Litter Loads Research Articles

Examining fuel treatment longevity through experimental and simulated surface fire behaviour: a maritime pine case study

The adequate prediction of fire behaviour characteristics for both scientific and management objectives is deeply impacted by the performance of fire behaviour models. Both the lack of experimentation and limitations in fire modelling constrain current understanding of fuel treatment effectiveness and longevity. The residual effect of a 10-year-old prescribed fire was quantified by both simulating fire behaviour and observing real-world fire behaviour in treated (T10) and untreated (U25) fuels in a 25-year-old maritime pine ( Pinus pinaster Aiton) stand in Portugal. Fire behaviour characteristics were measured in experimental surface fires (n = 36). Surface-fire behaviour was simulated using BehavePlus with custom fuel models for T10, U25, and U15 (the untreated fuel complex when the stand was 15 years old). The T10 fuel complex had significantly less decomposing litter load and shrub cover and load than the U25 fuel complex. The observed rate of fire spread did not differ between fuel complexes after accounting for the effects of other environmental variables, but flame length in T10 was 25% lower than that in U25. BehavePlus simulations contradicted the difference observed in flame length. Inconsistent and misleading assessments of fuel treatment effectiveness with detrimental impacts on the outcomes of fuel management may result from the generalized practice of solely using simulation in lieu of experimental fires.

Forest Fuel Inventory in 5 and 9-Year-Old Acacia Mangium Plantations

This study was conducted to determine the fuel components on forest floor of two different age stands and to estimate the fuel loading of the various fuel components. This study was carried out at Bukit Tarek Forest Reserve, Hulu Selangor, Selangor Darul Ehsan, at two stand age of Acacia mangium of 5 and 9-year-old. Fuel components of downed woody material and duff were sampled along transects lines. Shrubs, litter, herbaceous and small trees ( 1 of total fuel (downed woody material, litter and herbaceous), 1.73 cm of duff depth, 37,030 stem haG 1 of shrubs density and 2,175 tree haG 1 of small trees. The 9 year-old stand showed 17.42 Mg haG 1 of forest fuel, 3.03 cm of duff depth, 39,151 stem haG 1 shrubs density and 3,515 tree haG 1 of small trees. Downed woody material made up of 89 and 74% of the total fuel weight for 5 year and 9-year-old stands, respectively. Comparison between two different age stands, showed that 5 year old stand has higher quantity of downed woody materials than 9 year-old stand with 20.66 and 12.82 Mg haG 1 , respectively. Based on diameter class interval, the weight of downed woody material, diameter class of 0-7.6 cm were higher compared to diameter class of >7.6 cm. The fuel weight for 0-7.6 cm diameter class was 12.48 and 9.94 Mg haG 1 for 5 and 9-year-old stands, respectively. Statistical analysis showed that the loading of downed woody material on 5-year-old stand was significantly greater than the 9 year-old stand. However, litter loading was greater on the 9-year-old stand than the 5-year-old stand. The study concludes that in terms of fuel loading, 5-year-old stand has higher fire risk than 9-year-old stand. This is due to the silviculture activities in the 5-year old stand

Education campaigns to reduce stormwater pollution in commercial areas: Do they work?

A monitoring and evaluation program was undertaken, involving six different styles of evaluation to determine whether a low-cost, eight month education campaign that operated within a small commercial district was successful at changing people's behavior and reducing stormwater litter loads. This project also tested newly developed guidelines for monitoring and evaluating all types of non-structural stormwater quality best management practices (BMPs). The project evaluated: the extent and quality of the campaign's implementation; the degree to which it changed the awareness, attitudes, self-reported behavior and actual behavior of merchants and the public; and the nature of changes in stormwater litter loads. Overall, the education campaign produced mixed results, with the net result being modestly positive. Specifically, it was: unsuccessful at significantly influencing the knowledge or attitudes of merchants or the public; modestly successful at influencing the behavior of merchants and the public; and modestly successful at reducing litter loads in stormwater. At a theoretical level, the project highlights how using different ‘styles’ of BMP evaluation can help to build a more complete picture of a BMP's performance. At a practical level, the project helped to improve the monitoring and evaluation guidelines and produced evidence-based design guidelines for future campaigns that aim to reduce littering in commercial areas.

