PHYTOGEOGRAPHY
PHYTOGEOGRAPHY
Phytogeography or plant geography is the study of the composition, distribution and ecology of
plants all over the world.
The distribution of vegetation on the earth is governed by a number of factors:
(a) Climatic factors: These include sunlight, temperature, precipitation, humidity, soil moisture etc.
(b) Edaphic factors: Soil nutrients, Soil texture, soil structure, acidity, alkalinity & nature of soil
profiles.
(c) Biotic factors: The biological components of an area (plants and animals), interactions between
different species of plants, competition etc.
(d) Topographic factors: These include relief, slope, aspect etc.
(e) Tectonic factors: These include plate movement, endogenetic movements, volcanism &
earthquakes.
(f) Human interference: The role of humans in the creation, preservation, modification and
destruction of plant species and forests.
PHYTOGEOGRAPHICAL REGIONS
In phytogeography, a Phytochorion (plural = phytochoria) is a geographic
area with a relatively uniform composition of plant species.
Adjacent phytochoria do not have a distinct boundary, rather a transitional
zone exists in between, containing species from both areas. This area of
overlap is known as Vegetation Tension Zone.
Traditionally, phytogeographic areas have been defined either as floristic
or phytogeographic zones and regions or as phytogeographic or floristic
kingdoms, regions and provinces.
The largest group of plants occupying a particular type of habitat with
uniform environmental conditions is called a Phytogeographic or Floristic
Kingdom. The next smaller unit is phytogeographic region or province.
PHYTOGEOGRAPHICAL REGIONS
The botanist Ronald Good, in his book, The Geography of
Flowering Plants (1947), divided the world’s plant species
growing on land into 6 floristic or phytogeographic
kingdoms.
These kingdoms are: Boreal or Holarctic, Neotropical,
Palaeotropical, Cape or South African, Australian and
Antarctic.
These kingdoms are divided into smaller units called
floristic regions.
Each of these provinces are divided into even smaller
units called floristic or phytogeographic provinces.
Source: Wikipedia
PHYTOGEOGRAPHICAL REGIONS
Boreal or Holarctic Kingdom:
This floral kingdom includes the whole of North America, except Central America,
Greenland, entire Europe, northern Asia and Arctic regions. This is the most extensive of
all floral kingdoms.
This kingdom is divided into 8 regions:
(a) Arctic and Sub-arctic region (with 3 provinces),
(b) Euro-Siberian region (with 11 provinces),
(c) Sino-Japanese region (with 6 provinces),
(d) Western & Central Asiatic region (with 4 provinces),
(e) Mediterranean region (with 4 provinces),
(f) Macronesian region (with 4 provinces),
(g) Atlantic North American region (with 6 provinces)
(h) Pacific North American region (with 7 provinces).
PHYTOGEOGRAPHICAL REGIONS
Palaeotropical Kingdom:
This includes most of Africa, South, SE and SW Asia and central parts of China. This
kingdom is divided into 3 sub-kingdoms namely African Sub-kingdom, Indo-Malaysian
Sub-kingdom and Polynesian Sub-Kingdom.
This 3 sub-kingdoms are in turn divided into 15 regions:
(i) North African-Indian Desert Region (with 2 provinces)
(ii) Sudanese park Steppe Region
(iii) North-east African Highland & Steppe Region
(iv) West African Rain forest Region
(v) East African Steppe Region
(vi) South African Region
(vii) Madagascar Region
(viii) Ascension & St. Helena Region
(ix) Indian Region
(x) Continental South-east Asiatic Region
(xi) Malaysian Region
(xii) Hawaiian Region
(xiii) New Caledonian Region
(xiv) Melanisian Region
(xv) Micronesian Region
PHYTOGEOGRAPHICAL REGIONS
Neotropical Kingdom:
This includes whole of South America, except southern Chile and Patagonia.
Certain plant species are common to Palaeotropical kingdom.
It is divided into 7 regions:
(i) Caribbean region (with 4 provinces)
(ii) Venezuelan & Guyanese region
(iii) Amazon region
(iv) South Brazilian region
(v) Andean region
(vi) Pampas region
(vii) Juan Fernandez region.
Plants that are unique to this region include potato, tomato, Maize, Cassava etc.
PHYTOGEOGRAPHICAL REGIONS
Cape or South African Kingdom:
This includes the southern tip of Africa, around the Cape of Good Hope. It is
divided into one region, the Cape floristic region and 1 province, the Cape
floristic province.
It is the only floristic kingdom that is completely within one country- South
Africa.
Home to 5 of South Africa’s 12 endemic plant families and 160 endemic
genera of plants.
Dominated by Fynbos, a type of shrubland, occurring on acid sands and
nutrient poor soils.
The fynbos is home to a large number of plants.
PHYTOGEOGRAPHICAL REGIONS
Australian Kingdom:
The Australian Kingdom includes the whole of Australia, characterized by
the typical Eucalyptus.
This kingdom is divided into 3 regions, which are:
(i) North & East Australian Region (with 4 provinces)
(ii) South West Australian Region
(iii) Central Australian Region (with 3 provinces)
The endemic flora of Australia have developed due to the physical isolation
of the country from the other southern continents.
PHYTOGEOGRAPHICAL REGIONS
Antarctic Kingdom:
Covering southern Chile, Patagonia, New Zealand, Antarctica and all
islands in the Southern Ocean, south of 40S latitude.
It is divided into 3 regions:
(i) New Zealand region (with 6 provinces)
(ii) Patagonian region (with 3 provinces)
(iii) Regions of Southern Temperate Islands
The most common species in this kingdom is the Southern Beech.
PHYTOGEOGRAPHICAL REGIONS OF INDIA
According to D. Chatterjee (1962), India can be divided into 9 phytogeographical regions:
(a) Western Himalaya, (b) Eastern Himalaya, (c) Indus Plains, (d) Gangetic Plains, (e)
Central India, (f) Deccan, (g) Western Coast of Malabar, (h) Assam and (i) Andaman &
Nicobar
WESTERN HIMALAYAS:
This region consists of N & S Kashmir, parts of Punjab & Kumaun region of Uttaranchal.
Avg. annual rainfall of 100-200 cm. At high altitudes, snowfall occurs in the winter season.
It is divided into 3 zones:
(a)Sub-montane (tropical & subtropical) zone: 300-1500 m amsl. The vegetation consists of
subtropical dry evergreen forests, subtropical pine and tropical moist deciduous
forests.
(b)Montane (temperate) zone: 1500-3500 m amsl. Consists of wet forests, Himalayan dry
and Himalayan moist temperate forests. Plants include oak, Rhododendron, Betula etc.
(c)Alpine zone: 3500-5000 m amsl. Alpine forest consisting of birch and fir forests and
birch and rhododendron forests. Plants include birch, rhododendron, Silver fir, Juniper
etc.
PHYTOGEOGRAPHICAL REGIONS OF INDIA
EASTERN HIMALAYAS:
This region extends from the east of Nepal to Arunachal Pradesh. Warmer & wetter than
the western Himalayas. The tree line and snowline are about 300 m higher than in the
west. It is also divided into 3 zones:
(a) Submontane (Tropical) zone: Extends from plains to 1800 m amsl. Consists of sal and
mixed deciduous forests.
(b) Montane (Temperate) zone: 1800-4000 m amsl. Consists of Oak and Rhododendron at
lower altitudes and conifers at higher altitude.
(c) Alpine zone: > 4000 m amsl. Extremely cold. Distinguished by complete absence of
trees and predominance of shrubs and meadows.
INDUS PLAINS:
Consists of a part of Punjab, Rajasthan, Delhi, a part of Gujarat and Kutch. Climate
consists of hot, dry summer and dry and cold winter. Annual rainfall is < 70 cm, but can be
as less as 10-15 cm. Saline soils predominate, except in cultivated areas. Vegetation
consists of tropical thorn forests and grasslands. E.g. Acacia.
PHYTOGEOGRAPHICAL REGIONS OF INDIA
GANGETIC PLAINS:
One of the richest vegetation zones in the world. Covers a part of Delhi, Uttar Pradsh,
Bihar, Jharkhand, a part of Odisha and WB. Avg. annual rainfall is 50-150 cm as one moves
from west to east. Can be divided into 3 zones: Upper Gangetic Plains (Delhi to Allahabad),
Middle Gangetic Plains (rest of UP, Bihar, Jharkhand) and Lower Gangetic Plains (WB &
Odisha). Consists of Tropical wet semi-evergreen, tropical moist deciduous forests,
tropical dry deciduous forests and mangroves.
