Development and validation of a simple approach to modelling tree shading in agroforestry systems

There have been a number of models developed which attempt to predict the shading patterns beneath individual tree or forest canopies. We describe a computer-based model which is able to estimate shading patterns through a discontinuous canopy of pruned trees. The model is designed to assist in the layout and management of agroforestry systems with widely spaced trees. The model was tested against data collected from a seven-year-old agroforestry system involving radiata pine, located near Canberra, Australia. The model was shown to slightly but consistently underestimate light penetration at ground level beneath the trees. However, the extent of bias (0.7% to 5%) was so small as to be of little significance in practice.     

A rainfall interception model for inhomogeneous forest canopy

The process of rainfall interception by an inhomogeneous forest canopy composed of tree crowns with some gaps among them were considered, and the previous theoretical models of rainfall interception were modified to model an inhomogeneous canopy instead of a statistically homogeneous canopy. The paper deals with the following. First, the process of rainfall interception in tree crowns and that of rainfall in the gaps among them are studied respectively to acquire the average rainfall interception of a forest canopy. Based on the model derived by Liu (1987) and setting the canopy density value, both the relevant partial equations and a formula to estimate rainfall interception were derived. Moreover, the new model was solved through a numerical method and was illustrated with typical values of some ecological factors; three groups of curves were acquired by calculation with the VisualBasic program. A model of rainfall interception by an inhomogeneous forest canopy is classified as a multi-layer model, which is different from previous models (models where all the parameters represent the whole canopy). The results from the model in this paper could be used to determine the relationship between interception and each ecological factor in detail. __________ Translated from Scientia Silvae Sinicae, 2007, 43(3): 8–14 [译自: 林业科学]     

Throughfall,stemflow and interception loss in a mixed white oak forest (Quercus serrata Thunb.)

Throughfall and stemflow measurements in a 60-year-old white oak stand (Quercus serrata Thunb.) were carried out during two periods totalling eleven months, from August to November 1993 and from May to November 1994, in order to clarify the rainfall partitioning of this forest. Troughs and spiral-type stemflow gauges connected to tipping bucket-gauges were used for throughfall and stemflow measurements. Seventy-five storms were analyzed individually. Coefficients of variation for throughfall and stemflow ranged between 5–25% and 20–70% respectively. Partitioning of net rainfall in throughfall and stemflow represent 72% and 10% of the gross rainfall respectively. Multiple regression analyses were carried out to determine the stemflow variability. In was determined that maximum rain intensity was highly correlated with stemflow and this variable explained a further 5.5% of the stemflow variation. Estimates of averaged lag time and drainage after rain cease for stemflow were 290 and 164 min, while estimates for throughfall were 60 and 104 min. respectively. The canopy saturation was estimated from continuous storms and showed a value of 0.6 mm. The trunk storage capacity was estimated at a value of 0.2 mm. The interception loss from the forest canopy was estimated in 18%. Interception loss was heighly correlated with rainfall characteristics such as duration and intensity.     

辽东山区不同森林植被类型枯落物层截留降雨行为研究

对辽宁东部山区具有代表性的油松林、落叶松林、红松林、柞木林及杂木林5种森林植被类型枯落物层截留降雨行为进行了比较研究。结果表明，枯落物截留量随林内雨量的增加而增加，呈显的线性关系；枯落物截留率在低的林内雨量级时下降梯度较大，以后随林内雨量增大而逐渐减少，最后趋于某一定值，枯落物截留达到饱和。曲线估计的饱和截留率为：杂木林30％，柞木林23％，落叶松林20％，油松林15％，红松林10％。林冠层与枯落物层截留量依林外雨变化呈显的线性关系，总截留率在低雨量级时保持在较高的水平，随后急剧下降，并逐渐趋于某一稳定性，达到最大截留能力。由曲线推算的最大总截留率，杂木林和 柞木林为45％，落叶松林为40％，红松林和油松林约为30％。枯落物生长季相对于林内雨的截留率为14．31％－43．15％，平均值为31．15％，相对于林外雨量的截留量为11．15％－32．30％，平均值为24．05％。     

Do socio-psychological factors matter in agroforestry planning? Lessons from smallholder traditional agroforestry systems

