Streuobst: a traditional agroforestry system as a model for agroforestry development in temperate Europe

The development of agroforestry for industrialised countries can be furthered by an understanding of the history and present functioning of traditional systems. In temperate Europe, fruit trees were traditionally grown on agricultural land undersown with crops or managed grassland (Streuobst). The historical evolution of this agroforestry system has been driven by the interaction of technical progress, market development and intervention by public authorities. Streuobst reached its peak in the 1930s, but has since been in continuous decline due to the development of intensively managed dwarf-tree orchards. However, even today, it still occupies approximately one million hectares in 11European countries and has a strong impact on the European fruit market. The profitability of streuobst is relatively poor due to its low labour productivity, but it has advantageous ecological and socio-cultural features, particularly in terms of biological diversity and landscape aesthetics. Accordingly, it finds strong acceptance among the general public, such that subsidised eradication programs have been abandoned and, in a number of countries, streuobst is now supported by non-governmental organisations and by state conservation policies. Modern agroforestry in temperate, industrialised countries should be oriented towards the creation of similar ecological and socio-cultural benefits in order to receive public support as a land-use system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Virtual trees and light capture: a method for optimizing agroforestry stand design

In agroforestry systems, the distribution of light transmitted under tree canopies can be a limiting factor for the development of intercrops. The light available for intercrops depends on the quantity of light intercepted by tree canopies and, consequently, on the architecture of the tree species present. The influence of tree architecture on light transmission was analysed using dynamic 3D architectural models. The architectural analysis of Acacia mangium and Tectona grandis was performed in Indonesian agroforestry systems with trees aged from 1 to 3 years. 3D virtual trees were then generated with the AmapSim simulation software and 3D virtual experiments in which tree age, planting density, planting pattern and pruning intensity varied were reconstructed in order to simulate light available for the crop. Canopy closure of trees was more rapid in A. mangium than in T. grandis agroforestry systems; after 3 years the quantity of light available for A. mangium intercrops was three times lower than under T. grandis. Simulations with A. mangium showed that practices such as pruning and widening tree spacing enable to increase the total transmitted light within the stand. On T. grandis, modification of the tree row azimuth resulted in changes in the spatial and seasonal distribution of light available for the intercrops. These results are discussed in terms of agroforestry system management.

Precision weighing lysimetry for trees, using a simplified tared-balance design

Four weighing lysimeters (1.8 m diameter, 1 m depth, weight 3.5-4.5 Mg) were used to estimate transpiration from single, isolated trees. The weighing mechanism incorporated a simple, new system of wire ropes around torsion tubes, producing a lever action through which most of the weight was tared off with a counter weight. Weight differences measured by load cell under the main lever arm were unaffected by hysteresis or temperature change. Sensitivity better than 100 g was achieved in windless conditions. Daily measurements over yearly periods (trees could be regularly replaced using extra pots) revealed both sigmoid seasonal patterns, and sigmoid diurnal changes closely related to micrometeorological variables, for a range of tree species. Measurements taken during rainfall demonstrated that an isolated tree intercepts considerably more precipitation than does a uniform crop covering the same ground area, and that substantial evaporation from the canopy takes place while it is raining.     

Belowground interactions for water between trees and grasses in a temperate semiarid agroforestry system

A fundamental hypothesis of agroforestry is the complementary use of soil resources. However, productivity of many agroforestry systems has been lower than expected due to net competition for water, highlighting the need for a mechanistic understanding of belowground interactions. The goal of this study was to examine root–root interactions for water in a temperate semiarid agroforestry system, based on ponderosa pines and a Patagonian grass. The hypotheses were: (a) A greater proportion of water uptake by pines is from deeper soil layers when they are growing with grasses than when they are growing alone; (b) Growth of grasses is improved by the use of water hydraulically lifted by pines. We used stable isotopes of O to analyze water sources of plants, and we measured sapflow direction in pine roots and continuous soil water content with a very sensitive system. We also installed barriers to isolate the roots of a set of grasses from pine roots, in which we measured water status, relative growth and water sources, comparing to control plants. The results indicated that pines and grasses show some complementary in the use of soil water, and that pines in agroforestry systems use less shallow water than pines in monoculture. We found evidence of hydraulic lift, but contradicting results were obtained comparing growth and isotope results of the root isolation experiment. Therefore, we could not reject nor accept that grasses use water that is hydraulically lifted by the pines, or that this results in a positive effect on grass growth. This information may contribute to understand the complex and variable belowground interactions in temperate agroforestry.     