CENTRAL INDIA:
This zone covers a part of Odisha, Madhya Pradesh, some parts of Gujarat, Vindhyan
region and Chattisgarh. The average annual rainfall is 100-170 cm. Biotic disturbances are
very common in this region, leading to degradation of the original forest cover into thorny
vegetation in open areas. Sal forests are found in areas having rainfall > 150 cm, mixed
deciduous forests in areas of 125-150 cm and thorny forests in areas having < 125 cm rain.
PHYTOGEOGRAPHICAL REGIONS OF INDIA
DECCAN:
This zone includes the whole of Peninsular India, from southern MP to the tip of
Kanyakumari, excluding the western Ghats. The avg. annual rainfall is about 100 cm. This
region may be divided into two sub zones- the Deccan Plateau consisting of teak forests
and Coromandal coast, consisting of halophytic species.
WEST COAST OF MALABAR:
This zone is a small one extending from Kanyakumari to Gujarat along the Western Ghats.
Warm & humid climate with rainfall > 400 cm. The climate is tropical on the coasts and
temperate in the hills. The vegetation consists of tropical wet evergreen, moist evergreen
and moist deciduous forests, with swamps near the coasts. The temperate forests are
locally known as Sholas.
PHYTOGEOGRAPHICAL REGIONS OF INDIA
ASSAM:
This zone covers the Brahmaputra Valley, Manipur and Naga Hills. It is an area of very
heavy rainfall and also has very high temperature. This leads to dense forests. Broadleaved tropical evergreen and some temperate forests are seen here. Important species
include Bamboo Canes, Orchids, Ferns, Magnolia etc.
ANDAMAN & NICOBAR ISLANDS:
This region includes the A&N and Lakhswadeep Islands. Warm & humid climate with high
temperature and annual rainfall. Tropical Evergreen, semi-evergreen, tropical deciduous
and mangrove forests dominate here.
PLANT TAXONOMY
Plants/animals are divided into different types at different
levels. This hierarchical classification of is also known as
Taxonomic Classification.
The Taxonomic classification is a binomial nomenclature
i.e. it has two names. This system was developed by Carl
Linneaeus in 1735.
This classification starts with Kingdom and generally ends
in species, although even lower levels are sometimes
identified.
The best way to remember this is King Patrick Came Over
For George’s Sword.
For an organism to be considered as plant, they should be
multi-cellular, eukaryotes, autotrophs and development of
cell wall.
PLANT TAXONOMY
All plants are placed in the Kingdom called Plantae.
All plants are divided into Divisions, commonly known as
Phylum (plural: phyla). There are 4 main phyla: Thallophyta
(no differentiated plant body), Bryophyta (differentiated
plant body without vascular tissue), Pteridophyta
(differentiated plant body with vascular tissues that don’t
produce seeds) and Spermatophyta (plants with
differentiated plant body with vascular tissues that produce
seeds).
The Spermatophytes are divided into two classes namely
Gymnosperms (meaning naked seeds) and Angiosperms
(enclosed seeds with fruits). Angiosperms are also known
as the flowering plants.
The Angiosperms are divided into 2 sub-classes:
Monocotyledons (containing one cotyledon i.e. seed leaf) or
Dicotyledons (containing 2 cotyledons).
PLANT TAXONOMY
These two classes of plants are divided into various Orders.
Further, the orders are divided into Families. These are
plants having many similarities. The main families of
plants are Grass (e.g. corn, sorghum etc.), Legume (alfalfa,
beans etc.), Lily (e.g. onion, garlic etc.), Gourd (e.g.
pumpkin, melon, cucumber etc.), Composite (e.g.
sunflower, daisy etc.), Nightshade (e.g. potato, tomato etc.)
and Parsley (e.g. carrots etc.).
The next 2 classifications are Genus (pl: genera) and
Species. Genus is denoted by capitalization of the first letter
and is the normal name of the plant. E.g.
The species denotes the individual plant, identified in
terms of colour of the flower, shape of leaves etc. Normally,
it is written in small.
E.g. Zea mays (Maize)
FORESTS & ITS TYPES
A forest is a large area dominated by trees. They are the dominant terrestrial
ecosystem in the world and account for 75% of the Gross Primary Productivity of
the Earth’s biosphere and 80% of the world’s plant biomass.
Many definitions of forest have been proposed by various agencies and scientists
from time to time. There are more than 800 definitions of forests!!!!
These definitions can be broadly divided into 3 types: Administrative, Land Use
and Land Cover:
Administrative definitions are based on the legal designation or status of land and
generally has no relation to the vegetation growing on it.
Land Use definitions are based upon the purpose that the land serves. E.g. timber
production. Under these definitions, things such as roads, infrastructure etc.
associated with the purpose or lands cleared for harvesting or affected by disease
etc. can also be considered as forests, even if they contain no trees at all.
FORESTS & ITS TYPES
Land Cover definitions generally define forests in terms of the type and density of vegetation
growing on the land.
Such definitions usually apply some kind of threshold such as tree density (nos. of trees per
unit area), canopy cover (the area of ground under tree canopy) or basal area (section of the
ground occupied by the cross-section of the tree trunk) etc.
Under such definitions, an area can be considered as forests only if tree grows there. However
areas with growing but immature trees can also be considered if they are expected to reach
maturity.
According to a Report made by the Convention for Biodiversity, a forest is “a land area of more
than 0.5 hectares, with a tree canopy cover of 10%, which is not primarily under agricultural or
specific non-forest use. In case of young forests or regions where tree growth is climatically
suppressed, the trees should be capable of reaching a height of 5 m in situ and of meeting the
canopy cover requirement”.
As of 2015, there were 3 trillion trees in the world, of which ~47% is in the tropics or subtropics, 20% in temperate zones and ~23% in coniferous and boreal forests.
FORESTS & ITS TYPES
The UNEP-WCMC classification of forests identifies 26 types of forests in the world on the
basis of the main types of trees and climatic zones. These 26 types are, in turn, classified into
6 broad types.
These broad types are:
 Temperate Needleleaf Forests
 Temperate Broadleaf and Mixed Forests
 Tropical Moist Forests
 Tropical Dry Forests
 Sparse Trees and Parklands
 Forest Plantations
Temperate Needleleaf Forests:
These occupy mostly higher latitudes in the northern hemisphere as well those in higher
elevation areas of warm temperate regions. They grow on nutrient-poor soils. Composed
almost entirely of coniferous forests, with pines, spruce, firs and larches forming the canopy
layer.
FORESTS & ITS TYPES
Temperate Broadleaf & Mixed Forests:
They are found in warmer temperate latitudes, but can be found in cool temperate regions of
the southern hemisphere. They include mixed deciduous forests, broad evergreen
rainforests, the sclerophyllus forests of Australia and Southern Beech forests.
Tropical Moist Forests:
Tropical Moist Forests are of different kinds. These include lowland broadleaf evergreen
rainforests of the Amazon basin, the peat swamp forests of South-East Asia and the high
forests of the Congo Basin. Seasonal tropical forests range from the rainforest zone 10 N&S
of the Equator to the Tropics.
Tropical Dry Forests:
They are characteristic of those tropical areas that are affected by seasonal droughts. The
seasonal rainfall means that the canopy layer is deciduous. However, sometimes the
proportion of evergreen forests increase, giving rise to sclerophyllous forests. Thorn forests
are found in areas of prolonged droughts, while Savannahs are found in fire-prone areas.
FORESTS & ITS TYPES
Sparse Trees and Parklands:
Sparse trees and Savannahs are forests with lower canopy cover of trees. They
occur mainly in transition areas from forested to non-forested areas. They
occur primarily in boreal zone or seasonally dry tropics. At high latitudes,
the tree cover is sparse and discontinuous. This is known as Taiga. In the dry
topics, savannah vegetation grows, with trees sufficiently widely spaced so
that the canopy is not closed. The open canopy allows sufficient light to reach
the ground to support unbroken layer of grasses.
Forest Plantations:
They are used for the purpose of timber and pulpwood. They are generally
not suitable as habitats for the native biodiversity. However, they can provide
important ecosystem functions like protecting watersheds and storing
carbon.
DEFORESTATION & DEGRADATION OF FORESTS
Forests are important resources for everyone, humans or animals. They provide us with a
number of important items in our daily life as well carry out important ecosystem
functions.
Unfortunately, they are also destroyed to considerable extent, mainly as a result of human
activities. Two main terms are commonly used: Deforestation and Forest Degradation.
Deforestation: According to FAO, deforestation is the conversion of forested lands to another
land use or long-term (10 years) reduction of the tree canopy cover below the 10% threshold.
Such conversion includes agricultural lands, pasture, urban areas, water reservoirs etc.,
but excludes such areas which are cleared for purposes such as logging or silviculture etc.
