Natural Regeneration – A Detailed Note
“The process or method or renewal of forest crop by natural or artificial means using the potential capability of trees to reproduce sexually or asexually, is called regeneration.”
OR; the renewal of a forest crop by artificial means, also the new crop so obtained is called regeneration._ (BCFT)
TYPES OF REGENERATION:
There are two types of regeneration:
- Natural Regeneration
- Artificial Regeneration
- Natural Regeneration:
The method of renewal of a forest crop by self-sown seed, by coppice or root suckers is called natural regeneration.
- Artificial Regeneration:
The method of renewal of forest crop by sowing, planting, cutting, Layering, Budding or other artificial means is called artificial regeneration.
PURPOSE OF REGENERATION:
- Old trees are removed to avoid rotting and allowing new crop (regeneration)
- To cope with the demand of people
- Removal of trees is also done to expel the inferior spp
- Regeneration is also necessary to increase the green cover
- Other effects like binding soil, controlling soil erosion, increasing water yield, improving the environment, etc.
- Natural regeneration can occur either by vegetative means or by seed.
- Under vegetative means, coppicing, layering, and root suckers are the common methods and by seed following conditions are necessary.
- Adequate seed supply
- Adequate light conditions, obtained by regulation of the density and composition of various strata or canopies.
- Suitable soil conditions for germination and establishment
- Suitable composition and degree of development of undergrowth to protect the seedling from desiccation and biotic influences without undue competition for light and nutrients
- Efficient protection from all kind of damages
- Adequate conservation or drainage of surface flow.
- Adequate drainage, infiltration, and aeration in soil.
- Effective soil conservation
METHODS OF NATURAL REGENERATION BY SEED:
There are different methods of regeneration comes naturally by seed on different sites.
- i) Natural Regeneration on Blank areas
- ii) Natural Regeneration of Forested areas
ECOLOGICAL BASIS OF NATURAL REGENERATION BY SEED:
Appearing of regeneration naturally by seeds depends upon the followings:
- New alluvial soil:
Deposition of soil occurs when river bands turn during its movement. This deposition results in deposition of alluvial soil.
In these soils, those spp can grow whose trees are present along the river. Because seed will shed and move along the water and get deposited in the alluvial soil to give off a new generation. For regeneration, seeds must be:
- light in weight
- should be of light demander spp
- should be of fast-growing spp
- Should be of leguminous spp, because of soil is not fertile.
Normally dispersed or shedding of seeds occur in July, August when the flood comes.
Here soil becomes fertile with vegetation and these changes in condition gives rise to Succession. For example in Sind province.
- Saccharum munja
- Saccharum spontum
- Tamarix dioca
- Populus euphratica
- Sub Climax:
- Saccharum spp
- Populus euphratica
- Acacia nilotica
- Acacia nilotica
- Prosopis spicegera
- Prosopis spicegera
- Salvadora spp
- Capparis aphylla
- Acacia senegal
- Land Slips:
In the hills, especially where the land is measured by shifting cultivation or overgrazing, landslips are frequent e.g. Dir, Swat, Kaghan provide new sites for colonization.
- Pinus wallichiana
- Cedrus deodara
- Picea smithiana
- Pinus wallichiana
- Cedrus deodara
- Abies pindrow
- Picea smithiana
- Sites where abundant cultivation has done:
In those areas where land has been cultivated abundantly the soil is compact, infertile. This comes to know from the history of the land.
Normally on these sites, when felling is done the roots remain there and give rise to new shoots. There are also often a few large trees still standing on the areas having been left as too troublesome to fell on the girdle, or as shade trees. They attract birds which carry seeds from outsides, also seeds are shed by there trees and helping in regeneration. E.g. here soil will be well drained; pioneers will be grasses afterward light demanders and then shade bearers spp will come.
CONDITIONS NECESSARY FOR SEED GERMINATION:
Following conditions are necessary for the germination of seed.
- Living embryo
- Rehydration of seed (Moisture)
- By imbibitions (sucking of water by seed)
- Results in swelling of seed
- Activates enzymes
- Starch è glucose
- Protein è peptones
- Lipids è lipase
- Necessary for oxidation
- Ideal 37 OC
- Optimum 68OF – 86 OF
- Minimum 32 OF and maximum 113 OF
- It may or may not be required
- Light is necessary esp for the cases of “coleoptiles”
- Required for light demanders like Pinus roxburghii
- Other factors include
- Soil air
- Nutrient availability
- Succession and Climax
- Crop composition
- Site _ on what type of area seeds are falling
- Over wood _ canopy cover
- Soil depth
- Soil condition
NATURAL REGENERATION BY SEED:
Natural regeneration by seed can be done under following Silvicultural Systems (it is a planned programme of Silvicultural treatments throughout the life of the stand to achieve stand’s structural objectives based on integrated resource mgt):
Following Systems are applied to obtain Natural Regeneration by Seed:
CLEAR FELLING SYSTEMS
- To cut down and remove all of the trees from a forest or other area of land is called clear felling
- It is a system in which successive areas are clearfelled and regenerated every year naturally or artificially
- The entire area is divided into as many units as there are a number of years in rotation of crop
- Eg for shisham, the rotation is 40 years, so no of units will be 40 see fig.