Most of the well planned rural development forestry programs of the 1970s, and agroforestry in particular, were either not adopted by the intended beneficiaries or failed to meet the needs and aspirations of the rural people, particularly in the developing countries. The reasons for non-adoption in some cases appear to be technical, bio-physical, social and economic (termed as rational reasons by the planners), but in other situations the reasons are not so easily recognisable and comprehended (termed irrational reasons). These irrational reasons are the perceptions and attitude of the farmer towards farm practices, and their role in agroforestry planning has remained almost completely neglected. The present study is based on a household survey of the farmers in traditional agroforestry systems of Western Himalaya and investigates the importance of perceptional and attitudinal aspects of the farmers with regard to agroforestry adoption and extension. In the present study, farmers’ perceptions of restrictions on felling of trees from their own land and attitudes towards agroforestry were the most important sociopsychological factors which influenced tree growing. This study implies a need to take into account the socio-psychological factors of the farmers for planning socially acceptable agroforestry programs. The importance of study of various de jure rules and regulations controlling the use of on-farm tree resources and related exemptions and their association with farmers’ perceptions and tree growing is highlighted to develop policies to encourage tree growing in agroforestry.     

Perennial crop-based agroforestry systems in Northeast Brazil

Land use systems in the Northeast Region of Brazil are dominated by large holdings and extensive cultivation of perennial crops such as cashew, coconut, carnauba wax palm, babaçu palm and so on. The common feature which links these crops is the silvopastoral system of livestock (chiefly cattle, sheep and donkeys) grazing under them. Agrosilvicultural systems involving cultivation of annual subsistence crops, and in some instances other perennials, in the stands of these perennial crops is also common. The paper presents the available information on the management, production, rate of growth, economic importance, etc. of these agroforestry systems involving cashew, coconut and carnauba palm. These systems are of considerable merit in the environmental, agricultural and socio-economic conditions of Northeast Brazil. However, practically no research nor even systematic data collection has been done on these so that there is an almost total lack of information on them. In order to improve the systems, they should be studied in detail and research undertaken on various components (crops, trees and livestock) individually as well as the system as a whole. Selection of suitable species of grass and other herbaceous crops, appropriate management techniques for both overstorey and understorey species in relation to the age of the overstorey species, optimal stocking rates of animals, etc. have to be determined so as to enable plantation owners and operators to realize the full potential of these systems.     

Relationship between annual rainfall and interception ratio for forests across Japan

Several previous studies in Japan have examined differences in rainfall interception amounts induced by differences in forest properties by comparing the annual rainfall interception ratios (annual rainfall interception divided by annual rainfall) from various sites without considering variations in meteorological conditions between sites. Rainfall interception actually depends on meteorological conditions as well as forest properties. This study examined variations in the annual interception ratio relating to the variation in annual rainfall, which would be the primary factor relating to the interception ratio, across Japan with the use of a rainfall interception model assuming the same forest properties (i.e., the canopy storage capacity, canopy closure, leaf area index (LAI), and the bulk coefficient for sensible heat transfer). The ratio ranged between 0.12 and 0.24 across Japan and was highly correlated to annual rainfall. This indicates that considering the variation in annual rainfall is critical for assessing the difference in rainfall interception amounts induced by forest properties. We reconsidered the results of previous studies in Japan that compared annual interception ratios between sites with different forest properties: (i) there is no clear difference in interception amounts between broadleaf and coniferous forests and (ii) there is a positive correlation in stem density and interception amounts for coniferous forests. These results still held when considering differences in annual rainfall between sites.     

Measuring crop yields in on-farm agroforestry studies

The paper describes the agronomic and statistical principles that form the basis for measuring crop yields in on-farm agroforestry studies. Agroforestry systems differ from agricultural systems because of the presence of tree/crop interfaces and the need for large plots, large borders and long-term monitoring. These differences accentuate the variability of crop performance on farms. Crop yield estimation per unit area in any agroforestry system involves essentially i) stratification of the plot into different, clearly distinguishable crop zones such as those under and free from the influence of trees, those on sloping and flat areas, and those on areas affected by pests, ii) drawing representative samples from each stratum, and iii) weighting the sample yields with weights proportional to the stratum area. The tree/crop interface areas may require further stratification and determination of yields of individual crop rows at different distances away from trees based on the nature and extent of tree/crop competition. The precision of yield estimation depends on how well one is able to define the strata as well as the variance of crop yields in space and time in each stratum. Studies that provide this information are urgently needed for developing practical recommendations for crop-yield measurements on farms.     

A mathematical model for generating land-use allocation alternatives for agroforestry systems

Agroforestry has been considered a viable land-use system particularly in the tropical regions. In developing or designing agroforestry systems, various concerns have to be addressed namely: (1) economic; (2) biological and physical; and (3) silvicultural and ecological considerations. This paper addresses these concerns from an interdisciplinary perspective. A land-use allocation model which ensures the simultaneous consideration of these concerns is proposed.     

