Plant Ecology
Plant ecology is a subdiscipline of ecology which studies the distribution
and abundance of plants, the effects of environmental factors upon the
abundance of plants, and the interactions among and between plants and
other organisms. Examples of these are the distribution of temperate
deciduous forests in North America, the effects of drought or flooding
upon plant survival, and competition among desert plants for water, or
effects of herds of grazing animals upon the composition of grasslands.
A global overview of the Earth's major vegetation types is provided by
O.W. Archibold. He recognizes 11 major vegetation types: tropical forests,
tropical savannas, arid regions (deserts), Mediterranean ecosystems,
temperate forest ecosystems, temperate grasslands, coniferous forests,
tundra (both polar and High Mountain), terrestrial wetlands, freshwater
ecosystems and coastal/marine systems. This breadth of topics shows the
complexity of plant ecology, since it includes plants from floating single-
celled algae up to large canopy forming trees.
One feature that defines plants is photosynthesis. Photosynthesis is the
process of a chemical reactions to create glucose and oxygen, which is
vital for plant life. One of the most important aspects of plant ecology is
the role plants have played in creating the oxygenated atmosphere of
earth, an event that occurred some 2 billion years ago. It can be dated by
the deposition of banded iron formations, distinctive sedimentary rocks
with large amounts of iron oxide.
At the same time, plants began removing carbon dioxide from the
atmosphere, thereby initiating the process of controlling Earth's climate. A
long term trend of the Earth has been toward increasing oxygen and
decreasing carbon dioxide, and many other events in the Earth's history,
like the first movement of life onto land, are likely tied to this sequence of
events.
One of the early classic books on plant ecology was written by J.E. Weaver
and F.E. Clements. It talks broadly about plant communities, and
particularly the importance of forces like competition and processes like
succession. The term ecology itself was coined by German biologist Ernst
Haeckel.
Plant ecology can also be divided by levels of organization including plant
ecophysiology, plant population ecology, community ecology, ecosystem
ecology, landscape ecology and biosphere ecology. The study of plants
and vegetation is complicated by their form. First, most plants are rooted
in the soil, which makes it difficult to observe and measure nutrient
uptake and species interactions.
Second, plants often reproduce vegetatively, that is asexually, in a way
that makes it difficult to distinguish individual plants. Indeed, the very
concept of an individual is doubtful, since even a tree may be regarded as
a large collection of linked meristems. Hence, plant ecology and animal
ecology have different styles of approach to problems that involve
processes like reproduction, dispersal and mutualism.
Some plant ecologists have placed considerable emphasis upon trying to
treat plant populations as if they were animal populations, focusing on
population ecology. Many other ecologists believe that while it is useful to
draw upon population ecology to solve certain scientific problems, plants
demand that ecologists work with multiple perspectives, appropriate to
the problem, the scale and the situation.
Historic Background
Plant ecology has its origin in the application of plant physiology to the
questions raised by plant geographers. Carl Ludwig Willdenow was one of
the first to note that similar climates produced similar types of vegetation,
even when they were located in different parts of the world. Willdenow's
student, Alexander von Humboldt, used physiognomy to describe
vegetation types and observed that the distribution vegetation types was
based on environmental factors.
Later plant geographers who built upon Humboldt's work included Joakim
Frederik Schouw, A.P. de Candolle, August Grisebach and Anton Kerner
von Marilaun. Schouw's work, published in 1822, linked plant distributions
to environmental factors (especially temperature) and established the
practice of naming plant associations by adding the suffix -etum to the
name of the dominant species.
Working from herbarium collections, De Candolle searched for general
rules of plant distribution and settled on using temperature as well.
Grisebach's two-volume work, Die Vegetation der Erde nach Ihrer
Klimatischen Anordnung, published in 1872, saw plant geography reach
its "ultimate form" as a descriptive field.
Starting in the 1870s, Swiss botanist Simon Schwendener, together with
his students and colleagues, established the link between plant
morphology and physiological adaptations, laying the groundwork for the
first ecology textbooks, Eugenius Warming's Plantesamfund (published in
1895) and Andreas Schimper's 1898 Pflanzengeographie auf
Physiologischer Grundlage.
Warming successfully incorporated plant morphology, physiology
taxonomy and biogeography into plant geography to create the field of
plant ecology. Although more morphological than physiological,
Schimper's has been considered the beginning of plant physiological
ecology.
Plant ecology was initially built around static ideas of plant distribution;
incorporating the concept of succession added an element to change
through time to the field. Henry Chandler Cowles' studies of plant
succession on the Lake Michigan sand dunes (published in 1899) and
Frederic Clements' 1916 monograph on the subject established it as a key
element of plant ecology.
Plant ecology developed within the wider discipline of ecology over the
twentieth century. Inspired by Warming's Plantesamfund, Arthur Tansley
set out to map British plant communities. In 1904 he teamed up with
William Gardner Smith and others involved in vegetation mapping to
establish the Central Committee for the Survey and Study of British
Vegetation, later shortened to British Vegetation Committee.
In 1913, the British Vegetation Committee organised the British Ecological
Society (BES), the first professional society of ecologists. This was
followed in 1917 by the establishment of the Ecological Society of America
(ESA)―plant ecologists formed the largest subgroup among the inaugural
members of the ESA.
Plant distributions is governed by a combination of historical factors,
ecophysiology and biotic interactions. The set of species that can be
present at a given site is limited by historical contingency. In order to
show up, a species must either have evolved in an area or dispersed there
(either naturally or through human agency), and must not have gone
locally extinct.
The set of species present locally is further limited to those that possess
the physiological adaptations to survive the environmental conditions that
exist. This group is further shaped through interactions with other species.
Plant communities are broadly distributed into biomes based on the form
of the dominant plant species. For example, grasslands are dominated by
grasses, while forests are dominated by trees.
Biomes are determined by regional climates, mostly temperature and
precipitation, and follow general latitudinal trends. Within biomes, there
may be many ecological communities, which are impacted not only by
climate and a variety of smaller-scale features, including soils, hydrology,
and disturbance regime. Biomes also change with elevation, high
elevations often resembling those found at higher latitudes.
Plant Ecophysiology
Ecophysiology (from Greek οἶκος, oikos, "house (hold)"; φύσις, physis,
"nature, origin"; and -λογία, -logia), environmental physiology or
physiological ecology is a biological discipline that studies the response of
an organism's physiology to environmental conditions. It is closely related
to comparative physiology and evolutionary physiology. Ernst Haeckel's
coinage bionomy is sometimes employed as a synonym.
Plant ecophysiology is concerned largely with two topics―mechanisms
(how plants sense and respond to environmental change) and scaling or
integration (how the responses to highly variable conditions—for example,
gradients from full sunlight to 95% shade within tree canopies—are
coordinated with one another), and how their collective effect on plant
growth and gas exchange can be understood on this basis.
In many cases, animals are able to escape unfavourable and changing
environmental factors such as heat, cold, drought or floods, while plants
are unable to move away and therefore must endure the adverse
conditions or perish (animals go places, plants grow places). Plants are
therefore phenotypically plastic and have an impressive array of genes
that aid in acclimating to changing conditions. It is hypothesized that this
large number of genes can be partly explained by plant species' need to
live in a wider range of conditions.
