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Journal of Environmental Professionals Sri Lanka: 2015 – Vol. 4 – No. 2 – 47-57
47
Linking Plant Diversity and Dietary Diversity of
Home Gardens:
Examining the Nexus through Structural Equation Modelling
W. M. D. K. Marasinghe, J. C. Edirisinghe# and L. D. M. N. Lokuge
Department of Agribusiness Management,
Faculty of Agriculture and Plantation Management,
Wayamba University of Sri Lanka, Makandura, Gonawila (NWP).
#Corresponding Author:
E-mail: jagathed@yahoo.com
ABSTRACT
Home gardens are the best solution to face global food crisis ahead. The diversified
diet helps to reduce the micronutrient deficiency and the risk of chronic diseases.
Purpose of this study is to identify the nexus between dietary diversity and plant
diversity of the home gardens in Kandy district, Sri Lanka and to understand the
determinants affecting the diversity of the home garden. One hundred and thirteen
home gardens, belonging to six Divisional Secretariat divisions in Kandy district
were randomly selected and data were collected by face to face interviews. Plant
diversity was measured by Shannon Index (SI) and dietary diversity by an index
prepared by using Food and Agriculture Organization’s Dietary Diversity Index
(DD20). Data were analysed through Structural Equation Modelling (SEM) method.
Age of the garden owner, education level of the spouse, Health Perception Index
(HPI), Constraints on Gardening Index (CGI) and Income Expectation Index (IEI)
significantly affect the plant diversity of the home garden. According to the SEM
results, there is a positive significant relationship between dietary diversity of the
household and plant diversity of home gardens.
KEYWORDS: Dietary diversity, Home gardening, Plant diversity, Shannon Index, Structural
Equation Modelling
Introduction
World hunger is becoming a more challenging issue, where developing nations have
been mostly affected. Every one in nine people on earth, does not have enough food
to lead a healthy active life and, hunger kills more people each year than AIDS,
malaria and tuberculosis combined. Amidst these facts, developing nations rank at
the top position, while being accountable for 98 percent of the world hunger
population (FAO, 2015).
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According to the causes of this alarming problem, some proclaim that rapid
population growth is the major root, while some argue that it is due to the poverty,
instability and poor infrastructure. Despite the causes, world hunger and food security
share a strong relationship, in a way which a failure of meeting the pillars of food
security (availability, access, stability and utilization) opens the path to the problem
of world hunger.
It is projected that, the global population will be 9.1 billion by 2050, and the food
production will have to be increased by 70 percent in order to feed everyone.
Moreover, nations should launch measures to combat poverty and hunger, while
adapting to climate changes, and using scarce natural resources more efficiently
(FAO, 2009). However, another global challenge lies with the reduction of arable
lands accompanied by the population growth and technological advancements
through creating a vague situation for the means of feeding the growing population.
In light of this, home gardening will have a greater impact as it is one of the most
convenient ways of ensuring household food security. A well-developed home garden
has the capability of fulfilling the daily dietary requirements of a family by supplying
most of the non-staple foods such as roots and tubers, vegetables and fruits, legumes,
spices and livestock products. Therefore, home gardening is increasingly becoming
popular among households as it provides direct access to nutritionally rich foods,
secures food provision during shortages, generates additional sources of income, and
increases purchasing power (FAO, 2010). As a result of this, it will weaken the
adverse impacts which will be arisen from reduction of arable lands and instabilities
of economic aspects.
However, Sri Lanka is also now experiencing a nutritional transition due to
urbanization, economic growth and changes in life style patterns. According to
Jayawardena et al. (2014), Non-Communicable Diseases (NCDs) have turned out to
be a severe burden during last two decades, while recording significant proportions
for hypertension, obesity, dyslipidaemia, metabolic syndrome, diabetes and pre-
diabetes. Furthermore, diet-related chronic diseases had been responsible for 18.3
percent of total mortality and 16.7 percent of hospital expenditure in Sri Lanka, while
lack of dietary diversity is becoming the major cause. Nutritionists have identified
dietary diversity as a key component of high quality diets (Ruel, 2006), where home
gardening plays a crucial role in generating dietary diversity.