Deforestation is normally reported in terms of net change over a large area.
Forest Degradation: According to FAO, forest degradation includes changes within the
forest which negatively affect the structure and function of the stand or site, and thereby,
lower the capacity to supply products and/or services. It is generally expressed in terms of
the reduction of canopy cover through logging, fire etc., so long as the canopy remains
above the 10% threshold.
DEFORESTATION & DEGRADATION OF FORESTS
Causes of deforestation:
1)
2)
3)
4)
5)
6)
Agricultural activities
Population growth
Urbanization
Forest fires
Unequal distribution of power and wealth
Many forest functions do not have economic value
Causes of Forest Degradation:
1) Climate Change: Changes in climate due to changes in atmospheric temperature is a
primary cause of forest degradation. These changes can cause unusually long dry or
cold periods, which can create undesirable environmental conditions for trees to
survive. In extreme cases, animals migrate to other areas, affecting the region’s
biodiversity.
2) Forest Fires: Can occur due to natural or man-made reasons. However, forest fires are
important reasons for degradation of forests. This can wipe out thousands of trees at one
go. This affects both the region’s economy as well as biodiversity.
DEFORESTATION & DEGRADATION OF FORESTS
Causes of Forest Degradation:
3) Pests and Diseases: Different kinds of pests and diseases can afflict plants in a forest,
leading to its degradation. These can affect certain aspects of forest ecology like
biodiversity and food chain relationship because of death of many plant and animal
species.
4) Air Pollution: Air pollution is a major cause for forest degradation. When air gets polluted
by toxic gases like sulphur dioxide etc., they can cause atmospheric acidification and can
produce acid rain, which can adversely affect soil and plant cover. Acid rain destroys
leaves, which can result in reduced photosynthesis and also alter soil moisture, which
supports the plants. Thus plants die, causing degradation.
5) Terrestrial Pollution: Discharge of different kinds of toxic chemicals on lands, adjacent to
forests can be harmful to the plants growing there. They also affect the food web within the
forest communities, thereby affecting its biodiversity and inducing its degradation.
6) Soil Erosion & Sedimentation: Erosion of river banks induces soil erosion and
sedimentation, which can destroy forest covers and lead to their degradation.
DEFORESTATION & DEGRADATION OF FORESTS
Impacts of Deforestation:
1) Atmospheric impacts: Deforestation contributes to global warming and adds to the
greenhouse effect. Tropical deforestation is responsible for 20% of the world’s greenhouse
gas emissions and about a third of the world’s total carbon emissions. Also, deforested
lands heat up faster, causing higher temperature. This induces rainfall.
2) Hydrological impacts: Hydrological cycle is also affected by deforestation. Trees extract
groundwater through their roots and release it to the atmosphere. When trees are cut down,
transpiration cannot occur, causing drier climate. Soil water content also goes down. Soil
cohesion is also affected by deforestation, causing soil erosion and in some cases, flooding
and even landslides. It also increases surface run-off, which moves faster than sub-surface
flows and causes decreased evapotranspiration. This causes less moisture transport.
3) Impacts on soils: Soil loss is enhanced due loss of root protection and increased runoff.
This can in turn induce higher sediment yield in rivers and cause problems like siltation.
E.g. Damodar. Deforestation can also induce landslides in steep slopes due to lack of soil
cohesion.
DEFORESTATION & DEGRADATION OF FORESTS
Impacts of Deforestation:
4) Biodiversity Loss: Deforestation causes loss of biodiversity, which in turn, induces
extinction of species. They provide habitat for wildlife and promotes medical conservation.
Deforestation can also reduce the ability of plants to resist pest attacks. 50,000 species are
being lost annually in tropical rainforests due to deforestation.
5) Economic Impacts: Living standards go down. Short-term exploitation of forests could
lead to short-term gains, but can cause long-term losses.
ESTIMATES OF DEGRADATION OF FORESTS
Since degradation involves reduction in the quality of the structure of the forest, many
proxies are used to estimate one. One such typical proxy is the canopy cover estimation
through remote sensing. However it is necessary to complemented by other methods also to
capture changes in forest values and goods.
Three commonly used proxies are used:
(a) Reduction in biomass for growing stock and biomass stock.
(b) Reduction in biodiversity and habitat fragmentation
(c) Reduction in soil quality, as indicated by soil cover, depth and fertility.
Growing Stock and Biomass Stock:
Growing stock: According to FAO, it is defined as “volume over bark of all living trees more
than X cm in diameter at breast height (dbh). Includes stem from the ground level up to a
top diameter of Y cm and may also include branches to a minimum diameter of W cm”.
Countries need to decide X, Y and Z. Generally, considered as stem volume in forests of all
living trees more than 10 cm dbh, over bark, measured from stump to the top of the bole.
ESTIMATES OF DEGRADATION OF FORESTS
Biomass Stock: Organic material, both below and above ground and both living and dead
(e.g. trees, grasses, litter, crops).
Two kinds of biomass:
(a) Above Ground Biomass: All living biomass above the soil, including stem, stump, bark,
branches, seeds and foliage. It is also known as Forest Biomass.
(b) Below Ground Biomass: All biomass of live roots. Fine roots of < 2mm are excluded.
Stem volume of an individual tree is estimated by the formula:
V = dbh2 /4  htot  fform
Where, V = volume (in m3), dbh = diameter at breast height (in m), htot = total height of tree
(in m), fform= Stem form factor (usually between 0.3 to 0.8, depending upon shape of the tree.
Above Ground Biomass of an individual tree is estimated by the formula:
AGB = exp[-2 + 2.42 ln(dbh)], where AGB = Above Ground Biomass (in kg) and dbh =
diameter at breast height (in cm).
The total Growing Stock or Biomass Stock can be calculated by estimating the V or AGB for
all trees in a forest and dividing it by the forest area.
ESTIMATES OF DEGRADATION OF FORESTS
Biodiversity and Habitat Fragmentation:
The biodiversity of a forest provides important ecosystem services such as pollination,
decomposition, seed dispersal, resilience and disease reduction, in addition to providing a
number of good and services. Thus, reduction of biodiversity is also an indicator of the
degradation of a forest.
The biodiversity indicators of forest degradation need to be studied at two scales: Stands
(comprising of individual groups of trees, distinguishable from other surrounding groups of
trees by their species composition) and Landscapes (multiple stands). Both scales are
important and require different, but sometimes overlapping, sets of indicators. These
indicators should be able to provide quantitative data that can be used to assess trends over
time.
The indicators used for biodiversity related degradation can be derived either from remote
sensing or ground based (species-based) surveys. The latter is complementary to the
former and allows more detailed measurement.
ESTIMATES OF DEGRADATION OF FORESTS
Remote Sensing Based Indicators:
Three biodiversity indicators of forest degradation are based primarily on remote sensing
and can be studied at both landscape and stand scales. These are Ecosystem State, Habitat
/Forest Fragmentation and Ecosystem Diversity.
Ecosystem State refers to the composition and structure of an ecosystem relative to the
ecosystem predicted to occupy a given site in the absence of environmental change or
disturbance. So it may be described as area of forest that has changed state from that which
is predicted for the site. The key parameters used are (i) dominant floristic (tree)
composition and (ii) stand structure that may be expected for a given stand. Loss of
biodiversity may lead to reduction of resilience (i.e. the ability of the forest to bounce back
from a disturbance).
A negative change of state refers to a loss of resilience that leads to a shift from one
ecosystem type to another, with changes and reduction in good and services. E.g. if a forest
is expected to have mixed tree species, but instead has uniform trees, then the state has
changed. A simple indicator of biodiversity-based forest degradation would be sum of the
unexpected forest types on a landscape relative to that predicted for that landscape.
ESTIMATES OF DEGRADATION OF FORESTS
Forest or Habitat Fragmentation refers to the division of a forest into smaller areas, known
as patches. This creates new edges between forests and non-forested vegetation. It can have
significant negative impacts on biodiversity through its impact on species composition and
stand structure like reduction in habitat area, a reduction in ‘interior space’ (i.e. habitat
unaffected by edges), increased exposure to edges as well as spatial and genetic isolation of
individual species. Thus, fragmentation is an excellent indicator of forest degradation.
Several metrics can be used to measure fragmentation. This includes (i) Mean Patch Size
(in hectares), which is total forest area/total number of patches. Decreasing mean patch
size = increasing degradation; (ii) Mean Perimeter-Area Ratio, which is the ratio of patch
perimeter to the area of all the patches in the landscape- increased ratio = increased
degradation; (iii) Mean Euclidean Nearest Neighbour Distance (in metres), defined as
mean distance between all landscape patches, based on shortest edge-to-edge distancesincreasing mean NN distance = increased degradation and (iv) Forest Integrity Index i.e. a
combined metrics of patch size, connectivity and edge effects; lower FII = reduced ability
to produce goods and services, hence increasing degradation.
