COVENANT UNIVERSITY
Department of Biological Sciences
NAME: OBUEKWE CHUKWUEMEKA AZUBUIKE
MAT NO: 12CQ014230
PROGRAMME: MICROBIOLOGY
COURSE: BLY121(PLANT DIVERSITY:FORMS AND FUNCTIONS)
TOPIC: THE DISTRIBUTION OF HIGHER PLANTS ON EARTH
{DR CONRAD O.A.}
ABSTRACT
Since photosynthesis first became a co-ordinated process, evolutionary development in the
autotrophic world has come a long way — from the prokaryotic blue-green algae to the eukaryotic
angiosperms and gymnosperms, Higher plants have come a long way in becoming the primary
producers on the earth. Plants, with an estimated 300,000 species, provide crucial primary
production and ecosystem structure.
The studies presented in this paper analyse diversity patterns of Higher plants ( ferns, gymnosperms,
and angiosperms) at continental to global scales. A revised version of the earlier world map of
vascular plant species richness and the first maps of species richness of mosses and gymnosperms
on a global scale are presented. Diversity patterns of vascular plants are correlated with different
measures of geodiversity (the diversity of the abiotic environment). Global centres of vascular plant
diversity coincide with highly structured, geodiverse areas in the tropics and subtropics. These are
the Chocó-Costa Rica region, the tropical eastern Andes and the north western Amazonia, the
eastern Brazil, the northern Borneo, and New Guinea, as well as the South African Cape region,
southern Mexico, East Himalaya, western Sumatra, Malaysia, and eastern Madagascar. Constraints
imposed by the physical environment, such as the length of the thermal vegetation period or water
availability, shape large scale trends of biodiversity. However, important centres of species richness
and endemism can only be explained when taking into account the history of the floras. The main
diversity centres in SE Asia are the same for gymnosperms as for all other vascular plants, but in
other parts of the tropics and subtropics there is low gymnosperm diversity. The exceptions to this
pattern are Mexico and California, which have almost as many species of gymnosperms as SE Asia.
VOCABULARY: VASCULAR PLANTS, ANGIOSPERMS, GYMNOSPERMS, TRACHEOPHYTES, SEED
BEARING PLANTS, BIOMES.
INTRODUCTION
Also known as Vascular Plants, Higher Plants evolved about 500 million years ago. They faced a
problem that did not exist for aquatic plants: they needed to live in two different worlds. They
needed to be part of the soil world, to get water, nutrients, and stability, but they also needed to be
in the air, to get sunlight and carbon dioxide. Land plants solved this problem by developing roots as
well as stems and leaves, and a system of vessels (xylem and phloem) to connect them. All four of
the land plant groups have these features (except mosses do not have vessels). Their differences are
seen in whether or not they have seeds or flowers, and in aspects of these features.
The first land plants appeared in the Silurian period of the Paleozoic era. Most botanists connect
them with the origin of the extinct forms of green algae. The transition to a terrestrial existence, to
live simultaneously in two different environments (air and soil) was accompanied by the elaboration
of devices for water supply, protection of reproductive organs from drying out and ensure that the
sexual process. To strengthen the roots in the soil appeared, formed stem with leaves for
photosynthesis in air. In parallel with their development of the differentiation of tissue systems:
developed conductive and mechanical systems of tissues, epidermis and stoma appeared, formed
multicellular organs of sexual reproduction - gametangia. Male gametangia are called antheridia,
they formed the male sex cells (gametes) - sperm or sperm. Female gametangia are called
archegonia, the female gametes are formed - the egg. All devices were expressed in the increasing
divergence in the structure of the gametophyte and sporophyte. In the life cycle of higher plants was
fixed, which occurred even in algae, the alternation of two phases (or generations) - sexual
(gametophyte) and asexual (sporophyte). On gametophyte develop organs of sexual reproduction,
and the sporophyte formed sporangia, within which, as a result of reduction (meiotic) division,
spores are formed from a haploid (n), ie single set of chromosomes.
HIGHER PLANTS: WHAT, WHEN AND HOW?
Higher plants (spread Moss family, Horsetail, lycopsids, ferns, gymnosperms and angiosperms).
However the major higher plants are the Angiosperms and Gymnosperms because of their vascular
system and their external morphology differentiated into true roots, stems and leaves.