With reference to the Sri Lankan context, the area under home gardens has been
reported as 14.3 percent (FAO, 2009), and reflected an annual growth of 1.6 percent
from the total number (DCS, 2002). Together with this increasing trend, if all
inhabitants are encouraged to practise home gardening, everyone will have access to
a high quality diet regardless of financial and space constraints. In this context, this
study aims to investigate the nexus between plant diversity and dietary diversity,
while identifying the determinants affecting the diversity of a home garden.
Journal of Environmental Professionals Sri Lanka: 2015 – Vol. 4 – No. 2 – 47-57
49
Methodology
Study Area and Data Collection
Home gardens in mid country are said to be high in diversity (Jacob and Alles, 1987).
Therefore, the Kandy district, a major area in the mid country, was selected as our
study area.
During February, 2015 to May, 2015, data were collected from 113 households who
practise home gardening in 15 Grama Niladhari (GN) divisions under six Divisional
Secretariat (DS) divisions (Kandy Four Gravels and Gangawata Korale, Kundasale,
Udunuwara, Yatinuwara, Pathadumbara and Harispattuwa) in Kandy district.
Data on demography, food consumption, perceptions on home gardening and home
gardening practices were obtained through face to face interviews with the support of
a pre tested questionnaire. In addition, a plant count of useful crops in home garden
was separately taken to calculate the biodiversity of the home garden.
Conceptual Framework
By employing five point Likert scaled questions, three indices which lie between 0
and 1, were constructed using the Equation 1. Specific scores were given to each
question and total scores were calculated to each household as;
The three indices are namely ‘Health Perception Index (HPI)’, ‘Constraints on
Gardening Index (CGI)’, and ‘Income Expectation Index (IEI)’. HPI expresses the
attitude of the home garden owner on gardening, with respect to health (both physical
and mental), food and nutrition security and safety. CGI shows the problems that the
owner faced while maintaining the home garden. This index takes into account the
availability of resources (land, labour and capital: credit, insurance, planting
materials, fertilizer and pesticides), pest and disease problems, conceptual and
marketing problems. IEI gives the level that the respondent’s objective of earning
money from his or her home garden.
Dietary Diversity 20 Index (DD20) gives the dietary diversity of the household as a
ratio. Using the Equation 2, DD20 was calculated by getting data on 24 hours dietary
recall. Twenty food groups were developed according to the dietary diversity
measurements given by Kennedy et al. (2010). These groups are cereals, pulses, white
roots and tubers, vitamin A rich vegetables, dark green vegetables, other vegetables,
vitamin A rich fruits, other fruits, red meat, white meat, eggs, fish and sea food, nuts
and seed, milk products, tea and coffee, soft drinks, spices, oils and fats, sweets and
other foods.
(1)
50
Shannon Index (SI) stated in the Equation 3, represents the proportional abundance
or evenness, accounting for the land shares allocated to each crop, as well as the
number of crops. It gives higher values when the relative abundance of the different
species in the sample is even and low values when few species are more abundant
than the others (Korale-Gedara et al., 2012).
Where, Pi denotes the proportion of ith species, while n denotes the number of species.
Data Analysis
Both descriptive and inferential statistics were used to analyse data. Analysis was
carried out in Stata 13, and a Structural Equation Modelling (SEM) was utilized to
identify the nexus between plant diversity and dietary diversity and also, to determine
the drivers of plant diversity.
Structural Equation Modelling (SEM)
Structural Equation Modelling (SEM) is a series of statistical methods, which is
expanding rapidly with its estimation techniques, modelling capacities, and breadth
of applications (Lei and Wu, 2007). SEM allows researchers to test a conceptual or
theoretical model through a combination of factor analysis and regression or path
analysis (Hox and Bechger, 2000).
In this study, we incorporated SI and DD20 to the SEM as endogenous variables,
while taking following as exogenous variables: age of the garden owner, gender of
the household head, education level of the spouse, size and total income of the
household, size of the home garden, HPI, CGI and IPI. Consequently, the nexus
between Shannon diversity and dietary diversity of an xth household was examined
through multiple regressions using the Equation 4 and 5, where ɛ1 and ɛ2 serve as
latent variables, which make disturbances through set of unspecified causes of the SI
and DD20, respectively.
Where, s and s are the coefficients to be estimated.
(2)
(3)
(5)
(4)
Journal of Environmental Professionals Sri Lanka: 2015 – Vol. 4 – No. 2 – 47-57
51
Results and Discussion
Descriptive Statistics of the Sample
Our sample consists of 113 respondents with an average household size of 4, while
recording a wide diversity for the age of the garden owner, with a mean of 53 years.