ESTIMATES OF DEGRADATION OF FORESTS
Ecosystem Diversity This indicator suggests that a certain percentage of a landscape
should be in each of several known forest types and that a broad composition of the forest
stand should be predictable, given certain pre-existing conditions.
High resolution satellite imageries can be used to assess ecosystem diversity at the
ecosystem scale, but not finer than that. Measurement at such a scale, expressed in terms
of % of forest ecosystems or change in area, can be done one of the many similarity indices
that compare a location or locations over time. One such index is the Sorensen’s Index of
Similarity.
2z/(x +y), where x = number of forest types in the landscape of interest or at time t; y =
number of forest types in the reference landscape or at time t + 1 and z = the number of
ecosystems common to both.
The index ranges from 0 to 1, with 1 indicating no difference.
ESTIMATES OF DEGRADATION OF FORESTS
Ground Based Indicators:
Three biodiversity indicators of forest degradation are based primarily on ground-based
studies and can be investigated at both landscape and stand scales. These are Forest Tree
Species, Functional Species and Invasive Alien Species.
Forest Tree Species: A significant departure from the expected species composition of trees
in a forest is indicative of degradation via the effects it has on the forest biodiversity as well
as the production of goods and services by the forests. Tree species composition can
change due to excessive fire, over-harvesting of commercially important species and other
such unsustainable practices. Mapping of tree species composition can provide an
important clue to the degradation state of the forests. However, it requires knowledge of the
forest ecosystem types, the expected i.e. normal species composition and the variance
found in similar ecosystems across the landscape.
Functional Species: Any change in forest composition and its abiotic components will result
in changes to the associated species. A subset of the total species composition that is more
important in providing ecosystem goods and services is known as Functional Species. If
they can be identified, then their declining abundance is an indicator of degradation.
ESTIMATES OF DEGRADATION OF FORESTS
Ground Based Indicators:
Invasive Alien Species: An invasive alien species is a species that is not native to a forest. It
has invaded the forest and is harming it. The invasion of this exotic species can result in the
reduction of ecosystem goods and services provided by the forests as well as its
biodiversity. Mapping the areas of forests affected by such species is an good indicator of
its degradation.
Soil Quality:
The presence of soil erosion in forests is an indicator of its degradation. Soil erosion can
have major impacts on a range of forests services- reduced water quality, pollution of
watersheds and is both a cause and an indicator of reduced soil fertility. Besides, forests are
inherently more susceptible to degradation, including soil erosion, than most agricultural
lands or pasture lands. More the erosion, more degraded is the forested area.
Soil erosion can be caused both by water and wind, but erosion by water is more common.
Besides, erosion can be visually estimated or measured using direct and indirect methods.
CONSERVATION OF FORESTS, WRT INDIA
Deforestation and associated degradation of forests is a serious problem all over the world; especially
more so in tropical countries like India.
In 2005, the United Nations Collaborative Programme on Reducing Emissions from Deforestation in
Developing Countries (REDD or UN REDD) programme was implemented to help developing countries
reduce the amount of greenhouse gas emission from deforestation and other forms of degradation of
forests.
In 2007, the REDD+ program, which was a voluntary climate change mitigation approach developed
by the parties to the UNFCCC, was initiated. REDD+ stands for Reducing Emissions from Deforestation
and Forest Degradation in Developing Countries and the Role of Conservation, Sustainable Management
of Forests and Enhancement of Forest Carbon Stocks in Developing Countries. This programme gave
monetary and technical incentives to developing countries to reduce deforestation-related
greenhouse gas emission.
REDD+ does not specify how each country will do this, but it requires that all countries aiming to
implement REDD+ must have (i) a national or strategy action plan, (ii) a national (and if apt, subnational) forest emission level, (iii) a robust and transparent national (and sub-national) forest
monitoring system and (iv) a system for providing information on how social and environmental
safeguards are being addressed throughout the REDD+ implementation.
FOREST LEGISLATIONS IN INDIA
But even long before REDD+ was initiated or implemented, India has managed its forests.
Forest Act of 1878 enabled govt. control of all Reserved Forests, including harvesting of timber
and restricting individual’s right to forests.
Indian Forest Act of 1927: Restricting people’s access to Government forests. Amended in 1989.
Forest Policy of 1952: It mentioned that village communities should not be allowed, under any
circumstances, to use forest at the expense of national interests. 4 types- Protected Forests,
National Forests, Village Forests and Tree Lands.
Forest Conservation Act of 1980: Prior to this, the control of forests was vested with the state
governments. In 1980, through this act, the Central Govt. of India re-asserted some control over
the forests.
Forest Policy of 1988: Asserted that forests are not to be used for commercial purposes, rather for
the protection of soils and environment. Thus revenue generation was made subservient to
maintaining ecological balance.
Forest Rights Act of 2006: Aimed to give back control of forested lands to forest dwellers.
JOINT FOREST MANAGEMENT
Following the Forest Policy of 1988, the Govt. of India started the Joint Forest Management
(JFM) policy in 1990 and revised it in 2000. JFM is a program of developing partnership
between fringe forest user groups and state forest departments, based on mutual trust and
jointly defined roles and responsibility with regard to forest protection and development.
The main objectives of JFM are:
(i) To ensure active participation of villagers in creation, management and protection of
forests.
(ii) To achieve ecological needs that are in sync with sustainable productivity of wood and
other non-timber forest resources.
(iii) To reduce shifting cultivation by land owning communities.
(iv) To productively utilize the degraded jhum areas, so that further soil erosion doesn’t
occur.
(v) To conserve biodiversity through people’s action
(vi) To create and generate forest-based economy for villagers.
Pilot experiments for JFM was initiated at Arabari in WB in 1972 and Sukhomajri in Haryana
in mid 1970s.
JOINT FOREST MANAGEMENT
28 State Governments have adopted the JFM program.
Almost 60% of forests in tribal districts of India are included in this program and the tribal
families living in these areas are also included in this program.
Afforestation and Reforestation: In many areas of India, afforestation and reforestation is
leading to recovery of previously deforested and degraded areas.
Afforestation is the planting of trees in areas that did not have a forest cover previously.
Reforestation is the re-establishment of forests in previously deforested areas.
In Asia, 1 million ha of land has been regained through these efforts between 2000 and 2003.
China has ruled that all people between 11-60 years must plant 3-5 trees per year or do an
equivalent amount of forest work.
JOINT FOREST MANAGEMENT
Under JFM, the Samanvit Gram Vanikaran Samriddhi Yojana (Integrated Village Afforestation &
Eco-development Scheme) was introduced.
The objectives of this are:
(i) Control removal of forest produce from forests by making the communities responsible
for monitoring removal.
(ii) Provide sustainable and assured employment to tribals in the area.
(iii) Create durable assets for tribals, which contribute to eco-development of the area.
(iv) Make self-income generation for the villagers.
(v) Check environmental degradation, soil erosion and conserve biodiversity.
The National Afforestation Programme (NAP) has also been implemented by the
Government of India to protect the forest cover of the country through various afforestation
schemes.
In addition to these, it is also possible to monitor areas of forest degradation and
deforestation by analysis of satellite imageries and identify hotspots as well as calculate
deforestation rates and total deforested areas.
PLANT ECOLOGY
Plant ecology is a sub-discipline of ecology that studies the distribution and abundance of
plants, the effects of environmental factors on such abundance and the interactions between
plants and other organisms.
Plant ecology can be studied at a different levels of organization, e.g. plant ecophysiology
(i.e. adaptation of plants to their physical environment), plant population ecology, plant
community ecology, ecosystem ecology and landscape ecology.
Plant communities are broadly classified in terms of biomes, based on the dominant plant
species found there. E.g. Grasslands are dominated by grasses and forests are dominated by
trees.
Biomes are impacted by climate and in many cases, by other factors like soils, hydrology,
geology, and other organisms living there.
Nevertheless, biomes constitute to be a habitat for plants and other organisms as well.
HABITAT
A Habitat is an area that is inhabited by a plant, animal or other organisms. It is
the zone in which the organism lives, finds shelter and food.
A habitat is made of up abiotic or environmental factors like geology/soil,
topography, temperature and location as well as biotic factors like availability of
food and the presence or absence of predators. Every organism, including
plants, have certain habitat needs in which they will thrive.
