Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) or poro (Erythrina poeppigiana) in Costa Rica

Predictive models were developed for Cordia alliodora branch and Theobroma cacao branch or leaf biomass,based on branch basal areas (r² 0.79) but the model of C. alliodora leaf biomass, although significant, was of very low accuracy (r² = 0.09) due to annual leaf fall. At age 10 years, shade tree stem biomass accounted for 80% of the total above-ground biomass of either tree. However, between the ages of 6 and 10 years, the biomass increment of T. cacao branches (3–4t.ha^–1.a^–1) was similar to that of the shade tree stems. During the same period, the net primary productivity was 35 and 28 t.ha^–1.a^–1, for the Erythrina poepigiana and and C. alliodora systems, respectively.Cocoa production under either of the shade trees C. alliodora or E. poeppigiana was 1000 kg.ha^–1.a^–1 (oven-dry; ages 6–10 yr). During the same period, C. alliodora timber production was 9 m³.ha^–1.a^–1 whilst the leguminous shade tree E. poeppigiana does not produce timber. Litterfall over the same 5 years, including crop and/or shade tree pruning residues, averages 11 and 23 t.ha^–1.a^–1, respectively. The main difference was due to E. poeppigiana pruning residues (10t.ha^–1.a^–1).Soil organic material reserves (0–45 cm) increased over 10 years from 198 to 240 t.ha^–1 in the E. poeppigiana plots and from 168–184 t.ha^–1 in the C. alliodora plots. These values, together with the productivity indices presented, provide evidence that the systems are sustainable.For economic reasons, the use of C. alliodora is recommended under the experimental conditions. however, on less fertile soils without fertilization, the greater biomass and hence nutrient return to the soil surface under E. poeppigiana, might make this the preferable shade tree.     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica III. Cycles of organic matter and nutrients

Models for cycles for organic matter and nutrients element (N, P, K, Ca and Mg) are presented for the agroforestry systems of cacao (Theobroma cacao) withCordia alliodora orErythrina poeppigiana in Turrialba, Costa Rica. For the models, system reserves (soil, humus, vegetation divided into leaves, branches, stems, fine roots, fruits) and transference between compartments (production and decomposition of litter residues) inputs (fertilizer, rainfall) and outputs (harvests) of the system are considered. The implications of the models are discussed in detail. Aspects of net primary production in the systems studied are considered. N fixation is calculated on the basis of balances. Analysis of soil water showed high variations that coincided with rainfall patterns and pruning of theE. poeppigiana. For part I see Vol. 4, No. 3, 1986 For part II see this issue Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesellschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica III. Cycles of organic matter and nutrients

Models for cycles for organic matter and nutrients element (N, P, K, Ca and Mg) are presented for the agroforestry systems of cacao (Theobroma cacao) withCordia alliodora orErythrina poeppigiana in Turrialba, Costa Rica.For the models, system reserves (soil, humus, vegetation divided into leaves, branches, stems, fine roots, fruits) and transference between compartments (production and decomposition of litter residues) inputs (fertilizer, rainfall) and outputs (harvests) of the system are considered.The implications of the models are discussed in detail.Aspects of net primary production in the systems studied are considered.N fixation is calculated on the basis of balances. Analysis of soil water showed high variations that coincided with rainfall patterns and pruning of theE. poeppigiana.For part I see Vol. 4, No. 3, 1986 For part II see this issueAgroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesellschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica II. Cacao and wood production,litter production and decomposition

During 7 years (1979–1985) cacao harvests (beans and husks) have been recorded for the agroforestry systems ofTheobroma cacao underCordia alliodora andErythrina poeppigiana shade trees. The mean oven dry cacao yields were 626 and 712 kg.ha^–1.a^–1 cocoa beans underC. alliodora andE. poeppigiana respectively. Harvests have gradually increased over the years and the plantation has now reached maturity.Annual extraction of N, P, K, Ca and Mg in fruits, which is relatively small, was calculated on the basis of chemical analyses. The following average values were found (kg.ha^–1.a^–1): At the age of 8 years, theC. alliodora trees have reached 26.7 cm diameter (DBH) and 14.0 m in height. Mean annual growth (from age 5 to 7) is 14.6 m³.ha^–1.a^–1.Natural plant residue production has been measured for 4 years (Nov. 1981–Oct. 1985). UnderE. poeppigiana it has reached a value of 8.91 t.ha^–1.a^–1 and underC. alliodora 7.07 t.ha^–1.a^–1. The shade trees have contributed 57 and 47% respectively. Transference and decomposition rates are high and important in the nutrient cycles.The nutrient content of the litter was analysed and corresponding average yearly transfers were (kg.ha^–1.a^–1): For part I see Vol. 4, No. 3, 1986.Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesselschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica II. Cacao and wood production,litter production and decomposition