A computerized database as decision support tool for the selection of agroforestry tree species

Whether in agroforestry in temperate or tropical zones, choosing the right species is one of the most crucial stages of experiments and for reforestation, erosion control or land-improvement projects.Over the last decade, ICRAF has developed a tool to help researchers, extension workers, foresters and others in the decision process. The Multipurpose Tree & Shrub Database (MPTS) contains information about more than 1,000 species. Most of these species are grown in the tropical and subtropical zones, but many of them have a potential for temperate areas as well.MPTS contains first-hand, site-specific information about multipurpose tree species. This information makes it possible for the user to compare his or her site conditions with the site conditions described in the database, and allows him/her to draw conclusions about the possible species performance. MPTS also contains secondary information from publications.Candidate species are searched by entering keywords from a list of 19 correlated criteria, such as soil information, expected services or wood and non-wood products. Detailed information about the selected candidates (e.g. morphology, management, environmental responses) is provided.Beyond this, MPTS is a quick reference tool for the multiple use of tree and shrub species. In future it will include a comprehensive guide to germplasm information. Current activities include the implementation of an interactive use-interface and links to related databases.     

Bio-amelioration of alkali soils through agroforestry systems in central Indo-Gangetic plains of India

A long-term field study was initiated during 1995 at Central Soil Salinity Research Institute, Regional Research Station, Lucknow(26°47′58′′ N and 80°46′24′′ E) to analyze the effect of agroforestry systems on amelioration of alkali soils. Three agroforestry systems(pastoral, silvipastoral and silvicultural) were compared with the control where no agroforestry system was introduced. Tree-based silvicultural and silvipastoral systems were characterized by tree species Prosopis juliflora and Acacia nilotica along with grass species Leptochloa fusca, Panicum maximum, Trifolium alexandrium and Chloris gayana. Growth of ten-year-old Prosopis juliflora and Acacia nilotica planted in combination with grasses was significantly higher over the silviculture system with the same species. Tree biomass yields of P. juliflora(77.20 t?ha-1) and A. nilotica(63.20 t?ha-1) planted under silvipastoral system were significantly higher than the sole plantation of(64.50 t?ha-1 and 52.75 t?ha-1). Fodder yield under the pastoral system was significantly higher than the silvipastoral system during initial years but it was at par with that of silvipastoral systems after eight years of plantation. The microbial biomass carbon in the soils of silvipastoral systems was significantly higher than in soils under sole plantation of trees and control systems. The Prosopis-based silvipastoral system proved more effective in reducing soil pH, displacing Na+ from the exchange complex, increasing organic carbon and available N, P and K. Improvement in soil physical properties such as bulk density, porosity, soil moisture and infiltration rate was higher in the Prosopis-based silvipastoral system than in the silviculture system or control. On the basis of biomass production and improvement in soil health due to tree + grass systems, silvipastoral agroforestry system could be adopted for sustainable reclamation of highly alkali soils.     

The agroforestry potential of combined production systems in north-eastern Mexico

In the semi-arid to sub-humid north-east of Mexico, no definite agroforestry practices were in use before the Spanish conquest, but present systems and practices offer a good basis for conversion to ecologically sustainable and productive multicrop systems which incorporate trees. In the mountains and on the coastal plain of the Gulf of Mexico, sub-humid tropical tree crops are found in mixture with semi-arid, mediterranean and even temperate species. Irrigation systems are energy and labour intensive and can be improved. Of special interest for farmers without access to finance, are non-irrigated systems mostly derived from the low dry forest (matorral), which yield crops, fruit and wood for different purposes and also serve for depasturing cattle. These latter practices have high potential for development and optimization.Integrated Expert, Agroforestry, CIM, Germany F.R., GTZ Project No. 81.9008.4     

Benefit-cost analysis of selected agroforestry systems in Northeastern Thailand

Potential productivity and financial returns from selected agroforestry systems and traditional monocrops located in the Phu Wiang watershed were estimated from limited trials of cropping alternatives using cost-benefit analysis. The agroforestry systems studied consisted of combinations of Eucalyptus (Eucalyptus camaldulensis), Leucaena (Leucaena leucocephala), or Acacia (Acacia auriculiformis) inter-cropped with cassava (Manihot esculenta) or mungbean (Vigna radiata). Evidence from trials at short, 3-year rotations, demonstrate that early supplementary and complementary relationships between some system components can imply synergistic financial gains. Although these biological interactions turn competitive over time, in this case, the gains should be sufficient to make early adopters consider the agroforestry systems financially preferable to traditional monocrops.     