There are over 352 000 species of vascular plants in the world. More than 95% of vascular plants are
flowering plants, also called angiosperms (e.g. grasses, orchids, maple trees). The other types of
vascular plants are gymnosperms (cone-bearing trees, e.g. pine trees, spruce trees) and seedless
plants (e.g. ferns, horsetails). 5111 species of vascular plants have been found in Canada. When
excluding species ranked as Extinct, Extirpated, Undetermined, Not Assessed, Exotic or Accidental,
the majority (71%) of vascular plants in Canada have Canada General Status Ranks (Canada ranks) of
Secure, while 13% have Canada ranks of Sensitive, 12% have Canada ranks of My Be At Risk and 4%
have Canada ranks of At Risk. A total of 25 species of vascular plants that used to be present in
Canada are now Extirpated from the country. A large number of species (1252) of vascular plants are
Exotic.
Angiosperm (Latin angi-, “enclosed”; Greek sperma, “seed”) is the common name for the division or
phylum comprising flowering plants, the dominant form of plant life. Members of the division are
the source of most of the food on which humans and other mammals rely and of many raw
materials and natural products. Included in the division are most shrubs and herbs, most familiar
trees except pines and other conifers, and specialized plants such as succulents, parasites, and
aquatic types. The flowering plants (angiosperms), also known as Angiospermae or Magnoliophyta,
are the most diverse group of land plants. Angiosperms are seed-producing plants, such as the
gymnosperms, that can be distinguished from the gymnosperms by a series of synapomorphies
(derived characteristics). These characteristics include flowers, endosperm within the seeds, and the
production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces
seeds within an enclosure; they are fruiting plants, although more commonly referred to as
flowering plants. The ancestors of flowering plants diverged from gymnosperms around 245–202
million years ago, and the first flowering plants known to exist are from 140 million years ago. They
diversified enormously during the Lower Cretaceous and became widespread around 100 million
years ago, but replaced conifers as the dominant trees only around 60–100 million years ago. The
number of living angiosperm species is estimated to be in the range of 250,000 to 400,000.
Flowering plants (Magnoliophyta) are the most successful of all plant groups in terms of their
diversity. The group includes more than 250,000 species, and at least 12,000 genera. This group is
usually referred to as angiosperms because, as their name implies, their seeds are enclosed in a
carpel (in a vessel). The carpel is the primary feature that distinguishes angiosperms from
gymnosperms. Angiosperms live in all terrestrial and aquatic habitats on earth. Except for conifer
forests and moss-lichen tundras, angiosperms dominate all the major terrestrial zones of vegetation.
Gymnosperms are primitive seed plants. They have a long evolutionary history. The earliest
gymnosperms appeared in the Paleozoic and became the dominant plants worldwide during the
Mesozoic and Caenozoic periods. Many species of existing gymnosperms emerged in the Tertiary
Period, then went through the Glacial period and survived and multiplied till now. The total number
of living gymnosperms of the world is about 850 species, belonging to 79 genera of 15 families.
Although the number of species of gymnosperms accounts for only 0.36% of that of the
angiosperms, they have formed large areas of various kinds of coniferous forests and are widely
distributed all over the world, especially on mountains from middle to alpine latitudinal zones in
cold-temperate and subtropical latitudes of the Northern Hemisphere. Gymnosperm (Latin gymn-,
“naked”; Greek sperma, “seed”) is the common name for any seed-bearing vascular plant without
flowers. There are several types: the cycad, ginkgo, conifer, yew, and gnetophyte. Gymnosperms are
woody plants, either shrubs, trees, or, rarely, vines (some gnetophytes). They differ from the other
phylum of seed plants, the flowering plants (Angiosperm), in that the seeds are not enclosed in
carpels but rather are borne upon seed scales arranged in cones. The gymnosperms are the most
ancient seed plants; they appear to have arisen from fern ancestors in the Devonian Period. Cycads
retain the most primitive characters of the extant seed plants. Gnetophytes are considered from
morphological and molecular evidence to share a common ancestry with the flowering plants. Living
gymnosperms are distributed worldwide, with a majority, particularly the conifers, in temperate and
subarctic regions. Cycads and gnetophytes are mainly tropical to subtropical. There are about 70
genera with 600 species of living gymnosperms, far less than many families of flowering plants.
