forestry

Soil texture classes:

The sides of the soil texture triangle are scaled for the percentages on the left side of the triangle are read from left to right across the triangle. Silt runs from to the bottom along the right side and is read from the upper right to lower left. The percentage of sand increases from right to the left along the base of the triangle. Sand is read from the lower right towards the upper left portion of the triangle. The boundaries of the soil texture classes are highlighted in blue. The intersection of the three sizes on the triangle gives the texture class. For instance, if you have soil with 20% clay, 60% silt, and 20% sand it falls in the “SILT LOAM” class.

Soil texture effects many other properties like structure, chemistry, and most notably, soil porosity, and permeability. Soil porosity refers to the amount of pore, or the open spaces between soil particles. Pores are created by the contacts made between irregular shaped soil particles. Fine textured soil has more pore space than coarse textured because you can pack more small particles into a unit volume than larger ones. More particles in a unit volume create more contacts between the irregular shaped surfaces and hence more pore space. As a result, fine texture clay soils hold more water then coarse textured sandy soils. Permeability is the degree of connectivity between soil pores. A highly permeable soil is one in which water runs through it quite readily. Coarse textured soils tend to have large, well-connected pore spaces and hence high permeability.
1. Loam: When rubbed between the thumb and fingers, approximately equal amount of sand, silt and clay is felt. Makes a weak ribbon (less than 2.5cm long).

2. Sandy loam: Varies from very fine loam to very coarse. Feels quite sandy or, gritty, but contains some silt and a small amount of clay. The amount of silt and clay is sufficient to hold the soil together when moist. Makes a weak ribbon(less than 2.5cm long).

3. Silt loam: Silt is the dominant particle in silt loam, which feels quite smooth or floury when rubbed between the thumb and fingers. Makes a weak ribbon (less than 2.5cm long).

4. Silty clay loam: Noticeable amounts of both silt and clay are present. Makes a medium ribbon (2.5 to 5cm long).

5. Clay loam: Clay dominates a clay loam, which is smooth when dry and silky when wet. Silt and sand are usually present in noticeable amounts in this texture of soil, but are overshadowed by clay. Makes a medium ribbon (2.5 to 5cm long).

Surface soil colours vary from almost white, through shades of brown and gray, to black. Light colours indicate a low organic matter content and dark colours can indicate a high content. Light or pale colours on the surface soil are frequently associated with relatively coarse texture, highly leached conditions and high annual temperature. Dark colours may result from high water table conditions (poor drainage), low annual temperature, or other conditions that induce high organic matter content and, at the same time, slow the oxidation of organic materials. However, soil coloration may be due to the colours imparted by parent materials. Shades of red or yellow, particularly where associated with relatively fine textures, usually indicate that subsoil material has been incorporated in the surface layer.

Subsoil colours, in general, are indications of air, water, and soil relationships and the degree of oxidation of certain minerals in the soil. Red and brown subsoil colours indicate relatively free movement of air and water allowed by the soil. If these or other bright colours persist throughout the subsoil, aeration is favourable. Some subsoil that are mottled (have mixed colours), especially in shades of red and brown, are also well-aerated.

Yellow-coloured sub soils usually indicate some drainage impediment. Most mottled sub soils, especially those where gray predominates, have too much water and too little air (oxygen) much of the time. The red-to-brown colour of subsoil comes from iron coatings under well-aerated conditions. In wet soils with low oxygen levels, the iron coatings are chemically and biologically removed, and the gray colour of background soil minerals shows.

Selection system is defined as a silvicultural system in which felling and regeneration are distributes over the whole of the area and the resultant crop is so uneven aged that trees of all ages are found nixed together over every part of the area.

Basic feature

• Felling distributed over the whole area.
• Resultant crops are completely uneven aged.
• The regeneration operations are carried out the life of the crop and thinning are done simultaneously for improving the growth and form of the trees.

Pattern of felling

• Selection system follows nature in respect of its pattern of felling.
• Scattered single mature trees are selected all over the area and felled to enable regeneration to replace them.
• Regeneration appears in small groups because of periodicity in seed years and age classes are found in small groups.
• Felling of scattered trees all over the area of a forest is possible when the area is small.
• In large area forest is divided into coupes which create certain interval in felling of specific area know as felling cycle.
• Felling cycle is defined as the time that elapses between successive main felling on the same area.
• The length of the felling cycle affects the silviculture of species, exploitation of forests and the nature of crop produced.
• Example –felling of 2% of growing stock in 10 years rotation would result removal of 20% of the growing stock in the coupe.
• Base on felling system it can be divided into two categories:

1. Ideal selection system- selection from whole area each year.
2. Periodic selection system –selection carried out over only a part of the forest each year.