Farmer perspectives on agroforestry opportunities and constraints in cape verde

In the água de Gato Watershed on the island of Santiago, Cape Verde Islands, 51 farmers were surveyed regarding their attitudes and knowledge of agroforestry. The farmers identified eight constraints to agroforestry implementation, with virtually all indicating that a source of loan funds was the major concern. Space or land constraints and availability of tree seedlings were identified as constraints by 94% and 88%, respectively. Despite these concerns, 92% of the farmers expressed a willingness to adopt or improve agroforestry practices in the watershed, with 73% expressing a willingness to establish fruit trees, 53% willing to establish trees or shrubs for fuelwood, and 16% willing to plant trees for shade.     

The tree tenure factor in agroforestry with particular reference to Africa

Rights over trees are often distinct from rights over land. Tree tenure consists of a bundle of rights over trees and their produce which may be held by different people at different times. These rights include the right to own or inherit trees, the right to plant trees, the right to use trees and tree products, the right to dispose of trees and the right to exclude others from the use of trees and tree products. Factors affecting who had rights include the nature of the tree, the nature of the use and the nature of the person or group. Landowners and tree plants tend to be relatively advantaged in terms of their rights to trees. Those with temporary claims to the land and, in some case, women, tend to be disadvantaged. The implications of tree tenure issues for the design of agroforestry projects are discussed.

---

Resumen Los derechos sobre los arboles muchas veces son distintos a los derechos sobre la tierra. La propiedad del arbol consiste en un lote o derechos sobre arboles y sus productos que pueden ser mantenidos por distintas personas en distintos tiempos. Estos derechos incluyen el derecho a poseer o heredar arboles, el derecho a plantar arboles, el derecho a usar arboles y los productos arboreos, el derecho a disponer de los arboles y el derecho a excluir a otros del uso de los arboles y los productos arboreos. Se incluyen en los factores que afectan quienes tienen determinados derechos la naturaleza de los arboles, la naturaleza de su uso y la naturaleza dela persona o grupo. Terratenientes y plantadores de arboles tienden a tener ventajas en terminos de sus derechos sobre los arboles. Aquellos con derechos temporales y en algunos casos las mujeres tienden a estar en desventaja. Aqui se discute la problematica de las implicancias de la tenencia de los arboles para el diseno de proyectos silvo-agropecuarios.

     

Temporal analysis of agroforestry systems for rural development

Temporal analysis is introduced as a method to assess the suitability of agroforestry projects for meeting rural development objectives. This form of analysis provides a common base for examining social, economic, ecological, and managerial aspects of agroforestry systems.Temporal analysis begins by describing projects and the activities comprising them for both an agroforestry system and the local population. Factors constraining the sequence of activities are then examined. The assumptions and values regarding the past, present, or future are also analyzed for all groups involved in the agroforestry system. The range of goal oriented behavior affecting scale and duration of projects may be dependent on this time horizon.By understanding these factors, the changes in activities of a social system that may result from a proposed agroforstry innovation can be anticipated. The nature of these changes and their perception by the local population can be evaluated.     

Structure and function of traditional agroforestry systems in the western Himalaya. I. Biomass and productivity

Species composition, biomass, and productivity patterns of three types of traditional agroforestry systems, namely, agrisilvicultural, agrihorticultural, and agrihortisilvicultural, commonly practiced in the western Himalaya, were studied. Species composition in the systems varied depending upon the size of the land holdings, and the basic requirements of the farmer. Among three systems agrihortisilvicultural was highly diverse in vegetation, with as many as 13 tree and 5 agricultural crops mixed together. This system showed the highest productivity up to 25.8 t ha⁻¹ yr⁻¹, out of which 68 percent was contributed by the trees and the remainder by the annuals. Agrisilvicultural system having predominantly annuals had the lowest productivity of 20.4 t ha⁻¹ yr⁻¹ with only 27 percent contribution by the trees. Total aboveground biomass in agrihortisilvicultural or agrihorticultural system was around 48 t ha⁻¹ and it was about 2-fold higher than agrisilvicultural system. In fodder trees, a significant percentage of annual production, up to 48 percent, was allocated in current twigs, while in horticultural trees a major portion, up to 63 percent was partioned towards fruits. Implications of the results have been discussed in context with the growing problems of fuel, fodder, and packaging material in the western Himalaya.     