Characteristics of litter waste in highway storm runoff

Litter characterization is an integrated part of the Caltrans First Flush Characterization Study. These data will provide a basis to develop potential treatment technologies and best management practices to control pollutants in runoff from freeways. During monitoring periods in Southern California areas, the first flush phenomenon was evaluated and the impacts of various parameters such as rain intensity, drainage area, peak flow rate, and antecedent dry period on litter volume and loading rates were evaluated. First flush phenomenon was generally observed for litter concentrations, but was not apparent with litter mass loading rates. Total captured gross pollutants, defined as larger than 0.5 cm, was 90% vegetation with only 10% being litter. The normalized cumulative litter loadings were determined from 1.25 to 13.39 kg/ha for dry litter weight and 0.40 to 8.99 kg/ha for dry biodegradable litter weight. The portions of biodegradable litter to non-biodegradable litter were roughly the same across the entire event. Event mean concentrations were ranged 0.0021 to 0.259 g/L for wet gross pollutants, 0.0001 to 0.027 g/L for wet litters and 0.00007 to 0.018 g/L for dry litters. The mass emission rates should be useful to estimate total litter production for developing total maximum daily loads.

The effects of the decomposition of mangrove leaf litter on water quality, growth and survival of black tiger shrimp ( Penaeus monodon Fabricius, 1798)

An experiment was conducted for 8 weeks at the Cantho University, Vietnam, to determine the acceptable level of mangrove leaf litter load and its effect on water quality, growth and survival rate of tiger shrimp ( Penaeus monodon). Shrimps were cultured in plastic tanks containing 50 L of brackish water (salinity of 15‰). Leaf litter of Rhizophora apiculata, Avicennia officinalis, Excoecaria agallocha and Acacia auriculiformis were loaded to tanks at rates of 0.0 (control), 0.125, 0.25, 0.5, 1.0 and 2.0 g L − 1 with and without aeration. Tiger shrimp post-larvae (PL; 0.05 ± 0.01 g) obtained from the shrimp hatchery of Cantho University were stocked at a density of 20 PL per tank and fed with pelleted feed containing 38% protein at a rate of 10% body weight (BW) day − 1 . The high leaf-loading rates significantly reduced dissolved oxygen (DO) and survival rates of shrimp in the non-aerated treatments, and all shrimps died after 2 days in the treatments with loading rates above 0.5 g L − 1 . Leaf litter loads significantly increased tannin content, chemical oxygen demand (COD), H 2S and pH in the aerated treatments. Stepwise regression analysis showed COD, tannin and H 2S concentrations had negative effects on shrimp growth in the aerated treatments. Tannin concentration was found to be highest in the treatments with Excoecaria (32 mg L − 1 ) and Avicennia (24 mg L − 1 ) leaves. However, there were no significant differences in growth and survival rates of shrimp among the aerobic treatments loaded with different leaf types. The results of this study showed that moderate load of mangrove leaves could play an important role in promoting shrimp growth and survival in aerobic condition. Mangrove leaves at a loading rate of 1 g L − 1 positively influenced both the survival and growth rate of shrimps.

The measurement and reduction of urban litter entering stormwater drainage systems: Paper 2 - Strategies for reducing the litter in the stormwater drainage systems

A previous South African study looked at the removal of litter from the drainage systems once it was already there. Yet the litter problem cannot be addressed in an effective and sustainable manner without an effective integrated catchmentwide litter management strategy. This strategy should include planning controls, source controls, and structural controls. The main focus of this paper is the source control of urban litter. It reviews international and local practice, and reports on the results of a two-year monitoring programme conducted in nine pilot catchments covering a range of different land uses, socio-economic levels and population densities in the City of Cape Town. It proposes preliminary guidelines for the reduction of urban litter loads entering the drainage system by dealing with litter pollution at its source.