- Each unit is felled and regenerated annually; such a unit is called felling coup or regeneration coup
The total area is divided into Coupes. Coupe Areas = Total Area / Rotation age
- Now if total area is 40,000 acres and rotation age for Shisham is 40 years then coupe area is:
Coupe area = 40,000 acres/ 40
Coupe area = 1000 acres
Each unit, which is felled each year, is 1000acres.
- The coupes are made equally productive; where the area is not uniform the coup size can vary
- The coup area is less if compartments are very productive, and more if less productive
- A planting target should be fixed for 10 years, 12 years, or 15 years, and regenerate the area within it.
- The size, form, and arrangement of coup vary. The coups can be scattered in the whole area
- The resulting coup is even aged
- Regeneration is natural, but can be Artificial is most cases
- Where the original spp are not valuable eg in Tropical Thorn Forest Prosopis cineraria, Beri, Capparis spp, etc are not valuable and its annual yield is 10 cft/ acre. We clear these forests and introduce shisham which has 15o cft/ acre timber value and 1500 cft/ acre firewood yield
- Where exotics are to be introduced eg Eucalyptus spp, hybrid poplar, etc
- Where trees have become too old to be retained
- Where spp are light demanders and can bear full frost, temperature, wind, etc.
- Suitable for those spp where seed supply is abundant
- Mainly applied in plains like in IPs where there is less risk of erosion, floods, etc
- Also applied in Tropical Thorn Forests and Tropical Dry Deciduous Forests
- Applied for spp having short rotation age and produce seed each year
- The crops obtained would be even aged
- A planting target is set to minimize catastrophes
When and How?
- From September to January
- In good seed year
- Can be carried out in Blocks and Strips in particular geometrical shapes
- Felling is done before germination period
Mostly not carried out when??
- Succession % is low
- Risk of invasion of undesired spp
- Less density of seed growing spp
- Unfavorable conditions
- Chances of flood or erosion
Merits of Clear Felling:
- It is simple ie felling does not require any technical skill
- It is cheapest in sense of production
- Cost of raising is less
- Light demander grow well
- Minimum damage due to extraction and felling
- Quickest method ie method of increasing the valuable stand and convert those into plantations
- Regeneration quick
- Quick return annually
- Desired spp and desired mixture can be introduced
- Spp composition is controlled
Demerits of Clear Felling:
- A danger of soil loss
- High rainfall increase swamp ness
- Weeds thick growth
- Complete exposure of forest
- Multiplication of diseases etc as fast as the forest obtained is Even aged (See also the demerits of the Even-aged stand)
- Hazards of erosion
- Less aesthetic
- Disturbance to Ecosystem, Wildlife, and Environment
- “When an individual tree or small group of trees from all over the forest are felled in order to create small gaps to stimulate or free regeneration and uneven-aged forest result in which trees of all age classes are distributed over the whole of the forest, such a system is called Selection system.”
- In this system, selected trees are felled
- Mainly applied for conifers in moist temperate forests.
- To get regeneration
- To get uneven-aged forest
- To get normal forest_ having trees of each age class
- To get an optimum mixture of spp
- To get a sustainable yield
- Selection system can be applied in:
- Coniferous forests
- Tropical Semi-evergreen forests
- Moist Temperate Forests _ Single Selection system
- Mangroves Forests_ Group Selection system
Execution / Implementation:
- 1st check the crop whether it is diseased free or not, check other defects like dead, defected, badly shaped, over mature, broken tops, etc
- 2nd mark the trees having exploitable diameter ie 24 inches
- 3rd girdling (a ring around a tree trunk made by removing the bark and underlying tissue in order to kill the tree) is done for the tree. It helps not only in getting best quality seeds but also helps in standing seasoning of the tree)
- 4th girdling not along roadsides as there are chances of theft, windblown, etc
- 5th chemicals can be used for the same purpose
- 6th felling cycles are concentrated ie area is divided into blocks called felling cycles.