During 7 years (1979–1985) cacao harvests (beans and husks) have been recorded for the agroforestry systems ofTheobroma cacao underCordia alliodora andErythrina poeppigiana shade trees. The mean oven dry cacao yields were 626 and 712 kg.ha⁻¹.a⁻¹ cocoa beans underC. alliodora andE. poeppigiana respectively. Harvests have gradually increased over the years and the plantation has now reached maturity. Annual extraction of N, P, K, Ca and Mg in fruits, which is relatively small, was calculated on the basis of chemical analyses. The following average values were found (kg.ha⁻¹.a⁻¹): At the age of 8 years, theC. alliodora trees have reached 26.7 cm diameter (DBH) and 14.0 m in height. Mean annual growth (from age 5 to 7) is 14.6 m³.ha⁻¹.a⁻¹. Natural plant residue production has been measured for 4 years (Nov. 1981–Oct. 1985). UnderE. poeppigiana it has reached a value of 8.91 t.ha⁻¹.a⁻¹ and underC. alliodora 7.07 t.ha⁻¹.a⁻¹. The shade trees have contributed 57 and 47% respectively. Transference and decomposition rates are high and important in the nutrient cycles. The nutrient content of the litter was analysed and corresponding average yearly transfers were (kg.ha⁻¹.a⁻¹): For part I see Vol. 4, No. 3, 1986. Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesselschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Litter production and nutrient cycling in coffee (Coffea arabica) or cacao (Theobroma cacao) plantations with shade trees

The relative importance of N fixation, organic material inputs and nutrient inputs in litterfall, as justifications for including shade trees in plantations of coffee or cacao, is discussed. According to existing data, N fixation by leguminous shade trees does not exceed 60 kg.N/ha/a. However, these trees contribute 5,000–10,000 kg. organic material/ha/a.Comparisons are made between the leguminous shade tree Erythrina poeppigiana and the non-leguminous timber tree Cordia alliodora. The former, when pruned 2 or 3 times/a., can return to the litter layer the same amount of nutrients that are applied to coffee plantations via inorganic fertilizers, even at the highest recommended rates for Costa Rica of 270 kg.N, 60 kg.P, 150 kg.K/ha/a. The annual nutrient return in this litterfall represents 90–100 percent of the nutrient store in above-ground biomass of E. poeppigiana, and hence the consequences of competition with the crop should not be a serious limitation. In the case of C. alliodora, which is not pruned, nutrient storage in the tree stems, especially of K, is a potential limiting factor to both crop and tree productivity.It is concluded that, in fertilized plantations of cacao and coffee, litter productivity is a more important shade tree characteristic than N fixation.An early version of this review was presented at the CATIE-IUFRO meeting Los Arboles de Uso Multiple en Sistemas Agroforestales, June 1985, Turrialba, Costa Rica.     

The role of cacao plantations in maintaining forest avian diversity in southeastern Costa Rica

