Plant litter
Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead
Characteristics and variability
Litterfall is characterized as fresh, undecomposed, and easily recognizable (by species and type) plant debris. This can be anything from leaves, cones, needles, twigs, bark, seeds/nuts, logs, or reproductive organs (e.g. the stamen of flowering plants). Items larger than 2 cm diameter are referred to as coarse litter, while anything smaller is referred to as fine litter or litter. The type of litterfall is most directly affected by ecosystem type. For example, leaf tissues account for about 70 percent of litterfall in forests, but woody litter tends to increase with forest age.[2] In grasslands, there is very little aboveground perennial tissue so the annual litterfall is very low and quite nearly equal to the net primary production.[3]
In soil science, soil litter is classified in three layers, which form on the surface of the O Horizon. These are the L, F, and H layers:[4]
- L – organic horizon characterized by relatively undecomposed plant material (described above).
- F – organic horizon found beneath L characterized by accumulation of partly decomposed organic matter.
- H – organic horizon below F characterized by accumulation of fully decomposed organic matter mostly indiscernible
The litter layer is quite variable in its thickness, decomposition rate and nutrient content and is affected in part by seasonality, plant species, climate, soil fertility, elevation, and latitude.[1] The most extreme variability of litterfall is seen as a function of seasonality; each individual species of plant has seasonal losses of certain parts of its body, which can be determined by the collection and classification of plant litterfall throughout the year, and in turn affects the thickness of the litter layer. In tropical environments, the largest amount of debris falls in the latter part of dry seasons and early during wet season.[5] As a result of this variability due to seasons, the decomposition rate for any given area will also be variable.
Latitude also has a strong effect on litterfall rates and thickness. Specifically, litterfall declines with increasing latitude. In tropical rainforests, there is a thin litter layer due to the rapid decomposition, Net primary production works inversely to this trend, suggesting that the accumulation of organic matter is mainly a result of decomposition rate.
Surface detritus facilitates the capture and infiltration of rainwater into lower soil layers. The surface detritus also protects soil from excess drying and warming.[8] Soil litter protects soil aggregates from raindrop impact, preventing the release of clay and silt particles from plugging soil pores.[9] Releasing clay and silt particles reduces the capacity for soil to absorb water and increases cross surface flow, accelerating soil erosion. In addition soil litter reduces wind erosion by preventing soil from losing moisture and providing cover preventing soil transportation.
Organic matter accumulation also helps protect soils from wildfire damage. Soil litter can be completely removed depending on intensity and severity of wildfires and season.[10] Regions with high frequency wildfires have reduced vegetation density and reduced soil litter accumulation. Climate also influences the depth of plant litter. Typically humid tropical and sub-tropical climates have reduced organic matter layers and horizons due to year-round decomposition and high vegetation density and growth. In temperate and cold climates, litter tends to accumulate and decompose slower due to a shorter growing season.
Net primary productivity
Net
Habitat and food
Litter provides
Plants
Certain plants are specially adapted for germinating and thriving in the litter layers.[12] For example, bluebell (Hyacinthoides non-scripta) shoots puncture the layer to emerge in spring. Some plants with rhizomes, such as common wood sorrel (Oxalis acetosella) do well in this habitat.[7]
Detritivores and other decomposers
Many organisms that live on the forest floor are
The consumption of the litterfall by decomposers results in the breakdown of simple carbon compounds into
As litter decomposes, nutrients are released into the environment. The portion of the litter that is not readily decomposable is known as humus. Litter aids in soil moisture retention by cooling the ground surface and holding moisture in decaying organic matter. The flora and fauna working to decompose soil litter also aid in soil respiration. A litter layer of decomposing biomass provides a continuous energy source for macro- and micro-organisms.[15][8]
Larger animals
Numerous reptiles, amphibians, birds, and even some mammals rely on litter for shelter and forage. Amphibians such as salamanders and caecilians inhabit the damp microclimate underneath fallen leaves for part or all of their life cycle. This makes them difficult to observe. A BBC film crew captured footage of a female caecilian with young for the first time in a documentary that aired in 2008.[16] Some species of birds, such as the
Nutrient cycle
During leaf senescence, a portion of the plant's nutrients are reabsorbed from the leaves. The nutrient concentrations in litterfall differ from the nutrient concentrations in the mature foliage by the reabsorption of constituents during leaf senescence.[3] Plants that grow in areas with low nutrient availability tend to produce litter with low nutrient concentrations, as a larger proportion of the available nutrients is reabsorbed. After senescence, the nutrient-enriched leaves become litterfall and settle on the soil below.