Scientific classification: Gymnosperms are contained in four phyla: Cycadophyta, Ginkgophyta,
Pinophyta, and Gnetophyta.
THE EVOLUTIONARY BRIGDE
The Green Algae are the cradle of the higher plants. In other words, they are regarded as one end of
an evolutionary bridge — with the higher plants being the other. But where in the higher plants did
the bridge span to? The Bryophyta are frequently regarded as the most elementary of land plants.
Some, however, would doubt this. It is perhaps unfortunate that because of its ubiquity Marchantia
is often the only liverwort that elementary botanical textbooks consider in any detail, and many
people may have formed the idea that this bryophyte is the most elementary of higher plants. In
reality it is quite advanced among the bryophytes because, for example, it has barrel-pores, which in
some species can to some extent open and close like stomata; well-developed air-chambers with
photosynthetic filaments the presence of archegoniophores and antheridiophores (both of which
are highly specialised structures); two kinds of rhizoids — smooth and peg-walled. So maybe when
we are thinking of the bryophytes as the place among the land plants to which we connect our
evolutionary bridge, we should not keep Marchantia too much in the forefront: rather, we should
think of something a little less advanced — e.g. Riccardia, Pellia.
Others would prefer to consider that the bridge should be connected to the simplest known vascular
plants — the Psilophytales. Such folk think that at least some of the bryophytes may have been
derived from this group, for it is known that even those psilophytalean examples which have
survived the rigours of fossilisation were not quite so far removed from the hornworts
(Anthocerotales) or maybe even the mosses and liverworts as one might at first suppose. In other
words Bryophytes could have been derived from the Psilophytales and as such might be regarded
more properly as a red herring in the present conception of the continuum of plant evolution. But
even though bryologists and pteridologists cannot give any clear-cut indication of what constituted
the first thoroughgoing land plant, they all agree that the ultimate origin of the Tracheophyta seems
to lie within the Chlorophyta. He who subscribes to a monophyletic origin of the land plants sees this
‘hypothetical ancestral form (or forms) somewhere between the Chlorophyta and the most primitive
known extinct Psilopsida but he knows it to be as yet a “missing link” unsupported by concrete fossil
evidence.’ Irrespective of what were in fact the bridging organisms between the Green Algae and
the most primitive land plants, it cannot be denied and one must never lose sight of the fact that at
no time earlier or later in the evolution of the Plant Kingdom was such a momentous evolutionary
transition set in motion as when those early members of the Plant Kingdom began to move from an
aqueous to a terrestrial environment.
BIODIVERSITY
The variety of life on Earth and its biological diversity is commonly referred to as biodiversity. `The
regions that contain similar ecological species groups create ecological groups that are
homogeneous habitats with similar ecologic and floristic composition, which can be used in habitat
classification. With development of restoration ecology and understanding of principles of
biodiversity, it is realized that species composition and diversity are fundamental characteristics of
ecosystems and vegetation diversity should be considered. Plant species distribution over a high
geographical range is controlled by climatic factors, mainly temperature and rainfall. Over a small
range, however, species distribution is related to edaphic factors The number of species of higher
plants and not just higher plants but also their lower counterparts, animals and microorganisms, the
enormous diversity of genes in these species; the different ecosystems on the planet such as
deserts, rainforests and coral reefs are all part of a biologically diverse Earth. Biological diversity
means the variability among all living organisms from all sources including inter alias, terrestrial,
marine and other aquatic ecosystems and biological diversity within a species and of ecosystems.
Biodiversity is the degree of variety in nature and not nature itself.
Out of the 1.4 million known species of living organisms only about 2,50,000 are higher plants and
1.03 million are animal (WWF, 1989). According to another estimate, worldwide there are 2,70,000
known species of vascular plants (Table-1).
