free of litter, with a light litter layer or the natural thickness. The density of 1-year-old pine seedlings was controlled mainly by litter biomass, whereas light availability increased the growth of older seedlings. Understorey vegetation did not appear to play a significant role in P. pinea regeneration in these Mediterranean climatic conditions. Management for natural regeneration of P. pinea should include scarification to reduce litter thickness and heavy thinning to significantly increase light availability.