Agroforestry systems for sustainable livelihoods and improved land management in the East Usambara Mountains, Tanzania

Forest destruction for agriculture continues to be a major threat to the rich biological diversity in the East Usambara Mountains in the north-eastern corner of Tanzania. The highest ratio of endemic plant and animal species found on 100 km2 anywhere in the world is depending on the remaining natural forests. Forests are vitally important for the local population in many different ways, and nationally they are an important source of water and hydroelectricity. The soils, of low fertility and mostly acidic Ferrasols, mainly have the nutrients in the topsoil. After clear-cutting, the soils soon become poor when the topsoil is eroded. High-value cardamom is nowadays unsustainably cultivated in the natural forests of the East Usambaras. The general aim was to study the possibilities to develop new profitable and sustainable agroforestry systems for the benefit of the local people that could contribute to relieving the pressure on the remaining natural forests in the East Usambara Mountains. Results from a spice crop agroforestry trial, established in cooperation with a local farmer, showed a clear advantage of intercropping cardamom (Elettaria cardamomum) and black pepper (Piper nigrum) with trees, especially with Grevillea robusta. The nitrogen fixing tree species Gliricidia sepium also improved the nitrogen and organic matter content of the soil over levels found in the natural forest. With improved agroforestry methods for spice production the households generated as much as13 times the net income obtained with traditional forest cultivation practices. There are thus sustainable and profitable ways to cultivate spices as cash crops in well-managed homegardens. However, the farmers need stable markets, access to credit and comprehensive extension services. The soil fertility depletion should be reversed with organic manure application and an enabling policy environment for the smallholder-farming sector. Strong farmers organisations and equal rights to resources and decision-making are needed. Organic spices have an increasing demand, and their export would be profitable for these farmers. What is, however, most needed for a change is a political will of a government that understands the importance of agricultural and forestry development for poverty reduction.

Productive coexistence and gain in agroforestry systems.

Productive coexistence and coexistence gain of populations were studied using nine years' data from field experiments of Taxodium ascendens-intercrop systems in Lixiahe, Jiangsu Province, China. A theoretical framework for productive coexistence in agroforestry was developed. Interaction patterns between trees and intercrops were presented within this framework. A model framework was developed to describe the coexistence gain and interaction of populations in T. ascendens-intercrop systems. Facilitation and resource sharing were identified as main contribution to the advantage of species combination in agroforestry. The model of population interaction developed in the present study was accepted for describing the interaction of populations in T. ascendens-intercrop systems, because it explained a high proportion of the variance of experimental data and fitted well the observations in most intercropping types. The model developed in the present study provides flexibility for describing different patterns of intra- and inter-specific interactions. Model coefficients were applied to the determination of the ecological compatibility of species. Managed T. ascendens-intercrop systems were advantageous as compared to a monoculture of trees or arable crops. In T. ascendens stands up to the age of three, arable crops contributed about 50-80 % of the total biomass yield of agroforestry. The diameter or height growth of T. ascendens was not significantly influenced by intercrops, indicating that intercropping under trees produced extra yields but did not depress the tree growth. When the trees were young (during the first three years), T. ascendens did not depress the crop yields, and a land equivalent ratio greater than unity was obtained together with a high yield of both components. The diameter and height of the trees were similar in four spacing configurations with an equal number of trees per hectare up to the age of eight, but wider between-rows open range were beneficial for the intercrops. The relationship between open-ranges and species coexistence was also analysed and the distribution of soil nutrients studied.

Soil fertility and nutrient status of traditional Gayo coffee agroforestry systems in the Takengon region, Aceh Province, Indonesia