Season of burn and nutrient losses in a longleaf pine ecosystem

Fire regulates the structure and function of longleaf pine ecosystems, including potential nutrient controls on productivity, forest floor and groundcover nutrient pools, and nutrient availability. Little is known about comparative influences of seasonality of fire, litter types, and mass on N and P balance and soil processes in longleaf pine ecosystems. This study primarily addresses the hypothesis that nutrient volatilization during growing season burning, due to combustion of live biomass, exceeds losses from winter burning of standing dead plant litter. Summer and winter burns were conducted experimentally in different groundcover types with ambient, double-ambient and no litter loadings to contrast 2–3 years of litter accumulation with very low and high fuels. As a comparison, the seasonal burns were repeated with fuel and temperature measurements on sites that had actual fuel accumulations ranging from 1 to 3 years following the last fire. Peak fire temperatures and duration of burning were similar, but with high variation across groundcover types and seasons due to variation in fuel moisture content. The highest pine litter loadings produced maximum mineral soil/litter interface temperatures that never exceeded 700°C. Groundcovers without pine litter burned incompletely and with low temperatures. Biomass and N content were greater in summer groundcover than winter groundcover, and were greater in wiregrass than old-field groundcover. More N was lost from growing season burning as biomass had higher N in green foliage at that time. With ambient litter loadings, mass losses were 88–94% of total litter and groundcover. Percentages of N lost were comparable (80–90% across all groundcovers and seasons), but amounts of N lost were below that estimated to be replenished by legume N fixation and regional atmospheric deposition over a dormant season prescribed fire cycle. Net N balances with growing season fire were generally negative only if growing season burning was projected exclusively over the long-term. P content was not significantly different among groundcovers, but summer standing stocks were higher than winter. No P losses were detected with any experimental treatments and, following burning, all P was returned to soil pools, attributable to soil surface temperatures remaining largely below 700°C. We conclude that frequent, dormant season, or even variable season burning should not seriously deplete long-term nitrogen balance of longleaf pine ecosystems.

Mediterranean fuel models and potential fire behaviour in Greece

The Mediterranean vegetation types of Greece were classified into typical fuel models by measuring the following fuel parameters in 181 representative natural fuel complexes: 1-h, 10-h, 100-h and 1000-h fuel loads; foliage load; litter load and depth; total fuel load; average height and soil cover of the herbaceous, small shrub (up to 0.5 m) and tall shrub (0.5-3.0 m) vegetation layers. The data set was statistically analysed by a two-stage clustering procedure that produced seven distinct fuel models: two for evergreen-sclerophyllous shrublands (maquis), one for kermes oak shrublands, two for phrygana, one for grasslands and one for the litter layer of Mediterranean pine forests. The indicative range (upper and lower limit) of potential fire behavior for every fuel model was calculated with the BEHAVE fire behavior prediction system, using as inputs the specific fuel parameter values of every model. The shrubland fuel models resulted in fires with high intensity and rate of spread, while the phrygana and grassland models in fast fires of medium to low intensity. The litter layer of the pine forests provided the least severe burning conditions.

A study of the litter loadings in urban drainage systems - methodology and objectives

The recently completed report on "The removal of urban litter from stormwater conduits and streams" (by Armitage et al.) notes that little data is available on the nature and quantity of litter that finds its way into the stormwater drainage systems. The Council for Scientific and Industrial Research (CSIR) estimated in 1991 that 780,000 tonnes of waste a year was entering the drainage systems of South Africa, representing a potential removal cost in excess of two billion rand. There is thus a considerable need for finding ways to reduce litter loadings through better catchment management. Although suggestions have been made as to how this might be achieved, there is very little scientifically verified data from anywhere in the world to show that any of these proposed methods would be effective in South Africa. Only through an improved knowledge of the litter loadings in South African urban drainage systems can appropriate strategies to reduce litter loadings be arrived at. This improved knowledge is one of the twin objectives of the Water Research Commission Project No. K5/1051 entitled "The reduction of urban litter in drainage systems through integrated catchment management." Under this project a three-year monitoring programme has been instituted in nine catchments covering a range of different land uses, socio-economic levels and densities in the Cape Metropolitan Area. This paper focuses on the methodology behind the monitoring programme and the objectives it is hoped to achieve.