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.     

Trade-offs analysis for possible timber-based agroforestry scenarios using native trees in the Philippines

To assess possible new agroforestry scenarios the tree–soil–crop interaction model in agroforestry systems (WaNuLCAS 3.01) was used based on-site specific data collected from Tabango (Central Philippines). Three native timber trees (Shorea contorta Vid., Pterocarpus indicus Juss., and Vitex parviflora Willd.) and one widely spread exotic specie (Swietenia macrophylla King.) were simulated under different intercrop scenarios with maize (Zea mays L.) and subsequently compared. Model simulation results quantified and explained trade-off between tree and crop. For example, higher tree densities will lead to a loss of crop yield that is approximately proportional to the gain in wood volume. However, beside this trade-off effect, there is considerable scope for tree intercropping advantage under a fertilization scenario, with systems that yield about 50% of the maximum tree biomass still allowing 70% of monoculture maize yield. Maximum tree yield can still be obtained at about 20% of the potential crop yield but intermediate tree population densities (400 trees ha⁻¹) and the resulting larger stem diameters may be preferable over the larger total tree biomass obtained at higher tree densities. Another advantage from intercropping systems is that trees directly benefit from the inputs (i.e., fertilizer) that are applied to the crops. The three native trees species studied have different performance in relation to productivity but are similar to (or even better than) S. macrophylla.     

The domestication and commercialization of indigenous trees in agroforestry for the alleviation of poverty

New initiatives in agroforestry are seeking to integrate into tropical farming systems indigenous trees whose products have traditionally been gathered from natural forests. This is being done in order to provide marketable products from farms that will generate cash for resource-poor rural and peri-urban households. This poverty-alleviating agroforestry strategy is at the same time linked to one in which perennial, biologically diverse and complex mature-stage agroecosystems are developed as sustainable alternatives to slash-and-burn agriculture. One important component of this approach is the domestication of the local tree species that have commercial potential in local, regional or even international markets. Because of the number of potential candidate species for domestication, one crucial first step is the identification of priority species and the formulation of a domestication strategy that is appropriate to the use, marketability and genetic potential of each species. For most of these hitherto wild species little or no formal research has been carried out to assess their food value, potential for genetic improvement or reproductive biology. To date their marketability can only be assessed by their position in the local rural and urban marketplaces, since few have attracted international commercial interest. To meet the objective of poverty alleviation, however, it is crucial that market expansion and creation are possible, hence for example it is important to determine which marketable traits are amenable to genetic improvement. While some traits that are relatively easy to identify do benefit the farmer, there are undoubtedly others that are important to the food, pharmaceutical or other industries that require more sophisticated evaluation. This paper presents the current thinking and strategies of ICRAF in this new area of work and draws on examples from our program. This revised version was published online in June 2006 with corrections to the Cover Date.     

A spatial database approach for estimating areas suitable for agroforestry in subSaharan Africa: aggregation and use of agroforestry case studies

The growing awareness of the importance and potential of agroforestry has resulted in an invaluable proliferation of site specific case studies. These presently exist in the necessary quantity and quality so as to facilitate their aggregate utilization in larger-scale research and application inquiry. We report here an approach for aggregating and using agroforestry case studies for agroforestry-related research at scales larger than the local site. The work presented here describes how ICRAF's agroforestry database — the primary source of case studies — can be used in combination with satellite imagery, and ancillary information, via matrix operations and a geographic information system, to produce a GIS-based agroforestry research tool for subSaharan Africa. This tool is used in a large-scale and preliminary way, to estimate the areas to which appropriate agroforestry systems in Africa might be extended.     

