Toward an understanding of tropical home gardens

Tropical home gardens are an agroforestry practice found worldwide. From an analytical perspective little is known about this practice. The universality of their complex structure would indicate the existence of common objectives. The objectives and resulting implementation strategies will dictate the form, layout, species composition and management style of each home garden. Understanding the interrelationships between these various elements is one step toward utilising the advantages of home gardens in a range of agroforestry practices.     

Soil quality assessment across different stands in tropical moist deciduous forests of Nagaland,India

To analyze the relationship between the management of three forest stand plantations and soil quality in the Dimapur district of the Northeastern Himalayan region,India,three forest soil profiles,covered by different species stands,at three depths were tested for 13 physical and chemical variables.Only four of these variables(electric conductivity,bulk density exchangeable Mg and available P)were included in a minimum data set,after using a varimax rotation algorithm in a principal component analysis,and subsequently used to calculate a soil quality index(SQI).Results showed higher SQIs in the surface layers(0–20 cm depth)than in the deeper ones.Average weighed SQI varied significantly(P<0.05)through the three considered forest sites,with the lowest value at site FS3.These findings reveal that the approach used here is suitable for preliminary screening of the impact of a forestry species on soil,to aid in species selection and improve soil health for afforestation and reforestation projects.     

The comparative value of wild and domestic plants in home gardens of a South African rural village

Rural inhabitants make considerable use of wild resources from communal areas around their settlements, as well as from arable and residential plots. These wild resources compete with the main crops planted in arable plots and home gardens, but play a significant economic and nutritional role in rural livelihoods. This paper reports upon a conservative financial evaluation of the wild plant resources harvested from home gardens and arable plots by inhabitants of rural village in the Bushbuckridge lowveld (South Africa), and examines their importance relative to other domesticated crops. On average, each household made use of four to five species of wild plants growing on their residential plot, whereas the mean number of crop plants was 3.4. The total value of all plants was R1694 (US$ 269) per household per year, or approximately R4200 (US$ 667) per hectare of home garden per year. Wild plants represented 31% of the value of all plants grown on residential plots, relative to the 69% for domesticated crops (including fruit trees). Approximately 72% of the total value of all plant products was consumed by the household, and the remaining 28% was sold.This revised version was published online in November 2005 with corrections to the Cover Date.     

Soil carbon stock in relation to plant diversity of homegardens in Kerala,India

Conservation of biodiversity and mitigation of global warming are two major environmental challenges today. In this context, the relationship between biodiversity (especially plant diversity) and soil carbon (C) sequestration (as a means of mitigating global warming) has become a subject of considerable scientific interest. This relationship was tested for homegardens (HG), a popular and sustainable agroforestry system in the tropics, in Thrissur district, Kerala, India. The major objectives were to examine how tree density and plant-stand characteristics of homegardens affect soil C sequestration. Soil samples were collected at four depths (0–20, 20–50, 50–80, 80–100 cm) from HG of varying sizes and age classes, and their total C content determined. Tree density and plant-stand characteristics such as species richness (Margalef Index) and diversity (Shannon Index) of the HG were also determined. Results indicated that the soil C stock was directly related to plant diversity of HG. Homegardens with higher, compared to those with lower, number of plant species, as well as higher species richness and tree density had higher soil carbon, especially in the top 50 cm of soil. Overall, within 1 m profile, soil C content ranged from 101.5 to 127.4 Mg ha⁻¹. Smaller-sized HG (<0.4 ha) that had higher tree density and plant-species density had more soil C per unit area (119.3 Mg ha⁻¹) of land than larger-sized ones (>0.4 ha) (108.2 Mg ha⁻¹). Soil C content, especially below 50 cm, was higher in older gardens. The enhanced soil-C storage in species-rich homegardens could have relevance and applications in broader ecological contexts.

