Litterfall
Encyclopedia
Litterfall is the transport of leaves, bark, twigs and other forms of dead organic material and its constituent nutrients from the aerial parts of the biosphere
to the top layer of soil, commonly known as the litter layer or O horizon.
Litterfall has occupied the attention of ecologists at length for the reasons that it is an instrumental piece of in ecosystem dynamics, is indicative of regional net primary productivity (NPP), and may be useful in predicting regional nutrient cycling and soil fertility.
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. 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.
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. 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 affect 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 of the litterfall, while in boreal forests, the rate of decomposition is slower and leads to the accumulation of a thick litter layer, also known as a mor
. Net primary production works inversely to this trend, suggesting that the accumulation of organic matter is mainly a result of decomposition rate.
s that live on the forest floor (this includes, but is not limited to bacteria
, fungi, mollusks
, arthropod
s, amphibian
s, reptile
s, and even some mammal
s). Sometimes litterfall even provides energy to much larger mammals, such as in boreal forests where lichen
litterfall is one of the main constituents of wintering deer
and elk
diets.
Most of the organisms that live in the litter layer are decomposers. 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.
, 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
. 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.
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 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 detritivore
s, 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.
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 phenolic compounds
and fulvic acid.
By the process of biological decomposition by microfauna
, bacteria
and fungi, CO2 and H2O, nutrient elements
, and an exceedingly resistant organic compound called humus are released. Humus composes the bulk of organic matter in the lower soil profile.
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. 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. Globally, data from various forest ecosystems shows an inverse relationship in the decline in nutrient ratios to the apparent nutrition availability of the forest.
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:
(moisture and temperature) and soil conditions.
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 above.
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. 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:
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. 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.
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.
Biosphere
The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...
to the top layer of soil, commonly known as the litter layer or O horizon.
Litterfall has occupied the attention of ecologists at length for the reasons that it is an instrumental piece of in ecosystem dynamics, is indicative of regional net primary productivity (NPP), and may be useful in predicting regional nutrient cycling and soil fertility.
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
Stamen
The stamen is the pollen producing reproductive organ of a flower...
of flowering plants). Items larger than 2 cm diameter are referred to as coarse litter
Coarse woody debris
Coarse woody debris is a term used in English-speaking countries for fallen dead trees and the remains of large branches on the ground in forests. Some prefer the term coarse woody habitat . A dead standing tree is known as a snag and provides many of the same functions as coarse woody debris...
, while anything smaller is referred to as fine litter or litter. The type of litterfall is most directly affected by ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
type.
For example, leaf tissues account for about 70 percent of litterfall in forests, but woody litter tends to increase with forest age. 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.
The litter layer is quite variable in its thickness, decomposition rate and nutrient content and is affected in part by seasonality
Seasonality
In statistics, many time series exhibit cyclic variation known as seasonality, periodic variation, or periodic fluctuations. This variation can be either regular or semi regular....
, plant species, climate, soil fertility, elevation, and latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
. The most extreme variability of litterfall is seen as a function of seasonality
Seasonality
In statistics, many time series exhibit cyclic variation known as seasonality, periodic variation, or periodic fluctuations. This variation can be either regular or semi regular....
; 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. As a result of this variability due to seasons, the decomposition rate for any given area will also be variable.
Latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
also has a strong affect on litterfall rates and thickness. Specifically, litterfall declines with increasing latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
. In tropical rainforests, there is a thin litter layer due to the rapid decomposition of the litterfall, while in boreal forests, the rate of decomposition is slower and leads to the accumulation of a thick litter layer, also known as a mor
MOR
Mor or MOR may refer to:In publications:* Mathematics of Operations Research, a quarterly publication on the mathematics of operations research.In mechanics:...
. Net primary production works inversely to this trend, suggesting that the accumulation of organic matter is mainly a result of decomposition rate.