Conduct of felling

1. Dead, dying, diseased, decay and deformed.
2. Undesirable species.
3. Immature tree to balance different age class.
4. Mature tree(above exploitable diameter)

Mode of regeneration:

Natural regeneration, artificial regeneration has to be accepted in some cases.

Tending
Weeding and clearing
Character of the crop produced:
Absolutely uneven aged

Advantages of selection system

1. Full use of site factors
2. Conserves soil and moisture to the fullest extent possible
3. Most resistant to injuries by insect pests and adverse climatic factors
4. Prevent invasion of grass and weeds.
5. Sufficient seed bearers for natural regeneration.
6. Produce more growing stock and large size tree per unit area.
7. Best system of producing large size tree.
8. Forest is superior biologically as well as in its aesthetic and scenic values.

Disadvantages of selection system

1. Considerable skill is required for regeneration felling
2. Cost of logging and extraction is higher
3. Felling, logging and extraction results in damage to the young crop
4. Quality of young crop might be low
5. Difficult to control grazing and fire in regeneration area
6. Success or failure of regeneration is difficult to assess.
7. Growing stock progressively degenerates with every felling

Condition of application

1. Topography
2. Catchments area
3. Low accessible area
4. Market requirement
5. Silvicultural consideration

Application
This is very common and traditional practice of forest management.

Symbiotic Relationship:

Much research in agroforestry systems is concerned with increasing the biological input of nutrients to trees and to the crops grown concurrently or consecutively or consecutively with them and with determining how and in what quantities these nutrients become available. The exchange of nutrients among the plants of the agroforestry system results largely from the activity of appropriate soil microorganisms. Associative or symbiotic microorganisms are responsible for nitrogen input and for the availability of other minerals, especially phosphorous, in the ecosystem. Other bacteria make available the nutrients of dead and decaying plants for uptake by the root systems of crop species. Symbiotic microorganisms like Rhizobium and Frankia have potential roles of nitrogen fixation, plant growth regulation, phosphate solubilization and concerned with nutrient transformations of decaying plant material.

The important nitrogen-fixing symbioses are:-1) those between many legume trees species and Rhizobium or Bradyrhizobium and 2) those between Frankia and woody species within the eight non leguminous plant families (so called acinorhizal plants that are nodulated by the nitrogen-fixing actinomycete. For temperature and warm temperate conditions, the most important of the Frankia associations are with Alnus (Betulaceae) or Elaeagnus and Hippophae (Elaeagnaceae), and in the tropics and subtropics, with members of the Casuarinaceae. The most promising candidates for agroforestry are the Casuarina and Allocasuarina genera.

Allelopatic Relationship:

Interference occurs when one plant species fails to germinate, growth more slowly, shows symptoms of damage, or does not survive in the presence of another plant species. Interference can result from competition, allelopathy, or other indirect influences. Competition is the phenomenon by which one plant removes limited resources (such as light, water, or nutrients) from the environment, thereby reducing the survival or growth of a neighboring plant. Allelopathy is the phenomenon in which a plant or microorganisms releases a natural product into the environment that subsequently reduces or enhances the survival or growth of neighboring plants.

Agroforestry intentionally combines woody perennials with agricultural crops or pasture plants in variety of spatial or temporal arrangements, thus the choice of species combinations may dramatically influencing the productivity and ultimate success of some agroforestry systems. The challenge in plant interference work is identifying which of trees various factors because the associated plant response. Allelochemicals originating in foliage teachings, root products, or mulches of crops or woody plants may result in reduced productivity or death of companion plants.
The concept of allopathy is at least 2,000 years old, though the team was not coined until 1973(Wills, 1985). During the past 30 years there has been a significant effort to understand the role of allelopathy in ecological processes.
Because agroforestry is a relatively new field, little work has been conducted on species compatibility (Wood, 1988). Some species currently used in agroforestry systems reportedly have allelopathic interference from Eucalyptus foliage leaching and volatiles and plant residues has been described. Also, residual mulches of Luceaena lecucocephala reportedly have allelopathic properties.

Alleopathy and intercropping: Allelopathy interference can result form natural products in intercrop foliage leaching, root products, and volatiles. There are four ways in which these chemicals are released into the environment.
1) Leaching: - Leaching is the removal of substance from plants by aqueous solutions such as rain, dew, and fog. Radioisotope labeling of plant tissue before leaching has shown that large quantities of both inorganic elements and may classes of organic natural products are leached from plant tissue.