Advantages of Selection System:
- Best for spp which are poor seeders
- Ideal for soil and water conservation
- Suitable for steep slopes
TYPES OF SELECTION SYSTEM:
- Single Tree Selection System:
- Removal of all the trees above exploitable dia ie 24 inches (for conifers)
- Thinning is performed
- Normal rotation is fixed
- Felling cycles are located (20 to 30 years)
- Total yield (ie total volume and number of trees) is calculated of trees which are to be cut down
- Felling preference is done ie more valuable trees are preferred
- Finally after felling villagers are allowed to take debris
- Group Selection System:
- Applied only for Chir and Spruce
- In areas where slope in 70%
- Trees of 120 inches are treated
- Group system proceeds from top to bottom
- 500 groups of one acre; each is felled annually
- 5000 acres in 10 years and felling cycle will be completed
- Rotation 120 to 140 years
- Exploitable dia is fixed at 20 inches
In this system, a series of (ie two or more) felling are carried out to get regeneration by seed, naturally.
TYPES OF SHELTERWOOD SYSTEM:
- Uniform Shelterwood System/ Shelterwood Compartment System
- Advanced growth (seedling which is present before seeding felling) is not left
- In this system, the canopy is opened out uniformly over the entire compartment or sub-compartment and the regeneration will form more or less uniform and even aged crop
- Mainly applied in chir pine forests
Preparation or Preparatory Felling:
- It is actually thinning
- For the successful application of this system, it is essential that the crop should have properly thinned out throughout its life until it is mature and ready for exploitation and regeneration.
- The successive thinning offer an opportunity for the improvement of the future stands by the removal of all defective trees.
- One of the main objectives of this felling is to make gaps in the canopy, provide space, and also the removal of wind fallen, 3D (dead, diseased, and dry), inferior quality, suppressed, double leader, abnormal, windthrown, fire injury, crooked stem, fluted stem, spiral grains, etc trees – fig
- Regeneration or Seeding Felling:
- In the mature crop, a seeding felling is carried out leaving a prescribed no of seed bearers as uniformly distributed over the area.
- Seed bearers should be:
- The best tree
- Have wide spreading crown
- Mature enough
- Providing fertile/ viable seed
- Dominant or co-dominant
- Straight, cylindrical bole
- Free from all diseases
- The number of seed bearers should be retained depends on several factors. If the spp in question produces seeds regularly and abundantly and the seeds are dispersed to considerable distances then a few seed bearers are left.
- Similarly, for light demanders, the no of seed bearers are fewer as compared to shade bearers.
- Southern aspect should have more seed bearers as compared to a northern aspect.
- It also depends upon the environmental conditions, aspect, Silvicultural characteristic of trees, etc.
- g. for chir pine, as few as 5 (on northern aspect) to 8 (on southern aspect) seed bearers are left per acre.
- For Fir, 35 seed bearers are required
- For Kail, 20 seed bearers are required
- For Deodar, up to 20 seed bearers per acre are required
- In plains, for Shisham, the number of seed bearers is 16 – 24 trees per acre
- Secondary Felling:
- Once regeneration appears on the forest floor the over wood is removed in one or more fellings to assist in the development of the new crop, provided if the spp is a strong light demander and regeneration with ease.
- For example, for chir pine, the seed bearers may be removed in a single felling.
- If the spp is regenerated with difficulty and/or the seedling require protection against drought or frost, the overwood may e removed in two or more fellings.
- The rate of the removal of the overwood is determined by the progress of regeneration.
- Final felling:
- It is the complete removal of the whole crop ie mature trees
- In this felling all the trees are removed including the seed bearers
- Group Shelterwood System
- Here felling is carried out in patches
- Advanced growth is left
- Patches are extended centrifugally
- Mainly applied for spp which are poor seeders and sensitive shade bearers like Deodar spp
- Also applicable for Abies pindrow and Pinus wallichiana, a group uniform system is introduced in Kaghan Valley and Shugran
- Advanced growth is gained
- Shelter to shade tolerant
- Less affected by snow, wind, storm, and other hazards
- Side shade is provided to seedling on the southern edge but the northern edge remains in full sunshine
- During enlarging, damage occurs due to extraction
- Extraction is also another problem
- Difficult mgt due to large no of gaps/ groups
- Irregular Shelterwood System
- This system resembles the group system in its initial stage.
- Gaps with advanced growth are located or artificially created to induce regeneration
- The regeneration period is longer than in case of the group system, becoming a significant proportion of the whole rotation, and may vary from 40 to 60 years.
- The crops produced are therefore much more uneven-aged then under the group system.
- The areas to be regenerated are allotted to a regeneration block and are adjusted at each riverain of the working plan
- The emphasis is on retaining superior stems for putting on increment
- Felling, for creating and enlarging the groups, is mainly concentrated on defective trees leaving well-formed trees till the end of the regeneration period.