A habitat is not always a geographical area; it can be an interior of a log, a rotten
wood, a rock or clump of moss and in the case of parasitic organisms, the body
of their host. Habitats can also be terrestrial, marine, freshwater etc.
Closely linked to the concept of habitat is the concept of Ecological Niche. While
the habitat is where an organism is found, the term ‘niche’ describes the way the
organism fits into the physical and biological environment of the habitat in
which it is living. Each species has its own unique niche.
ENVIRONMENTAL FACTORS OF A HABITAT
The main environmental factors controlling the habitat of an organism, say plants,
are (a) geology and soil, (b) topography, (c) latitude and (d) climate.
Geology & Soil:
The geology and soil of an area profoundly influence its suitability as a habitat. This
is because the type of rock found in a habitat determines the kind of soil that would
be found there. This in turn depends on mechanical and chemical weathering
processes. Large fragments of rocks are broken up into smaller pieces by
mechanical weathering. Water fills up the cracks in the rock and the water expands
when it freezes. This causes mechanical disintegration of rocks. Chemical
weathering can also break rocks. CO2 in the atmosphere dissolves in water to form
carbonic acid. This acid reacts with the rock. E.g. limestone dissolves to become
calcium bicarbonate, the feldspars in igneous rocks like granites can break into
potassium carbonate and clay minerals. This potassium carbonate accumulates in
the colloidal clay particles and organic matter and become available for plant use.
ENVIRONMENTAL FACTORS OF A HABITAT
Topography:
The topography of a habitat can be an important
factor in the suitability of an area as a habitat for
plants or any other organisms. Since temperature
decreases with altitude, the top of mountains are
normally snow covered. This means that not many
plants can grow close to the peak of mountains.
The aspect of slopes is important for the intensity
of
sunlight. Scree
slopes
are
generally
characterized by poor soil development, which
inhibits significant plant development. Lowland
areas such as bogs and swamps may have poor
drainage conditions and some plants cannot
tolerate waterlogging at all. Even small changes in
topography can have dramatic effects on plant
communities. In waterlogged soils, for example,
ferric iron (Fe3+) is reduced to more soluble ferrous
iron (Fe2+), which can be fatal for some plants.
Source: Chapman (1999)
ENVIRONMENTAL FACTORS OF A HABITAT
Latitude:
The sun is the main source of light and heat on the earth surface. It is the
variation of solar energy that causes temperature fluctuation between
places. The solar energy reaching lower latitudes, particularly the equator,
is more per unit area that that reaching the poles because (a) there is more
loss of solar energy at higher latitudes and (b) that energy reaches the earth
at an oblique angle. Thus, it has to cover a larger area. Thus small amount
of energy has to cover a bigger area. However, more than the angle at which
the solar rays hit the earth surface, the rotation of the earth around the sun
along a tilted axis causes more complication. Equinoxes and solstices can
affect the amount of sunlight received. In addition, the low latitudes have
considerable cloud cover, which also affects the amount of sunrays
available there.
ENVIRONMENTAL FACTORS OF A HABITAT
Climate:
The climate of an area is also a determining factor of a habitat. Snow, ice, rainfall,
temperature etc. can all determine the suitability of a habitat. Excessive climatic factors
can be a deterrent and species may have to develop special adaptations in such situations.
Plants that grow in areas where the winter temperature falls below freezing can tolerate
much lower temperatures than plants growing in warm areas. Even within same species,
the degree of tolerance to temperature, depends on where the plant lives.
Temperature cycles are important, particularly for species that experience summer or
winter dormancy. Many plant seeds will germinate only if sown fresh under specific and
ideal conditions. If they become dormant once, they will need much longer time to get
back to germinating conditions again.
Precipitation is also an important factor. In arid areas, the plants may shed their leaves in
the summer and grow them back in the cold season, while the coniferous plants do the
reverse. Where there is permafrost, the surface layer of soil will become solid in winter
and waterlogged in summer.
BIOTIC INTERACTIONS IN A HABITAT
The biotic components of a habitat includes food availability, presence or
absence of other organism in the habitat and the interactions between one
another.
In plant ecology, based on the abovementioned factors, there are 6 types of
interaction between plants and other organisms like animals.These are:
(a) Predation
(b) Competition
(c) Mutualism
(d) Parasitism
(e) Defence
(f) Evolution
BIOTIC INTERACTIONS IN A HABITAT
Predation:
Predation is the process whereby one organism kills and feeds on another organism. The
organism that attacks and kills the other organism is called the predator and the victim
is called the prey. Generally, plants are the prey and they are fed upon by a variety of
other organisms, notably animals, which do not always kill them, but puts pressure on
the plant species. Predation can be aspecific or species-specific. Generally, the most
tender parts of the plants like leaves, stems etc. are attacked by other animals, especially
when the plant has no defence mechanism in place. Masticating (i.e. chewing) animals,
generally engage in aspecific predation. In other cases, some species feed on a single
type of plant throughout their life. E.g. pandas and bamboos or silkworms and mulberry
leaves.
However, plants can be the predators too. For example, carnivorous plants like the
pitcher plant can trap smaller organisms like insects and derive some of their nutrients
from them. There are various types of mechanisms used for such trapping like pitfall
traps (catching the prey in a rolled leaf that contain digestive enzymes or bacteria),
flypaper traps (use of a sticky mucilage), snap traps (involving the use of rapid leaf
movements), bladder traps (sucking in the prey with the help of a bladder that creates an
BIOTIC INTERACTIONS IN A HABITAT
Predation:
internal vacuum) and lobster traps (forcing the prey to move towards a digestive organ
with inward-pointing hairs).
However, apart from small insects, some carnivorous plants are also known to ‘eat’ other
plants. For example, the pitcher plant, Nepenthes ampullaria is known to blank the floors
of rainforests with ground pitchers, which trap vegetative detritus falling with rain from
the canopy layer above. Similarly the some species of the plant Utricularia traps a lot of
algae in their bladders, while the genus Pinguicula can trap a lot of pollens on their
leaves, which they consume.
BIOTIC INTERACTIONS IN A HABITAT
Competition:
Competition is defined as an ecological process where multiple species compete for the
same common resources at hand. In the case of plants, these resources include
environmental factors such as light, minerals, space etc. Sometimes an individual plant
interferes with the needs of another, while in other cases, members of one plant
community meddles with the resource needs of another community. Nutrient availability
is an important factor in competition between plant species as it can alter their
competitive abilities. For example, low nitrogen availability can limit plant growth and
their competitive abilities. Some factors like CO2 can have direct effects on relative
competitive abilities.
Plant competition is generally indirect i.e. through the resource. However, plants having
the same life forms and growth requirement may have more direct competition. In such
cases, some plants are known to produce substances that are toxic to others to keep them
from growing near them. These chemicals may leach from roots to soils or may
accumulate in the soils when leaves drop and decay. Such chemicals can not only be toxic
for other species, but it can also cause inhibition of the producing plants’ seeds and
spores. This direct form of competition between plants is known as Allelopathy.
BIOTIC INTERACTIONS IN A HABITAT
Mutualism:
Symbiosis is a biological interaction between two different types of organisms, living in a
close and semi-permanent relationship. E.g. Lichens are an example of symbiosis
between a fungus and a cyanobacterium or alga. If the two species benefit from one
another, that kind of symbiosis is called Mutualism. Seed plants have different kinds of
mutualism, the most prominent of which is the pollination of flowers by bees, birds etc.
The pollinators are attracted to the colour, odour and nectars of the plant. Once on the
plant, the pollinator gets a coating of the pollen of that plant, which it can carry over with
itself. So the pollinator gets the food and the plants get a better way to spread it pollens.
Seed and fruit dispersal mechanisms are also well-developed, co-evolved mutualisms.
If the relationship is such that only one of the interacting organisms benefit from it, while
it is of no consequence to the other, that form of a relationship is called Commensalism.
E.g. a bird lives on a tree. Thus, it provides a benefit to the bird, but the tree doesn’t gain
anything from this relationship.
BIOTIC INTERACTIONS IN A HABITAT
Parasitism:
Parasitism is a kind of biological interaction between two organisms, in which one
benefits and the other is harmed. Some bacteria, viruses and fungi live on host plants,
normally higher (vascular) plants and derive nutrients from them. Sometimes one
vascular plant may parasitize on another vascular plant and thus gain nutrients and
water for their own photosynthesis. Similarly, a leech sucking blood is another example
of parasitism between two organisms.
Depending on where the parasite lives on the host, they can be ectoparasites (living
outside the host body) or endoparasites (living inside the host body). Parasitism can also
result in various diseases caused to the host. Parasites that have characteristics of both
ecto- and endoparasites are called mesoparasites. A parasite that feeds on another
parasite is called an epiparasite.