Taxonomic Group Number of Species
Bacteria 3,600
Blue green algae 1,700
Fungi 46,983
Bryophytes 1,700
Gymnosperms 750
Angiosperms 2,50,000
Global patterns of angiosperm diversity
Even though the map presented in Fig.1 shows species richness of all vascular plants, the patterns
mainly reflects angiosperm diversity. Fig.2 shows that the absolute maximum of gymnosperm
diversity peaks at less than 60 species per 10,000 km2. The proportion of fern species within floras
reaches maxima of approximately 15% only on some oceanic islands or in montane rainforests (see
below). Thus, 85 to 99% of the patterns shown in Fig. 1 are patterns of angiosperm diversity. Areas
representing global maxima of vascular plant species richness are the Chocó-Costa Rica region,
tropical eastern Andes and north western Amazonia, eastern Brazil, northern Borneo, and New
Guinea, as well as the South African Cape region, southen Mexico, East Himalaya, western Sumatra,
Malaysia, and eastern Madagascar. In general, regions of high geodiversity especially in mountain
areas of the humid tropics and subtropics, harbour the highest species numbers. A comparison of
species richness of biomes, shows that tropical broadleaf forest reaches species numbers up to
10,000 species per 10,000 km2, e.g., in the mountain ranges of Costa Rica (Davis et al. 1997) or c.
5,000 species on 1,200 km2 at the Mt. Kinabalu, Borneo. These absolute maxima are closely linked
to mountainous areas. However, also lowland forests, e.g., in the western Amazon basin, harbour
very high plant diversity. A high number, 473, of tree species and a total of 1,000 vascular plant
species are documented in 1 ha lowland rainforest in the Amazonian part of Ecuador (Valencia et al.
1994), and 3,000 species have been found in 24 ha in Chribibiquete-Araracuara-Cahuinarí region of
Colombian Amazon (Davis et al. 1997). Tropical and subtropical coniferous forests and
Mediterranean climate areas are also very species rich. In contrast, Tundra and Taiga regions
harbour lowest mean species richness, whereas absolute minima can be found in hyperarid areas of
the Sahara and Atacama desert, as well as in Arctic and Antarctic environments.
FIG. 1
Global patterns of gymnosperm diversity
Though new genera are still being described, the gymnosperms might be one of the best
documented groups of Higher plants. However, until now, there has been no global map of total
gymnosperm diversity. Thus, in Fig. 2 we present a first draft of a species richness map of all
gymnosperms at the global scale. The most important centres of gymnosperm diversity are located
in SE Asia. Especially the forests of the Chinese provinces of Yunnan and Sichuan with almost 60
species co-occurring on an area size of 10,000 km2 are very species rich. Other centres with more
than 30 species per 10,000 km2 are SE China in general (with more than 100 species in total), New
Caledonia, northern Borneo with Mt. Kinabalu, the central range of New Guinea, southern Mexico,
and California. Large areas of the southern hemisphere harbour no or only few gymnosperm species.
Exceptions are New Caledonia with more than 40 species, eastern Australia, Tasmania, and New
Zealand, the South African Drakensberg area, and parts of the South American Andes.
FIG. 2
The largest contiguous coniferous forests of the world, the northern hemisphere boreal forests or
taigas, harbour only few species with only 5 to 10 species co-occurring in an area of 10,000 km2.
Less than 15 species in total can be found in the almost 10 Mio. Km2 in Siberia. Only few
gymnosperm species are found in tropical Africa. The whole continent harbours 90 species, which
are mainly concentrated in southern Africa and the Mediterranean. There are, e.g., only two species
documented for West Tropical Africa and less than 15 species in the rainforests of the central Congo
basin. Areas without or with very few species are large parts of the Sahara, southern parts of the
Arabian penninsula, the western part of the Amazon basin and parts of the Cerrado and Caatinga
regions in South America, and the central dry lands of Australia.
GEOGRAPHICAL DISTRIBUTION OF HIGHER PLANTS
The study of the geographical distribution of plants over the earth is one of the most profound
interest, not only to the botanist but to mankind in general. To the former it is of especial interest on
account of the intimate relations existing between it and the origin of the different species of plants.
It is a trite remark that although there may be places identical in temperature, in soil, in humidity,
and other circumstances governing the stations of plants in both North America and Europe, and in
South America and Africa, still it does not necessarily follow that the species of plants in these
identical localities are alike or even at all similar. Indeed, researches show it to be rarely or never the
case. In almost every country, however, there seems to be a certain though sometimes a small
proportion of plants which are found in other and distant parts of the world, Where we find an
isolated example of a group of plants existing in one country, while its nearest congeners are in
another perhaps thousands of miles off, we naturally feel interested in trying to discover the cause
of this wide separation, and the means by which the plant has reached its present location. The
geographical distribution of higher plants is one of the most difficult and important subjects
connected with the study of plants. Before it can be well organized it will be necessary to bring
together very many more observations of plants in all parts of the world than is possible now.
