🌲 Role Of Trees
Role Of Trees.
This lesson introduces core social and farm forestry concepts and their practical relevance for sustainable land use and farm livelihoods.
Role Of Trees
Lec.11 ROLE OF TREES IN SOIL FERTILITY
ECONOMICS OF AGROFORESTRY
ROLE OF TREES IN SOIL FERTILITY
Soil is one of the most important natural resources to suffer as a result of tree cutting. If it is
not protected, its productivity declines and it may become difficult to sustain the human and
animal population even at its present level. Therefore, protection of this resource is important
and an understanding of how this resource is influenced in an agroforestry system is necessary.
Tree Root Patterns
It is generally assumed that trees have deep and spreading roots and hence are capable of
exploiting more soil volume and taking up nutrients and water from deeper layer not usually
contacted by herbaceous crops. This process of taking up nutrients from deeper soil profiles and
eventually depositing at least some portion of them on the surface layers through litter-fall and
other mechanisms is referred to as 'nutrient pumping' by trees. It is well known that the
development of plants depends on site characters and environmental factors. Many woody
species have the largest number of roots and the majority of the fine roots are located in the
uppermost fertile portion of the soil profile. Some tree species are shallow rooted. Prosopis
chilensis has a shallow and spreading root system whereas P. juliflora, is known to have a very
deep root system.
Role of trees in soil fertility
a) Organic matter and nutrient addition to the soil
Tree species contain large quantities of 'living' biomass .About 20 to 25 per cent of the
total living biomass of the trees is in roots and there is a constant addition of organic matter to
the soil through dead and decaying roots. The major addition of organic matter and other
nutrients to the soil from the trees standing on it is through litter fall ie., dead and falling
leaves, twigs, branches, fruits etc.
b) Dinitrogen fixation by trees
There is a possibility for improvement of the fertility status of agricultural lands' through
additional amounts of nitrogen added to the soil by the tree legume component. Mimosoideae
and Fabaceae are well known to fix nitrogen.Therefore, among the various avenues of addition
of nitrogen to a soil through natural and biological means, the most significant one brought
about by the presence of trees on agricultural lands could be nitrogen fixation by leguminous
trees. For example, Leucaena leucocepha/a grown for forage for 9 months yields about 12,600
kg forage, 3,600 kg protein and 575 kg nitrogen per ha.
c) Nutrient cycling
The nutrient cycling model consists of the soil-plant system that is partitioned into several
compartments. The crown surface forms the boundary of the system where input of
bioelements occurs through precipitation. The soil surface is the entry point for inputs into the
soil compartment, occurring through fertilizers, rainfall and stem flow. The surface layer may
be considered the zone of intensive root activity, with the subsoil constituting the extensive
root activity zone. The lower end of the extensive root layer is the boundary 'of the ecosystem
to the hydrosphere and lithosphere. Bioelements transported beyond this layer are lost from the
ecosystem and appear as output from the system.
ECONOMIC ANALYSIS OF AGROFORESTRY SYSTEM
A) Analysis at different times
-
Ex ante economic analysis
-
Ex post economic analysis
Ex ante economic analysis
The main aim of Ex ante economic analysis of a potential agroforestry system is to give
the various interested parties some idea of whether a system that is technically feasible is
economically viable and if so, whether it has a chance of meeting specified objectives. It may
also help to prioritize the various technology options available and/ or guide scientists to
formulate or propose other technologies.
Ex post economic analysis
The main aim of the ex post economic analysis of an agroforestry system that is already
on the ground is to determine whether a such system should be readjusted so as to better meet the
objectives . Such an analysis would also indicate the areas for adjustments.
B) Analysis from different view points
Private economic analysis
Public economic analysis
Private economic analysis
Private economic analysis is referred to as Financial analysis . In private economic
analysis, the objectives of the individual or group are taken in to account. This is reflected in the
inputs and outputs to be considered as well as the values given to them. Common objectives for
individuals are to obtain higher levels of income and leisure time as well as the avoidance of risk
that results from widely fluctuating income and consumption.
Public economic analysis
Public economic analysis referred as Economic analysis and that it takes into consideration
costs and benefits outside the farm or area where the system is present.
C ) Evaluation criteria (Tools used to economic analysis)
a) Benefit Cost Ratio
b)Net Present Value
c)Internal Rate of Return
a) Benefit Cost Ratio:
B:C ratio = Total discounted Benefits/Total discounted Costs
B:C ratio = [ ∑ [n] ( Bt ) / ( 1+r) [t ] ] / [ ∑ [n] ( Ct )/ ( 1+r ) [t ] ]
Where ‘B’ are the benefits accruing in year ‘t’
‘C’ are the costs accruing in year ‘t’
‘r’ is the selected discount rate
The BCR should be greater than one for agroforestry, then only it can be considered
worthy
b)Net Present Value :
The net present value of AF system is obtained by present worth of costs from the present
worth of benefits. The NPV should be positive .
