Forest regeneration is the process by which new tree seedlings become established after forest trees have been harvested or have died from fire, insects, or disease. Regeneration is key to sustainable forestry and can be accomplished through two basic approaches:
- natural regeneration, which occurs when new seedlings or sprouts are produced by trees left on or near the site (as with aspen)
- artificial regeneration, more commonly known as tree planting
Natural Regeneration of Forest
Regeneration from seed or vegetative parts may observe in Natural Regeneration. Reforestation of a stand by Natural seedlings
1) Natural Regeneration from Seed: Successful natural regeneration from seed depends upon Seed production, Seed dissemination, Seed germination, Establishment and seedlings.
a) Seed Production: Seeds are cultured ovules, which contain the embryo. An embryo is a miniature plant consisting of seed leaves (cotyledons) attached to rudimentary stem (hypocotyl) with a growing tip (Plumule) and a root tip (radicle) at the other end. Seed production depends upon various factors such a species, age of tree, site, weather conditions, season of maturity, alternate bearing, attack of pests and diseases and birds.
b) Seed Dissemination: For the continued existence of a species, it is necessary that seeds are carried away from the parent plant, because seeds germinating immediately below the parent tree commonly do not get established. Seed dissemination gives young seedlings a better chance of survival for they are saved to a large extend from competition with the parent plant. The means of dispersal adopted by the seeds of different species vary widely. The four important agencies by which seed dispersal is secured are i) Wind, ii) Water, iii) Animals, iv) Explosive mechanism or ejection mechanism in fruit itself.
c) Seed Germination: Germination of seed depends upon several internal and external factors such as Permeability of seed coat, Availability of moisture in seed, Oxygen, Nature of embryo (dormancy), Temperature, Moisture in soil, Oxygen and light. Besides this some factors,
1) Age of Tree,
2) Flowering Phase,
3) Sound or health of seed condition,
4) Coppice origin trees,
5) Size of seed,
6) Plant per cent,
7) Type of dissemination,
8) Soil type / nutrition,
9) Pest and disease,
10) Non insect pests.
d) Seedlings Establishment: Successful establishment of newly germinated seedlings in sufficient number as a member of forest crop is undoubtedly, the weakest link in the whole chain of process (a to c) which make up the regeneration of forest crops.
The Factors Responsible, for Seedlings Establishment are as:
1)Climate: Light / moisture rainfall / temperature / frost
2) Edaphic – Soil / nutrient / aeration / texture / structure.
II) Natural Regeneration by Coppice and Root Suckers: Coppice : Stool shoots generally arise from the adventitious buds formed between the wood and the bark of the stump and are comparatively short lived than those produced by dormant buds. These shoots are called coppice shoots.
Classification of Coppice Regeneration:
1) Seedlings Coppice
2) Stool Coppice and
3) Root collar Shoots
4) Pollard Shoots
Natural Regeneration by Root Suckers: Shoots arises from the roots, may occur naturally or artificially.
When a natural seed source is absent, sites can be regenerated by planting longleaf pine seedlings. These are produced in tree nurseries and grown as either bare-root or container planting stock. Woody plant competition should be controlled by mechanical, herbicide and/or fire treatments for site preparation. Container-grown seedlings can then be planted anytime from July to March, while bare-root seedlings are best planted from November to February, when soil moisture is adequate. To obtain 300 well-established seedlings per acre, 500 or more seedlings may be planted as a hedge against mortality, which can sometimes be as high as 40 percent but is often lower.
Basic Steps in Artificial Regeneration:
1) Choice of Species:
i) The choice of species is very important in artificial regeneration. Therefore, before choosing the tree species, the purpose of growing the trees has to be specified.
ii) Climate and microclimate: The choice of species depends upon the prevailing climatic and micro-climatic conditions.
iii) Soil requirements: a) Wet soils – Salix species, Populus species, etc. b) Water – logged soils, Eucalyptus robusta, E. saligna etc. c) Sandy loam – Albizia procera, Acacia nilotica, Dalbergia sissoo, etc.
iv) Market faci ities
v) Growth rate: Fast growing tree species – Acacia nilotica (Babul), Leucaena leucophala (Subabool), Melia azedarach (Bakain), P. deltoides (Poplar), Salix species (Willow)
vi) Availability of Exotics: In simple it meaning pertains to, not native to the area of question. The exotic can be described as “an organism in an area which is not native of the area but has its origin in some other region. For example, Eucalyptus species, Leucaena leucocephala, Robinia pseudacacia, Populus deltoides etc.
vii) Base of establishment.
viii) Management objectives. The artificial regeneration depends upon the objectives of management.
ix) Site conditions: The site is the complex of physical and biological factors of an area that determine what forest of other vegetation may ^arry.
x) Succession: The succession is the gradual replacement of one community by another in the development of vegetation towards a climax.
xi) Cost of growing: This is also very important factor affecting the choice of species.
xii) Availability of seed /propagation material : The seed source should be sound.