A model simulating above- and below-ground tree architecture with agroforestry applications

Modelling plant growth and architecture requires two consecutive and complementary approaches. The first is a qualitative botanical analysis, in which the development sequence of a tree is studied by the identification of various levels of organisation and of homogeneous subunits. All of these — architectural unit, axis, growth unit — follow particular growth processes which can be described by using the second approach, the quantitative analysis. Modelling of the functioning of meristems based upon stochastic processes has been carried out since 1980, in combination with a large amount of experimental work on temperate and tropical plants. Calculations involved in tree simulations from field data are based upon the probabilistic Monte Carlo method for the topological part and on analytical geometry for the morphological part. Computer graphics methods are then used to visualise the computed plant. Several sectors in agroforestry are concerned with application of such plant architecture modelling: tree growth and yield, radiative transfers, timber quality and mechanics, simulation of competition, interaction between plant morphology and physiology.     

Productivity of Theobroma cacao agroforestry systems with timber or legume service shade trees

Timber production and cocoa yields were studied (initial 10?C11?years) in two experimental plantations: a Cocoa-Legume system (CL, Erythrina poeppigiana, Gliricidia sepium or Inga edulis), and a Cocoa-Timber system (CT, Cordia alliodora, Tabebuia rosea or Terminalia ivorensis, plus I. edulis for inter-site comparisons). These trials had two major goals: (1) to evaluate the use of mono-specific timber shade canopies as an alternative to traditional, mono-specific, legume service shade tree canopies; and (2) to determine the production potential of ten cocoa clonal bi-crosses under these shade tree species. Within each site, shade tree species did not influence dry cocoa bean yield nor pod counts (total number of pods produced, number of healthy pods harvested, pod losses due to monilia [Moniliophthora roreri], black pod [Phytophthora palmivora] or other causes??birds and squirrels in this study-, and total pod losses). Significant differences were found between cocoa bi-crosses for both cocoa bean yield and pod counts. Sites differed only in terms of total pod losses (43% in CL; 54% in CT) and their causal factors (mainly monilia in CL; both monilia, squirrels and birds in CT). At CT, all timber tree species grew rapidly, reaching 30?C34?cm?dbh, 17?C25?m total tree height and 97?C172?m³?ha^?1 total stem volume (age 10?years). Timber species should be promoted for the shade component of cacao plantations given their potential production and the fact that their presence did not negatively affect cocoa yields.     

Application of the pipe model theory to non-destructive estimation of leaf biomass and leaf area of pruned agroforestry trees

The relationship of branch cross sectional area (CS) to leaf biomass (LM) and leaf area (LA) was studied in three agroforestry tree species,Calliandra calothyrsus Maissn.,Erythrina berteroana Urban andErythrina poeppigiana (Walpers) O.F. Cook, to develop a non-destructive method for the estimation of LM and LA for trees managed with periodic pruning. Variation in these relationships was observed according to the bifurcation level and, in theErythrina spp., by clone. All the relationships were linear except the CS-LM relation in small branches ofE. poeppigiana, where it was initially exponential. At main branch level the relationship of CS to LM and LA was linear in all cases but the regression parameter values varied between species and clones, with determination coefficient (R²) 0.88–0.99. It was concluded that the ratio of main branch CS to LM and LA can be used for non-destructive estimation of the latter variables. The method has the additional benefit that the regression parameter value reflects the allocation of dry matter within a tree and, consequently, may give indications about its possible uses in different agroforestry systems.Work carried out at the Centro Agronómico Tropical de Investigación y Enseñanza (CATIE), Turrialba, Costa Rica.     