While not very commonly encountered and can’t be directly compared to parasitism,
Amensalism is a biological interaction where one organism inflicts harm on the other,
without gaining any direct benefit. This is commonly not seen in plants.
BIOTIC INTERACTIONS IN A HABITAT
Defence:
Most organisms, including plants and animals, respond to predation, competition and parasitism
by developing a number of defense mechanisms. These mechanisms can be mechanical or
chemical. Mechanical defense mechanisms include the development of spines, e.g. cactus, to
protect their water from herbivorous animals as well as coating on leaves and stems with resins,
lignin, silica and wax, which may make feeding difficult. Some other plants may exhibit
Thigmonasty i.e. response to touch. The leaves of the plant Mimosa close rapidly whenever it is
directly touched or experiences vibration or even thermal and electrical stimuli.
In contrasts to mechanical defense, many plants secrete chemicals which are known as Secondary
Metabolites or Allelochemicals. These allelochemicals may influence growth, behaviour and
survival of animals that feed on plants, especially herbivores. These anti-herbivory compounds are
divided into 3 types- nitrogen compounds, terpenoids and phenolics. Allelochemicals may be
qualitative or quantitative. Qualitative Allelochemicals are toxins that directly interfere with the
predator’s metabolism, by blocking specific biochemical reactions. They are found in low
concentrations (less than 2% of dry weight) within the plants. Quantitative Allelochemicals are
found in greater quantities (5-40% dry weight) and act as digestibility reducers i.e. they make the
plant cell walls indigestible to the animal. Some plants can also use toxins to prevent the growth of
plants in their vicinity, particularly that use the same resources.
BIOTIC INTERACTIONS IN A HABITAT
Evolution:
The interaction between plants can also regulate the diversity of existing species. Plant
growth strategies can act as a selective force on plants. The Allee Effect i.e. the positive
relationship between fitness and population size/density in small populations can be a
mechanism by which plant-plant interaction may have a selective impact. At low
densities, low amount of pollen availability may affect pollination of flowers and even
seen dispersal. Such interactions can also have important implications for global
environmental changes.
It is important to bear in mind that the biotic and abiotic components of a habitat interact
with one another and in a complex manner. These interactions define the niche of every
species that inhabit that particular habitat.
PLANT COMMUNITIES
In ecology, a community is defined as an interactive assemblage of species occurring
together within a particular geographical area, a set of species whose ecological function
and dynamics are in some way interdependent.
In plant ecology, a plant community may be defined as “an aggregate of living plants having
mutual relations among themselves and to the environment” (Oosting, 1956).
It may also be defined as “a collection of plant populations found in one habitat type in one
area, and integrated to a degree by competition, complementarity and dependence” (Grubb,
1987).
Thus, a plant community has 3 basic characteristics: (a) it consists of plants of two or more
different species, (b) the species are such that they are ecologically related and can live
and grow together in a particular habitat, (c) it has a well-developed structure, which has
developed as a result of continuous interaction between the different species themselves
and between the species and their physical environment.
A group of plant community in any region is known as Vegetation. However, a critical
consideration is the proportion of different species present.
CHARACTERISTICS OF PLANT COMMUNITIES
A plant community has certain characteristics.
Life Forms: Life forms describe the relationship between plant life and climatic factors. It describes
the degree of adjustment that plant life has to make to climatic conditions, particularly when the
latter is unfavourable. The Danish botanist Raunkiaer in 1934 proposed 5 life forms of plants based on
the amount and kind of protection afforded to the buds and shoots apieces i.e. the position of the buds
relative to soil surface. These are:
(i)
(ii)
(iii)
(iv)
(v)
Phanerophytes: Buds on shoots projecting into the air, with buds more than 2.5 m above soil
surface. E.g.Woody trees & shrubs.
Chaemaephytes: Buds on persistent shoots near the ground, no more than 2.5 m above the soil
surface. E.g. creeping woody plants and herbs.
Hemicryptophytes: Buds at or near the soil surface, protected by leaf litter and soils. E.g. plants
growing in rosettes or tussocks.
Cryptophytes: Plants whose buds are buried in soil, well below the surface. E.g. Tuberous and
bulbuous herbs. They have 3 sub-types- geophytes (resting in dry ground), helophytes (resting in
marshy ground) and hydrophytes (resting by or submerged in water).
Therophytes: An annual plant which completes its life cycle quickly when the conditions are
favourable and then survive the unfavourable season as a seed.
CHARACTERISTICS OF PLANT COMMUNITIES
Growth Forms: Essentially the same thing as life forms, though some distinction can be
made on the basis of shoot architecture.
The most common growth forms are:
(i) Herbs: Plants that lack above-ground woody tissue. They include grasses and weeds.
They have rapid growth.
(ii) Shrubs: Smaller woody plants, usually less than 3 m in height. They have multiple stems
arising from or close to ground level.
(iii) Trees: Long woody plants, more than 3 m in height, usually with a single main stem.
They have delayed reproduction and have permanent structures like a well-developed
trunk.
(iv) Vines or Climbers: They have elongate stems, which may or may not be woody. They
may produce tendrils, which help them to cling to shrubs and trees.
(v) Mosses & Lichens
CHARACTERISTICS OF PLANT COMMUNITIES
Stratification: Every plant community is characterized by differences in the heights of its
constituent plants. This is known as Stratification. Trees are generally taller than shrubs,
which are generally taller than herbs; herbs are taller than vines, mosses and lichens.
Tropical forests are generally characterized by intense stratification, resulting in
disproportionate distribution of solar energy.
Zonation: Horizontal changes in the physical environment are reflected in the zonational
changes in plant communities. For example, within a terrestrial community, changes in
soil condition may occur, resulting in a progression from moist soils to dry soils.
Accordingly, the plants growing would change in response to the changing moisture levels.
Horizontal Dispersion: The horizontal spacing of plants or dispersion can also be used to
characterize plant communities. Three basic patterns are identified- Random, Uniform and
Clumped. Although communities may be truly random in distribution, some degree of
uniformity or clumping is almost always seen, sometimes in combination. The
concentration of resources (e.g. nutrients, water) at one location can lead to clumping as do
reproductive patterns. In agricultural areas or areas where allelopathic plants grow, there
is a regular distribution of plants.
VERTICAL STRATIFICATION OF COMMUNITIES
Different plant species grow in a favourable habitat, but they have different life/growth
forms through various processes like adaptation, natural selection and competition. The
competition among species to get sunlight for photosynthesis is perhaps the primary reason
for the development of various ‘layers’ of plants at varying elevation from ground. This is
known as the Vertical Stratification of plant communities.
In general, there are 4 strata in any plant community:
(1) Dominant Layer: This is the topmost layer of a plant community and is determined by
the canopy of the tallest trees. The uppermost stratum is called the Canopy or Crown.
The canopy represents the highest limit of plant growth in a particular community. A
secondary layer, known as the Co-dominant Layer is often found immediately beneath
the dominant layer, composed of plants slightly shorter than those extending to the
canopy.
(2) Shrub Layer: The second layer in a plant community is dominated by shrubs. It is located
immediately below the dominant layer and is also known as Layer 2.
(3) Herb Layer:The third layer is composed of herbaceous growth forms. Known as Layer 3.
(4) Ground Layer:This layer is the lowermost layer and is composed of mosses and lichens.
VERTICAL STRATIFICATION OF COMMUNITIES
Source: Singh (2001)
COMMUNITY DEVELOPMENT
Plant communities develop over time by passing through a series of phases or stages.
The concept was proposed by Clements (1916), who suggested that in a given habitat, with
favourable environmental conditions, there are 5 stages through which a plant community
develops:
(a)
(b)
(c)
(d)
Nudation Phase: At this stage, a bare area, devoid of vegetation is formed or created.
Migration Phase: Arrival of seeds in this newly created area.
Ecesis Phase: Seeds are established in the area, germinate and gives rise to new plants.
Reaction Phase: Competition between plants begin and also interaction of the plants
with the physical environment commences.
(e) Stabilization Phase: Equilibrium exists between the plant populations and the physical
environment of the habitat.
Succession is a natural change in the structure and species composition of a community.
Clements originally restricted it to plants only and referred to it being an unidirectional and
irreversible change from one plant community to another. However, other organisms
associated with the plants may also change. Additionally, it is not irreversible always.
COMMUNITY DEVELOPMENT
SUCCESSION:
Succession, thus means, a series of changes to the vegetation community. There are 2 main types of
successions: Primary & Secondary Successions.
