Temporal changes (Cyclic and non-Cyclic)

TEMPORAL CHANGES

In any ecosystem, dynamic changes take place, these changes may be fast or slow.  Due to these changes, vegetation pattern in the ecosystem goes on changing, or we can say that another community is replacing one community.  But a stage comes, which shows stability, which is called as climax stage.  Hence, those natural serial stages, through which serial changes occur in the community and vegetation pattern is also changed, is called as succession.  Succession goes on by different pathways and is affected by different factors, Succession depend mainly on the following factors.

            1.         It is a sequence of environmental and vegetation changes.

            2.         It is based on the Disturbances of area.

            3.         In succession, different steps occur in a serial.

During the succession, continuous vegetation changes occur and one type of plant community is replaced by another type of plant community.  That is why, succession is the most dynamic stage.  Following are the type of changes that occurs in the vegetation.

Replacement changes

When in any community one type of vegetation stand destroyed due to any cause like forest fire, change in climate and change in edaphic factor, then new vegetation appears at this place which is known as replacement change.  This replacement change may be two types, which is Non-cyclic Type and Cyclic Type.

Non-cyclic Replacement

It is considered as normal change.  When an individual of any species die away, then another member of the community occupies this area.  But it may be same species or it may be other species like after the death of chestnut tree; area is covered by Chestnut Oak, Red oak and Red maple.  

Such changes are taking place at species level.  It is not based on one species replaced by other species.  So, it takes a long time for the development.  

When a large dominant tree died away, then at its place seedlings of different species appear.  But out of these so many seedlings, signal the significant change in the community.  But if slowly this process is continued then the floristic composition of the community will be completed changed.  So, such changes are created inside the community.

Cyclic Changes

When a series of vegetation and habitat changes with time then these are known as cyclic changes with time, and then these are known as cyclic changes. When Watt studied the seven different types of communities, then in each community, different type of patches was observed and all the patches were selected with each other.  

These changes were in the definite order, which may beupgrade series or downgrade series, like in the cairngorms community, colliona vulgaris is found at the peak level, which becomes dominant after the death of cladiona silvakita.  When cladiona disintegrates and base soil is exposed, then calliona stems starts the growth.  

Another species Arctostaphyllos also initiate the growth in the bare soil and slowly it becomes dominant.  With these changes, the environmental gradient is associated in grassland in Daccota of North-West, where where wheats, small shrubs and grasses occur.  In normal conditions, Botelua, Stipa, Corax and Agropyron occur.  In the downward series, development of saline takes place.  

Then due to leaching of soluble salts, alkaline soil develops.  It is having less ion exchange capacity, so the vegetation is destroyed.  In this case Botelua becomes dominate but in the saline soil it is replaced by Agropyron, Digitalis and Puccinalla, while in the upgrade series, calcification and sodium ion concentration reduces it to low shrub stage the first grass stage the second stage and final stage can be seen and these changes takes place in a cyclic manner. Polygonum, Lepidium, Atriplex, Plantago indicates shrub stage.

The first grass stage is indicated by Agropyron.  Puccinalla and Disticlis and second grass stage is indicated by Buchloe grass is dominant and in the first stage Boutelua, Stipa, Corax, and Agropyron are dominant.  So, the cyclic changes are intracommunity changes, while directional changes are intercommunity changes.  

The upgrade series of cyclic changes may be confused with succession (so, the replacement changes may be simple to complex changes).  Non-cyclic changes are simple, while cyclic changes are complex changes.  These changes are within the climax and within the direction and the cyclic series is the internal dynamics of community.