Kaczmarz method

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Quadratic Lie algebra

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[[File:Gmelina leaves forest floor.JPG|thumb|Leaf litter, mainly White Beech, ''[[Gmelina leichhardtii]]'', from [[Black Bulga State Conservation Area]], NSW, Australia]]
'''Litterfall''', '''plant litter''', '''leaf litter''', '''tree litter''', '''soil litter''', or '''duff''', is dead [[plant]] material, such as [[leaf|leaves]], [[bark]], [[Needle (botany)|needles]], and [[twig]]s, that has fallen to the ground. This [[detritus]] or dead organic material and its constituent nutrients are added to the top layer of soil, commonly known as the litter layer or [[O horizon]] ("O" for "organic"). Litter has occupied the attention of ecologists at length for the reasons that it is an instrumental factor in ecosystem dynamics, is indicative of ecological [[Productivity (ecology)|productivity]], and may be useful in predicting regional [[nutrient cycle|nutrient cycling]] and [[Fertility (soil)|soil fertility]].

== Characteristics and variability ==
[[File:Western Hemlock litter.JPG|thumb|left|Plant litter, mainly western hemlock, ''[[Tsuga heterophylla]]'', in [[Mount Baker-Snoqualmie National Forest]], Washington state, USA.]]
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 woody debris|coarse litter]], while anything smaller is referred to as fine litter or litter. The type of litterfall is most directly affected by [[ecosystem]] type. There are foxes in the deciduous forest.

For example, leaf tissues account for about 70 percent of litterfall in forests, but woody litter tends to increase with forest age.<ref>{{cite journal |author=W. M. Lonsdale |year=1988 |title=Predicting the amount of litterfall in forests of the world |journal=[[Annals of Botany]] |volume=61 |issue=3 |pages=319–324}}</ref> 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.<ref name="Schlesinger">Schlesinger, William H. Biogeochemistry: An Analysis of Global Change. 2nd Edition. Academic Press. 108, 135, 152–158, 180–183, 191–194. (1997).</ref>

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:<ref>{{cite web|title=Soil Classification|url=http://www.landfood.ubc.ca/soil200/classification/soil_horizon.htm|work=Faculty of Land and Food Systems|publisher=The University of British Columbia|accessdate=March 20, 2012}}</ref>
{{Unbulleted list
| 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]]. 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.<ref>{{cite journal |author=A. V. Spain |year=1984 |title=Litterfall and the standing crop of litter in three tropical Australian rainforests |journal=[[Journal of Ecology]] |volume=72 |pages=947–961 |jstor=2259543}}</ref> As a result of this variability due to seasons, the decomposition rate for any given area will also be variable.

[[File:Litterfall-Latitude.gif|thumb|alt=Alt text|Litter fall in the North American Baldcypress Swamp Network, Illinois to Louisiana, 2003<ref>[http://www.nwrc.usgs.gov/special/bald-cypress/results.htm Litter Fall in the North American Baldcypress Swamp Network, Illinois to Louisiana, 2003]</ref>]]
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,<ref name = Packham>{{Cite book | last1 = Packham | first1 = J.R. | last2 = Harding | first2 = D.J.L. | last3 = Hilton | first3 = G.M. | last4 = Stuttard | first4 = R.A. | title = Functional Ecology of Woodlands and Forests | publisher = [[Chapman & Hall]] | year = 1992 | location = London | pages = 133–134, 246–247, 265 | isbn = 0412439506}}</ref> while in [[boreal forests]], the rate of decomposition is slower and leads to the accumulation of a thick litter layer, also known as a [[Humus|mor]].<ref name="Schlesinger" /> 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. Soil litter protects soil aggregates from raindrop impact, preventing the release of clay and silt particles from plugging soil pores.<ref>{{cite journal|last=Chanasyk|first=D.S.|coauthors=Whitson, I.R., Mapfumo, E., Burke, J.M., Prepas, E.E.|title=The Impacts of Forest Harvest and Wildfire on Soils and Hydrology in Temperate Forests: A Baseline to Develop Hypotheses for the Boreal Plain|journal=Journal of Environmental Engineering Science|year=2003|volume=2|pages=S51-S62|doi=10.1139/S03-034}}</ref> 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 [[Aeolian_processes|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.<ref>{{cite journal|last=Ice|first=George G.|coauthors=Neary, D.G., Adams, P.W.|title=Effects of Wildfire on Soils and Watershed Processes|journal=Journal of Forestry|year=2004|volume=102|issue=6|pages=16–20(5)|url=http://www.colorado.edu/geography/class_homepages/geog_3511_s12/readings/Fire_Watersheds_JForestry.pdf|accessdate=March 20, 2012}}</ref> Regions will high frequency wildfires have reduced vegetation density and reduced soil litter accumulation. Climate also influences the depth of plant litter. Typically humid tropic and sub-tropic 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 accuculate and decompose slower due to a shorter growing season.