Soil erosion under a successional agroforestry sequence: a case study from Idukki District,Kerala, India

The Western Ghats of Kerala have been settled over the past 40 years by landless immigrants. Natural forests and cardamom (planted under forest canopy) have been widely replaced by small-holder cultivation. Settlers plant cassava and other annuals in the initial 3–5 years following clearing of the forest canopy. These crops are gradually replaced by black pepper, the dominant crop 5–15 years after clearing. Finally, other perennial crops, planted during the period when pepper was dominant, mature. A highly mixed “home garden” cropping phase is most common on sites 15–20 years after the forest canopy was removed. Soil erosion on sites cleared 1–3 years previously averaged 120 t/ha in the 1988 monsoon season. Over the same period, soil erosion under mature cardamom, pepper and mixed cultivation averaged 0.65, 3.5, and 1.45 t/ha respectively. Erosion levels appear to be related to cover at ground and intermediate (1–4 m) heights above the surface. Soil organic matter is high in the cardamom areas, declines rapidly when the forest canopy is cleared, remains low in pepper, and appears to rebuild to levels as more mixed agroforestry systems become established. Overall, there appears to be a succession in which high erosion and declining organic matter levels are temporary features associated with the conversion of sites from forests and cardamom to other phases.     

A little-leaf disease of Eucalyptus in Kerala,India*

A little-leaf disease of Eucalyptus tereticornis, E. grandis and E. globulus characterized by stunting of plants and considerable reduction in size of leaves and internodes, was recorded during survey of nurseries and plantations in Kerala State. The survey indicated that though the little leaf disease was widespread, its incidence was quite low. Transmission of the symptoms by sap and graft techniques was unsuccessful. However, positive fluorescence and staining of phloem tissues by Dienes' stain indicates that this disease may be caused by mycoplasmalike organisms (MLO).     

Dynamics of Homegarden Structure and Function in Kerala, India

Homegardens in Kerala have long been important multi-purpose agroforestry systems that combine ecological and socioeconomical sustainability. However, traditional homegardens are subject to different conversion processes linked to socioeconomic changes. These dynamics were studied in a survey of 30 homegardens. On the basis of a cluster analysis of tree/shrub species density and subsequent further grouping using homegarden size as additional characteristic, six homegarden types were differentiated. These were assessed regarding structural, functional, management and dynamics characteristics. Four development stages of homegardens were found along a gradient from traditional to modern homegardens. Fifty percent of the homegardens still displayed traditional features, whereas 33% incorporated modern practices. The process of modernisation includes a decrease of the tree/shrub diversity, a gradual concentration on a limited number of cash-crop species, an increase of ornamental plants, a gradual homogenization of homegarden structure and an increased use of external inputs. One homegarden was characterised as an adapted traditional homegarden combining multispecies composition and intensive management practices using internal inputs with commercial production. In comparison to modern homegardens, this homegarden type offers an example of an alternative development path in adapting homegardens to changing socioeconomic conditions. The study of structural and functional dynamics of homegardens offers the opportunity to understand the trends in socio-economic sustainability and how these relate to ecological sustainability.     

Fodder grass productivity and soil fertility changes under four grass+tree associations in Kerala, India

Adapted tree+grass combinations make a valuable contribution to forage production in the Indian peninsula, but knowledge of the interactive effects between trees and grasses on their production is limited. We, therefore, conducted a field experiment involving combinations of four trees and grasses, besides monospecific grass controls, for seven years, to investigate grass productivity in association with leguminous and non-leguminous multipurpose trees (MPT) having disparate canopy architecture, and to assess the end-of-rotation soil fertility changes. Post rotation changes in herbage productivity were evaluated by growing teosinte (Zea mexicana) for three years. The four MPTs were Acacia auriculiformis, Ailanthus triphysa, Casuarina equisetifolia and Leucaena leucocephala. Grasses included Pennisetum purpureum (hybrid napier), Brachiaria ruziziensis (congo signal), Panicum maximum (guinea grass) and teosinte. Lower tree branches were pruned from fifth year. Understorey herbage production increased until three years in all tree+grass combinations, but declined subsequently, as tree crowns expanded. Overall, casuarina among MPTs, and hybrid napier and guinea grass among forage crops, were more productive than others. Pruning MPTs generally favoured greater herbage production. Understorey light levels for acacia, ailanthus, casuarina and leucaena were 17, 60, 55 and 55% of that in the open at five years. During the post-rotation phase, MPT plots were characterised by higher soil nutrient capital and consequently teosinte yields were higher than in the treeless control treatment. All previous tree-grass combinations showed an increasing trend till two years after MPT felling. Yield levels declined subsequently, despite at variable rates. Careful selection of the tree and grass components is, therefore, crucial for optimising herbage productivity in silvopastoral systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Litter dynamics of six multipurpose trees in a homegarden in Southern Kerala, India