Reinvasion of a Riparian Forest Community by an Animal-dispersed Tree Weed Following Control Measures

Patterns of seed dispersal and the effects of mulching upon Celtis sinensis Pers. seedling establishment were investigated following the removal of this tree weed from a riparian forest community. At the commencement of the study there was virtually no representation of C. sinensis in the soil seed bank. However, subsequent rates of seed immigration were high since mature individuals of C. sinensis remained on the boundary of the site. Fruit bats (Pteropus spp.) were the principal dispersal vectors. Seed rain density of C. sinensis was best fitted by an inverse power distribution, with seed densities in excess of 20 m−2 detected at 70 m from the seed source. Extrapolation from this relationship suggested that a site would have to be more than 350 m from a seed source to reduce the C. sinensis seed rain to less than 1 m−2. More than 98% of the seed rain occurred below the canopies of the native tree species that remained following the removal of C. sinensis. For these trees, subarboreal C. sinensis seed distributions were not homogeneous, with peak seed densities occurring at different distances from tree trunks in each of the two years that seed distributions were assessed. Mulching with compacted sugar cane trash, corresponding to litter loadings of 6–12 kg m−2, was imposed early in the study, some weeks before the C. sinensis seed rain commenced. These treatments had no measurable effect upon C. sinensis germination, but substantially reduced seedling survival and had variable effects upon the early growth of seedlings. The potential roles of seed limitation vs establishment limitation are discussed in relation to the management of animal-dispersed invasive species. It is argued that an understanding of the likely levels and patterns of invasion is essential for the formulation of management strategies that can effectively reduce the invasion and impacts of these plants.

Microhabitat availability and seedling recruitment ofLobelia urens: a rare plant species at its geographical limit

AbstractIn Britain,Lobelia urens(L.) (the heath lobelia) occurs in rough grassland, is rare and only found in southern England, where it is at the northern limit of its range. Emergence and survival ofL. urenswas investigated at six locations in two geographically distinct sites experiencing spring, autumn or no grazing in two consecutive years. Four factors were evaluated qualitatively, as a means of characterizing microhabitats for germination and survival: all permutations of higher plant cover, bryophytes, plant litter and surface depressions. The potential effect of adjacent plants on recruitment was also assessed using the nearest neighbour distance (NND). Grazing created depressions, removed plant litter and increased the proportion of sites with higher plant cover. It also resulted in a more open sward with higher NNDs. None of these changes stimulated recruitment. Instead, small increases in the frequency of some rare or very rare microhabitat types were vital in making grazed rough grassland more suitable for emergence. Reduced litter loads and a greater quantity of moss were two key responses. Overall, survival ofL. urenswas less than 1% and was particularly favoured by moss and an increase in NNDs. Shading from higher plants, with or without plant litter, decreased emergence, but the precise role of litter was complex and most probably related to its quantity. In an experimental seed bed, only empty depressions favoured emergence. The microhabitat relationships ofL. urenswere unusually consistent among locations and consecutive years.L. urensrequires high soil surface temperatures but also adequate water for large scale recruitment, and such conditions are encouraged by grazing. The particular problems of experimental design and statistical analysis of data from recruitment experiments are also discussed.

Quantitative site and soil descriptors to improve the utility of forest soil surveys

Forested landscapes frequently have a higher degree of heterogeneity than agricultural landscapes at the site and hillslope scales. The terrain may have a high proportion of rock outcrop, standing trees, fallen logs, and various forms of biotic disturbance. Aspects of the soil and land surface are not well characterised in current description systems even though they influence landscape processes, productivity and management. Explicit methods for locating observations and describing components of the soil and land have been developed and tested in a forested granitic landscape in southeast NSW, Australia. Potential sampling patches were generated by computer prior to fieldwork using terrain analysis methods in a Geographic Information System. Areal density and height of rock outcrop was measured along two 10 m transects using a line intercept method. Estimation of area occupied by sub-surface boulders was made using a soil probe to a depth of 0.5 m at every metre along the transects. All of the rock fragments with an axis >0.05 m were excavated from the soil pit and three axes measured with a ruler. The dimensions of the soil pit were also recorded, allowing calculation of volumetric rock content in various size classes. Rock fragments 0.005–0.05 m were sieved and weighed from disturbed horizon samples to estimate mass percentage of different grades of rock fragment. The volume of dead wood per ha was estimated using a line intercept method, while the volume of live wood was estimated using basal area wedges. Surface cover and disturbance were estimated as percentages and types at metre intervals along the transects. Litter was collected, dried and weighed, and expressed on a mass per ha basis. The methods were developed and used in conjunction with conventional soil description methods (McDonald, R.C., Isbell, R.F., Speight, J.G., Walker, J., Hopkins, M.S., 1990. Australian Soil and Land Field Handbook, 2nd Edition. Inkata Press, Melbourne, 197 pp.), an expanded set of morphological descriptions (McKenzie, N.J., Jacquier, D.W., 1997. Aust. J. Soil Res. 35, 803–826), and laboratory measurements to provide quantitative estimates of soil and hydraulic properties across forested landscapes. Statistical models were developed to predict the distribution of individual attributes across the catchments with specified levels of confidence. Some properties (such as rock outcrop, percent clay in the B horizon) could be predicted with some reliability across the catchments, while others (such as litter loads, surface cover) could not. Many of the predictable attributes are directly useful to forest managers and also enable estimation of more complex properties (e.g. plant-exploitable soil volume or hydraulic properties). Selected results clearly demonstrate the utility of the additional site and soil descriptors presented in this paper.