A framework for a modular modelling approach for agroforestry

There are a number of problems with conventional methods for implementing models of agroforestry systems, including the difficulties of building, modifying and understanding them. One way of addressing these problems is to adopt a modular modelling approach, in which a model is constructed by linking a number of submodels, which in turn may consist of smaller computational units.This paper presents a basic framework for the design of a modular modelling approach suitable for agroforestry modelling. This approach is based on a close correspondence between the notion of module in modelling and of subroutine in a programming implementation of a model, so that selecting and linking modules is analogous to choosing and issuing calls to subroutines. This approach has the potential for enabling the complex modelling structures that are required for agroforestry modelling, such as spatial aspects and the representation of individual trees, to be handled in a consistent and uniform manner.The approach requires that subroutines should be held as symbolically-represented structures, rather than just source code in a programming language, so that they can be referenced as discrete units, and internally modified by symbol-processing operations. It is shown that the logic-programming language Prolog is well-suited to the task of representing subroutines in template form, ready to be fleshed out and combined into a single program in response to the selections made by a user. Prolog's suitability for the development of a user-friendly model design interface is also discussed, enabling models to be constructed simply by selecting options from a menu of design choices.     

Using plant architectural models for estimation of radiation transfer in a coconut-based agroforestry system

Software modules have been developed to predict the radiative environment of plant stands consisting of computer 'mock-ups' of plants. The architecture of plants used for the computation of radiative characteristics was described at the level of individual organs and simulated according to botanical rules. Three-dimensional stochastic numeric mock-ups were computed for coconut (Cocos nucifera L.) and for cacao (Theobroma cacao L.) according to the 'AMAP' methodology. Then the numerical radiative models were applied to these 'virtual plants' to describe the radiative budgets of individual plant parts and entire plants. Modelled light transmission through virtual coconut canopies was in good agreement with field measurements for different treatments and management practices including palm ages, varieties, and planting densities. In a second stage, combining the computer models of coconuts and cacao in a multistrata system, the fraction of radiation that was transmitted through the coconut canopy and intercepted by cacao was sucessfully simulated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth of widely spaced trees. A case study from young agroforestry plantations in France

Pessimistic forecasts often suggest that widely spaced trees enjoying free growth (no competition with other trees) will fail to provide high quality timber. This challenges the temperate agroforestry practice of planting widely spaced trees to produce high quality timber. We analyse tree growth data from recent temperate agroforestry plantations aged three to eight years, featuring low tree plantation densities (50 to 400 stems ha−1), the association of trees with intercrops (silvoarable systems) or animals (silvopastoral systems), and the use of plastic shelter tubes to protect trees (1.2 to 2.5 m high) and avoid damage by cattle or sheep in pastures or facilitate maintenance in silvoarable systems. The plantations are located in climates ranging from Mediterranean, dry central temperate plains, cold and wet central uplands to mild oceanic areas. Some plantations included a forestry control (high density of plantation, no tree shelter, no intercropping nor grazing). Trees were evaluated for height and diameter growth and stem form (straightness and absence of knots). Trees in most agroforestry plots grew satisfactorily, often faster than in forestry control plots. In some experimental plots, average annual height increments as high as 1 m and diameter increments as high as 1.5 cm were observed. Few agroforestry plantations were unsuccessful, and the reasons for the failures are discussed: animal damage in silvopastoral plots, but also a wrong choice of tree species unsuitable for local soil and climate characteristics. From these early results we can formulate some guidelines for designing future agroforestry plantations in temperate climates, concerning tree density, use of tree shelters and care required for widely spaced trees. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth and yield of some indigenous trees in an Amazonian agroforestry system: a rural-history-based analysis