Multipurpose trees, the integral components of homegardens, contribute significantly to the closed nutrient cycling processes and sustainability of the ecosystem. Although, the litter production and probable nutrient returns via litter in homegardens have been documented, quantification and characterization of the decomposition and bioelement release from the litter have received relatively little scientific attention. The objective of the present study is to explore the litter dynamics of six locally important multipurpose trees (Mangifera indica L., Artocarpus heterophyllus Lamk., Anacardium occidentale L., Ailanthus triphysa Dennst., Artocarpus hirsutus L. and Swietenia macrophylla L.), in an agroforestry homegarden in Southern Kerala, India. Litterfall and nutrient additions in the six species ranged from 383 to 868 g m⁻² yr⁻¹, nitrogen, 6.4 to 8.8, phosphorus, 0.17 to 0.42 and potassium, 1.1 to 2.8 g m⁻² yr⁻¹. The annual litter output in the homegarden was 425 kg with A. hirsutus, M. indica, A. heterophyllus and A. occidentale recording significantly higher litter and nutrient additions. Leaf litter decay studies revealed A. heterophyllus and A. occidentale to be the most labile litter species and S. macrophylla the most recalcitrant. The decay rate coefficients varied significantly among the species. Foliage decomposition rates related to the initial chemical composition of the litter revealed best correlation with lignin. NPK release was almost complete by the end of decay in all species inspite of the initial phases of accumulation observed for nitrogen and phosphorus. Two-way analysis of variance test revealed significant differences in the contents of the three elements as a function of species and time elapsed. Macronutrients were released in the order K>N/P. The higher rates of decay and nutrient turnover in M. indica, A. heterophyllus and A. occidentale foliage indicated the potential of using these species’ litter as nutrient inputs in agriculture while A. triphysa, A. hirsutus and S. macrophylla perform better as organic mulches taking a longer time for decay and hence nutrient release.     

Adoption of intercropping in rubber smallholdings in Kerala, India: a tobit analysis

Natural rubber (Hevea brasiliensis) is one of the major plantation crops of the state of Kerala in India and intercropping is practised during the initial gestation period of the crop. In this paper a to bit model was used to study the decision making behaviour of farmers in adoption and extent of adoption of intercropping in three regions of Kerala. The availability of family labour and the type of intercrops were found significant in explaining the adoption behaviour in all three regions. The perception of profitability of intercropping was also found to influence decision on adoption. The probability of adoption of intercropping was highest for three intercrops, banana (Musa spp.), cassava (Manihot esculenta) and pineapple (Ananas comosus). Targeting extension efforts to groups of farmers with available family labour and popularising selected intercrops may result in higher rates of adoption of intercropping in all three regions of the state.This revised version was published online in November 2005 with corrections to the Cover Date.     