We conducted 600 ten-minute, fixed-radius point counts in two climatically different seasons in forest, abandoned cacao (Theobroma cacao), and managed cacao habitat from September 1997 through April 1998 in the Talamanca lowlands of Costa Rica. A total of 1,464, 1,713, and 1,708 individual birds and 130, 131, and 144 total species were detected in forest, abandoned cacao, and managed cacao, respectively. Independent of season, cacao habitats had a significantly greater number of individuals and species per point than forest. Community similarity analyses based on guild categorizations revealed a significant degree of similarity among all habitats; however, habitat affinity analyses showed cacao habitats having significantly less forest specialists than forest. A multiple linear regression model for actively managed cacao habitat using habitat and landscape variables revealed density and diversity of canopy tree species to be significantly correlated with numbers of forest specialist species detected per point. Although nearest distance to forest was negatively correlated with the number of forest specialist species per point, it was not a significant variable in the model, possibly indicating the complex and unpredictable nature of bird movements within the complex habitat mosaic of Talamanca. The present forest bird community of the Talamanca lowlands is poor in forest specialist species relative to other forested Caribbean lowland sites. The broad patterns of avifaunal distribution illustrated by our results suggest, therefore, that although cacao plantations cannot substitute for forest, they provide habitat for a large number of species which depend to some degree on forests. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nutrient cycling in two traditional Central American agroforestry systems

A preliminary nutrient cycling study quantified total and temporal nutrient inputs via litterfall and pruning residues in two agroforestry systems: (1) Coffea arabica (perennial crop)-Erythrina poeppigiana (leguminous shade tree); and (2) C. arabica-E. poeppigiana-Cordia alliodora with emphasis on the effect of the timber tree C. alliodora. The total annual input of litterfall plus pruning residues was similar in both associations. Total annual input from E. poeppigiana was less than half in the association with C. alliodora than without, but the litterfall from this latter species compensated for the loss. Large differences in the total annual nutrient input of K, Ca and Mg was found between associations, but not for N or P. The amount of nutrients recycled by the associated trees reached the recommended level of fertilizer required for coffee production. The inclusion of C. alliodora within the C. arabica-E. poeppigiana association resulted in a more evenly distributed annual nutrient input.     

Benefits and costs of intercropping reforestation in the Atlantic lowlands of Costa Rica.

Agroforestry options as a means of promoting reforestation were testedby establishing with 10 farmers simple comparisons between pure plantations andtimber trees with annual or perennial intercrops. Two year-old intercroppedtrees on-farm had 22–48% greater height and 24–38% greater diameterthan trees in pure plantations. The exception was Cordiaalliodora that did not respond significantly to intercropping withcassava (Manihot esculenta). Only intercrops with the mostvaluable crops on agricultural soils produced a return to labour above thedailywage rate. On non-agricultural soils, farmers only intercrop a small area oftheir plantations with subsistence crops to meet home consumption needs. In thecontext of Costa Rica intercropping appeared to have a limited potential tofinance the reforestation costs of farmers.     

Production and phenology of the fruit shrub Eugenia stipitata in agroforestry systems in Costa Rica

Arazá (Eugenia stipitata), a fruit shrub originating from Western Amazonia, was evaluated growing in association with timber shade trees (Acacia mangium or Cordia alliodora) or with plantain (Musa sp.) as a potential commercial species for the tropical moist lowlands of Talamanca, Costa Rica. Height and crown width of the four-year-old shrubs varied between 2.7–2.8 m and 2.9–3.1 m, respectively. Flowering was positively correlated with initial fruit formation 1 month later and initial fruit formation with fully developed fruits a subsequent month after that. Three to four-year-old plants produced 20.0, 20.0, and 24.5 t ha⁻¹ yr⁻¹ (fresh fruits) in associations with A. mangium, C. alliodora and plantain, respectively, with higher production in rainy months. Fruit production in later years under C. alliodora (six to eight-year-old shrubs) was 26.5 t ha⁻¹ yr⁻¹. Where markets exist for E. stipitata fruit, the association can be recommended for tropical humid lowlands of Central America.     

Initial growth of pioneer timber tree species in a Taungya system in the humid lowlands of Costa Rica

The temporary association of annual crops in juvenile tree plantations (Taungya system) can reduce or offset the initial costs of reforestation and hence provide incentives for tree planting on private farms. A replicated systematic spacing design, derived from a Nelder-fan design, was used to study the effects of tree-crop distance on growth and development of the timber species salmwood (Cordia alliodora) or eucalyptus (Eucalyptus deglupta), associated with maize (Zea mays) or cassava (Manihot esculenta), during the first year after transplanting the trees on two sites on alluvial soils in the humid lowlands of Costa Rica. Association with maize did not affect mean tree growth. However, mean eucalyptus and salmwood heights of 7–8 m and 3–4 m, respectively, after one year in pure plantation or associated with maize, were only 4.7 m and 1.4 m, respectively, when associated with cassava. Wider tree – crop spacings were more important for initial salmwood growth than for eucalyptus. It was concluded that the shoot growth characteristics (continuous or episodical growth) of the timber species is a very important consideration when selecting associated agricultural crop species and tree-crop distances.     