However, a few facts are known which are both interesting and suggestive. In order to make their
presentation as definite as possible, this section of the term paper will be restricted to a brief
account of the geographic distribution of vascular plants.
One of the two great groups of vascular plants is known as the Gymnosperms, a group which in our
region is represented by pines, spruces, hemlocks, cedars, etc. In the tropics the group is
represented by a very different type of trees, known as the Cycads. They resemble in general habit
tree-ferns, or palms. The group of Gymnosperms with which we are acquainted have been called
Conifers on account of the very characteristic cones which they bear. Several principles connected
with geographic distribution may be illustrated by considering briefly these two groups of
Gymnosperms. The Cycads are absolutely restricted to the tropics, a few forms reaching into semi-
tropical conditions, as in southern Florida. If a comparison be made between the eastern and
western tropics, it will be discovered that the Cycads are almost equally divided between, the two
regions. For an unknown time, but certainly a very long one, these eastern and western Cycads have
been separated from one another. As a consequence they have become so unlike that one kind of
Cycad is never found in both hemispheres. Their long separation from one another, and their
somewhat different conditions of living has resulted in working out differences of structures which
botanists recognize as species, genera, etc. The Conifers, on the other hand, are characteristic of
temperate regions. If the distribution of Conifers were indicated upon a world map, there would be
shown a heavy massing of them in the northern region and a lighter massing in the southern region,
the two being separated from one another by a broad tropical belt. This tropical belt is traversed in
just two places; one is by means of the East Indian bridge, across which certain Australasian forms
reach China and Japan; the other is the chain of the Andes mountains, along which a single northern
type has, worked its way into the southern part of South America, The two great masses of Conifers,
therefore, lie in the northern and southern hemispheres, rather than in the eastern and western
hemispheres, as is the case with the Cycads. This long separation has resulted just as it did with the
Cycads; that is, the northern and southern Conifers are not any longer alike, but differ so widely
from one another that botanists cannot discover any form which is common to both the northern
and southern hemispheres, excepting the single one already mentioned, which has succeeded in
crossing the tropics by means of the Andes bridge. Another interesting fact in connection with the
distribution of the Conifers is that their great centers of display are in regions which border the
Pacific Ocean, and they have often been spoken of as a Pacific group. There are three special centers
of display; one is the China-Japan region, a second is the general Australasian region, and the third is
western North America just why this border region of the Pacific is especially favorable for this sort
of plant life is a question which we do not as yet pretend to answer. Another fact which illustrates
this persistent distribution in connection with the Pacific is that in the case of the Conifers which
belong to the southern hemisphere, the continental masses which pair in the display of similar forms
are Australia and South America. Another fact, which is true of all large groups, is that certain forms
have a very extensive distribution, and others are very much restricted in their occurrence. For
example, the greatest genus of Conifers is the genus made up by the pines, at least seventy kinds of
which are recognized. This great genus sweeps throughout all the north temperate regions of the
globe. There is a similar extensive distribution of the different kinds of spruce, larch, juniper, etc. On
the other hand, the giant redwood, known as Sequoia, is restricted to certain comparatively small
areas in California. In China and Japan, and also in Australia, there are numerous illustrations of
forms very much restricted in their occurrence.
Nigeria harbours rich diversity of vascular plants having 285 families (42 ferns and fern allies, 5
gymnosperms, and 238 angiosperms), 1541 genera, and 5029 species (including 183 intraspecific
taxa consisting of 45 subspecies, 133 varieties, and 5 forms). Leguminosae, Poaceae, Rubiaceae,
Orchidaceae, and Cyperaceae are the largest 5 families. Primitive families of angiosperms are quite
scarce excepting the aquatic Nymphaeceae. The 243 seed plant families consist of 171 tropical
families, 56 cosmopolitan families and 16 temperate families, the tropical elements are absolutely
dominant.
