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most popular working definitions of ecosystem health (Costanza et al. 1992) is “An
ecological system is healthy and free from distress syndrome if it is stable and sustainable – that is, if it is active and able to maintain its autonomy and organization
over time and is resilient to any kind of stress”. Ecosystem health is linked to the
concept of sustainability, which is seen to be a comprehensive, multi-scale, dynamic
measure of system resilience, organization and vigour. According to this definition,
an unhealthy system is one that is not sustainable and will eventually cease to exist
with time, unless appropriate corrective measures are taken well in time.
Health is a measure of overall performance of a complex ecosystem that is built
up from the behaviour of its various components. Such measures of system health
imply a weighted summation or a more complex operation over the component
parts, where the weighting factors incorporate an assessment of the relative importance of each component to the functioning of the whole system. This assessment of
relative importance incorporates “values”, which can range from subjective and
qualitative to objectives and quantitative as we gain more knowledge about the system under study.
This diversity of definitions arises from the fact that different workers have given
importance to different factors that impact an ecosystem health. These definitions
can be grouped into the following major categories:
Health as homeostasis
Health as the absence of disease
Health as diversity or complexity
Health as stability or resilience
Health as vigour or scope of growth
Health as balance between system components
Same issues arise when we try to arrive at a comprehensive definition of “mangrove health”. Each of the aspects has to be considered to arrive at a definition that
meets the end user’s requirement. To develop a “mangrove health assessment
model”, the first step is to identify environmental indicators of the mangrove ecosystem health that need to be included in the multi-parametric health model. The
choice of these indicators and the weighting factors to be assigned to each of them,
may differ from one mangrove zone to the other depending on the biological, ecological, environmental and geomorphic setup. As mentioned earlier, the choices of
indicators and their weighting factors could be subjective as it may depend on the
researcher’s perceptions, understanding and knowledge about the particular mangrove forests, including its biological, ecological, environmental and geomorphic
settings.
Monitoring the health of mangrove ecosystem has also been attempted using
satellite derived vegetation indices. One of the most popular and widely used vegetation indices is NDVI (Normalized Difference Vegetation Index). It is defined as
the normalized ratio of the spectral reflectance measured in red and near infra-red
(NIR) wavelength regions {NDVI = (NIR-RED)/(NIR + RED)}.NDVI is, basically,
determined by the degree of absorption by leaf chlorophyll in the red wavelength,
which is proportional to leaf chlorophyll density, and by the reflectance in NIR
wavelength region, which is proportional to green leaf density. NDVI has been
Ajai and H.B. Chauhan
most popular working definitions of ecosystem health (Costanza et al. 1992) is “An
ecological system is healthy and free from distress syndrome if it is stable and sustainable – that is, if it is active and able to maintain its autonomy and organization
over time and is resilient to any kind of stress”. Ecosystem health is linked to the
concept of sustainability, which is seen to be a comprehensive, multi-scale, dynamic
measure of system resilience, organization and vigour. According to this definition,
an unhealthy system is one that is not sustainable and will eventually cease to exist
with time, unless appropriate corrective measures are taken well in time.
Health is a measure of overall performance of a complex ecosystem that is built
up from the behaviour of its various components. Such measures of system health
imply a weighted summation or a more complex operation over the component
parts, where the weighting factors incorporate an assessment of the relative importance of each component to the functioning of the whole system. This assessment of
relative importance incorporates “values”, which can range from subjective and
qualitative to objectives and quantitative as we gain more knowledge about the system under study.
This diversity of definitions arises from the fact that different workers have given
importance to different factors that impact an ecosystem health. These definitions
can be grouped into the following major categories:
Health as homeostasis
Health as the absence of disease
Health as diversity or complexity
Health as stability or resilience
Health as vigour or scope of growth
Health as balance between system components
Same issues arise when we try to arrive at a comprehensive definition of “mangrove health”. Each of the aspects has to be considered to arrive at a definition that
meets the end user’s requirement. To develop a “mangrove health assessment
model”, the first step is to identify environmental indicators of the mangrove ecosystem health that need to be included in the multi-parametric health model. The
choice of these indicators and the weighting factors to be assigned to each of them,
may differ from one mangrove zone to the other depending on the biological, ecological, environmental and geomorphic setup. As mentioned earlier, the choices of
indicators and their weighting factors could be subjective as it may depend on the
researcher’s perceptions, understanding and knowledge about the particular mangrove forests, including its biological, ecological, environmental and geomorphic
settings.
Monitoring the health of mangrove ecosystem has also been attempted using
satellite derived vegetation indices. One of the most popular and widely used vegetation indices is NDVI (Normalized Difference Vegetation Index). It is defined as
the normalized ratio of the spectral reflectance measured in red and near infra-red
(NIR) wavelength regions {NDVI = (NIR-RED)/(NIR + RED)}.NDVI is, basically,
determined by the degree of absorption by leaf chlorophyll in the red wavelength,
which is proportional to leaf chlorophyll density, and by the reflectance in NIR
wavelength region, which is proportional to green leaf density. NDVI has been
Ajai and H.B. Chauhan