Primary Succession is the development of a sequence of vegetation on a previously unoccupied, bare
land or in a newly formed water body. It is relatively uncommon to find such pristine areas, but they
can be found in sand dunes, newly cooled lava flows, new volcanic islands, landslide deposits and
debris left behind by melting glacial ice.
Most bare lands of the earth are exposed because the existing vegetation has been destroyed by
natural events like fire or flooding or volcanism or due to human interferences. The vegetation
recolonizing such areas would be affected by conditions not available in the primary succession like
remnants of soils, organic matter, seeds and some plants that survived the changes. Secondary
Succession refers to the changes in the vegetation communities developed on such previously
vegetated and disturbed sites.
The sequence of vegetation types that occur in a primary successions is called a Sere. Thus Hydrosere
refers to a series of aquatic communities, Xerosere to communities developed in dry areas and
Lithosere to those developed in rocks.
PRIMARY SUCCESSION
The various stages through which primary succession is a hypothetical terrestrial
community will pass includes the following:
(i) The initial plant-free site is a dry environment, which is not due to arid climate,
but excessive evaporation in the absence of plant cover. The first plants that
develop on bare rocks are called Pioneer Species and include mainly algae and
lichens, which can adapt to the initial environment well and quickly.
(ii) Wind-blown dust particles settle into the area around the pioneer species. Some
lichens can secrete acids, which react with the minerals in the dust and the host
rocks. Thus, pedogenesis starts and the first layer of soil forms in due course,
which is thin and is occupied by micro-organisms.
(iii) The soil cover increases over time, such that a few soil-living organisms like
mites, ants etc. evolve. At this stage, soil living organisms evolve rapidly and
there are also sporadic appearance of plants, although large areas still remain
devoid of plants. This community is known as the Pioneer or Open Community.
PRIMARY SUCCESSION
(iv) Progressively, mosses start replace the pioneer community. The mosses spread over the soil like a
sheet, reducing evaporation and thus, conserving soil moisture. Dense moss cover also adds organic
materials to the soils. Gradually, new species like perennial grasses are developed along with animal
species like nematodes and spring tails. This grass cover eventually spreads over the entire habitat,
forming a relatively dense vegetation cover. The increased vegetation reduces ground temperature
and sunlight, but increases soil moisture further. The plant community developed at this stage of the
succession is called a Closed Community.
(v) Once the closed community has developed, competition between the plants begins for the
resources available. There are two types of competition- among species (intra-species) and between
species (inter-species). In either case, the strongest species survive and the weak ones perish. At this
stage, the closed community consists of herbaceous plants.
(vi) Eventually, large shrubs start to grow in the community and the herbs are replaced by scrubs. At
this stage, the seeds of flowering plants are brought in from neighbouring areas. This gives rise to
trees, which are much taller in height that shrubs. The vegetation community at this stage consists of
trees, shrubs, herbs like grasses and some mosses. This is known as a Forest Community.
(vii) The final stage in the development of the plant community is marked by growth of very tall trees,
which occur in large numbers and have well-developed root systems. The soil cover is well-developed
and the vegetation community is well-stratified. Such a community is called a Climax Community.
SECONDARY SUCCESSION
Secondary succession occur when plants develop over previously occupied, but disturbed
sites. These disturbances may be due to natural processes like volcanic eruption, prolonged
drought or glaciation, catastrophic floods or due to human interferences like burning of the
vegetation, land use changes, deforestation etc.
However, the initial stage of secondary succession almost always contains some remnants
of the existing plant community, such that it is not a completely bare, rocky area.
Furthermore, the total time taken to reach the climax community in secondary successions
is much shorter.
When the vegetation community of an area is disturbed by human activities before reaching
the climax stage, the resulting vegetation is called a Sub-climax Vegetation. When such
disturbances continue for a long period of time, normal seral development do not take
place. Instead, the seres are deflected by these factors. The vegetation developed on
Deflected Seres persist so long as the disturbing forces persist. They may even reach a
climax in this state, which is known as Plagioclimax and the vegetation thus developed is
called Plagioclimax vegetation.
After some time, when the disturbing forces cease to exist, the vegetation succession
returns to the normal pattern.
CLIMAX VEGETATION
The Climax Community is developed when the succession process is complete.
It indicates a mature ecosystem, whereby the vegetation is in equilibrium with
the physical environment prevailing in the area.
It is an ecosystem in which the biomass increases to maximum and the food
chain becomes complex and becomes a food web.
The vegetation developed prior to attaining climax is called Sub-climax
community. Such communities may persist due to several controls on climax.
There have been several theories that have been proposed to explain the
occurrence of climax in a vegetation community. The most important ones are
the Monoclimax Theory, Polyclimax Theory, Polyclimatic Climax Theory and
Climax Pattern theory.
CLIMAX THEORIES
Monoclimax Theory: Proposed by Clements (1916, 1936). Only one type of climax
community can develop in an area, determined by the prevailing climate in the area. All
types of vegetation, terrestrial or aquatic, tend to attain that climax community.
Polyclimax Theory: Tansley (1939) proposed this theory based on earlier work by others.
This theory suggests that there could be multiple climax communities within an area,
controlled not only by climate, but also other factors like soils, nutrients, moisture, fire,
biological activities etc.
Polyclimatic Climax Theory: This theory was developed by Tuxen in the mid 1930s and
again by Ellenburg in 1959. It states that there could be more than one climatic climax
community in a macroclimatic region and that soils play an important role in the
development of these climax communities.
Climax Pattern Theory: Developed by Whittaker (1953), this theory suggests that the plant
community in an area is adapted as a whole to the environmental factors prevailing there
like genetics of the species, site, climate, soil, biological activities, fire and dispersal
opportunities. Thus, there are no individual types of climaxes and no one factors exerts
control on climax. There is a continuity of climaxes along environmental gradients.
CAUSES OF SUCCESSION
Since succession involves change of type of plants i.e. evolution of plant
communities, it may be said that where there has been a succession, there
have been some change in the environmental conditions.
The changes in vegetation caused by the plants themselves is known as
Autogenic Succession. However, if the changes are brought about by external
factors, they are known as Allogenic Succession.
Autogenic Succession can be caused by such factors as changes in soil
brought about by the organisms that live there. These changes include the
accumulation of organic matter in the soils or changes in the soil pH due to
the plants growing there.
The structure of the plants themselves can also bring about changes in the
community. E.g. when trees mature, they provide shade to the floor. Thus,
shade-tolerant species may start to invade the floor of the forest.
CAUSES OF SUCCESSION
Allogenic changes are caused by external environmental forces.
These include soil changes due to erosion, leaching or deposition of silts and clay can
change the nutrient content and water relationships in the ecosystem; so can fire.
Animals can cause pollination and bring about dispersal of seeds. They can bring about
changes in the nutrient content of soils by creating patches in the habitat. This may create
regeneration sites, which may be favourable for certain species and not so hospitable for
others.
Climatic factors are also important. However, they are important mainly in the longer time
scale. Changes in both temperature and rainfall can alter the communities.
Climate change may increase the amount of allogenic succession more in the years to
come.
Humans are also having noticeable influence on the allogenic succession.
HUMAN INFLUENCE ON SUCCESSION
Although succession can be brought about by both autogenic and allogenic causes,
much of the vegetation in the modern world are no longer in primary succession.
Secondary succession have been brought about primarily by humans.
The most obvious example is the clearance of vegetated lands for agriculture. Here
plants are grown for a few months only and then the land is left fallow to be used
again later. Thus the ground is maintained permanently in the colonization stage of
a secondary sere. Only weeds can survive in such ground conditions.
Grazing by domesticated animals or mowing activities can preserve grasslands
and prevent succession to scrubs.
Large tracts of tropical rainforests have been destroyed to create grazing grounds
for cattle. This has caused nutrient loss from the system via export of wood,
leaching and burning, followed by erosion of the top soil. Many of these lands have
been colonized by fast-growing species that didn’t grow there earlier.
PLANT RESPONSE TO PHYSICAL ENVIRONMENT
Different types of plants respond to their physical environment differently. However, within ecology,
there are two existing thoughts as to how plants respond to the environment.
One line of thought is known as Phytosociology. This approach considers plant communities as
individual social units. Each community is hierarchically divided and a phytosociologist’s aim is to
describe the plant communities, discover their causal explanation, and study their development and
geographic distribution.
The other approach is known as Gradient Analysis. This approach considers global vegetation, not as
discrete, classifiable, units, but as a continuum spanning across various environmental changes.
Gradients are abstract dimensions of the environment where, depending upon the ordination method
(i.e. arrangement) used, the relative position of the habitat reflects the similarity of species
composition or ecological conditions between them.