Fuelwood characteristics of tree species in homegardens of Kerala, India

Indiscriminate use of natural resources in the past has lead to fuelwood shortages in many parts of the tropical world. To surmount this domestic energy crisis, not only degraded sites must be planted with trees having high fuel value potential, but also agroforestry promoted on arable lands. To enable choice of species for such energy plantations/agroforests in the humid tropics of peninsular India, we assessed the heat of combustion and physical properties that determine combustion of phytofuels, such as ash content, specific gravity and moisture content. Bark and wood samples of 45 multipurpose tree species in the homegardens of Kerala, India and three fuel materials of local importance (coconut [Cocos nucifera] endocarp, dried coconut spathe and dehiscent rubber [Hevea braziliensis] pericarp) were evaluated. Variations abound in the calorific values and physical properties of species and tissue-types. In general, heat of combustion and specific gravity followed the sequence: heartwood > sapwood > bark, while mean ash percentage followed a reverse order (bark > sapwood > heartwood). Ash content had a negative correlation with heat of combustion, but specific gravity exerted a positive influence. Furthermore, ash content and wood specific gravity were inversely related. Although green moisture content increased in the order: bark < heartwood < sapwood, it failed to show any predictable relationship with heat of combustion.This revised version was published online in November 2005 with corrections to the Cover Date.     

Agroforestry farming systems in the homesteads of Kerala,southern India

Kerala State on the southwestern coast of India in the tropical humid zone has a predominantly agricultural economy, a very high density of population and therefore high pressure on cultivable land. The farmers there undertake cultivation of an array of crops — tree crops, plantation crops, seasonals and biennials — all in intimate mixtures on the same piece of land around the homesteads. Farm animals and poultry and sometimes fisheries also are essential components of the system. The close association of agricultural crops, tree crops and animals in the homesteads represents an excellent example of sustainable and productive agroforestry homegardens. Optimum utilization of available resources of land, solar energy and technological inputs and an efficient recycling of farm wastes are important characteristics of the systems. This paper attempts to describe and evaluate the systems' stability, productivity and sustainability, and identify its merits and constraints as well as research needs.     

Litter of multipurpose trees in Kerala,India: variations in the amount,quality, decay rates and release of nutrients

In a field study involving 8–9 year-old woodlots of nine fast growing tree species in Kerala, India, the amount and nutrient content of litterfall were monitored. Decay rate constants and litter half-lives were estimated by fitting a single exponential model to the litter decomposition data. Annual litter production ranged from 3.43 Mg ha⁻¹ (Pterocarpus) to 12.69 Mg ha⁻¹ (Acacia). Litterfall of Acacia, Ailanthus, Pterocarpus and Casuarina followed a uni-modal distribution pattern. Nutrient content of litter samples showed considerable variations, owing to species and sampling time. Based on mean litter N content, the nine species were broadly divided into high, medium and low detrital N species. Litterfall accounted for substantial nutrient recycling within the system. Results of the litter bag study revealed that residual litter mass declined exponentially with time for Ailanthus, Pterocarpus, Casuarina and Leucaena. Paraserianthes showed a linear trend, while Emblica and the two Artocarpus species exhibited a bi-phasic pattern of mass loss. Both initial lignin content and lignin–N ratio had a negative, although modest influence on decay rate coefficients, while initial N content exerted a positive influence. Nutrient release from the decomposing litter followed either a tri-phasic pattern characterised by an initial accumulation, followed by a rapid release and a final slower release phase, or a bi-phasic pattern that is devoid of the initial accumulation phase.     

遭遇全球化的印度喀拉拉邦棕榈藤工业

自从1991年,印度政府改变了其政策,从保护工业发展到增强竞争能力,以应对全球化所带来的影响。这种政策上的变化对印度经济的所有领域都产生了影响。印度喀拉拉的棕榈藤业最先是原住民开始的,现在已变得更有组织性,更加以市场为导向。对1991年前后的各类变量(如资本结构,盈利,附加值和产品的营销)进行比较,揭示了一些有趣的趋势。本项研究强调,在全球化大潮中,合作经济因为没有抵挡横业内竞争和加强资本流动的能力,再加上管理方面的不足,其效率相当低。全球化导致私营部门所有权发生了变化。由于解雇工人,原材料和电力费用在生产成本中的比例减少。同时人工成本在生产成本中的比例略有上升。藤业的营销方式也会发生很大的变化。在1991年之前,藤产品的营销主要集中在喀拉拉邦,而现在大约55%的单位将他们的产品出口到其他邦,其中20%也出口到其他国家,以获得更高的价格。另外,也借助产品的多样化,促进销售,如在纸质和电子媒体上做广告和质量控制来获取市场份额。全球化为藤产业带来新的机遇,也给工人的生存安全带来负面影响。     