ECOLOGICAL DISTRIBUTION OF HIGHER PLANTS AND MAJOR BIOMES
It is a trite remark that although there may be places identical in temperature, in soil, in humidity,
and other circumstances governing the stations of plants in both North America and Europe, and in
South America and Africa, still it does not necessarily follow that the species of higher plants in these
identical localities are alike or even at all similar. Indeed, researches show it to be rarely or never the
case. In almost every country, however, there seems to be certain though sometimes a small
proportion of plants which are found in other and distant parts of the world.
Biomes of the World
Ecologists divide the Earth’s ecosystems into biomes; regions in which the dominant vegetation has
a distinctive growth form. Growth form is the outward appearance or shape of the leaves or body of
a plant. For example, tree, grass, and shrub are different plant growth forms. Trees and shrubs can
be further subdivided into evergreen or deciduous, and broadleaf or needle-leaf (coniferous) growth
forms. Ecologists recognize at least ten different biomes. The world’s major land biomes include
tropical rain forest, tropical dry forest, tropical savanna, desert, temperate grassland, temperate
woodland and shrubland, temperate forest, northwestern coniferous forest, boreal forest, and
tundra. Each of these biomes is defined by a unique set of abiotic factors – particularly climate – and
has a characteristic higher plant ecological community.
Global distribution of major terrestrial biomes (Adapted from PhysicalGeography.net © Dr.
Michael Pidwirny, University of British Columbia – Okanagan).
Tropical Rain Forest
Tropical rain forests are home to more species than all other land biomes combined. The leafy tops
of tall trees – extending up to 70 meters above the forest floor – form a dense covering called a
canopy. In the shade below the canopy, a second layer of shorter trees and vines forms an
understory. Organic matter that falls to the forest floor quickly decomposes and the nutrients are
recycled.
Dominant higher plants: broad-leaved evergreen trees; ferns; large woody vines and climbing plants,
orchids and bromeliads.
Eco- Geographic distribution: parts of South and Central America, Southeast Asia, parts of Africa,
southern India, and northeastern Australia.
Tropical Dry Forest Tropical dry forests grow in places where rainfall is highly seasonal rather than
year-round. During the dry season, nearly all the trees drop their leaves to conserve water. A tree
that sheds its leaves during a particular season each year is called deciduous. The areas associated
are generally warm year-round; alternating wet and dry seasons; rich soils subject to erosion.
Dominant higher plants: tall, deciduous trees that form a dense canopy during the wet season;
drought-tolerant orchids and bromeliads; aloes and other succulents.
Eco-Geographic distribution: parts of Africa, South and Central America, Mexico, India, Australia, and
tropical islands.
Tropical Savanna
Receiving more seasonal rainfall than deserts but less than tropical dry forests, tropical savannas, or
grasslands, are characterized by a cover of grasses. Savannas are spotted with isolated trees and
small groves of trees and shrubs. Compact soils, fairly frequent fires, and the action of large animals
such as rhinoceros prevent some savanna areas from turning into dry forest warm temperatures;
The area is characterised by seasonal rainfall; compact soil; frequent fires set by lightning.
Dominant high plants: tall, perennial grasses; sometimes drought-tolerant and fire resistant trees or
shrubs.
Eco-Geographic distribution: large parts of eastern Africa, southern Brazil, northern Australia.
Desert
All deserts are dry in fact, a desert biome is defined as having annual precipitation of less than 25
centimeters. Beyond that, deserts vary greatly, depending on elevation and latitude. Many undergo
extreme temperature changes during the course of a day, alternating between hot and cold. The
organisms in this biome can tolerate the extreme conditions.
Dominant higher plants: cacti and other succulents; creosote bush and other plants with short
growth cycles
Eco-Geographic distribution: Africa, Asia, the Middle East, United States, Mexico, South America,
and Australia.
Temperate Grassland
Characterized by a rich mix of grasses and underlaid by some of the world's most fertile soils,
temperate grasslands – such as plains and prairies – once covered vast areas of the midwestern
United States. Since the development of the steel plow, however, most have been converted to
agricultural fields. Periodic fires and heavy grazing by large herbivores maintain the characteristic
plant community
Dominant High plants: lush, perennial grasses and herbs; most are resistant to drought, fire, and cold
Eco-Geographic distribution: central Asia, North America, Australia, central Europe, and upland
plateaus of South America.