Structure and function of traditional agroforestry systems in the western Himalaya. II. Nutrient cycling

Budget of nutrient in plant and soil, and their rates of recycling in three types of traditional agroforestry systems in mid elevations of the western Himalaya were studied. Concentration of nitrogen and potassium was significantly higher in fruits and leaves than in branches, boles, and litter. Grewia optiva, an important fodder tree, was found to be rich in potassium, vegetable crops in nitrogen, and weeds in phosphorus. Maximum store of nutrients was estimated in aboveground biomass of agrihortisilvicultural system: nitrogen 532, phosphorus 40, potassium 461, calcium 400, and magnesium 298 kg/ha; it was closely followed by that in agrihorticultural system, and both these had sbout 2-fold higher nutrient stock as compared to agrisilvicultural system. In the case of the former two systems, considerable quantity of nutrients up to nitrogen 169, phosphorus 14, potassium 165, calcium 97, and magnesium 65 kg/ha, for example in agrihortisilvicultural system, was recycled through debris of crops and weeds, and tree leaf litter, while the recycling rate was almost half in agrisilvicultural system. Through ‘harvest’ potassium was depleted in the largest quantity from the system, followed by nitrogen, magnesium, calcium, and phosphorus; much higher loss occurred through agricultural and/or horticultural edible parts as compared to fuel and fodder biomass. For example, the loss through agricultural crops and horticultural fruits for nitrogen in agrihortisilvicultural system was up to 75 percent and 38 percent respectively of the total annual uptake. This heavy loss makes the system unstable from a nutrient point of view particularly for nitrogen and potassium until external inputs are added through organic and inorganic fertilizers. Agrihortisilvicultural system is remarkably efficient in view of biomass productivity for fuel, fodder and fruits, and also from nutrient point of view provided losses through harvest are compensated externally.     

Tropical floodplain agroforestry systems in mid-Orinoco River basin,Venezuela

Agricultural studies in seasonally flooded areas in the tropics have been limited. Orinoco alluvial soils are more fertile than adjacent non-flooded soils, and have been considered as potential areas for further agricultural development. Traditional agroforestry practices offer some possibilities to overcome the most limiting factors of floodplain cultivation. Indigenous knowledge of these traditional agroforestry practices was assessed and some indicators of the system's nitrogen and biomass dynamics were monitored. Nitrogen inputs by sediment and plant residues were 1668 and 47 kg ha^–1, respectively. Traditional selection of sediment by tree-and-grass barriers and litter management strategies increase nutrient-use efficiency in floodplain agroecosystems.

---

Resumen Estudios agrícolas en areas tropicales sujetas a inundación estacional han sido limitados. Los suelos aluviales o vegas del Orinoco son más fértiles que suelos cercanos no sujetos a inundación y por lo tanto han sido considerados como areas potenciales para desarrollos agrícolas. Prácticas tradicionales de agroforestería constituyen una alternativa en el control de importantes factores limitantes en la agricultura de vegas. El conocimiento técnico autóctono asociado con prácticas agroforestales tradicionales de vegas fue evaluado y algunos indicadores de la dinámica de nitrógeno y biomas adel sistema fueron monitoreados. La contribución de nitrógeno por sedimentos y hojarasca fue de 1668 and 47 kg ha^–1 respectivamente. La selección del tipo de sedimento a depositarse en la parcela agrícola, por medio de barreras de vegetación, y el manejo adecuado de resíduos orgánicos constituyen estrategias tradicionales que aumentan la eficiencia de uso de nutrientes en sistemas agrícolas de vegas.

     

Biophysical interactions in tropical agroforestry systems

The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interactions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offset the large competitive effect of hedgerows with crops for water and/or nutrients. Whereas improved soil fertility and microclimate positively influence crop yields underneath the canopies of scattered trees in semiarid climates, intense shading caused by large, evergreen trees negatively affects the yields. Trees in boundary plantings compete with crops for above- and belowground resources, with belowground competition of trees often extending beyond their crown areas. The major biophysical interactions in improved planted fallows are improvement of soil nitrogen status and reduction of weeds in the fallow phase, and increased crop yields in the subsequent cropping phase. In such systems, the negative effects of competition and micro-climate modification are avoided in the absence of direct tree–crop interactions. Future research on biophysical interactions should concentrate on (1) exploiting the diversity that exists within and between species of trees, (2) determining interactions between systems at different spatial (farm and landscape) and temporal scales, (3) improving understanding of belowground interactions, (4) assessing the environmental implications of agroforestry, particularly in the humid tropics, and (5) devising management schedules for agroforestry components in order to maximize benefits. This revised version was published online in June 2006 with corrections to the Cover Date.