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Floristics and Structure of Southwestern Bangladesh Homegardens

Md. Enamul Kabir
School of Environment, Resources & Development, Asian Institute of Technology, Pathum Thani. Thailand

Edward L. Webb
School of Environment, Resources & Development, Asian Institute of Technology, Pathum Thani. Thailand

Abstract/ Executive Summary:

Homegardening is a traditional agroforestry practice in Bangladesh. Diverse species composition in a complex structure is a characteristic feature of Bangladesh homegardens. This study investigated the floristic and structural characteristics of homegardens from 402 randomly selected households in southwestern Bangladesh. A total of 419 species in 109 families were recorded. Fifty-nine per cent of all species were native to the Indian Subcontinent, including six IUCN Red-Listed for Bangladesh. Seventy-five per cent of all species were planted. Trees and herbs predominated and accounted for about 71% of all the identified species. The median homegarden of 800 m2 contained 34 species and 107 individual trees and shrubs. The recorded species were used for nine different purposes. In general, native species were more commonly used for all purposes except food, commerce, and fibre. The vertical architecture of the homegarden was complex. Common species were consistent with the general floristic profile reported from other tropical homegardens. Homegardens provided year-round subsistence and economic benefits from balanced adoption of multiple-use plants in different strata on limited homestead space. The results suggest considerable potential for the establishment and development of homegardening systems for the sustainable supply of subsistence livelihoods, while contributing to biodiversity conservation.

Keywords: Composition, Conservation, Diversity, Tropical agroforestry

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Program Area: Knowledge Management

Commodity: Flower

Objectives:

This study explored and quantitatively assessed the species richness and structural characteristics of a large sample of homegardens in southwestern Bangladesh. Exploration of biophysical conditions is an important aspect of any research on homegardens, as the species composition, diversity and structure will guide further investigation on management, utilization and valuation of homegardens.

Methodology:

Sampling design Six major regions/districts (administrative unit), locally called zilla, were selected from southwestern Bangladesh. Each district consists of a number of sub-districts, locally called thana (administrative unit). Two sub-districts from each selected district (n = 12) were selected randomly. In the absence of systematically arranged households and sub-district information on households, we used the following method to select study households in an unbiased manner. Every day, a new local guide was hired to assist in selecting households for the inventory. The research team did not tell the local guide the reason for selecting households. Immediately after selecting a household, she/he was requested to stay away from the household in order to prevent bias in future household selection. In this way, a total of 402 households from six selected districts (Figure 1) were selected randomly for primary data collection. Data collection A botanical inventory was conducted in the homegarden of each sampled household. The inventory was conducted continuously from April 2005 to January 2006. All vascular plant species, except small grasses, < 25-cm high, present in each selected homegarden were identified and recorded to species level, or by local name and later confirmed from the Bangladesh National Herbarium. The botanical inventory was conducted once in each selected homegarden. Thus, seasonal variation in plant composition and structure was not assessed. Every tree and shrub individual was counted, except those in hedgerows, due to the difficulty in differentiating stems. Individuals of herbs and climbers (woody and non-woody) were not counted due to difficulty in differentiating stems. Individuals of species of all life forms on the Bangladesh IUCN Red List were counted. The height of each freestanding tree and shrub individual was measured and recorded. A SUUNTO clinometer was employed to measure height for individuals more than 1-m tall, and a scaled measuring pole for the individuals up to 1 m. Height for the individual herb, climbers (woody and non-woody), tree and shrub species in hedgerows was not measured. The geographical location and altitude of each sample homegarden was recorded using a GARMIN GPS.Data analysis Each species recorded in the homegardens was classified by family, habit according to the morphology of the plant in its full growth potential (tree, shrub, herb or climber), domesticity (planted vs. naturally established), origin (native or introduced to the Indian Subcontinent), stratum (ground [up to 2 m], understorey [> 2 to 5 m], middle canopy [> 5 to 15 m], overstorey [> 15 to 25 m], or emergent [> 25 m]), conservation status (Bangladesh IUCN Red List, Khan et al. 2001), and use by people. Frequency – the fraction of homegardens containing the species (Cox 1990) – was calculated for all recorded species. Abundance – number of individuals per species – was calculated only for tree and shrub species (except those in hedgerows). The total of the relative values of abundance and frequency for each species of tree and shrub (except in hedgerows) was used in computing the importance value. For trees and shrubs, relative importance value was then used to rank species per life form. For herbs and climbers, relative frequency was used to rank species per life form. A stylized vertical profile diagram was created using the total number of strata found in the homegardens, and the common species name in each stratum was determined from the importance value of each species in its respective life form. A performance curve was used to verify the adequacy of the sampling effort (Ostrom 1990). A species–sample size curve, with the number of homegardens surveyed as the sample size, was constructed to verify whether the curve had reached asymptote.

Source of Information: International Journal of Biodiversity Science and Management 4 (2008) 54–64

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Achievement/Findings:

Geographic isolation, absence of harvestable public forests, low-annual per capita income (US$350), agricultural lands (0.05 ha) and forestlands (0.01 ha), and extreme poverty (about 50% of the population lives on less than US$1 a day) in southwestern Bangladesh have led to generally resource-poor conditions. The primary forests have already lost their full potential to supply basic needs for forest products and services for the country. In addition, the small area of agricultural land per capita, coupled with the negative impact of shade from perennials on annual crop productivity, restricts people’s ability to grow perennials in combination with agricultural crops in homegardens. However, the need for forest-based products and services has escalated with the growing population. Therefore, southwestern Bangladesh farmers have been cultivating, managing and conserving diverse plants in and around their dwelling houses to be self-reliant in meeting their own needs for forest products and services. Agroforestry homegardening systems in Bangladesh should play an important role in biodiversity conservation and livelihood supplementation.

Knowledge Management: Journal