2) Choice of Method: The success of artificial regeneration depends, to a great extent upon the choice of method. There are mainly two methods of this regeneration, viz. i) Sowing and, ii) Planting.
i) Sowing: Sowing, in the simplest words, is the process of scattering the seeds in a particular place e.g. nursery bed, field etc.
Advantages of Sowing:
a) It is the cheapest method and costs less,
b) Sowing is direct method and no other complications,
c) It takes less time and thus the work is completed soon,
d) In sowing method, there is no question of disturbances of roots.
e) Sometimes, sowing is done directly in the field (in forests), and hence it does not require any nursery.
f) The sowing being the simple method, is supposed to be less cumbersome.
ii) Planting: Planting is another method of artificial regeneration. However, planting is described as the transferring nursery stock to the planting site as contrasted with transplanting in the nursery.
Advantages of Planting:
a) More Success, b) Less seed needed c) No damage, d) Cheaper weeding
Disadvantages of Planting:
a) Need of nursery
b) Disturbance of roots
c) Time consuming,
d) Need of skilled labour
e) Incurred high costs
3) Site Selection: The selection of site is also a crucial factor in artificial regeneration. There are several factors which affect the site preparation.
Following are the factors which are essential to carry out the preparation:
1) Ground Cover
2) Physical Factors: a) Topography, b) Exposure, c) Soil type, d) Erosion hazards, e) Size of treatment area and f) Access
3) Preparation requirement: To create a suitable environment for establishment of desirable species.
4) Man Power and Equipment: The site selection and preparation methods require good skill and useful equipment.
5) External Constraints: a) Legal responsibilities, b) Smoke management guidelines, c) Proximity to sensitive areas and d) The attitude of adjacent farmers / land owners.
6) Spatial Arrangement: This is also called as Spacing.
Artificial Regeneration by Vegetative Method:
Planting material besides seeds for e.g. Bare root seedlings, containerized seedlings, cuttings, layering, rhizomes, suckers, offsets, bulbs, corms are also used for vegetative propagation material.
Propagation by Cuttings: Cuttings are of two types, 1. Stem cutting 2. Root cutting
1. Stem Cutting: Very few species response well for this method. The species, which easy to root are suitable for this method of planting. Particularly species of di-cotyledons group having active cambium layer e.g. Shisam, Nimbara Drumstick, Mulberry Inga dulsis, Dhaman, Pangara, Pimpal, and Banyan Tree etc.
Depending upon the maturity of stem cutting are grouped into:
i) Hard Wood Cutting: Mature woody branches are used.
ii) Soft Wood Cutting: Recently mature branches are used e.g. mulberry-Inga dulsis.
iii) Root-cutting: Roots are used for preparation of cutting e.g. Sandalwood, Pangara.
2. Stumps: In few species, stumps are used for planting e.g. Teak, Shivan, Shisam, Cassia spp. Stums are easy to transport, require less space and can be transported to long distance. These are prepared at the time of planting operation or just before planting operation. Fresh uprooted seedlings are used to transplant easily. 20% stem portion and 80% taproot is kept while preparing the stump. Fine edge knife or implement is to be used so as to avoid the damage, stem portion is cut 5 to 6 cm above the collar region is kept intact and remaining portion or roots are cut to prepare stump. The stumps are then packed in bundles, keeping stem portion on one side and roots on another side, the stumps should be transported immediately. For transportation stumps are covered with moist gunny bag cloth to avoid desiccation. They can be transported within 2-3 days without much loss.
These stumps are planted on start of monsoon after 3-4 rain showers when soil becomes sufficiently moist and soil temperatures are warm. Stumps are planted by preparing small holes in slating portion with the help of crowbar so that new shoot will rise straight. Then the stumps are inserted inside and soil is pressed firmly so as to avid water stagnation in the hole. The cooler region is kept just near to the soil surface.
3. Root Suckers: Root suckers can also be used for planting purpose e.g. Pomegranate, Kokum, Salaim Anjan, Shisam, Nimbara, Pangara, Erythrona etc. The layers, grafted plants, budded plants can be used to prepare planting material. These all are only used in forestry for conservation of superior genotype. It is used for commercial plantation as they are short lived, spreading and not develop long straight (trunk), particularly suitable for timber purpose.
Planting by root cuttings in sandal wood, pangara. Planting by root suckers e.g. Pala, Anjan, Pomegranate, Kokum, Salai, Shisam, Nimbara, Erythrina Supersa.
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