With respect to the educational status, it seems that there is no significant gap between
the level of education of the household head and the spouse, where 89.4 percent of
the sample accounts for male household heads. Further, data highlight that, not all
households engage in home gardening, utilize it as an income source. While reporting
an average of Rs. 55,500/= for the total income, only 64 percent of the sample makes
a contribution from home gardening for the total income. However, out of this 64
percent, export agricultural crops and fruit crops appear as most prominent crops
which are popular among majority of households in generating income (Figure 1).
Besides, it is interesting to note that, size of the home garden, number of plant species
and number of plants are reflecting a wide array, implying a growing trend of home
gardening regardless of the space limitations (Table 1).
Table 1. Descriptive statistics of the sample
Attribute
Mean
Standard
Deviation
Min.
value
Max.
value
Age of the owner
52.5
11.1
22
83
Household size
4.0
1.3
1
8
Education level of the household head
12.1
2.2
0
19
Education level of the spouse
12.3
2.4
0
19
Total income (Rs.)
55505.6
31010.0
8750
180000
Size of the home garden (perches)
44.8
54.9
8
480
Number of plant species
36.0
16.3
6
85
Number of plants
270.7
390.7
12
3669
Figure 1: Different varieties employed in home gardens in Kandy district
0
10
20
30
40
50
60
70
Vegetables Fruits Export
Agricultural
Crops
Livestock Other
52
SI and DD20 Indices
As SI shows both richness and abundance of species in a particular community, it is
a better indicator to express the plant diversity. The left-skewed distribution of the SI
infers that, a greater proportion of our sample is rich in plant diversity (Figure 2).
Conversely, the DD20 seems to be more or less like a symmetric distribution,
highlighting that dietary diversity of the households in the sample is almost fairly laid
between low and high indicators (Figure 3). This may be due to the diversity which
exhibits in the household income because, purchasing power creates a strong link
with the dietary diversity. Literature too suggests that there is a positive relationship
between the dietary diversity and income (Theil and Finke, 1983; Pollack, 2001;
Regmi, 2001; Ruel, 2003; Rashid et al., 2006) and thus, household income might play
a vital role in this regard.
Figure 2: Distribution of the SI
Figure 3: Distribution of the DD20
3.63.22.82.42.01.6
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Shannon Index
Density
0.720.660.600. 540.480.42
14
12
10
8
6
4
2
0
Dietary Diversity 20 Index
Density
Journal of Environmental Professionals Sri Lanka: 2015 – Vol. 4 – No. 2 – 47-57
53
SEM
Conforming to the key assumption of having uncorrelated disturbances of effect
variables with their specified causal variables, Chi-square test for the model was not
significant denoting the fact that the model we employed for the analysis is adequate.
Therefore, rest of the study is based on the interpretations which produced through
the path diagram and the corresponding output of the SEM (Figure 4, Table 2).
Amidst the significant variables, age, education level of the spouse and HPI show a
positive relationship with the SI, while with the CGI and IEI, a negative relationship
is observed.
People gather knowledge through experience. They realize the usefulness of high
biodiversity with the time. Therefore, they tend to grow a greater number of crop
species. This may be the reason to have a positive and significant coefficient for age
of the owner.
Figure 4: Path diagram of the SEM
1
1
In SEM, the path diagram consists of boxes and circles, which are connected by arrows.
Observed variables are represented by rectangles (or square boxes), and latent indicators by
circles (or ellipses). The causal relationship in the model illustrates by single headed arrows
or paths, while the variable at the tail causes the variable at the head of the arrow. Statistically,
the single headed arrows or paths represent regression coefficients (Wright, 1921).
HPI
CGI
IEI
Age of the garden owner
Gender of the head
Spouse’s education level
Size of the home garden
Total income
Household size
Shannon Index
Dietary Diversity 20
54
Table 2: Outcome of the SEM
Variables
Coefficient
Structural Shannon Index
Age of the garden owner
0.009**
Gender of household head
-0.015
Education level of the spouse
0.056***
Household size
0.056
Total income
0.000
Size of the home garden
0.001
HPI
0.885**
CGI
-1.161***
IEI
-0.460*
Constant
1.488***
Dietary Diversity 20 Index
Shannon Index
0.032**
Constant
0.488***
Note: *** Significant at 1%, ** Significant at 5%, * Significant at 10%
Further, it is not surprising to see a significant positive relationship between the plant
diversity and the education level of the spouse as well. Education increases the
knowledge of people and their comprehension. On the other hand, in Sri Lanka, the
role played by the house wife gives a substantial contribution to facilitate better food,
and secure good nutritional status of her family, and hence, she always guides the
family members in every household chores. From a sample which 89.4 percent
accounts for male headed household heads, the education level of the house wife
plays a critical role in making her home garden a highly diversified one, as her
ultimate objective lies within maximizing dietary diversity of her household members
through a home garden which is rich in plant diversity.
