The forests are a home to both living and non-living
organisms. Forests undergo regular changes. One
set of the flora, fauna and vegetation gives way
to another combination. Without external, human-influenced
intervention a forest goes a cycle of growth that
may take over a hundred years. Natural fire is
an agent of change as is commercial logging. Whether
natural or induced the forest would undergo changes
over time.
Such changes are called ecosystem successions.
Scenario One.
Primary succession takes place on stripped areas
not previously covered by vegetation. Pools of
water, sand or rock are examples of primary succession.
There are steps involved in this type of succession.
The first step is soil building; soil is developed
from the interaction of primitive plants (colonizers)
and rock over long periods. Ultimately some soil
is created which helps larger vegetation. New
plants germinate, grow and reproduce and thus
a new succession sets in.
In scenario one this is what is taking place.
Glaciers have retreated leaving behind barren
land. Soil building starts when lichens (organism
comprising fungus and algae that support each
other), mosses and shrubs make an appearance.
Soil building continues with the colonization
of this land by the shrubs which have since been
joined by dwarf trees. Lastly spruces (coniferous
evergreen trees) too engulf the area.
Scenario Two.
In the second scenario the assumption is made
that a land which was being used for agriculture
has now been abandoned. What will happen is that
in the first year there will quickly be a cover
of crabgrass (which has branching stems and may
reach a height of 3 feet or more) which is the
annual weed. For the next three years i.e. from
year two to year four perennial weeds too crop
up. Such weeds include horseweed, broom sedge,
ragweed and aster. From the fifth to the fourteenth
year pine seedlings and saplings are introduced
by nature. The young pine trees grow stronger
and sturdier during the 25 -50 years bracket.
In about 150 years we have mature tress and a
hardwood forest.
Let us now consider the meaning of ‘biotic’
and ‘abiotoc’ factors. Biotic are
living factors. Examples of biotic factors include
plants, animals, fungi, protist and bacteria are.
As against these abiotic are nonliving factors.
Examples in this category are habitat (pond, lake,
ocean, desert, mountain) or climatic conditions
such as temperature, cloud cover, rain or snow
(or lack of it) hurricanes, storms (or absence
of these). All of these factors affect the living
organisms.
Abiotic, meaning not alive are nonliving factors
that affect living organisms. Environmental factors
such habitat (bodies of water like pond, lake,
ocean, desert, oasis, mountains etc.) or weather
such as temperature, clouds, rain, snow, hurricanes,
etc. are abiotic factors.
These biotic and abiotic factors interact to
create an ecosystem which simply is a community
of living and nonliving things considered as a
unit.
The Influence of Changing Factors
The interaction referred to above gives each
factor a place for it in the system. This results
in a equilibrium. If a change comes through natural
phenomena or is introduced from outside, the entire
system gets altered. For example the pollution
that we are experiencing or clearing the jungles
for farming or irrigation alters the equilibrium
status. The damage to the ecosystems can be seen
in terms of global warming, acid rain and such
other disorders.
It would of interest to note that some types
of plants require fire to stimulate their regeneration.
The cones of the jack pine, for example, only
release their seeds when they are subjected to
great heat. When a fire opens up a clearing the
trees get a start on quick growth as there is
competition among various species of vegetation.
Plenty of nutrients in the soil are left behind
by the fire in the form of ashes. Also there are
no trees to deny the seedlings sunshine through
the tree shade.
The jack pine seeds germinate and grow quickly.
This is the adaptive characteristic of the forest.
It is not only the fires (which may be controlled
to save human lives and property). There are other
causes for damages and disturbances to nature.
These are disease, insect infestation, and severe
climatic conditions like blizzards. Through these
the forest gets new space for new species of plants
and wildlife.
Apart from fires, natural or otherwise, timber
harvesting and logging as also clearing of forests
for human habitation are also causes for succession
in the ecosystem.
We have seen the explanation of ecosystem; how
they are formed and disturbed and the regeneration.
The moral is that humans must respect the laws
of nature and not temper with it because the damage
caused thereby would be greatly detrimental to
everyone.
Bibliography:
‘Ecosystem Succession’ Retrieved
on October12, 2004.
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