Effect of recurrent fires on soil nutrient dynamics in a tropical dry deciduous forest of Western Ghats,India

The role of forest fires in the soil dynamics and global carbon cycle has not been comprehensively studied in tropical forests as the effects of fire on tropical forest soils can be extremely variable. This study was aimed to understand how repeated fires affect physical and chemical properties of soil in a tropical dry deciduous forest and alter soil fertility and health. The study was carried out in the dry deciduous forest of Mudumalai Tiger Reserve. Soil samples were collected from unburned (B0) to six-time burned (B6) plots. Samples were collected from each plot from three different depths viz. 0–10 (Top), 10–20 (Middle), and 20–30 cm (Bottom) and analyzed for soil physical and chemical properties. Soil pH, EC, WHC decreased with increasing fire frequencies while bulk density increased. Organic Carbon, Total N, and available P decreased with increasing fire frequencies whereas extractable K initially increased but decreased with the very high frequency of fires. NO₃^?N slightly decreased with high fire frequencies but NH₄^?N decreased significantly with increasing fire frequency. These results provide a new insight regarding the influence of repeated fires on soil that will be valuable to understand the effect of fire on the recovery of soils and nutrient dynamics.     

Successional patterns and gap phase dynamics of a humid tropical forest of the Western Ghats of Kerala, India: ground vegetation, biomass, productivity and nutrient cycling

The population dynamics of the ground vegetation and its energetics such as biomass accumulation and net primary productivity, and the nutrient cycling patterns in the humid tropical forest of the Western Ghats in India are largely determined by gap age and by whether gaps are formed naturally or through selection felling. Responses of plant categories such as herbs, shrubs, tree seedlings and saplings also vary depending upon gap type and age. An exotic species such as Chromolaena odorata occurred only in selection-felled gaps ((9 ± 3)−(49 ± 4) individuals (100 m)⁻²). Nilgirianthus ciliatus, a dominant shrub, plays a key role in the gaps in determining population dynamics of others. The net primary productivity of the ground vegetation, which is about 31.17 ± 4.26 kg (100 m)⁻² year⁻¹ in an undisturbed site, increased a year after gap formation to 102.82 ± 6.46 kg (100 m)⁻² year⁻¹ in natural gaps and to 71.82 ± 2.36 kg (100 m)⁻² year⁻¹ in selection-felled gaps. Five years after gap formation, net primary productivity of the ground vegetation declined considerably, this being related to decline in fast-growing shrub and secondary tree species in the vegetation and gap closure. A similar trend was also recorded for the rates of nutrient uptake and nutrient accumulation in the vegetation.

In natural gaps the soil nutrient level increased gradually with gap age. This could be attributed to slow release of nutrients from the fallen trunks and nutrient storage in the rapidly recovering vegetation. In contrast, in selection-felled gaps, the quantities of soil nutrients such as nitrogen, phosphorus and magnesium were higher in 1-year-old gaps than in undisturbed sites, owing to the release of these nutrients from leaf litter and wood debris which were deposited in larger quantities within the gap itself, and owing to sparse ground vegetation resulting from the greater disturbance of the soil, in the first 1 or 2 years. The fractional annual turnover rates of elements of the ground vegetation and the soil were higher in 1-year-old gaps and declined with gap age. The significance of these results for forest management is discussed.     