People who are concerned with their health and food, try to have a balanced diet.
They prefer to consume fresh and chemical free food. Gardening may lead to realizing
those aspects, while improving the conditions of the living environment. Not only the
physical fitness, but also the mental fitness can be achieved when engaging in home
gardening. According to The Wellness Beat (2013), a Netherlands study has
proclaimed that gardening can fight stress even better than other relaxing leisure
activities. Moreover, another study in Norway has suggested that paying fullest
efforts in gardening may deliver better mental health. Further, FAO (2010) declared
that home gardens through an established tradition, are greatly capable of improving
household food security and alleviating micronutrient deficiencies. In light of this, it
is obvious to gain a positive significant coefficient to the HPI, because, as long as the
owner of the home garden being aware of these benefits, it may drive towards positive
attitudes and ultimately, a better plant diversity.
Journal of Environmental Professionals Sri Lanka: 2015 – Vol. 4 – No. 2 – 47-57
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However, enthusiasm on any activity is definitely reduced if someone has to meet
with constraints, and same applies to the gardening as well. As the problems of
gardening increases, people may get fed-up with it. Even though the household
income is not significant with the plant diversity in this study, its role in generating a
higher capital is enormous. Mmom (2009) stated that the relationship between
biodiversity and household income should be positive, while a similar association has
been revealed in the Kandy district by Korale-Gedara et al. (2012). So that, in a nature
where the capital and income share quite a strong link with each other, the limitations
of these influences will surely demotivate the owner, and as a result, plant diversity
of the home garden will be adversely affected. This may be the reason for the
significance of CGI with a negative coefficient.
Being complying with the findings of Abdoellah et al. (2006), Bernholt et al. (2009)
and Major et al. (2005), this study too implies a negative relationship between the
degree of commercialization and plant diversity, by reporting a negative coefficient
for the IEI. When the objective becomes the commercialization, people tend to grow
more plants in the same species as it facilitates more convenient management, than
that of managing multiple plants in different species. Thus, a reduction of plant
diversity can be expected, when people take home gardening as an income source.
In addition to the above consequences, it is noteworthy to consider the significant
positive nexus between the SI (plant diversity) and DD20 (dietary diversity) reflected
by the outcome of the SEM. Being simultaneously significant with the determinants
of the plant diversity, it implies that age of the owner, education level of the spouse,
HPI, CGI and IEI will have a significant impact on the dietary diversity in the same
manner as they influence the plant diversity. Hence, increasing plant diversity in
home gardens may lead to a more dietary diversity in household consumption, which
drives towards the achievement of food and nutritional security of households.
Conclusions and Recommendations
By employing SEM, this study reveals a positive nexus between the plant diversity
and dietary diversity in home gardens in Kandy district, highlighting age of the garden
owner, education level of the spouse, HPI, CGI and IEI as significant drivers. As a
result of these consequences, home gardening can play a major role in delivering a
healthy diet to the community. Therefore, sound management of the significant
determinants is essential in order to ensure the household food and nutrition security.
As lack of bio diversity is visible in the home gardens which are managed by young
members, they should be encouraged and, knowledge should be properly
disseminated through universities, research and other agricultural institutions. In
addition, by introducing incentives and subsidy schemes, government should lend a
hand to the people who show reluctance to engage in home gardening due to the
financial constraints.
56
Furthermore, when people shift towards commercial cultivation, it may have a
negative impact on the diversity and structure of the home garden. In this context, if
people come up with the purpose of achieving economic advantages, it may drive
households away from the concerns on yielding sustainable benefits of home
gardening. Hence, such groups should be motivated not only to maintain high relative
abundance, but also to conserve high species richness, and so that, all relevant parties
that are responsible for bio diversity, agriculture and health should have a greater
responsibility in this regard.
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