Lithosere
Encyclopedia
A lithosere is a plant
succession
that begins life on a newly exposed rock
surface, such as one left bare as a result of glacial
retreat, tectonic uplift
as in the formation of a raised beach
, or volcanic eruptions. For example, the lava fields of Eldgjá
in Iceland
where Laki
and Katla
fissures erupted in the year 935 and the solidified lava
has, over time, begun to form a lithosere.
Pioneer species
are the first organism
s that colonise an area, of which lithoseres are an example. They will typically be very hardy (i.e., they will be xerophytes, wind-resistant or cold-resistant). In the case of a lithosere the pioneer species will be cyanobacteria and algae, which create their own food and water
—i.e., they are autotrophic and so do not require any external nutrition
(except sunlight
). For example, the first lithosere observed after the volcanic explosion of Krakatau was algae. Other examples of lithoseres include communities of moss
es and lichen
s, as they are extremely resilient and are capable of surviving in areas without soil
.
As more mosses and lichens colonize the area, they, along with natural elements such as wind and frost shattering, begin to weather
the rock down. This over time creates more soil, leading to increased water retention. Early on, when there is little water, lichens dominate as they are more suited to a lack of water; but as water retention increases, mosses become more dominant as they are faster growing, and these further break the rocks down. The amount of soil is also increased by the decaying mosses and lichens. This improves the fertility of the soil as humus is increased, allowing grass
es and fern
s to colonise. Over time, flowering plant
s will emerge, followed by shrub
s. As the soil gets progressively deeper, larger and more advanced plants are able to grow. This is the case in Surtsey
, a "new," small volcanic island located off the south coast of Iceland. Surtsey was "created" in the 1960s and currently its plant succession has reached the stage where ferns and grasses have begun to start growing in the south of the island where the lava cooled first.
As the plant succession develops further, tree
s start to appear. The first trees (or pioneer trees) that appear are typically fast growing trees such as birch
, willow
or rowan
. In turn these will be replaced by slow growing, larger trees such as ash
and oak
. This is the climax community
on a lithosere, defined as the point where a plant succession does not develop any further—it reaches a delicate equilibrium with the environment
, in particular the climate
.
In the off chance of a phenomenon which effectively removes most of the lifeforms in these areas, the resultant landscape is considered to be a disclimax, where there is a loss of the previous climax community. Factors which interrupt succession include: human intervention (plagioclimax), change in relief of land (topoclimax), change in animal species (biotic climax) or change in soil such as an increase in acidity (edaphic climax) . In most cases, should the area be left to regenerate as normal when the limiting factor is removed, the area eventually becomes a climax community again (secondary succession).
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
succession
Ecological succession
Ecological succession, is the phenomenon or process by which a community progressively transforms itself until a stable community is formed. It is a fundamental concept in ecology, and refers to more or less predictable and orderly changes in the composition or structure of an ecological community...
that begins life on a newly exposed rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
surface, such as one left bare as a result of glacial
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
retreat, tectonic uplift
Tectonic uplift
Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...
as in the formation of a raised beach
Beach
A beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...
, or volcanic eruptions. For example, the lava fields of Eldgjá
Eldgjá
Eldgjá is a volcanic canyon in Iceland. Eldgjá and the Katla volcano are part of the same volcanic system in the south of the country. Eldgjá means "fire canyon" in Icelandic....
in Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
where Laki
Laki
Łąki may refer to the following places in Poland:*Łąki, Lower Silesian Voivodeship *Łąki, West Pomeranian Voivodeship *Łąki, Lublin Voivodeship...
and Katla
Katla
Katla is one of the largest volcanoes in Iceland. It is situated to the north of Vík í Mýrdal and to the east of the smaller glacier Eyjafjallajökull. Its peak reaches in height and is partially covered by the Mýrdalsjökull glacier. The Eldgjá canyon is part of the same volcanic system...
fissures erupted in the year 935 and the solidified lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
has, over time, begun to form a lithosere.