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 affect 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.Habitat and food
Litterfall is the principal, and sometimes only, source of energy and shelter for the saprobionts and detritivoreDetritivore
Detritivores, also known as detritophages or detritus feeders or detritus eaters or saprophages, are heterotrophs that obtain nutrients by consuming detritus . By doing so, they contribute to decomposition and the nutrient cycles...
s that live on the forest floor (this includes, but is not limited to bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, fungi, mollusks
Mollusca
The Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...
, arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s, amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s, reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, and even some mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s). Sometimes litterfall even provides energy to much larger mammals, such as in boreal forests where lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
litterfall is one of the main constituents of wintering deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...
and elk
Elk
The Elk is the large deer, also called Cervus canadensis or wapiti, of North America and eastern Asia.Elk may also refer to:Other antlered mammals:...
diets.
Most of the organisms that live in the litter layer are decomposers. Their consumption of the litterfall results in the breakdown of simple carbon compounds into carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
(H2O), and releases inorganic ions (like nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
) 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.
Nutrient cycle
During leaf senescenceSenescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
, 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
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
. 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
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
, 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 nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
(N) and phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
(P). The accumulation of these nutrients in the top layer of soil is known as soil immobilization. Once the litterfall has settled, decomposition of the litter layer, accomplished through the leaching of nutrients by rainfall and throughfall
Throughfall
In Hydrology, throughfall is the process which describes how wet leaves shed excess water onto the ground surface. These drops have an erosive power because they are larger than rain drops, however, if they travel a shorter distance their erosive power is reduced...
and by the efforts of detritivore
Detritivore
Detritivores, also known as detritophages or detritus feeders or detritus eaters or saprophages, are heterotrophs that obtain nutrients by consuming detritus . By doing so, they contribute to decomposition and the nutrient cycles...
s, 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.
Leaching
Leaching (agriculture)
In agriculture, leaching refers to the loss of water-soluble plant nutrients from the soil, due to rain and irrigation. Soil structure, crop planting, type and application rates of fertilizers, and other factors are taken into account to avoid excessive nutrient loss.Leaching may also refer to ...
is the process by which cations such as iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
(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
Podzolization
Podzolization is the comprehensive name for the process of mobilization and precipitation of dissolved organic matter, together with aluminum Al and iron Fe as they are leaching down from the A and E horizons to the B horizon . Through this process the overlying eluvial horizons are getting bleached...
and is particularly intense in boreal and cool temperate forests that are mainly constituted by coniferous pines whose litterfall is rich in phenolic compounds
Natural phenol
Natural phenols, bioavailable phenols, plant phenolics, low molecular weight phenols or phenoloids are a class of natural products. They are small molecules containing one or more phenolic group. These molecules are smaller in size than polyphenols, containing less than 12 phenolic groups...
and fulvic acid.
By the process of biological decomposition by microfauna
Microfauna
Microfauna refers to microscopic organisms that exhibit animal-like qualities. Microfauna are represented in the animal kingdom and the protist kingdom...
, bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
and fungi, CO2 and H2O, nutrient elements
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
, and an exceedingly resistant organic compound called humus are released. Humus composes the bulk of organic matter in the lower soil profile.
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
Asymptote
In analytic geometry, an asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity. Some sources include the requirement that the curve may not cross the line infinitely often, but this is unusual for modern authors...
as those nutrients decrease. Knowing this, ecologists have been able to use nutrient concentrations as measured by remote sensing
Remote sensing
Remote sensing is the acquisition of information about an object or phenomenon, without making physical contact with the object. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth by means of propagated signals Remote sensing...
as an index of a potential rate of decomposition for any given area. Globally, data from various forest ecosystems shows an inverse relationship in the decline in nutrient ratios to the apparent nutrition availability of the forest.
Once nutrients have re-entered the soil, the plants can then reabsorb them through their root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s. Therefore, nutrient reabsorption during senescence
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
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 climateClimate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
(moisture and temperature) and soil conditions.
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 above.
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
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
(if possible) and recorded on a spreadsheet. 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)
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. 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.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)