Temperate Woodland and Shrubland This biome is characterized by a semiarid climate and a mix of
shrub communities and open woodlands. In the open woodlands, large areas of grasses and
wildflowers such as poppies are interspersed with oak trees. Communities that are dominated by
shrubs are also known as chaparral.
Dominant Higher plants: woody evergreen shrubs with small, leathery leaves; fragrant, oily herbs
that grow during winter and die in summer.
Eco-Geographic distribution: western coasts of North and South America, areas around the
Mediterranean Sea, South Africa, and Australia.
Temperate forests
They contain a mixture of deciduous and coniferous trees. Coniferous trees, or conifers, produce
seed-bearing cones and most have leaves shaped like needles. These forests have cold winters that
halt plant growth for several months. In autumn, the deciduous trees shed their leaves. In the spring,
small plants burst out of the ground and flower.
Dominant plants: broadleaf deciduous trees; some conifers; flowering shrubs; herbs; and a ground
layer of ferns.
Geographic distribution: eastern United States; southeastern Canada; most of Europe; and parts of
Japan, China, and Australia.
Northwestern Coniferous Forest
Mild, moist air from the Pacific Ocean provides abundant rainfall to this biome. The forest is made
up of a variety of conifers, ranging from giant redwoods, along the coast of northern California. To
spruce, fir, and hemlock farther north. Moss often covers tree trunks and then forest floor.
Flowering trees and shrubs such as dogwood and rhododendron are also abundant. Because of its
lush vegetation, the northwestern coniferous forest is sometimes called a "temperate rain forest.."
Dominant plants: Douglas fir, Sitka spruce, western hemlock, redwood.
Geographic distribution: Pacific coast of northwestern United States and Canada, from northern
California to AlaskaBoreal Forest.
Boreal Forest
Along the northern edge of the temperate zone are dense evergreen forests of coniferous trees.
These biomes are called boreal forests, or taiga Winters are bitterly cold, but summers are mild and
long enough to allow the ground to thaw. The word boreal comes from the Greek word for "north,"
reflecting the fact that boreal forests occur mostly in the Northern Hemisphere.
Dominant plants: needleleaf coniferous trees such as spruce and fir; some broadleaf deciduous
trees; small, berry-bearing shrubs
Geographic distribution: North America, Asia, and northern Europe
Tundra The tundra is characterized by permafrost, a layer of permanently frozen subsoil. During the
short, cool summer, the ground thaws to a depth of a few centimeters and becomes soggy and wet.
In winter, the topsoil freezes again. This cycle of thawing and freezing, which rips and crushes plant
roots, is one reason that tundra plants are small and stunted. Cold temperatures, high winds; the
short growing season, and humus-poor soils also limit plant height
Dominant plants: ground-hugging plants such as sedges, shrubs and short grasses.
Geographic distribution: northern North America, Asia, and Europe.
Global Vascular plant distribution in relation to topography, soils, micro-climate and other
influencing factors.
Topography, soils, climate, disturbance, herbivory and competition can affect distributions of higher
plant species and hence community composition (Körner 2003). In mountain systems, climate can
have a major effect on vegetation. As a result, most communities have been identified as being
particularly at risk from predicted changes in climate (Grabherr et al. 2000; Walther et al. 2005).
With increasing temperatures and changes in snow cover regimes predicted for many regions
around the world (Hennessy et al. 2003; Pauli et al. 2007; IPCC 2007; Van de Ven et al. 2007), it is
important to determine the relative importance of environmental factors including climate on
current vascular plant composition within and among the various eco-geographical habitats of the
world.
Over the past few decades there has been increasing concern about the effects of human activities
on the natural environment (McNeill 2001). Lately, because of urban and agronomy development,
forests and rangelands destruction and natural changes, some of these higher plants are reported as
extinct species It became clear that ecosystem interference largely predates the 20th century and
that it has far reaching consequences beyond the major industrialised areas of the world (Crosby
1972; Richards 2003; Simmons 1989; Turner et al. 1990). Along with the effects of habitat
destruction, nutrient loading is one of the most important threats to plant diversity, leading to
declines of distribution area and even regional extinction . If climatic factors such as temperature
and precipitation change in a region beyond the tolerance of a species phenotypic plasticity, then
distribution changes of the species may be inevitable. There is already strong evidence that plant
species are shifting their ranges in altitude and latitude as a response to changing regional climates.
