Ecological Basis of Agroforestry

Ecological basis of agroforestry
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By Keith Shepherd and Fergus Sinclair. Agroforestry: Fertilizer Trees. By Kung'u James. Labour inputs and financial profitability of conventional and agroforestry-based soil fertility management practices in Zambia. Prospects for integrating conservation agriculture with fertilizer trees in Africa. Download pdf. Remember me on this computer. Enter the email address you signed up with and we'll email you a reset link. Land forms appear mainly as a cause of soil erosion hazard: there is now an identifiable body of knowledge about land use, including agroforestry, on steep lands Novoa and Posner ; Siderius ; Young a.

Only the underlying geology is unrepresented: its effects are considerable, but operate indirectly, via landforms, hydrology and soils. Table 4 Effects of the factors of the physical environment on agroforestry systems. Fauna includes pests and diseases. The last column refers to initial letter of factors in the first column. Important basic information on landforms mainly slope and hydrology mainly drainage and depth to water table ; and. This consisted of a set of basic items of information, with descriptors and classification systems, together with a computerized base for input, storage and selective retrieval Young Recognizing the varied requirements of different users, three levels, or degrees of detail, were included: summary, intermediate and detailed.

The input form to the data base is given as Table 5 Appendix , and examples of outputs at summary and detailed levels as Table 6 Appendix. Data input at any level can be output at the same or a less detailed level.

Agroforestry - a viable alternative for social, economic and ecological sustainability

The concept of how the environmental data base should be used is shown in Figure 3. Having identified a site or area of interest, it should be possible to select five kinds of data, drawn from comparable environments around the world: suitable trees, suitable crops, existing agroforestry systems, recent or current research work, and publications. This would form a first gathering of data to which, as with all computerized data bases, the skill, experience and judgement of designers of agroforestry systems could then be applied.

Let it be said that this ideal has not yet been achieved: the data base, as a framework, has not yet been expanded into a store or data bank. It is possible that this may be done in the future, although substantial manpower and funding will be required. However, the aims of the EDB may soon be achieved through the combined efforts of four other data bases: those on agroforestry systems, multipurpose trees, experimental work and the ICRAF Library Nair, Section 1, this volume; von Carlowitz, , and Section 1, this volume; Huxley b; Labelle The agroforestry systems and multipurpose tree inventories both contain sections on environment, with a substantial although not complete identity with the EDB on kinds of information collected and descriptors used Table 7.

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The data base on current agroforestry experiments uses the EDB as part of its input, whilst the computerized library index allocates publications, where relevant, to a broad climatic zone, and makes use of environmental terms as keywords. By the end of , it may thus become possible to achieve substantially the aim pictured in Figure Here are multipurpose trees, crops, existing agroforestry systems, current research work, and publications from similar environments around the world;. Do you sincerely need a classification system?

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That is, do your purposes require a set of boxes, with defined boundaries, into which information can be poured? And of course, the soil scientist cannot get very far by being told she has an Orthic Ferralsol, she needs full soil profile descriptions supported by analytical data. But wait a minute! As a background to your biometeorological analysis, do you really want the full gamut of soil description?

Would it not be helpful to group your soil moisture research into results obtained 'on Vertisols', regardless of whether they are Pellic, Chromic, or do or do not have a strong, coarse blocky structure? Well, conversely, soil scientists are wont to group climates into a small number of broad classes, within which the fascinating variety of soils occur. Broad classes come into their own when planning research programmes. To have several stations, in different countries, directing attention at common problems, the environmental framework within which they are grouped has to be quite frighteningly generalized.

With respect to soil classification, it has been said that 'scientists who are otherwise calm and reasonable people are liable to behave quite differently when discussing this subject,' and it may well be that the same applies to climatic classification.

A recent review of classifications of climate, soil and vegetation was written as the basis for a CGIAR review of agro-ecological characterization Young Let us, like the young ladies set upon by robbers in The Wallet of Kai Lung', rush away from this subject, screaming loudly to conceal the direction of our flight.

Figure 3 Using environmental information on agroforestry. Modified from Young Properties which can be derived from data collected are included. Items additional to those shown are included in some descriptions in the Agroforestry Systems data base.

The Library data base allots a class only for ecozone climate ; other factors are represented by indexing terms, shown by asterisks. Table 8 is an attempt at a set of broad environmental classes, intended for those whose purposes require 'large boxes'.

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There is no doubt that climate must be the starting point, with all else superimposed and I speak as a soil scientist! The principle is to start from the basic climatic regions, with their associated vegetation; then for each of them, to consider what is the 'normal' situation with respect to the other factors, and what conditions constitute special cases.

Taking first climate, let us start with the three worlds of the tropics: the humid or rain forest lands, the subhumid lands or savannas, and the dry lands. Some people show a strange reluctance to recognize as a distinct zone the subhumid or 'wet-and-dry' tropics, best described by Koppen's untranslatable term, wechselfeuchten , 'changing-wet' as opposed to immerfeuchten , always wet. This gives three large boxes for the tropics. Mediterranean and temperate climates would be added to extend such a basic classification beyond the tropics.

Next, we have the indisputable fact that conditions at m altitude are not the same as at sea level. But where to draw the line?

From a physiological viewpoint, there is an argument for the substantially higher point where frost appears. Finally, take out the climates with two clear dry seasons as distinctive, and we have 9 boxes for the tropics.


Sad to relate, IITA lies very close to the dry boundary of the humid tropics, whilst ICRAF 's Machakos field station could be put as highland or lowland, and oscillates from year to year between bimodal subhumid and that rather rare climatic type, semi-arid with two crop failures instead of one. Now let us dispose of all the other factors with as little complexity as possible. Vegetation may be subsumed under climate. For landforms, let gentle to moderate slopes be considered 'normal', i. There are three distinctive conditions: steeplands, with steep and moderate slopes dominant; flat lands, the alluvial areas, with landforms of depositional origin; and valley floors, the dambos, mbugas, fadamas and the like of Africa.

For soils, the 'normal' circumstance can be taken as the zonal soil: ferralsols and acrisols US Oxisols and Ultisols for the rain forest zone, luvisols US Alfisols for the savannas, and the various kinds of calcimorphic soils for the semi-arid zone. By attribution, steep lands have zonal soils together with shallow lithosols, and flat lands have alluvial soils and gleys. This leaves the following as special cases, on which there is known, or believed, to be a distinctive role for agroforestry:. Soils developed from basic rocks nitosols, no US equivalent , which are usually more fertile;. Table 8 A simplified classification of tropical environments as a basis for agroforestry. Young Following upon the principles set out in the 'Framework for land evaluation', sets of detailed guidelines have been published on evaluation procedures for rain-fed agriculture, forestry, extensive grazing and irrigated agriculture.

How simple it might appear to be, by combining these, to devise a system of land evaluation for agroforestry! What needs to be done, and why it is not so straightforward, has been set out elsewhere Young ,b. The present discussion will be restricted to the two basic questions asked in land evaluation:. On the first of these, a substantial part of the efforts of ICRAF and others has been directed at showing how well-designed agroforestry systems, provided they function as it is hoped they will, are an improvement on present forms of land use.

This has been appraised in terms of economics, sustainability and the welfare of the people. The second question might be rephrased in our context as, 'Which agroforestry system, where? It other environments, the same system will work rather less well, and in many others not at all - the trees will die of drought, aluminium toxicity or attack by pests. Neither the agroforestry land utilization types nor their optimum environments have yet been systematically described and evaluated.

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