Crown development and biomass production of pollardedErythrina berteroana,E. fusca andGliricidia sepium in the humid tropical lowlands of Costa Rica

Leguminous trees are widely used to support climbers such as black pepper (Piper nigrum L.) and vanilla (Vanilla planifolia Andr.), to provide shade to crops and to maintain soil fertility. Pruning or pollarding provides the means to maximize benefits from the trees, particularly through the production of biomass as a soil amendment. At the same time, excessive shading is reduced. In order to quantify the degree of shading of black pepper by the support trees during a six-month pollarding cycle, this study monitored crown development (part I) and light transmission (part II) of three widely used species,Erythrina berteroana Urban,E. fusca Loureiro andGliricidia sepium (Jacq.) Steud.The two sites were in the humid Atlantic Lowlands of Talamanca, southern Costa Rica (mean annual rainfall 2460 mm, no distinct dry season), on alluvial soils (typic Tropofluvents) with low levels of K, P, Mn and Zn. Two-year-old trees, that had been established from cuttings as live supports for black pepper, were used for the study. They were pollarded twice per year. The variables measured/estimated monthly were: stem diameter at breast height (dbh); height, foliated height, depth, diameter, leaf area and leaf biomass of crowns; length, diameter, number and inclination of branches. Leaf nutrient contents were also determined.Following pollarding,G. sepium was the first to resprout, followed byE. berteroana andE. fusca. G. sepium with its few but erect and long branches had slender, columnar crowns. while those ofE. berteroana andE. fusca were more spherical. Four months after pollarding,G. sepium started shedding leaves at the base of its branches. Average crown diameter after six months were 2.2 m forE. berteroana, 1.9 m forE. fusca and 1.5 m forG. sepium; average crown depths after six months were 2.8 m, 2.1 m, and 2.7 m, respectively, for the three species. For 1600 trees ha^–1 and two prunings per year, foliar biomass production from prunings alone (i.e., without litter fall), calculated from regressions with length and basal diameter of branches as independent variables, was 3.8 t, 3.4 t and 2.3 t dry matter ha^–1 a^–1 forE. berteroana, E. fusca andG. sepium, respectively; these estimates agreed well with measured values. The corresponding N contents were 146 kg, 124 kg and 90 kg, respectively. While N contributions from the prunings exceeded 50% of the fertilizer recommendations for black pepper, the contributions were <10% for P and <40% for K. Linear regressions between leaf area and branch dimensions, and quadratic regressions between foliar biomass and crown diameter showed high coefficients of determination (0.83>R ²>0.99). Correlations between foliar biomass, dbh, and dbh increments were generally weak. Conclusions from the study appear to be valid also for other agroforestry systems where the same species are planted under similar ecological conditions for reasons other than as live supports.