The structure of four home gardens in the Petén,Guatemala

Forest-covered home gardens around the tropical world vary in their structure, but serve to supply food and other products for direct family consumption or marketing. Little quantitative data exist defining home garden structure. Thus, this study was undertaken to examine the variation in home garden structures in response to market or household needs and the subsequent variation in light interception and productivity.Four home gardens were studied in the Department of the Petén, in northern Guatemala. Areal extent and height of canopies were mapped in transects through four gardens representing a range of site water regimes and market orientation. Light intensities incident on the ground were measured along each transect to assess light use. Results showed structural complexity, with full canopy closure in the one or more layers within the canopy for most gardens. The garden architectures made efficient use of light and space, with intersive management for food and fuel production. Farmers grew the crops for both cash and family subsistence. One home garden on a comparatively dry site with shallow soil seemed less structured, with only a single broken canopy layer, but with diverse species of plants.The results indicate that development of gardens in this area utilized existing trees, thinning them to leave the most useful, and inserting other desirable trees and shrubs in the understory and in open spaces. This strategy seemed to maximize light use, regardless of market orientation.This look at the structure and composition of four home gardens, in a forested area of current immigration, demonstrated (1) variety of organization and plant components, (2) different architecture for different soil/site conditions and market orientations, and (3) efficient use of available light through the arrangement of plants.     

Biosocial and bionumerical diversity of variously sized home gardens in Tabasco, Mexico

The evaluation of species and structural diversity of home gardens strongly depends on the methods used. We distinguish the biosocial and the bionumerical method. The first is widely used and takes data of the whole population of trees of home gardens to calculate diversity. The bionumerical method calculates diversity from data of a fixed number of randomly selected trees. We apply both methods to analyze if structural and species diversity varies with home garden size, a theme of considerable conservation interest, and compare results. We inventoried the tree component of a sample of 61 home gardens from rural areas in Tabasco, Mexico, which we assigned to three size categories: small (≤1,000 m²), medium sized (>1,000 and ≤2,000 m²), and large home gardens (>2,000 m²). Average species richness and Shannon diversity indices determined by the biosocial method were significantly different among home garden size classes. Average species richness determined by the bionumerical method did not differ among size classes. Both methods showed highest total observed and estimated species richness in the large home gardens, which contain many unique species. Both methods showed similar overall species composition among size classes and highest structural diversity in large home gardens. We conclude that it is important for conservation to maintain large home gardens in local mosaics, and that the biosocial and bionumerical methods are complementary. The bionumerical method allows straight comparison of population diversity within and among systems, but lacks attention for rare and unique species. The biosocial method evaluates how much diversity families custody.     

Coinoculation of bioinoculants improve Acacia auriculiformis seedling growth and quality in a tropical Alfisol soil

We conducted a study to find out if arbuscular mycorrhizal(AM) fungi(Acaulospora scrobiculata,Scutellospora calospora) and phosphate solubilizing bacteria(PSB, Paenibacillus polymyxa) inoculation either individually or in combinations can improve Acacia auriculiformis seedling growth, uptake of nutrients and quality in a phosphorus deficient tropical Alfisol. The seedlings were assessed for various growth and nutrient uptake parameters after 60 days of treatment. Inoculation with P.polymyxa stimulated mycorrhizal formation. Seedling height, stem girth, taproot length, number of leaves and leaf area, plant dry matter production, nodulation, and nodular dry weight were significantly higher for seedlings that were either dual inoculated or triple inoculated compared to individual inoculation of AM fungi or PSB, and uninoculated seedlings. Dual and triple application of AM fungi and PSB also significantly improved the nutrient contents of shoots and roots and nutrient uptake efficiencies. The calculated seedling quality indexes of the AM fungi and PSB inoculated seedling were 25–208% higher than uninoculated seedlings. These findings show that A.auriculiformis seedlings when dual inoculated or triple inoculated performed better than seedlings inoculated with the microbes individually and compared with uninoculated control seedlings. We conclude that bioinoculation is important for the production of high-quality A.auriculiformis seedlings in tree nurseries for planting in nutrient deficient soils.