Litterfall is the dominant pathway for nutrient return to the soil, especially for
By the process of biological decomposition by microfauna, bacteria, and fungi, CO2 and H2O, nutrient elements, and a decomposition-resistant organic substance called humus are released. Humus composes the bulk of organic matter in the lower soil profile.[3]
The decline of nutrient ratios is also a function of decomposition of litterfall (i.e. as litterfall decomposes, more nutrients enter the soil below and the litter will have a lower nutrient ratio). Litterfall containing high nutrient concentrations will decompose more rapidly and asymptote as those nutrients decrease.[21] Knowing this, ecologists have been able to use nutrient concentrations as measured by remote sensing as an index of a potential rate of decomposition for any given area.[22] Globally, data from various forest ecosystems shows an inverse relationship in the decline in nutrient ratios to the apparent nutrition availability of the forest.[3]
Once nutrients have re-entered the soil, the plants can then reabsorb them through their roots. Therefore, nutrient reabsorption during senescence presents an opportunity for a plant's future net primary production use. A relationship between nutrient stores can also be defined as:
- annual storage of nutrients in plant tissues + replacement of losses from litterfall and leaching = the amount of uptake in an ecosystem
Non-terrestrial Litterfall
Non-terrestrial litterfall follows a very different path. Litter is produced both inland by
Collection and analysis
The main objectives of litterfall sampling and analysis are to quantify litterfall production and chemical composition over time in order to assess the variation in litterfall quantities, and hence its role in nutrient cycling across an environmental gradient of climate (moisture and temperature) and soil conditions.[25]
Ecologists employ a simple approach to the collection of litterfall, most of which centers around one piece of equipment, known as a litterbag. A litterbag is simply any type of container that can be set out in any given area for a specified amount of time to collect the plant litter that falls from the canopy above.
Litterbags are generally set in random locations within a given area and marked with
- litterfall (kg m−2 yr−1) = total litter mass (kg) / litterbag area (m2)[28]
The litterbag may also be used to study decomposition of the litter layer. By confining fresh litter in the mesh bags and placing them on the ground, an ecologist can monitor and collect the decay measurements of that litter.[7] An exponential decay pattern has been produced by this type of experiment: , where is the initial leaf litter and is a constant fraction of detrital mass.[3]
The mass-balance approach is also utilized in these experiments and suggests that the decomposition for a given amount of time should equal the input of litterfall for that same amount of time.
- litterfall = k(detrital mass)[3]
For study various groups from edaphic fauna you need a different mesh sizes in the litterbags[29]
Issues
Change due to invasive earthworms
In some regions of glaciated North America, earthworms have been introduced where they are not native. Non-native earthworms have led to environmental changes by accelerating the rate of decomposition of litter. These changes are being studied, but may have negative impacts on some inhabitants such as salamanders.[30]
Forest litter raking
Leaf litter accumulation depends on factors like wind, decomposition rate and
See also
- Coarse woody debris
- Detritus
- Forest floor
- Leaf litter sieve
- Leaf mold (a type of compost)
- Soil horizon
References
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- ^ a b c d e f g h i Schlesinger, William H. Biogeochemistry: An Analysis of Global Change. 2nd Edition. Academic Press. 108, 135, 152–158, 180–183, 191–194. (1997).
- ^ "Soil Classification". Faculty of Land and Food Systems. The University of British Columbia. Retrieved March 20, 2012.
- JSTOR 2259543.
- ^ "Litter Fall in the North American Baldcypress Swamp Network, Illinois to Louisiana, 2003". Nwrc.usgs.gov. 2013-08-19. Retrieved 2014-04-09.
- ^ ISBN 0-412-43950-6.
- ^ PMID 32336913.
- doi:10.1139/S03-034.
- ^ Ice, George G.; Neary, D.G.; Adams, P.W. (2004). "Effects of Wildfire on Soils and Watershed Processes" (PDF). Journal of Forestry. 102 (6): 16–20(5). Retrieved March 20, 2012.
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- ^ Fiers, Frank Fiers; Ghenne, Véronique (January 2000). "Cryptozoic copepods from Belgium: Diversity and biogeographic implications". Belgian Journal of Zoology. 130 (1): 11–19.
- ISBN 92-5-105366-9.
- ^ Writer David Attenborough, Director Scott Alexander, Producer Hilary Jeffkins (2008-02-11). "Land Invaders". Life in Cold Blood. BBC. BBC One.
- ISBN 0-395-78321-6.
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- ^ Breymeyer, A.I., B. Berg, S.T. Gower, & D. Johnson. “Temperate Coniferous Forests” Scientific Committee on Problems of the Environment (SCOPE). Vol. 56: Global Change: Effects on Coniferous Forests and Grasslands Carbon Budget, Ch. 3. (1996).
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- ^ Melillo, J.M., & J.R. Gosz. “Interactions of Biogeochemical Cycles in Forest Ecosystems” Scientific Committee on Problems of the Environment (SCOPE). Vol. 21: The Major Biogeochemical Cycles and Their Interactions, Ch. 6. (1983).
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- ^ Simmons, Jeffrey A. “Measuring Litterfall Flux.” West Virginia Wesleyan College (2003).
- ^ "Spatial variations of nitrogen deposition and its effect on forest biochemical processes". Forest Research. Retrieved March 27, 2011.
- ^ Estrella, Stephanie. “Standard Operating Procedures for Litterfall Collection, Processing, and Analysis: Version 2.0.” Washington State Department of Ecology. (2008).
- ^ Bastrup-Birk, A., & Nathalie Bréda. “Report on Sampling and Analysis of Litterfall” United Nations Economic Commission for Europe Convention on Long-Range Transboundary Air Pollution: International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests. (2004).
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