| Forest floor |
Forest floor………………….
· The forest floor is the most distinctive features of a forest soil.
· Forest floor is generally used to designate all organic matter, including litters & decomposing layers, resting on the mineral soil surface.
· The forest floor is the zones in which vast quantities of plant & animals remain disintegrate above the surface of the mineral soil & together with the subterranean portion of the plants, forms the soil organic matter fraction.
Physical / Distinctive features of forest floor…………………
· All the layers of forest floor posses very low bulk density. Less than 1g/cc. sometimes reducing up to 0.12g/cc.
· Bulk density is less in litter layer, whereas it is higher in humus.
· Forest floor has greater water holding capacity.
· The field capacity & saturation capacity are higher in mor humus than mull humus.
· Forest floor has greater hydrologic conductivity which allows water to infiltrate the soil.
· Forest floor has the high percentage of large pores which leads to measures aeration on wet sides, but causes drying layer quickly on exposed sites.
Functions of forest floor…………………….
· The organic matter of forest floor maintains productivity of soil.
· It serves as a source of carbon, during the decomposition process, for many organisms.
· It provides a source of food & habitat for many micro flora & fauna.
· It maintains the nutrient cycles particularly nitrogen, phosphorus & sulfur through microbial activity.
· It insulates soil surfaces from extreme temperature & moisture.
· It offers mechanical protection from raindrops impact & erosional forces.
· It improves infiltration rates.
Significance of organic matter in soil productivity………………………..
Organic matters have significance on the physical, chemical & biological composition of soil.
1) Effect on soil physical properties:
· Humus increases the water holding capacity of soil.
· It decreases water runoff through soil & increases soil aeration especially in heavy textured soil.
· It improves soil structure.
· It acts as a sponge in soil & has the ability to hold water into the soil.
2) Effect on chemical properties of soil:
· Humus acts as store house of nutrients into the soil.
· It acts as buffer in soil, which control the both extreme acidity & alkalinity.
· It strongly holds the nutrients elements & fertilizer & reduces leaching.
3) Effect on biological properties of soil:
· It serves as a sources of food & habitat for man, micro-organism.
· It acts as source of nitrogen for plant growth.
Chemical properties of soil…………………………
I. Fresh litter is composed of a large number of complex organic compounds, the relative percentages of which vary in different plant parts in different species of different ages with the soils on which they are produced.
II. The relative ash content of plant parts is the lowest bole wood & highest for leaves. The ash content of gymnosperm litter ranges from 2%-6% while in angiosperms ranges from 4%-14%.
III. The leaves of hardwood species generally contain higher concentrations of N, P, K, Ca & Mg than coniferous species.
IV. Ash content of litter of pioneer forest species developed in infertile sites is less than climax species developed in mesic & fertile lands.
V. Acidity is more in mor humus than mull humus (pH 3-8). Again the F layer pH may vary from 3 to 5.
VI. The C/N ratio is more in mor humus than mull humus.
Stratification of forest floor …………..
Three layers or strata of the forest floor are designated by forest soil scientists. They are ----------
“L” or litter layer:
· It consists of unaltered dead remains of plants & animals.
· It must be recognized while the litter is essentially unaltered.
· In some stage of decomposition from the moment it hits the floor, it should be considered as part of the humus layer.
“F” layer:
· It is a zone immediately below the litter consisting of fragmented, partly decomposed organic materials that are sufficiently well preserved to permit identification as to origin.
“H” layer:
· It consists of well decomposed amorphous organic matter.
· It is largely coprogenic whereas the F layer has not yet passed through of soil fauna.
· The humified H layer is often not recognized because of having a friable crumb structure.
Humus ……………………………….
· Waksman (1936) defined as –all the plant & animal residues brought upon or into the soil & undergoing decomposition.
· Completely decomposed organic matters are generally known as humus.
· It is a dark brown amorphous mass consisting of plants & animals residues together with synthesized cell substances of soil organisms.
Types /Classification of humus………………………….
· Muller (1979) classified humus into two types based on morphological characteristics. They are -----mor humus & mull humus.
· Again on the basis of the action of associated organisms, Russian scientists classified as –mor, mull & duff mull humus.
1. Mor humus (Raw humus):
· Superficial deposits of organic remains are called mor humus.
· It contains an organic layer that is sharply differentiated from underlying mineral horizon.
· Fungi is the most important micro-organisms in mor humus.
2. Mull humus:
· The intricate mixture of amorphous humus is called mull humus.
· It consists of organic matters & mineral soil base (Ca, Mg, Na, K) content is more in such humus.
· Bacteria , actinomycetes & fungi are dominant micro-organism in mull humus.
· This type of humus is not sharply differentiated from mineral soils (formed under hard wood forests).
3. Duff mull humus:
· It possesses some of the characteristics of both mull & mor humus.
· This type of humus result from continued mixing of mineral soil into the lower part of the forest floor by ants or rodents without destroying the organic horizons.
· This type of humus are often known as modern in North America .
· They exist under most natural hardwood & mixed pine hardwood stands.
Factors affecting the rate of litter decomposition…………………………….
· Physical & chemical condition of materials to be decomposed: the rate of breakdown of fresh litter can be quite rapid. In a study, it is found that beech leaves lost 64% of their weight, oak leaves 80% & elm, birch leaves broke down completely after 1 year.
· Temperature & moisture content of the area: litter decomposition rates can be quite slow on cold, dry site. In temperate region, it takes 3 years for the litters to be decomposed while it takes only 3 months in tropical region because of high temperature & moisture content.
· Species composition: litters of broadleaved species is easier to be decomposed than coniferous species.
· Micro-organisms: presence of favorable micro-organism influences the rate of litter decomposition. An estimate show that annual amounts of deciduous leaf litter converted to animal faces (debris) range from 20% to 100%.
Forest floor accumulation……………………………
· The accumulation of organic matter on the forest floor is largely the function of the annual amount of litter fall minus the annual rate of decomposition.
· Although many environmental forests affect the rate of decomposition, it is remarkably uniform among tree species growing under similar soil & climatic conditions.
· It is influenced not only the annual rate of decomposition but also by the age of the floor or elapsed time since the last fire or other disturbances.
· The increase in organic accumulations is rather rapid in the early stage of stand improvement & in the 1st decade or so following burning, but eventually a condition near equilibrium is reached in which the rate of decomposition is about equal to the annual input of organic matters.
| Page No | 1 2 3 4 5 6 7 8 9 10 11 12 |
| Prepared by Rasel 23 |