When compared to the reported past migration rates of plant species, the rapid pace of current
change has the potential to not only alter species distributions, but also render many species as
unable to follow the climate to which they are adapted. The environmental conditions required by
some species, such as those in alpine regions may disappear altogether. The result of these changes
is likely to be a rapid increase in extinction risk. Adaptation to new conditions may also be of great
importance in the response of plants. Predicting the extinction risk of plant species is not easy
however. Estimations from particular periods of rapid climatic change in the past have shown
relatively little species extinction in some regions, for example. Knowledge of how species may
adapt or persist in the face of rapid change is still relatively limited. Changes in the suitability of a
habitat for a species drive distributional changes by not only changing the area that a species can
physiologically tolerate, but how effectively it can compete with other plants within this area.
Changes in community composition are therefore also an expected product of climate change.
The winds undoubtedly exercise an immense influence on the distri- bution of plants. Many seeds
are furnished with a pappus or feathery appendage, by means of which they are easily carried along
by the wind. Many of these belong to the Composite, such as the dandelion, the thistles, hieraciums,
etc. Others are provided with wings, as in the ash and the maple ; still others with cottony or
feathery tails, as in the anemones and clematis. Again, many are so minute as to be visible to the eye
only in the form of smoke, and are so numerous as to be almost uncountable.
CONCLUSION
The appearance of a plant group in a given area isn’t accidental, but occurs in response to changes in
climatic, topographic, edaphic and biotic parameters. In fact, vegetation groups are determined by
the combined effects of a whole range of ecological factors. Thus, change in the soil, topography and
grazing factors can lead to vegetation responses in each area of the landscape .The regions that
contain similar ecological species groups create ecological groups that are homogeneous habitats
with similar ecologic and floristic composition, which can be used in habitat classification. Higher
Plant species distribution over a high geographical range is controlled by climatic factors, mainly
temperature and rainfall. Over a small range, however, species distribution is related to edaphic
factors. Unfortunately, nowadays higher plant species conversation is less considerable on a global
platform.
REFERENCIES/BIBLIOGRAPHY AND LITERATURE CITATIONS
PATTERNS OF VASCULAR PLANT DISTRIBUTION AT CONTINENTAL TO GLOBAL SCALES
Jens Mutke , Wilhelm Barthlott(2008)
THE DIVERSITY OF ANGIOSPERMS AND GYMNOSPERMS
www.academia.edu.com
THE GREEN ALGA: CRADLE OF THE HIGHER PLANTS(Tuatara; vol 23, issue3)
H.W. johston,( Botany Department, Victoria University of Wellington, NZ)
VASCULAR PLANT DISTRIBUTION
C.M. Pickerg, K Green,( school of environment, griffith university, australia)
PLANT PHYLOGENY AND PHYTOGEOGRAPHY
Encyclopaedia Britannica
DIVERSITY AND DISTRIBUTION OF VASCULAR PLANTS IN NIGERIA
Abiodun E. Ayodele(university of Ibadan, Ibadan), Yong yan(institute of botany, the chinese
academy of sciences)
GEOGRAPHIC DISTRIBUTION OF SEED BEARING PLANTS
www.birdsnature.com
BIODIVERSITY AND ECOLOGY OF VASCULAR PLANTS
Chris dinsen rogers(ph.D)
POPULAR SCIENCE MONTHLY
The local distribution of plats and theory of adaptation(Laster frankward, vol 9)
Modes of distribution of plants(joseph E. james, vol 17)
WIKIPEDIA, the free encyclopaedia
www.wikipedia.com
ENCARTA ENCYCLOPEDIA
RELATIONSHIP BETWEEN ENVIRONMENTAL FACTORS AND PLANT DISTRIBUTION
Salman Zare, Mohammad Jafari(Faculty of Natural Resource, University of Tehran, Iran)
MAJOR BIOMES OF THE WORLD-TEACHERS DOMAIN
www.teachersdomain.com
GLOBAL PATTERNS AND DETERMINANTS OF VASCULAR PLANT DIVERSITY
Holger Kreft, Walter Jetz(Nees Institute for Biodiversity of Plants, University of Bonn)
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