2) Root Exudation: - Root exudation is the release of substances into the surrounding medium by healthy, intact plant roots. A variety of natural with leaves, the amounts of organic materials are much smaller (Rovira, 1969). Boulterand colleagues (1986) found that greater amounts of amounts of amino acids were exuded into sand by pea roots than into solution culture. Similarly, exudation in soils can be expected to bary with soil physical and chemical properties. Root exudation usually is increased greatly by wilting conditions and root damage.

3. Volatization: - Volatization is the release of natural products into the atmosphere. A variety of plants either secretes or excretes metabolic products into special structures such as incomes and glands into intercellular spaces and canals or onto leaf surfaces. In hot dry weather, natural products with high vapor pressure released into the atmosphere where they may be associated directly by plants or adsorbed onto soil surface.

Allelopathic interference can result from natural products released from mulches of plant residue. To improve nitrogen of crop plants plant residue mulches particularly of nitrogen-fixing species are commonly used in agroforestry systems. These plant residues may in fact result in allelopathic interference and decreases crop production.
Examples of Allelochemicals: Phenols, Benzoic acid, Aldehydes, Acetophenon, Cinnamic acid, Quinonenes, Flavonoids, tannins, Gentistic acid, etc.

Various abnormal conditions and features of wood which permanently reduce the economic value of wood are termed as defects. However, defect caused by fungal attack and decay in wood is known as Unsoundness. The term is generally applied to the discontinuity of tissues and abnormal fibre development in wood, and unsoundness to some form or stage of decay in wood. These defects and or unsoundness in wood may either just reduce its utility or render it entirely valueless.

Defects in wood can be broadly classified into two categories which are as follows:

(A) NATURAL DEFECTS (Knots, Shakes, Cross grain, Compression)

(B) OTHER THAN NATURAL DEFECTS: These defects include the

(1) Defect caused during treatment of felled timber (Seasoning defects and Conversion defects); the seasoning defects include:- (Warping, Split, Shake, Collapse, Case hardening) and the defects due to conversion includes:-( Box heart, Machine burnt, Machine notches, Miscut, Imperfect grain)

(2) Defect resulting from activity of external agent (animals, insects and fungus)

(A) NATURAL DEFECTS:

1. Knots: Knots are common types of natural defects. As the tree increases in diameter it covers the bases of the lateral branches. The portions of the branches enclosed within the wood are called knots. If the branches are alive at the time of inclusion, their tissues are continuous with main stem of the trees are called live knots. But when a branch dies and a part of it is gradually covered by the live tissues of the wood is called dead knots.

Knots vary in its size from Pin head several centimeters in diameters.
Classification of Knots:
(i) Pin knots: less than 6.5 mm in diameter.
(ii) Small knots: 6.5mm to 20mm in diameter
(iii) Medium knots: 20mm to 40mm in diameter
(iv) Large knots: above 40mm in diameter

Knots spoil the appearance and reduce the strength properties of wood. It also raises the seasoning defects and makes difficulties during wood working.

2. Shakes: A separation of fibre along the grain of standing or freshly felled timber is called shakes. This forms crack or fissures that is generally confined to the interior part of the timber but sometimes extends to one surface.
For example: If a tree is growing in high wind areas, different stresses are set up inside it. A tension occurs on the windward side whereas compression occurs on the leeward side. If the tree is not sufficiently elastic, then separation of tissues takes place inside the trunk.

3. Cross grain: This is general term depending the deviation of the wood fibres from a direction parallel to the longitudinal axis of the tree. This can be diagonal, spiral or interlocked types in nature.

4. Reaction wood: A distinctive anatomical characteristics form typically in parts of leaning trees and its branches is called reaction wood. In branches of trees, the under parts have compression wood denser and darker than upper part.

5. Compression failures: Minor fractures are running across the grain and the fibres show crinkles structures due to compression.

6. Resin pocket: Due to excessive accumulation of resin, resin patches are found in wood is called resin pocket.

7. Constriction due to climber: This defect occurs due to climbing plants. These climbing plants do considerable damage to the tree by binding round the stem.

(B) SEASONING DEFECTS: This is caused by faulty techniques of seasoning. The different types of permanent distortion of timber and ruptures of tissues constitute separately or together, they are referred as seasoning defects.

Types of seasoning defects:

(a) Warping: The distortion in converted timber caused departure from its original plane usually during seasoning period is called warping. Warping can be culping, bowing, twist, string.

(b) Check, Split and Shakes: These are the examples of separation or ruptures of the wood along the grain. These three forms differ in whether the crack is confined to the interior of the wood or extends to the surface.

• Check: In check, there is a separation of fibres, which crack or fissures do not extend through the piece from one face to face of wood. This term is applicable for the converted timber.

• Split: Crack extends from face to face of the wood. An end split is one that occurs at the end of log or a piece of timber.