==Net primary productivity==
Net [[primary production]] and litterfall are intimately connected. In every terrestrial ecosystem, the largest fraction of all net primary production is lost to [[herbivores]] and litterfall. Therefore these factors must be accounted for. Ecologists account for this effect by subtracting the accumulated litterfall from the net primary production, resulting in what is called the ''true increment'' of net primary production. Due to their interconnectedness, global patterns of litterfall are similar to global patterns of net primary productivity.<ref name="Schlesinger" />

==Habitat and food==
Litter provides [[Habitat (ecology)|habitat]] for a variety of organisms.

[[File:Oxalis acetosella 5724.jpg|thumb|right|Common wood sorrel (''[[Oxalis acetosella]]'') in [[Ivanovo Oblast]], Russia]]
===Plants===
Certain plants are specially adapted for germinating and thriving in the litter layers. For example, bluebell (''[[Hyacinthoides non-scripta]]'') shoots puncture the layer to emerge in spring. Some plants with [[rhizome]]s, such as common wood sorrel (''[[Oxalis acetosella]]'') do well in this habitat.<ref name = Packham/>

===Detritivores and other decomposers===
Many organisms that live on the forest floor are [[decomposers]], such as [[fungi]]. Organisms whose diet consists of plant detritus, such as [[earthworm]]s, are termed [[detritivore]]s. The community of decomposers in the litter layer also includes [[bacteria]], [[amoeba]], [[nematode]]s, [[rotifer]], [[springtail]]s, [[cryptostigmata]], [[Enchytraeidae|potworms]], insect [[larva|larvae]], [[Mollusca|mollusks]], [[Oribatida|oribatid mite]]s, [[woodlouse|woodlice]], and [[millipede]]s.<ref name = Packham/> Their consumption of the litterfall results in the breakdown of simple carbon compounds into [[carbon dioxide]] (CO2) and [[water]] (H2O), and releases inorganic [[ions]] (like [[nitrogen]] and [[phosphorus]]) into the soil where the surrounding plants can then reabsorb the nutrients that were shed as litterfall. In this way, litterfall becomes an important part of the nutrient cycle that sustains forest environments.

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.<ref>{{cite book|last=Bot|first=Alexandra|title=The Importance of Soil Organic Matter|year=2005|publisher=Food and Agriculture Organizations of the United Nations|location=Rome|isbn=92-5-105366-9|pages=Chapter 3|url=http://www.fao.org/docrep/009/a0100e/a0100e00.htm#Contents}}</ref>