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Resumen Los árboles leguminosos se usan frecuentamente como soportes vivos para plantas trepadoras como pimienta negra (Piper nigrum L.) y vainilla (Vanilla planifolia Andr.), para dar sombra y para reducir el desgaste de los suelos. La poda de los árboles reduce la cantidad mantener la fertilidad de sombra y produce biomasa que sirve como enmiendas. Con el objectivo de cuantificar el grado del sombreado de pimienta negra por los árboles durante un cíclo de poda de seis meses, se monitoreó en este estudio el desarrollo de la copa (parte I) y la transmisión de luz (parte II) de tres especies usados como soportes vivos:Erythrina berteroana Urban,E. fusca Loureiro yGliricidia sepium (Jacq) Steud.Los dos sitios estan en la zona tropical húmeda de Talamanca Baja, en el sureste de Costa Rica (precipitación promedia 2460 mm, sin estación seca) en suelos aluviales (Typic Tropofluvents) y pobres en K, P, Mn y Zn. Los árboles fueron establecidos de estacas. Cuando este estudio empezó, los árboles tenían dos años de edad y fueron podados dos veces por año. Los parámetros medidos ó estimados mensualmente fueron: diámetro del tronco a la altura del pecho (DAP); altura, altura foliada, profundidad, diámetro, área foliar y biomasa foliar de las copas; largo, diámetro, número y inclinación de las ramas. Además se determinó el contenido de nutrientes de las hojas.Despues de la poda,G. sepium fue el primero en rebrotar, seguido porE. berteroana yE. fusca. G. sepium con sus ramas escasas pero largas y erectas, formó una copa delgada y columnar, mientras que las copas deE. berteroana yE. fusca fueron más esféricas. Cuatro meses después de la poda,G. sepium empezó a perder las hojas en la base de sus ramas. El promedio del diámetro de la copa después de seis meses fue de 2.2 m paraE. berteroana, 1.9 m paraE. fusca y 1.5 m paraG. sepium; el promedio de la profundidad de la copa después de seis meses fú de 2.8 m, 2.1 m y 2.7 m, respectivamente para las tres especies. Para 1600 árboles ha^–1 y dos podas por año, la producción estimada de biomasa foliar de la poda (sin tomar en cuenta la hojarasca caída antes), calculada de regresiónes con el largo y el diámetro basal de las ramas como variables independientes, fue de 3.8 t, 3.4 t y 2.3 t de matéria seca ha^–1 a^–1 paraE. berteroana, E. fusca yG. sepium, respectivamente; estos valores calculados concordaron bien con valores medidos. El contenido de N correspondiente fué de 146 kg, 124 kg, y 90 kg, respectivamente. Mientras que la contribución de N procedente de las podas excedió 50% de una recomendación de fertilización común para pimienta negra, la contribución de P fue inferior al 10%, y menos del 40% para K. Regresiones lineales entre área foliar y las dimensiones de la ramas, y regresiones cuadraticas entre biomasa foliar y el diámetro de la copa mostraron altos coeficientes de determinación (0.83>R ²>0,99). Las correlaciones entre biomasa foliar, el DAP y incrementos del DAP fueron generalmente débiles. Las conclusiones de éste estudio parecen válidas tambien para sistemas agroforestales donde las especies estudiadas son plantadas bajo condiciones ecológicas similares para propósitos diferentes de como soportes vivos.

     

Fine-root dynamics of coffee in association with two shade trees in Costa Rica

Fine-root dynamics (diameter < 2.0 mm) were studied on-farm in associations of Coffea arabica with Eucalyptus deglupta or Terminalia ivorensis and in a pseudo-chronosequence of C. arabica-E. deglupta associations (two, three, four and five years old). Coffee plants were submitted to two fertilisation types. Cores were taken in the 0–40 cm soil profile two years after out-planting and subsequently in the following year in depth layers 0–10 and 10–20 cm, during and at the end of the rainy season, and during the dry season. Fine root density of coffee and timber shade trees was greater in the coffee fertilisation strip as compared to unfertilised areas close to the plants or in the inter-rows. Coffee fine roots were more evenly distributed in the topsoil (0–20 cm) whereas tree fine roots were mostly found in the first 10 cm. Although the two tree species had approximately the same fine root length density, lower coffee / tree fine root length density ratios in T. ivorensis suggest that this shade tree is potentially a stronger competitor with coffee than E. deglupta. Coffee and tree fine root length density for 0–10 cm measured during the rainy season increased progressively from two to five-year-aged associations and coffee fine root length density increased relatively more than E. deglupta fine root length density in the four and five-year-aged plantations suggesting that contrary to expectations, coffee fine roots were displacing tree fine roots.     