Little is known about the traditional coffee cultivation systems in Central Aceh, Indonesia, where coffee production is a major source of income for local Gayo people. Based on field observations and farmer interviews, 14 representative agroforestry coffee plantations of different age classes (60-70 years, 30-40 years, and 20 years) as well as seven adjacent grassland and native forest sites were selected for this study, and soil and coffee leaf samples collected for nutrient analysis. Significant differences in soil and coffee leaf parameters were found between former native forest and Sumatran pine (Pinus merkusii) forest as previous land cover indicating the importance of the land use history for today’s coffee cultivation. Soil pH as well as exchangeable Na and Ca concentrations were significantly lower on coffee plantations compared to grassland and forest sites. Soil C, N, plant available P, exchangeable K, and Mg concentrations showed no consistent differences between land use groups. Nitrogen (N), phosphorus (P), and potassium (K) concentrations of coffee leaves were in the sufficiency range, whereas zinc (Zn) contents were found to be consistently below the sufficiency threshold and significantly lower in coffee plantations of previous pine forest cover compared to those of previous native forest cover. While the results of this study provided insights into the nutrient status of coffee plantations in Central Aceh, the heterogeneity of site conditions, limited sampling size, and scarcity of reliable data about the land use history and initial soil conditions of sampled sites preclude more definitive conclusions about the sustainability of the studied systems.

Agroforestry systems of timber species and cacao: survival and growth during the early stages

In recent times, increased emphasis has been placed on diversifying the types of trees to shade cacao (Theobroma cacao L.) and to achieve additional services. Agroforestry systems that include profitable and native timber trees are a viable alternative but it is necessary to understand the growth characteristics of these species under different environmental conditions. Thus, timber tree species selection should be based on plant responses to biotic and abiotic factors. The aims of this study were (1) to evaluate growth rates and leaf area indices of the four commercial timber species: Cordia thaisiana, Cedrela odorata, Swietenia macrophylla and Tabebuia rosea in conjunction with incidence of insect attacks and (2) to compare growth rates of four Venezuelan Criollo cacao cultivars planted under the shade of these four timber species during the first 36 months after establishment. Parameters monitored in timber trees were: survival rates, growth rates expressed as height and diameter at breast height and leaf area index. In the four Cacao cultivars: height and basal diameter. C. thaisiana and C. odorata had the fastest growth and the highest survival rates. Growth rates of timber trees will depend on their susceptibility to insect attacks as well as to total leaf area. All cacao cultivars showed higher growth rates under the shade of C. odorata. Growth rates of timber trees and cacao cultivars suggest that combinations of cacao and timber trees are a feasible agroforestry strategy in Venezuela.

Effects of transformation processes in 'jubraka' agroforestry systems of the Nuba Mountains, Sudan, on nutrient fluxes

Intensification processes in homegardens of the Nuba Mountains, Sudan, raise concerns about strongly positive carbon (C) and nutrient balances which are expected to lead to substantial element losses from these agroecosystems, in particular via soil gaseous emissions. Therefore, this thesis aimed at the quantification of C, nitrogen (N), phosphorus (P) and potassium (K) input and output fluxes with a special focus on soil gaseous losses, and the calculation of respective element balances. A further focus in this thesis was rainfall, a valuable resource for rain-fed agriculture in the Nuba Mountains. To minimize negative consequences of the high variability of rainfall, risk reducing mechanisms were developed by rain-fed farmers that may lose their efficacy in the course of climate change effects predicted for East Africa. Therefore, the second objective of this study was to examine possible changes in rainfall amounts during the last 60 years and to provide reliable risk and probability statements of rainfall-induced events of agricultural importance to rain-fed farmers in the Nuba Mountains. Soil gaseous emissions of C (in form of CO2) and N (in form of NH3 and N2O) of two traditional and two intensified homegardens were determined with a portable dynamic closed chamber system. For C gaseous emission rates reached their peak at the onset of the rainy season (2,325 g CO2-C ha-1 h-1 in an intensified garden type) and for N during the rainy season (16 g NH3-N ha-1 h-1 and 11.3 g N2O-N ha-1 h-1, in a traditional garden type). Data indicated cumulative annual emissions of 5,893 kg CO2-C ha-1, 37 kg NH3-N ha-1, and 16 kg N2O-N ha-1. For the assessment of the long-term productivity of the two types of homegardens and the identification of pathways of substantial element losses, a C and nutrient budget approach was used. In three traditional and three intensified homegardens observation plots were selected. The following variables were quantified on each plot between June and December in 2010: soil amendments, irrigation, biomass removal, symbiotic N2 fixation, C fixation by photosynthesis, atmospheric wet and dry deposition, leaching and soil gaseous emissions. Annual balances for C and nutrients amounted to -21 kg C ha-1, -70 kg N ha-1, 9 kg P ha-1 and -117 kg K ha-1 in intensified homegardens and to -1,722 kg C ha-1, -167 kg N ha-1, -9 kg P ha-1 and -74 kg K ha-1 in traditional homegardens. For the analysis of rainfall data, the INSTAT+ software allowed to aggregate long-term daily rainfall records from the Kadugli and Rashad weather stations into daily, monthly and annual intervals and to calculate rainfall-induced events of agricultural importance. Subsequently, these calculated values and events were checked for possible monotonic trends by Mann-Kendall tests. Over the period from 1970 to 2009, annual rainfall did not change significantly for either station. However, during this period an increase of low rainfall events coinciding with a decline in the number of medium daily rainfall events was observed in Rashad. Furthermore, the availability of daily rainfall data enabled frequency and conditional probability calculations that showed either no statistically significant changes or trends resulting only in minor changes of probabilities.