[[File:Eutropis multifasciata in leaf litter.JPG|thumb|left|A skink, ''[[Eutropis multifasciata]]'', in leaf litter in [[Sabah]], Malaysia]]
===Larger animals===
Numerous [[reptile]]s, [[amphibian]]s, [[bird]]s, and even some [[mammal]]s rely on litter for shelter and forage. For example, amphibians such as [[salamander]]s and [[caecilian]]s 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.<ref>{{cite episode | title = Land Invaders| series = [[Life in Cold Blood]] | credits = Writer David Attenborough, Director Scott Alexander, Producer Hilary Jeffkins | network = BBC | station = BBC One | airdate = 2008-02-11}}</ref>
Some species of birds require leaf litter both for foraging and as material used to construct [[nest]]s, such as the [[ovenbird]] of eastern North America.<ref>{{cite book | last1 = Dunn | first1 = Jon | last2 = Garrett | first2 = Kimball | title = Warblers | publisher = [[Peterson Field Guides]] | location = New York | year = 1997 | pages = 451 | isbn = 0-395-78321-6}}</ref> Sometimes litterfall even provides energy to much larger mammals, such as in [[boreal forest]]s where [[lichen]] litterfall is one of the main constituents of wintering [[deer]] and [[elk]] diets.<ref>{{cite journal |author=Richard L. Ward & C. Les Marcum |year=2005 |title=Lichen litterfall consumption by wintering deer and elk in western Montana |journal=[[Journal of Wildlife Management]] |volume=69 |issue=3 |pages=1081–1089 |jstor=3803347 |doi=10.2193/0022-541X(2005)069[1081:LLCBWD]2.0.CO;2}}</ref>

== Nutrient cycle ==
During leaf [[senescence]], a portion of the plant’s nutrients are reabsorbed into the leaves. The nutrient concentrations in litterfall differ from the nutrient concentrations in the mature foliage by the reabsorption of constituents during leaf senescence.<ref name="Schlesinger" /> Plants that grow in areas with low nutrient availability tend to produce litter with low nutrient concentrations, but a larger proportion of the available nutrients is reabsorbed. After senescence, the nutrient-enriched leaves become litterfall and settle on the soil below.

[[File:litter-nutrient cycle2.gif|frame|right|alt=Alt text|A budget for organic matter in a mature (120-year-old) Scots pine [[monoculture]] (SWECON site). Based on data from Andersson et al.(1980). Units are in kg of organic matter per ha. Att. -attached; Surf. -surface; min. -[[mineral]]; and veg. -[[vegetation]]<ref>Breymeyer, A.I., B. Berg, S.T. Gower, & D. Johnson. “[http://www.icsu-scope.org/downloadpubs/scope56/Chapter03.html 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).</ref>]]

Litterfall is the dominant pathway for nutrient return to the soil, especially for [[nitrogen]] (N) and [[phosphorus]] (P). The accumulation of these nutrients in the top layer of soil is known as [[immobilization (soil science)|soil immobilization]]. Once the litterfall has settled, decomposition of the litter layer, accomplished through the leaching of nutrients by rainfall and [[throughfall]] and by the efforts of detritivores, releases the breakdown products into the soil below and therefore contributes to the [[cation]] exchange capacity of the soil. This holds especially true for highly weathered tropical soils.<ref>{{cite journal |author=J. Chave, D. Navarrete, S. Almeida, E. Álvarez, L. E. O. C. Aragão, D. Bonal, P. Châtelet, J. E. Silva-Espejo, J.-Y. Goret, P. von Hildebrand, E. Jiménez, S. Patiño, M. C. Peñuela, O. L. Phillips, P. Stevenson & Y. Malhi |year=2009 |title=Regional and seasonal patterns of litterfall in tropical South America |journal=[[Biogeosciences]] |volume=7 |issue=1 |pages=43–55 |doi=10.5194/bg-7-43-2010 |url=http://frutos.uniandes.edu.co/pagina/Documentos/Pdf/Chave%20Litterfall%2009.pdf |format=[[Portable Document Format|PDF]]}}</ref>

[[Leaching (agriculture)|Leaching]] is the process by which cations such as [[iron]] (Fe) and [[aluminum]] (Al), as well as organic matter are removed from the litterfall and transported downward into the soil below. This process is known as [[podzolization]] and is particularly intense in boreal and cool temperate forests that are mainly constituted by [[coniferous]] pines whose litterfall is rich in [[natural phenol|phenolic compounds]] and [[fulvic acid]].<ref name="Schlesinger" />

By the process of biological decomposition by [[microfauna]], bacteria, and fungi, CO2 and H2O, nutrient [[Chemical element|elements]], and an exceedingly resistant organic compound called [[humus]] are released. [[Humus]] composes the bulk of organic matter in the lower soil profile.<ref name="Schlesinger" />