There are 3 types of environmental gradients: Direct Gradients are gradients that have direct
physiological effects on plant growth, but are not consumed by them like temperature, air, soil pH
etc.; Resource Gradients are those gradients, which are directly consumed by plants for their growth,
e.g. CO2, oxygen, nutrients etc.; Indirect Gradients involve complex gradients, e.g. elevation, which
influence plant growth indirectly through direct gradients. These gradients are site-specific.
PLANT RESPONSE TO PHYSICAL ENVIRONMENT
There are 2 forms of gradient analysis: direct gradient
analysis, where vegetation changes along a known
environmental gradient are studied and indirect gradient
analysis, where the differences in species composition at
various sites are arranged and compared, without any
previous knowledge of environmental differences.
But which of these approaches is right? It depends on the
consideration of the environment itself. In some places,
the nature of environment changes rapidly. E.g. a cliff
plunging into sea or along the edge of a river. On one
side, could be a terrestrial community and on the other
an aquatic one.
In the figure, the environment changes rapidly, such as a
step, with species A & B occurring up to the edge of the
step, but not beyond it. Similarly, species C & D occur in
the altered environment and may represent different
communities. Similar changes in the biotic environment
can also occur, for example, at the edge of a forest, wit
rapid drop in amt. of sunlight and increased leaf litter
under the trees. So some community boundaries can be
clear and well-defined.
Source: Chapman (1999)
PLANT RESPONSE TO PHYSICAL ENVIRONMENT
In most cases, however, environmental change will be
gradual with respect to various types of gradients like
altitude, depth of soil, amount of waterlogging, snow
depth etc. On these gradients, there will be a point when
a particular species becomes less common and
eventually ceases to occur. When and how the species
become absent depends on the nature of interaction of
that species with the environment.
If several species interact with the environment in more
or less the same way along a particular gradient, then
they will become less common or absent at a same
common place along the gradient and a distinction line
will be seen, giving the impression of individual
communities.
If, however, the species respond to the environment
along the gradient in different fashion, then a continuum
of variation in vegetation structure will be found.
Source: Chapman (1999)
PLANT ADAPTATIONS
Adaptations refer to the adjustments or changes in the behaviour, physiology
and structure of a plant or animal to become more suited to the environment
in which it lives.
These adaptations allow the organism concerned to reduce competition for
space and food, reduce predation and increase reproduction.
There are two main types of adaptations- Structural Adaptations and
Behavioural Adaptations.
Structural Adaptations are the ways that something is built or made;
Behavioural Adaptations are the ways in which something acts naturally or
by instinct.
STRUCTURAL ADAPTATIONS
1) Adaptations to get food: Leaves and stems absorb energy from sun for
photosynthesis.
2) Adaptations to get water and nutrients: Roots soak up water and nutrients
from the soil.
3) Adaptations for reproduction: (i) Brightly coloured flowers with nectar
attract pollinators such as birds, bees and other insects; (ii) Sweet fruits
attract animals that spread seeds to faraway places; (iii) some seeds are
shaped to catch the wind.
4) Adaptations for defence: (i) Thorns and spines can act as defensive
mechanisms against predatory animals; (ii) some plants can release
allelochemicals that inhibit predators and can cause itches.
BEHAVIOURAL ADAPTATIONS
1) Adaptations to get food: (i) Plants learn to grow towards the sun; (ii) Vines
can climb up other trees to get sunlight; (iii) Roots go down into the soil;
(iv) Predatory plants can trap small insects.
2) Adaptations to get water and nutrients: Desert flowers can stay dormant
for months and can come alive when there is rainfall.
3) Adaptations for reproduction: Plants drop seeds to grow new offspring.
PLANT ADAPTATIONS IN DIFFERENT ECOSYSTEMS
Tropical Rainforests:
(1) Due to the hot and wet climate prevalent in tropical rainforests, the bark of the trees is thin and
smooth. This doesn’t allow other plants to grow on them.
(2) The leaves of trees here have adapted to withstand high amount of rain. They are big, thick and
waxy and have ‘drip trips’ to let the water drain off quickly. This also prevents fungal and bacterial
growth, keeping the leaves healthy.
(3) Many creepers, ferns and mosses grow on the trees. Lianas are climbing woody creepers that wraps
rainforest trees. Their roots are in the ground, but they can reach the canopy layer to get sunlight.
(4) Many large trees have buttresses that can rise for a substantial height above the ground before
blending with the trunk. These buttress roots can provide extra stability and increase the surface
area of a trees so that it can breathe in more CO2.
(5) Some trees have ‘stilt’ or ‘prop’ roots that can grow above ground and provide more stability.
(6) Given the intense competition for sunlight, the plants arrange their leaves so that they can get their
share of the sun.
(7) The flowers at the ground level are meant to attract land pollinators as there is no wind there.
PLANT ADAPTATIONS IN DIFFERENT ECOSYSTEMS
Tropical Grasslands:
(1)When rainfall is sufficient, grasses in tropical grasslands grow very
quickly, but when water is insufficient, they turn brown to save moisture.
They store nutrients and moisture in their roots when water is short. This
allows them to withstand fire outbreaks in the dry season.
(2)Some trees like the Baobab produce leaves in the form of small finger-like
clusters. This helps them to decrease water loss. It also has thick bark,
which allows it to save more moisture.
(3)Some trees like the Acacia can develop long, tap roots that can reach deep,
groundwater sources.This is known as Hydrophillic root system.
(4)The plants in the tropical grasslands can shed their leaves during the dry
season to conserve energy and water.
PLANT ADAPTATIONS IN DIFFERENT ECOSYSTEMS
Temperate Grasslands:
(1) The roots of the grasses in the temperate grasslands extend deep into the
soil to extract soil moisture.
(2) The root systems are quite extensive and can’t be damaged easily by the
grazing animals.
(3) Some of the plants have thick roots to prevent fire and during a fire event,
even if the above-ground portion of the plant perishes, the roots survive
and sprout again later.
(4) The Prairie grasses have long, narrow leaves, which lose less water than
broad-leaved trees.
(5) Many grasses take advantage of windy conditions to maximize wind
pollination.
PLANT ADAPTATIONS IN DIFFERENT ECOSYSTEMS
Deserts:
(1) Some desert plants store their water in their leaves and stems. They are
called succulents.
(2) Some plants have no leaves or seasonal leaves, which grow only after
rains.This helps to minimize water loss.
(3) Long root systems penetrate deep in the soil to reach the groundwater
level easily.
(4) Leaves with hair and wax coating on stems help provide shade to the plant
and also reduce water loss.
(5) Spines and thorns act as defence mechanisms against predators.
PLANT ADAPTATIONS IN DIFFERENT ECOSYSTEMS
Mangroves:
(1) Mangrove areas are characterized by waterlogged and highly saline soils. Thus the
mangroves have special vertical roots known as pneumatophores, which allow some
oxygen to get into the otherwise anoxic soils.
(2) The major mangrove species all have prop or stilt roots.
(3) Production of viviparous propagule is a reproductive strategy that can tolerate high salt
content of mangrove ecosystems.
(4) Some species of mangroves have leaves with glands that can give out the salt that they
can normally store, when the salt stress is high.
(5) Under salinity stress, osmoprotectants accumulate in chloroplasts and mitochondria,
which minimize water loss.
(6) Mangroves can turn their leaves to reduce the surface area exposed to sun. This helps to
reduce water loss through evaporation.
PLANT ADAPTATIONS IN DIFFERENT ECOSYSTEMS
Taiga:
(1) Most trees in the Taiga are evergreen, which allows them to have photosynthesis when
temperatures are warm enough.
(2) Many trees have needle-shaped leaves, which allow the snow to fall down easily in
winter and also minimizes water loss.
(3) Waxy coating on needles help prevent evaporation.
(4) The needles are dark in colour, allowing more heat to be absorbed.
PLANT ADAPTATIONS IN DIFFERENT ECOSYSTEMS
Tundra:
(1) The tundra contains permanently frozen soil or permafrost. The thicker active layer of
this soil allows penetration of roots to extract nutrients.
(2) Plants adapt to the Tundra by growing close to the ground, becoming dormant through
the winter and reproducing through divisions.
(3) Plants grow in clumps and some plants have hairy growth that prevents the plants from
wind and cold.
(4) Some plants have dish-like flowers, which allow concentration of solar energy in the
centre of the flower. This helps to keep the flowers warm.
(5) Some plants like lichens and mosses can grow in wet places or areas where there are
bare rocks, without any soil cover.
(6) Mosses have tiny thread-like rootless, called rhizoids, which absorb mineral and
moisture from the soil.