Effects of transformation processes in 'jubraka' agroforestry systems of the Nuba Mountains, Sudan, on plant diversity

Deutsche Forschungsgemeinschaft

Competition in tree row agroforestry systems. 3. Soil water distribution and dynamics

The purpose of this study was to test the hypothesis that soil water content would vary spatially with distance from a tree row and that the effect would differ according to tree species. A field study was conducted on a kaolinitic Oxisol in the sub-humid highlands of western Kenya to compare soil water distribution and dynamics in a maize monoculture with that under maize (Zea mays L.) intercropped with a 3-year-old tree row of Grevillea robusta A. Cunn. Ex R. Br. (grevillea) and hedgerow of Senna spectabilis DC. (senna). Soil water content was measured at weekly intervals during one cropping season using a neutron probe. Measurements were made from 20 cm to a depth of 225 cm at distances of 75, 150, 300 and 525 cm from the tree rows. The amount of water stored was greater under the sole maize crop than the agroforestry systems, especially the grevillea-maize system. Stored soil water in the grevillea-maize system increased with increasing distance from the tree row but in the senna-maize system, it decreased between 75 and 300 cm from the hedgerow. Soil water content increased least and more slowly early in the season in the grevillea-maize system, and drying was also evident as the frequency of rain declined. Soil water content at the end of the cropping season was similar to that at the start of the season in the grevillea-maize system, but about 50 and 80 mm greater in the senna-maize and sole maize systems, respectively. The seasonal water balance showed there was 140 mm, of drainage from the sole maize system. A similar amount was lost from the agroforestry systems (about 160 mm in the grevillea-maize system and 145 mm in the senna-maize system) through drainage or tree uptake. The possible benefits of reduced soil evaporation and crop transpiration close to a tree row were not evident in the grevillea-maize system, but appeared to greatly compensate for water uptake losses in the senna-maize system. Grevillea, managed as a tree row, reduced stored soil water to a greater extent than senna, managed as a hedgerow.

Enhanced biodiversity and pollination in UK agroforestry systems

Monoculture farming systems have had serious environmental impacts such as loss of biodiversity and pollinator decline. The authors explain how temperate agroforestry systems show potential in being able to deliver multiple environmental benefits.

A sustainable agricultural landscape for Australia: A review of interlacing carbon sequestration, biodiversity and salinity management in agroforestry systems

Transformation of the south-western Australian landscape from deep-rooted woody vegetation systems to shallow-rooted annual cropping systems has resulted in the severe loss of biodiversity and this loss has been exacerbated by rising ground waters that have mobilised stored salts causing extensive dry land salinity. Since the original plant communities were mostly perennial and deep rooted, the model for sustainable agriculture and landscape water management invariably includes deep rooted trees. Commercial forestry is however only economical in higher rainfall (>700 mm yr−1) areas whereas much of the area where biodiversity is threatened has lower rainfall (300–700 mm yr−1). Agroforestry may provide the opportunity to develop new agricultural landscapes that interlace ecosystem services such as carbon mitigation via carbon sequestration and biofuels, biodiversity restoration, watershed management while maintaining food production. Active markets are developing for some of these ecosystem services, however a lack of predictive metrics and the regulatory environment are impeding the adoption of several ecosystem services. Nonetheless, a clear opportunity exists for four major issues – the maintenance of food and fibre production, salinisation, biodiversity decline and climate change mitigation – to be managed at a meaningful scale and a new, sustainable agricultural landscape to be developed.