• Shakes: Separation of wood fibre along the grain and occurs in different shapes such as star, ring, etc. Shakes may be Heart and Star shake, Radial shakes and Cup and ring shake.

(c) Case hardening: During the wood seasoning, surface layer of wood usually dry before the interior layers and tend to shrink but they are prevented from doing so by the wetness of the wood. This is situation is called Case hardening. The case harder timber is liable to cuping, warping and other forms of distortion during planning and resawing.

(d) Collapse: This is abnormal and irregular shrinkage of wood. This defect is seen when very wet heartwood is dried.

(C) DEFECTS DUE TO CONVERSION: Timbers may sometimes contain defects due to faulty conversion.
Some of them are:

(a) Boxed heart: This term is applied to the timber, which is sawn in a way that the pith or the centre heart falls entirely within the surface throughout its length.
(b) Machine burnt: Defect due to overheating.
(c) Machine notches: Due to bad holding and pulling.
(d) Miscut: Careless during sawing of wood.
(e) Imperfect grain: Not matching with grain alignment.

(D) FUNGAL DEFECTS:

(a) Stain: Fungi causing stain in wood, when it feeds only on food materials stored in the sapwood. In this case, fungi do not attack the heart wood which normally does not contain food material within the cell. Stain defect does not affect strength properties of wood. For example: Ceratocystis.

(b) Decay: This is observed due to wood destroying or wood rotting fungus of wood. These fungi nourish cell wall material and break down the cell structure and enzymatic activities. Decay fungi attack both sapwood and heartwood. This defect reduces the strength properties of wood.

(E) DEFECTS DUE TO INSECTS AND OTHER ANIMALS:

(a) Insects: Insects borers and termites together constitute one of the most destructive biological agencies causing defects in timber. Some insects infest standing trees others infest felled logs before conversion or converted timber. The damage is visible in the form of tunnels and wood dust packed galleries in timber.

(b) Other animals:

• Marine borer: Mostly these insects are found in costal regions and affects wood. For example: Crustaceans, Molluscs, etc

• Birds and mammals: In birds, only wood peakers do some damage to individual trees by excavating holes in stem. Similarly, some of the animals such as deer, boar, etc cause serious wounds by peeling of the bark and damaging the cambium part of the tree.

So, defects in the wood is necessary to identify so as to prevent the timber from being damaged by insect, fungi and other animals so as to obtain the desired quality of timber.

Soil structure is the way soil particles aggregate together into what are called peds. Peds come in a variety of shapes depending on the texture, composition, and environment.

1. Spheroidal: Granular structure consists of spheroidal peds or granules that are usually separated from each other in a loosely packed arrangement. When the spheroidal peds are especially porous, the term crumb is sometimes used. They typically range from less than to greater than 10mm in diameter.

Granular and crumb structures are characteristics of many surface soils (usually A horizons), particularly those high in organic matter. Consequently, they are the principal types of soil structure affected by management. They are especially prominent in grassland types of soils that have been worked by earthworms.

2. Platy: Platy structure, characterized by relatively thin horizontal peds or plates, may be found in both surface and subsurface horizons. In most instances, the plates have developed as a result of soil-forming processes. However, unlike other structure types, platy structure may also be inherited from soil parent materials, especially those laid down by water or ice. In some cases compaction of clayey soils by heavy machinery can create platy structure.

3.Blocky: Blocky peds are irregular, roughly cube like, and range from about 5 to 5omm across. The individual blocks are not shaped independently, but are moulded by the shapes of the surrounding blocks. When the edges of the blocks are sharp and the rectangular faces distinct, the subtype is designated angular blocky. When some rounding has occurred, the aggregates are referred as sub-angular blocky. These type are usually found in B horizon, where they promote good drainage, aeration, and root penetration.

4.Prismatic: Columnar or prismatic structure are characterized by vertically oriented prisms or pillar like peds that vary in height among different soils and may have a diameter of 15omm or more. Columnar structure, which has pillars with distinct, rounded tops, is especially common in subsoil high in sodium. When the tops of the prisms are relatively angular and flat horizontally, the structure is designated as prismatic. Both prisms like structures are often associated with swelling types of clay. They commonly occur in sub-surface horizons in arid and semiarid regions and, when well developed, is a very striking feature of the profile. In humid regions prismatic structure occurs in poorly drained soils and in frangipanes.


Water logging is when the soil surface area becomes saturated; soil pores are full of water. Excess water can’t drain away.
Reasons:
• Heavy rain
• Poor drainage
• Poor irrigation management
• Rising water table
• Undulated land form

Control measures:
• Drain out water
• Land filling
• Water tolerant
• Wetland management
• Good irrigation facilities