Pioneer species
Pioneer species
Pioneer species are species which colonize previously uncolonized land, usually leading to ecological succession. They are the first organisms to start the chain of events leading to a livable biosphere or ecosystem...
are the first organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s that colonise an area, of which lithoseres are an example. They will typically be very hardy (i.e., they will be xerophytes, wind-resistant or cold-resistant). In the case of a lithosere the pioneer species will be cyanobacteria and algae, which create their own food 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...
—i.e., they are autotrophic and so do not require any external nutrition
Nutrition
Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....
(except sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
). For example, the first lithosere observed after the volcanic explosion of Krakatau was algae. Other examples of lithoseres include communities of moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
es and 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...
s, as they are extremely resilient and are capable of surviving in areas without soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
.
As more mosses and lichens colonize the area, they, along with natural elements such as wind and frost shattering, begin to weather
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
the rock down. This over time creates more soil, leading to increased water retention. Early on, when there is little water, lichens dominate as they are more suited to a lack of water; but as water retention increases, mosses become more dominant as they are faster growing, and these further break the rocks down. The amount of soil is also increased by the decaying mosses and lichens. This improves the fertility of the soil as humus is increased, allowing grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...
es and fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s to colonise. Over time, flowering plant
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
s will emerge, followed by shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
s. As the soil gets progressively deeper, larger and more advanced plants are able to grow. This is the case in Surtsey
Surtsey
Surtsey is a volcanic island off the southern coast of Iceland. At it is also the southernmost point of Iceland. It was formed in a volcanic eruption which began 130 metres below sea level, and reached the surface on 15 November 1963. The eruption lasted until 5 June 1967, when the island...
, a "new," small volcanic island located off the south coast of Iceland. Surtsey was "created" in the 1960s and currently its plant succession has reached the stage where ferns and grasses have begun to start growing in the south of the island where the lava cooled first.
As the plant succession develops further, tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
s start to appear. The first trees (or pioneer trees) that appear are typically fast growing trees such as birch
Birch
Birch is a tree or shrub of the genus Betula , in the family Betulaceae, closely related to the beech/oak family, Fagaceae. The Betula genus contains 30–60 known taxa...
, willow
Willow
Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...
or rowan
Rowan
The rowans or mountain-ashes are shrubs or small trees in genus Sorbus of family Rosaceae. They are native throughout the cool temperate regions of the Northern Hemisphere, with the highest species diversity in the mountains of western China and the Himalaya, where numerous apomictic microspecies...
. In turn these will be replaced by slow growing, larger trees such as ash
Ash tree
Fraxinus is a genus flowering plants in the olive and lilac family, Oleaceae. It contains 45-65 species of usually medium to large trees, mostly deciduous though a few subtropical species are evergreen. The tree's common English name, ash, goes back to the Old English æsc, while the generic name...
and oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
. This is the climax community
Climax community
In ecology, a climax community, or climatic climax community, is a biological community of plants and animals which, through the process of ecological succession — the development of vegetation in an area over time — has reached a steady state. This equilibrium occurs because the climax community...
on a lithosere, defined as the point where a plant succession does not develop any further—it reaches a delicate equilibrium with the environment
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....
, in particular the climate
Climate
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...
.
In the off chance of a phenomenon which effectively removes most of the lifeforms in these areas, the resultant landscape is considered to be a disclimax, where there is a loss of the previous climax community. Factors which interrupt succession include: human intervention (plagioclimax), change in relief of land (topoclimax), change in animal species (biotic climax) or change in soil such as an increase in acidity (edaphic climax) . In most cases, should the area be left to regenerate as normal when the limiting factor is removed, the area eventually becomes a climax community again (secondary succession).
Sources
- Codrington, S. B. (2005) Planet Geography. Solid Star Press. pp. 322-323. ISBN 0957981937
- Smithson, P.; K. Addison. (2002) Fundamentals of the Physical Environment. Routledge. pp. 432-433. ISBN 0415232937
- Verma, P. S.; V.K. Agarwal. (2000) Environmental Biology: Principles of Ecology. Chand (S.) & Co Ltd.,India. pp. 303-304. ISBN 8121908590