- It is flexible
- It protects the soil and can bear wind and snow damage better than even aged crops
- Retention of best stems for more increment
- Less sacrifice of immature trees.
- More shade
- More yield/ increment
- (Similar to Group system)
- Strip Shelterwood System
- Where wind velocities are high and protection from the sun is necessary on hot dry slopes, this felling is carried out against the direction of the wind
- Introduced by Germans in Pakistan
- Felling is carried out in Strips
- To make it possible to fell timber on hill slopes with minimum damage to young growth
- The width of strip 5-time height of tree of plus tree
- First seeding felling is carried out during a good seed year on the leeward direction (against the direction of the wind)
- When the regeneration is sufficiently advanced on this strip, it is subjected to secondary felling
- Narrow strips adjacent to first strips on windward side are made.
- When regeneration is established in the second strip then secondary felling is done in this strip.
- At the same time, final felling is done in the first strip and a fresh strip is formed _ see fig
- Shelterwood strip and Group System
- It is the combination of strip and group system
- During seeding felling advanced growth are extended in strips
- Other felling are ie Secondary and Final fellings follow the same sequences as in strip system
- Regeneration is speeded up due to presence of advanced growth present already as compared to strip system – fig
- Punjab Shelter wood System
- Similar to Uniform Shelterwood System
- Applied in Muree Hills and parts of Kashmir
- Here advanced growth is retained (12 inch @ DBH) in PB IV
- A no of pole crops is also retained
- A few seed bearers are also left to ensure regeneration
- All other trees are cut
- Proper thinning and cleaning of the young crop is done
- CONCEPT OF PERIODIC BLOCKS
To facilitate all the Silvicultural operations like weeding, thinning, pruning up to felling total area is divided into areas called Period Blocks.
- Number of Period Blocks
The number of PBs can be computed by the following formula:
Number of PBs. = Rotation age / Regeneration Period
- It is the time from Seeding Felling to Secondary Felling.
- For chir, it is 25 years to 30 years.
- It is the time from Germination of a seedling to the establishment.
- It depends upon many factors like seeding factors of locality, hardiness of spp, and natural hazards.
- It is the time up to which a tree is grown or allowed to grow
- The time from germination to harvesting
- For chir, it is from 80 – 100 years
- It depends upon the demand and is fixed accordingly
Hence, Number of PBs = 80 years ÷ 4
Or; Number of PBs = 4
- Area of Period Block
It can be calculated by the following formula:
Area of PB = Total Area / No of PBs
Let total area is 1000 acres and no of PBs is 4, then Area of PB is:
Area of PB = 1000 acre ÷ 4 => 250 acres
- Introduced by Germans
- Applied in a compartment or sub-compartment
- The main objective is to protect regeneration against wind and intense light.
- It is basically evolved from strip system
- The design is like a wedge
- In hilly areas, the apex of the wedge should be downward
- Other dimensions are given in the given figure
- Based upon the suggestion to protect from wind as compared with square and circles
- Applied and elaborated by Dr. Phillips
- Applied first in coniferous forests
- Conifer + broad-leaved forests
- In plains and hills
- 1st : select patches at a 250ft interval in a compartment, see fig
- 2nd : start felling from the central patches
- 3rd : Progress from the apex of the wedge, see fig
- 4th : Rest of the dimensions are given in the fig
- Logging easy
- Regeneration natural
- Prevention from wind and other hazards
TWO STORIED HIGH FOREST:
- A Silvicultural system which originates from seed or seedling plants resulting in the two-layered structure of forest crop is called Two Storied High Forest
- Eg Shisham and mulberry in Changa Manga
- Mainly applied in Irrigated Plantations
- The major spp grown in the irrigated plantation is at present Shisham and Mulberry
- The former is pronounced light demander while the later is shade bearer
- Shisham produces good firewood and also very good timber if retained; while mulberry is mostly used in the sports industry and besides used for timber production.
Method of regeneration:
- For shisham by stump planting or root suckers
- For mulberry by stumps
- At 6th year of shisham thinning is don
- Plant spacing is 10ft into 10ft
- Then, under wood mulberry is introduced
- Spp composition: 60% shisham, and 40% mulberry
- Usual rotation of Shisham is 22 years
- The area is restocked after debris burning and mulberry is introduced again
- At the end of 2nd rotation, the crop is felled leaving about 10 standards per acre
- Same procedure for third rotation
- In this way, a continuous supply of rotation is maintained
- Leveling is done in the planting area
- 2 – 3 weeding during the first year
- Cleaning is carried out during 3rd year
- Seedling or root suckers are preferred over coppice
- Thinning carried out during 6th, 11th, and 16th
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