NPV = ∑ (Bt - Ct ) ( 1+r ) [t ]
Where ‘B’ is the benefit in a year ‘t’
‘C’ is the costs in a year ‘t’
‘r’ is the selected discount rate
c)Internal Rate of Return:
IRR calculates the maximum rate of interest that a project can repay on loans while still
recovering all investment and operating costs. The IRR determines the earning power of the
money invested in a particular venture.
Present worth of incremental
net benefit stream at the
lower discount ate
IRR = Lower discount Rate + Diff .between the
discount rates X ________________________
Sum of the Present worth of
incremental Net benefit stream of
both discount rates
Types of Economic Analysis
1. Labour input analysis: showing the flow of labour inputs required for the introduction
and maintenance of an agroforestry technology .
2. Material input analysis: showing the flow of material inputs required for the
introduction and maintenance of an agroforestry system
3. Cash flow analysis : showing the flow of cash expenditures and receipts results from the
introduction and maintenance of an agroforestry technology. Such an analysis should
include loans and repayments when applicable.
4. Discounted cost / benefit analysis : determining the profitability of the agroforestry
system.
Data requirements for Analysis of Agroforestry systems
Inputs : Quantitative Aspects
Inputs are called as resources or production factors or goods and services used
to produce an output. The main inputs are land, labour and capital which includes
buildings, equipment, livestock, seeds and fertilizers.
a) Land should be specified in hectares, tenure status, productive capacity and how
it is used over time.
b) Labour input is expressed in work days or hours by type, activity, and timing
during and over the years.
c) Capital inputs are specified in weight, volume, or numbers by type
( planting material, fertilizres, agricultural chemicals, water, tools, fodder,
equipments,, etc., and source ( farm produced, purchased or hired) .
Outputs : Quantitative Aspects
Outputs are goods or services produced by the an activity . Major goods are crops
and livestock products, wood fuel, timber. Service outputs are live fence, soil
conservation works, nitrogen fixation, etc. The outputs need to be specified in terms of
units such as volume, weight, numbers, quality and timing.
D) Valuation of Inputs
In a financial analysis, inputs are valued at their market price or at their opportunity cost
to the individual concerned. In principle, market prices are applied when inputs are commonly
purchased or hired by the individual. Opportunity costs are used where most of the inputs are
provided by the farm family.
In a public analysis, the shadow price of the input, representing the true economic
worth to society as a whole, has to be used.
a) Land:
When a farmer wants to change the existing land use to an agroforestry land use, there is
no need to value such land. If a farmer has to purchase or rent a land to introduce an agroforestry
system, such purchase or rental price has to be entered into the financial analysis.
b) Labour :
In financial analysis, all labour hired is valued at its market price while all family labour
is valued at its opportunity cost.
c)Capital:
In a financial analysis all purchased materials, equipments are valued at their market
price.
E ) Valuation of outputs
Similar to the inputs valuation, outputs are valued at the market price or opportunity cost
in a private economic analysis and at shadow price in a public economic analysis.
Agricultural Products: Outputs are valued at the market price or opportunity cost in a
private economic analysis and at shadow price in a public economic analysis.
Fuel Wood : In a private economic analysis, fuel wood is valued at the local market price if
commonly sold and /or purchased by the farmers concerned. To value the standing volume of
fuel wood, the price to be used should be the net of the cost of labour for collecting it and
transport cost. If neither is the case, fuelwood is valued either in terms of alternative fuels used
by the farmers or in terms of labour savings made. A frequently used alternative fuel source is
kerosene and sometimes dried cattle dung.
Tree Fodder : Tree leaves and pods have increasingly been recognized as potential sources
of animal fodder, especially in arid and semi-arid conditions. However, we have no data on the
production of tree fodder and its valuation. In a private economic analysis, tree leaves may be
valued at market price if they can be sold locally. However, if leaves are not sold, they can be
evaluated on the basic energy or protein value.
Deriving the shadow price of tree fodder for a public economic analysis requires adjustment
of market and opportunity prices, subsidies and taxes.
Leaf Litter : Leaf litter from trees and shrubs may be used to add nutrients and organic matter
to the soil. So far, there are no recorded Instances of leaf litter being sold commercially. The
market price may be derived, however, on the basis of nutrient content and prices of
commercially available fertilizers.
Environmental Outputs
i) Preservation of productive capacity of a resource
ii) Improvement of the productive capacity of a resource
iii) Preservation /Improvement of the productive capacity of a resource
Examples of AF technologies with environmental output are tree based soil and water conservation measures, soil improvement through nitrogen fixing trees, wind protection through shelterbelts and preservation of forest areas or woodlands
In a private economic analysis of environmental benefit, only those points are considered which directly benefit the farmers but in a public economics analysis, all benefits are considered albeit they do not benefit the creator.
The valuation of environmental outputs may be handled in different ways
- Difference in output stream of the production system affected by the environmental
activity
- Cost of preventing / reducing the damage done to the environment due to the lack of
an environmental activity
- Purchase price of the land affected by the environmental activity.
Summary Cheat Sheet
| Topic | Key takeaway |
|---|---|
| Main focus | Role Of Trees. |
| Section context | Revise this lesson with the rest of Social and Farm Forestry for stronger conceptual continuity. |
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