Financial returns, stability and risk of cacao-plantain-timber agroforestry systems in Central America

Diversification of agroecosystems has long been recognized as a sound strategy to cope with price and crop yield variability, thus increasing farm income stability and lowering financial risk. In this study, the financial returns, stability and risk of six cacao (Theobroma cacao L.) – laurel (Cordia alliodora (R&P) Oken) – plantain (Musa AAB) agroforestry systems, and the corresponding monocultures, were compared. Production and cost data were obtained from an on-going eight-year old experiment. The agroforestry systems included a traditional system and a replacement series between cacao (278, 370, 556, 741 and 833 plants ha^–1) and plantain (833, 741, 556, 370 and 278 plants ha^–1) with a constant laurel population (timber tree; 69 trees ha^–1). An ex-post analysis was conducted using experimental and secondary data to build a simulation model over a 12-year period under different price assumptions. The probability distribution functions for the three commodity prices were modeled and simulated through time, accounting for their possible autocorrelation and non-normality. The expected net incomes from the agroforestry systems were considerably higher than from monocultures. The agroforestry systems were also less risky. Agroforestry systems with proportionally more cacao than plantain were less risky, but also less stable. The timber component (C. alliodora) was a key factor in reducing farmer's financial risks. Methodologically, the study illustrates a technique to evaluate both expected returns and the corresponding financial risks to obtain a complete, comparable profile of alternative systems. It shows the need to allow for the possibility of non-normality in the statistical distributions of the variables entering a financial risk and return analysis.     

Species and site selection for timber production on farm boundaries in the humid Atlantic Lowlands of Costa Rica and Panama

In 1987–89 the CATIE-GTZ Agroforestry Project set up experiments with five timber tree species planted in single lines on twelve farm boundaries in cooperation with local farmers. When the trees were five years old, their height, diameter and total stem volume were: Acacia mangium 17 m, 19 cm and 67 m³ km^–1, Cordia alliodora 14 m, 20 cm and 46 m³ km^–1, Eucalyptus deglupta 22 m, 24 cm and 85 m³ km^–1, Tectona grandis 17 m, 20 m and 64 m³ km^–1, Terminalia ivorensis 18 m, 23 cm and 104 m³ km^–1. Considering these excellent growth rates, planting of Cordia alliodora, Eucalyptus deglupta and Tectona grandis in lines on farm boundaries should be promoted. T. ivorensis and A. mangium are not recommendable for sites with impeded drainage because of mortality caused by root rot, mostly due to Rosellinia sp.     

Soil carbon dynamics and residue stabilization in a Costa Rican and southern Canadian alley cropping system

Agroforestry systems can play a major role in the sequestration of carbon (C) because of their higher input of organic material to the soil compared to sole crop agroecosystems. This study quantified C input in a 19-year old tropical alley cropping system with E. poeppigiana (Walp.) O.F Cook in Costa Rica and in a 13-year old hybrid poplar (Populus deltoides × nigra DN-177) alley cropping system in southern Canada. Changes in the level of the soil organic carbon (SOC) pool, residue decomposition rate, residue stabilization efficiency, and the annual rate of accumulation of SOC were also quantified in both systems. Carbon input from tree prunings in Costa Rica was 401 g C m⁻² y⁻¹ compared to 117 g C m⁻² y⁻¹ from litterfall at the Canadian site. In southern Canada, crop residue input from maize (Zea mays L.) was 212 g C m⁻² y⁻¹, 83 g C m⁻² y⁻¹ from soybeans (Glycine max L.) and 125 g C m⁻² y⁻¹ for wheat (Triticum aestivum L.), and was not significantly different (p < 0.05) from the sole crop. The average yearly C input from crop residues in Costa Rica was significantly greater (p < 0.05) in the alley crop for maize (134 g C m⁻² y⁻¹) and Phaseolus vulgaris L. bean crops (35 g C m⁻² y⁻¹) compared to the sole crop. The SOC pool was significantly greater (p < 0.05) in the Costa Rican alley crop (9536 g m⁻²) compared to its respective sole crop (6143 g m⁻²) to a 20 cm depth, but no such difference was found for the southern Canadian system. Residue stabilization, defined as the efficiency of the stabilization of added residue (crop residues, tree prunings, litterfall) that is added to the soil C pool, is more efficient in southern Canada (31%) compared to the alley cropping system in Costa Rica (40%). This coincides with a lower organic matter decomposition rate (0.03 y⁻¹) to a 20 cm depth in Canada compared to the Costa Rican system (0.06 y⁻¹). However, the average annual accumulation rate of SOC is greater in Costa Rica (179 g m⁻² y⁻¹) and is likely related to the greater input of organic material derived from tree prunings, compared to that in southern Canada (30 g m⁻² y⁻¹) to a 20 cm depth.     