Over the years farmers of Japanese descent in the Brazilian Amazon have planted indigenous trees that yield various products and services: fruit, seeds,bark, latex, oil, and shade and wind breaks for understory crop plants. Production of timber is often the intended end use of such planted trees. Long-term growth performance of these trees nevertheless has not been well documented. The authors constructed 65-year growth curves for nine indigenous tree species based on measurements of diameter at breast height (dbh), height, and tree age data provided by farmers in the Brazilian State of Pará. An index of wood prices used to calculate state stumpage taxes was then applied to mean stem wood growth curves to produce price curves. These price curves estimate both present value of standing timber, and the value added from annual growth of standing timber in the agroforestry systems studied. The results of this study provide local farmers with a tool to estimate potential annual income from the growth of their trees, and a basis for planning timber harvest rotations. This study's approach may be applicable in other parts of the tropics, where growth information about indigenous trees commonly used in agroforestry is lacking.This revised version was published online in November 2005 with corrections to the Cover Date.     

The potential use of the pejibaye palm in agroforestry systems

The pejibaye's potential for the small holder, especially in an agroforestry environment, is summarized: the fruit can be a significant addition to the family diet and income, both directly and as animal feed; on farm processing of the fruit for baking and other culinary uses has great potential and excedents can be marketed; small scale palmito production can also play an important part in the diet and farm income; oil production may be interesting after improved varieties are developed. The pejibaye's ecological requirements and limitations, its agronomic requirements and practices for small-scale production and its role in agroforestry systems are discussed. A list of Latin American researchers and germplasm contacts is given.     

Contribution of trees to soil carbon sequestration under agroforestry systems in the West African Sahel

Consequent to recent recognition of agricultural soils as carbon (C) sinks, agroforestry practices in the West African Sahel (WAS) region have received attention for their C sequestration potential. This study was undertaken in the Ségou region of Mali that represents the WAS, to examine the extent of C sequestration, especially in soils, in agroforestry systems. Five land-use systems were selected in farmers’ fields [two traditional parkland systems, two improved agroforestry systems (live fence and fodder bank), and a so-called abandoned land]. Soil samples taken from three depths (0–10 cm, 10–40 cm, and 40–100 cm) were fractionated into three size classes (2,000–250 μm, 250–53 μm, and <53 μm) and their C contents determined. Whole-soil C contents, g kg⁻¹ soil, across three depths ranged from 1.33–4.69 in the parklands, 1.11–4.42 in live fence, 1.87–2.30 in fodder bank, and 3.69–5.30 in abandoned land; and they correlated positively with silt + clay content. Using the ¹³C isotopic ratio as an indicator of relative contribution of trees (C3 plants) and crops (C4 plants) to soil C, more tree-origin C was found in larger particle size and surface soil and indicated that long-term tree presence promoted storage of protected C in deeper soil. Existing long-standing agroforestry practices of the region such as the parklands seemed to have little advantage for sequestering additional C, whereas improved agroforestry practices such as live fence and fodder bank introduced in treeless croplands seemed to be advantageous.     

A dynamic model for studying flow of water in single trees

Flow of water in a single tree was modeled in terms of the Darcy equation using a catena of four compartments: root, stem (further divided into discs), branches and leaves. Within each compartment or disc, water content was related to both water potential and conductivity of the xylem tissue using power or logarithmic functions, thus introducing both capacitance and variable resistance to flow in the model. Transpiration from the leaves to the atmosphere was used as the upper boundary to the model, and the soil-root interface as the lower boundary. Parameters for the water content, water potential and conductivity functions, together with physical dimensions were obtained by direct measurement or from the literature. A sensitivity analysis showed that the largest changes in simulated water potential and flow were associated with changes in the parameters directly controlling conductivity. Simulation of both smoothed diurnal changes and stepwise changes showed a phase lag down the tree, with flow tending to approach a steady state, but with changes in the gradients of water potential, water content and conductivity. A preliminary test of the model was made against field data using the Penman-Monteith equation to estimate the transpiration rate in a well-watered Pinus contorta Dougl. stand. Stem flow, water potential and water content were measured directly on a representative tree, which was subsequently harvested to provide dimensions and laboratory estimations of the parameters in the functions by direct measurement.