Growth parameters and nutrient content in four multipurpose tree species with potential characteristics for agroforestry systems in a Cerrado region in Botucatu, São Paulo State, Brazil

In order to evaluate growth characteristics, adaptability, biomass production, nutrient recycling, nutrient distribution and the ability to regenerate degraded land, a trial using four multipurpose tree species (Leucaena leucocephala, Leucaena diversifolia, Acacia melanoxylon and Mimosa scabrella) was undertaken over two years in a distrophic red yellow latosol (oxisol) following a randomized block experimental design with four replications. At the age of two years, A. melanoxylon and L. diversifolia were the tallest species (5.25 and 4.97 m, respectively) and A. melanoxylon and M. scabrella had the largest diameters at 20 cm from tree base. Mimosa scabrella and A. melanoxylon had the highest dry matter production and quantity of nutrients in the above ground biomass. In all species, the highest nutrient contents were found in the leaves, followed by branches and stems. From all species, the highest Nutrient Utilization Efficiency Indexes were obtained for sulphur, phosphorous, and magnesium; L. diversifolia was the most efficient for nitrogen, potassium, calcium, sulphur, and manganese, while A. melanoxylon was the most efficient for phosphorus, magnesium, boron, iron, and zinc. Litter production levels over a three month period were as follows: M. scabrella > A. melanoxylon > L. diversifolia > L. leucocephala. Litter nutrient content was higher in M. scabrella than in the other species.

Origin of and resulting floristic composition from seedbanks in agroforestry systems of Tomé-Açu, Eastern Amazon.

2016

Agroforestry systems and food security among smallholder farmers of the Brazilian Amazon: A strategy for environmental global crisis.

2008

Growth of native trees in two agroforestry systems.

Agroforestry systems with eucalyptus prevail in Central and Southeast Brazil, and little information is available about systems using native trees. The aim of the present study was to evaluate the development of seven native tree species grown under two agroforestry systems. The experiment was conducted starting in 2007 in 12-hectare area in the municipality of São Carlos, São Paulo state, Brazil. The tree species planted in the two systems (a silvopastoral system and an agrisilvicultural system) were: 'capixingui' (Croton floribundus) and 'mutambo' (Guazuma ulmifolia) (tutors), 'jequitibá-branco' (Cariniana estrellensis), 'canafistula' (Peltophorum dubium) and 'ipê felpudo' (Zeyheria tuberculosa) (timber trees), and 'angico-branco' (Anadenanthera colubrina) and 'pau-jacaré' (Piptadenia gonoacantha) (N-fixing trees). Data were collected for 48 months. The results show differences among tree development, which was evaluated as growth in height and diameter, as well as sensitivity to insect and disease damage. The overall results show that the agrisilvicultural system allowed better tree development. The species with best performance in the two systems were capixingui, mutambo and canafístula. Ipê-felpudo and jequitibá-branco showed the worst results. The high variability among individuals of the same species indicates the possibility of high production advances with selective breeding of these species.

The bioeconomic potential for agroforestry in Australia's northern grazing systems.

Although agriculture generates 16% of Australia's greenhouse gas emissions, it also has the potential to sequester large quantities of emissions through land use management options such as agroforestry. Whilst there is an extensive amount of agroforestry literature, little has been written on the economic consequences of adopting silvopastoral systems in northern Australia. This paper reports the financial viability of adopting complementary agroforestry systems in the low rainfall region of northern Australia. The analysis incorporates the dynamic tradeoffs between tree and pasture growth, likely forest product yields, carbon sequestration and livestock methane emissions in a bioeconomic model. The results suggest there are financial benefits for landholders who integrate complementary agroforestry activities into existing grazing operations at even modest carbon prices.