Impact factors on fine root seasonal dynamics in Fraxinus mandshurica plantations

Fine root turnover plays important roles in carbon allocation and nutrient cycling in forest ecosystems. Seasonal dynamics of fine roots is critical for understanding the processes of fine root turnover. From May to October 2002, soil core method was used for estimating the seasonal pattern of fine root (diameter < 1 mm) parameters (biomass, specific root length (SRL) and root length density (RLD)) in a Manchurian ash (Fraxinus mandshurica) plantation located at the Maoershan Experiment Station, Heilongjiang Province, northeast of China. The relationships of fine root biomass, SRL and RLD with available nitrogen in soil, average soil temperature per month in 10 cm depth and soil moisture content were analyzed. Seasonal variation of fine root biomass was significant (P < 0.05). The peak values of fine root biomass were observed both in spring and in autumn, but SRL and RLD were the highest in spring and lowest in autumn. Specific root length and root length density were higher in spring and summer, which means that fine root diameter was thinner. In autumn, both parameters decreased significantly due to secondary incrassation of fine root diameter or the increase of tissue density. Seasonal dynamics of fine roots was associated with available nitrogen in soil, soil temperature in 10 cm depth and moisture content. Fine root biomass has a significant relationship with available NH₄ ⁺-N in soil. Available NO₃ ⁻-N in soil, soil temperature in 10-cm depth and moisture content have a positive correlation with fine root biomass, SRL and RLD, although these correlations are not significant (P > 0.05). But the compound effects of soil available N, soil temperature and soil moisture content are significant to every root parameter. The variations of these three root parameters in different seasons show different physiological and ecological functions in different growing periods. Translated from Scientia Silvae Sinicae, 2006, 42(9): 7–12 [译自: 林业科学]     

Timber harvest,damage to crop plants and yield reduction in two Costa Rican coffee plantations with Cordia alliodora shade trees

Both model and field estimations were made of the damage inflicted to coffee plants due to the harvest of timber shade trees (Cordia alliodora) in coffee plantations. Economic analyses were made for different coffee planting densities, yields, and both coffee and timber prices.Damage due to tree felling and log skidding should not be a major limitation to the use of timber shade trees in coffee plantations. The timber price that would balance all discounted losses and benefits to zero, for scenarios with and without trees ranged between 8–20 US $/m³ (current overbark log volume at the saw mill yard is US$ 66/m³). There will be lower margins for coffee damage in high yielding plantations, specially in years of good coffee prices. Nevertheless, the use of timber shade trees is recommended even in these scenarios.     

Implementing on-farm agroforestry research: lessons learned in Talamanca,Costa Rica

The rapid appraisal and farmer selection procedures, preceding the establishment of over fifty agroforestry research trials on farms in Talamanca, Costa Rica are described. The highest probability of success and impact of these long-term collaborative trials is obtained by selecting innovative, experienced, motivated and locally respected farmers. The methodological lessons learned from implementing three types of researcher managed trials (shade-cacao; black pepper on living support posts; timber production in boundary lines) are discussed. The importance of fitting farmer selection criteria to project objectives, experimental designs to on-farm limitations, and project goals to farmers' goals, are emphasized.     

A comparison of agrisilvicultural systems with plantation forestry in the Atlantic Lowlands of Costa Rica

Survival and growth data (ages 0–5 years) are presented for two timber species (Acacia mangium, Cordia alliodora) planted in monocultures or in association with a sequence of agricultural cropsZea mays, Zingiber officinale andEugenia stipitata (a fruit shrub) in the tropical humid Caribbean lowlands of Costa Rica. Average annual height and diameter growth rates were 3.2 m and 4.0 cm (C. alliodora), 3.5 m and 3.8 cm (A. mangium).C. alliodora associated with crops gave the greatest productivity with an average total stem volume increment of 19 m³ ha^–1 yr^–1. Root rot ofA. mangium (mainlyRosellinia sp.), leading to tree mortality, was greater in pure plots compared to associated plots.A. mangium can not be recommended for similar sites because of this problem.