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.<ref>{{cite journal |author=Scott D. Bridgham, John Pastor, Charles A. McClaugherty, & Curtis J. Richardson |year=1995 |title=Nutrient-use efficiency: a litterfall index, a model, and a test along a nutrient-availability gradient in North Carolina peatlands |journal=[[The American Naturalist]] |volume=145 |issue=1 |pages=1–21 |url=http://ceeb.uoregon.edu/Bridgham/pubpdfs/art_5.pdf |format=[[Portable Document Format|PDF]]}}</ref> 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.<ref>Melillo, J.M., & J.R. Gosz. “[http://www.icsu-scope.org/downloadpubs/scope21/Chapter06.html 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).</ref> Globally, data from various forest ecosystems shows an inverse relationship in the decline in nutrient ratios to the apparent nutrition availability of the forest.<ref name="Schlesinger" />

Once nutrients have re-entered the soil, the plants can then reabsorb them through their [[root]]s. 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

==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.<ref>Simmons, Jeffrey A. “Measuring Litterfall Flux.” West Virginia Wesleyan College (2003).</ref>

Ecologists employ a simple approach to the collection of litterfall, most of which centers around once 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 (biology)|canopy]] above.
[[Image:Litterbags.jpg|thumb|Litterfall and [[throughfall]] collectors at beech stand in Thetford, East Anglia<ref>{{cite web|url=http://www.forestresearch.gov.uk/fr/INFD-75PJ9E |title=Spatial variations of nitrogen deposition and its effect on forest biochemical processes |publisher=Forest Research |date= |accessdate=March 27, 2011}}</ref>]]
Litterbags are generally set in random locations within a given area and marked with [[GPS]] or local coordinates, and then monitored on a specific time interval. Once the samples have been collected, they are usually classified on type, size and [[species]] (if possible) and recorded on a spreadsheet.<ref>Estrella, Stephanie. “Standard Operating Procedures for Litterfall Collection, Processing, and Analysis: Version 2.0.” Washington State Department of Ecology. (2008).</ref> When measuring bulk litterfall for an area, ecologists will weigh the dry contents of the litterbag. By this method litterfall flux can be defined as:

:litterfall (kg m−2 yr−1) = total litter mass (kg) / litterbag area (m2)<ref>Bastrup-Birk, A., & Nathalie Bréda. “[http://rod.eionet.europa.eu/obligations/526/overview 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).</ref>

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.<ref name = Packham/> An [[exponential decay]] pattern has been produced by this type of experiment: <math>\frac{X}{X_o} = e^{-k}</math>, where <math>X_o</math> is the initial leaf litter and <math>k</math> is a constant fraction of detrital mass.<ref name="Schlesinger" />

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)<ref name="Schlesinger" />

==Issues==
===Change due to invasive earthworms===
{{Main|Earthworms as invasive species|Invasive earthworms of North America}}
In some regions of Australia and 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.<ref>{{Cite journal | last1 = Maerz | first1 = John C. | last2 = Nuzzo | first2 = Victoria A. | last3 = Blossey | first3 = Bernd | title = Declines in Woodland Salamander Abundance Associated with Non-Native Earthworm and Plant Invasions | journal = Conservation Biology | volume = 23 | issue = 4 | year = 2009 | url= http://faculty.bennington.edu/~kwoods/classes/forests/fall11/readings11/Maerz%20et%20al%202009%20ConsBiol.pdf | accessdate = 28 April 2012}}</ref>

==See also==
{{Commons category|Plant litter (ecology)}}
* [[Coarse woody debris]]
* [[Detritus]]
* [[Forest floor]]
* [[Leaf litter sieve]]
* [[Leaf mold]] (a type of [[compost]])
* [[Soil horizon]]

==References==
{{Reflist|32em}}

==External links==
* http://www.forestresearch.gov.uk/fr/INFD-75PJ9E

[[Category:Ecology terminology]]
[[Category:Environmental terminology]]
[[Category:Biology terminology]]
[[Category:Soil improvers]]
[[Category:Ecology]]
[[Category:Ecological restoration]]
[[Category:Habitat]]

[[pt:Serrapilheira]]

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Kaczmarz method

Quadratic Lie algebra