Biodiversity: Remote Sensing and GIS

1. INTRODUCTION

The great variety of life on earth has provided for man’s needs over thousands of years. This diversity of living creatures forms a support system which has been used by each civilization for its growth and development. Science has attempted to classify and categorize the variability in nature for over a century. This has led to an understanding of its organization into communities of plants and animals. This information has helped in utilizing the earth’s biological wealth for the benefit of humanity and has been integral to the process of ‘development’. This includes better health care, better crops and the use of these life forms as raw material for industrial growth which has led to a higher standard of living for the developed world. The diversity of life on earth is so great that if we use it sustainably we can go on developing new products from biodiversity for many generations. This can only happen if we manage biodiversity as a precious resource and prevent the extinction of species. 

Definition:

‘Biological diversity’ or biodiversity is that part of nature which includes the differences in genes among the individuals of a species, the variety and richness of all the plant and animal species at different scales in space, locally, in a region, in the country and the world, and various types of ecosystems, both terrestrial and aquatic, within a defined area.

What is biodiversity?

Biological diversity deals with the degree of nature’s variety in the biosphere. This variety can be observed at three levels; the genetic variability within a species, the variety of species within a community, and the organisation of species in an area into distinctive plant and animal communities constitutes ecosystem diversity.

Genetic diversity: Each member of any animal or plant species differs widely from other individuals in its genetic makeup because of the large number of combinations possible in the genes that give every individual specific characteristic.

Species diversity: The number of species of plants and animals that are present in a region constitutes its species diversity. This diversity is seen both in natural ecosystems and in agricultural ecosystems. Some areas are richer in species than others. Natural undisturbed tropical forests have much greater species richness than plantations. Areas that are rich in species diversity are called ‘hotspots’ of diversity. India is among the world’s 15 nations that are exceptionally rich in species diversity.

Ecosystem diversity: There are a large variety of different ecosystems on earth, which have their own complement of distinctive inter linked species based on the differences in the habitat. Ecosystem diversity can be described for a specific geographical region, or a administrative entity such as a country, a state or a taluka. Distinctive ecosystems include landscapes such as forests, grasslands, deserts, mountains, etc., as well as aquatic ecosystems such as rivers, lakes, and the sea. Each region also has man-modified areas such as farmland or grazing pastures. Ecosystems are most natural in wilderness areas.

Evolution and the Genesis of Biodiversity:

The origins of life on earth some three and a half billion years ago are obscure. Life was probably initiated as a product of organic reactions in the Earth’s primordial seas. Most species appear to have a life span extending over several million years. Their adaptability to gradual changes in their habitat, and interactions with newly formed species produce groups of inter linked organisms that continue to evolve together. Food chains, prey-predator relationships, parasitism (complete dependence on another species), commensalism (a partnership beneficial to both species), etc. are important examples. A behavioural pattern of the different species comprising a community of species links them to each other through their breeding biology, feeding patterns, migrations. As ancient species became extinct due to geological upheavals, they left behind empty ‘niches’ in the habitat that stimulated existing species to fill them through the formation of new species. The Earth’s ancient history has seen periods of mega extinctions, which have been followed by periods of formation of new species. Though these repeatedly led to a drastic reduction in the number of species, the diversity of life recuperated each time by gradually increasing the number of species existing on earth. This however took millions of years, as evolution is a very slow process. Thus when man came on the scene some 2 million years ago, the earth was richer in species than ever before. During the recent past however, extinctions due to the activities of modern man have begun to take place so rapidly that nature has had no time to evolve new species. The earth is losing species more rapidly than ever before. The diversity of life at all three organisational levels, genetic, species and ecosystem, is thus being rapidly modified by modern man. This is a great loss to future generations who will follow us.

2. BIOGEOGRAPHIC CLASSIFICATION OF INDIA

Our country can be conveniently divided into ten major regions, based on the geography, climate and pattern of vegetation seen and the communities of mammals, birds, reptiles, amphibian, insects and other invertebrates that live in them. Each of these regions contains a variety of ecosystems such as forests, grasslands, lakes, rivers, wetlands, mountains and hills, which have specific plant and animal species. India’s biogeographic Zones are: the cold mountainous snow covered Trans Himalayan region of Ladakh; the Himalayan ranges and valleys of Kashmir, Himachal Pradesh, Uttarakhand, Assam and other North Eastern States; the Terai, the lowland where the Himalayan rivers flow into the plains; the Gangetic and Brahmaputra plains; the Thar Desert of Rajasthan; the semi-arid grassland region of the Deccan plateau Gujarat, Maharashtra, Andhra Pradesh, Karnataka and Tamil Nadu; the Northeast States of India; the Western Ghats in Maharashtra, Karnataka and Kerala; the Andaman and Nicobar Islands and the long western and eastern coastal belt with sandy beaches, forests and mangroves.