Spatial Variation of Forest Floor Loading in Pine Stands of the Tsitsikamma

SYNOPSIS A lack of litter breakdown was recorded in Pinus taeda stands on the Tsitsikamma plateau, particularly in humus layers. A total litter mass of 195 t/ha was recorded in these stands. Litter was also significantly more compacted in these stands, and a lack of fungal occurrence was recorded. Accumulation of humus was also observed in Pinus elliottii and Pinus pinaster stands, but total litter loading there did not exceed 82 t/ha, In contrast, decomposition of Pinus radiata litter was adequate. Slash burning after clearfelling is recommended in these pine stands, except for P. radiata.

Leaf-litter accretion and decomposition in interior and coastal old-growth redwood stands

Litter fall and litter decomposition were measured in old-growth coastal redwood (Sequoiasempervirens (D. Don) Endl.) forests. Hillside and bottomland areas at inland and coastal locations were selected as representative sites. Both litter-bag and insitu mass-balance analyses were used to determine decomposition rates. Average annual litter fall at the four sites ranged from 3120 to 4690 kg•ha−1•year−1. Decomposition rate constants (k) calculated from the mass-balance analysis ranged from 0.117 to 0.238 year−1. Values of k estimated from the litter-bag analysis ranged from 0.273 to 0.405 year−1. Equilibrium litter loads from mass-balance analysis ranged from 15 700 to 30 000 kg•ha−1. Equilibrium litter loads estimated from litter-bag analysis ranged from 7760 to 14 500 kg•ha−1. Litter-layer equilibrium was between 12 and 26 years using the mass-balance analysis and between 7 and 11 years with the litter-bag study. The mass-balance method for calculating decomposition constants showed that litter at coastal sites decomposed faster than at inland sites. There were no differences between upland and bottomland sites. The litter-bag method, in contrast, indicated that litter at inland sites decomposed faster than at coastal sites. Significant regressions of litter decomposition constants as functions of summer average relative humidity, temperature, vapor-pressure deficit, and litter moisture were found with the mass-balance method. There were no significant regressions of temperature and moisture variables with litter decomposition constants calculated with the litter-bag analysis.

Litter Accumulation Problems Identified in P. Pinaster Stands of the Cape Province

SYNOPSIS Litter loading in first rotation P. pinaster stands on high quality sites can increase by more than 4 t/ha a year and early results indicate that this accumulation continues in second rotation stands. The accumulation of litter aggravates the fire hazards and increased problems with accessibility will make silvicultural treatments more expensive. Nutritional problems may also develop on marginal sites. Where these problems have been identified, serious consideration should be given to litter reduction by the use of controlled burning.

Mortality of lignotuberous seedlings of Eucalyptus species after an intense fire in montane forest

AbstractThe survival of lignotuberous seedlings of Eucalyptus pauciflora, E. dalrympleana and E. dives following an intense experimental fire was monitored in montane forest in the Brindabella Ranges, Australian Capital Territory. Percentage survival was the same for each species (60%), but it was shown that an individual was more likely to survive if it was large and growing vigorously before the fire. Survival was also enhanced if the individual was growing in a patch of low litter load and if it experienced a locally low fire intensity. Lignotuberous seedlings of E. dalrympleana, a species of the subgenus Symphyomyrtus, recovered more quickly than the other two species which are of the subgenus Monocalyptus. This result parallels conclusions concerning different initial growth rates between seedlings of the subgenera.