3. VALUE OF BIODIVERSITY

Environmental services from species and ecosystems are essential at global, regional and local levels. Production of oxygen, reducing carbon dioxide, maintaining the water cycle, protecting soil is important services. The world now acknowledges that the loss of biodiversity contributes to global climatic changes. Forests are the main mechanism for the conversion of carbon dioxide into carbon and oxygen. The loss of forest cover, coupled with the increasing release of carbon dioxide and other gases through industrialization contributes to the ‘greenhouse effect’. Global warming is melting ice caps, resulting in a rise in the sea level which will submerge the low lying areas in the world. It is causing major atmospheric changes, leading to increased temperatures, serious droughts in some areas and unexpected floods in other areas.

Biological diversity is also essential for preserving ecological processes, such as fixing and recycling of nutrients, soil formation, circulation and cleansing of air and water, global life support (plants absorb CO2, give out O2), maintaining the water balance within ecosystems, watershed protection, maintaining stream and river flows throughout the year, erosion control and local flood reduction. Food, clothing, housing, energy, medicines, are all resources that are directly or indirectly linked to the biological variety present in the biosphere. This is most obvious in the tribal communities who gather resources from the forest or fisher folk who catch fish in marine or freshwater ecosystems. For others, such as agricultural communities, biodiversity is used to grow their crops to suit the environment. Urban communities generally use the greatest amount of goods and services, which are all indirectly drawn from natural ecosystems. It has become obvious that the preservation of biological resources is essential for the well-being and the long-term survival of mankind. This diversity of living organisms which is present in the wilderness, as well as in our crops and livestock, plays a major role in human ‘development’. The preservation of ‘biodiversity’ is therefore integral to any strategy that aims at improving the quality of human life.

Sustainable management of natural resources has become a key issue for survival of life on planet Earth. In this effort, conservation of biodiversity has been put to the highest priority through Convention on Biodiversity (CBD). It is realized that the threats to the species/ ecosystems are the greatest in recent times, mainly due to human exploitation of biological resources. However, natural hazards and their adverse impacts also contribute to the loss of biodiversity. Thus, there is an urgent need to conserve gene pool in situ before it is lost forever. For this, the most appropriate method would be to assess the ecological sustainability by understanding the ecosystem/landscape complexities and their uniqueness. Landscape elements have been found to be very useful to generate scientific basis for further decision making in conservation.

Landscape

Commonly refers to the landforms of a region in aggregate or to the land surface and its habitats at scales of hectares to many square kilometres or it can be defined as ‘the mosaic of different land uses, land cover or landforms in a particular area’. Remote Sensing (RS) and Geographic Information System (GIS) are very effective tools to analyse these at various levels viz., macro-level, meso-level and micro-level. RS provides spatial data whereas GIS has made planners and managers job a lot easier and have provided very useful insights to characterize landscape at meso-level or macro-level studies. Vegetation is a dominant expression of natural assemblage of various coexisting plant communities in a landscape (including herbs, shrubs and trees). In nature, these communities form a mosaic of patches of various sizes and shapes, which is an indicator of the past activities. Thus by analysing the patches, commonly known as patch characterization, the very nature of the landscape can be defined. Patch characterisation is based on the analysis of various parameters like fragmentation, porosity, patchiness, interspersion, juxtaposition etc. Since the much mosaicked nature of communities is directly influenced by parent material, soil, climate and human activities, hence patch characterisation can reveal the hidden relationships. Even though succession is an ever-going process in nature, the pace of such change has been altered by human activities in the last 70 years or so. The trend is still continuing and posing a serious threat to biodiversity. This has led to the loss of forested areas/habitats and thus depletion in floral and faunal diversity. Diversity in Indian ecosystems is an amalgamation of natural ‘virgin’ as well as disturbed and human modified systems. Thus, understanding of ecosystem needs to be done at landscape level Major threats to biodiversity include habitat alteration, over-harvesting, pollution, climatic change, exotic species, and increase in human and cattle population.

Remote sensing technology

Remote sensing refers to the activities of recording/observing/perceiving (sensing) objects or events at far away (remote) places. In remote sensing, the sensors are not in direct contact with the objects or events being observed. The information needs a physical carrier to travel from the objects/events to the sensors through an intervening medium. The electromagnetic radiation is normally used as an information carrier in remote sensing. The output of a remote sensing system is usually an image representing the scene being observed. A further step of image analysis and interpretation is required in order to extract useful information from the image. The human visual system is an example of a remote sensing system in this general sense. In a more restricted sense, remote sensing usually refers to the technology of acquiring information about the earth's surface (land and ocean) and atmosphere using sensors on-board airborne (aircraft, balloons) or space borne (satellites, space shuttles) platforms.

Remote sensing for biodiversity conservation

Remote sensing technology provides synoptic coverage of the Earth’s surface and hence is an ideal tool for biodiversity characterization at various levels. Geographic Information System has come as a handy tool to carry out criteria-based spatial modelling. Various parameters can be considered for multi-criteria analysis. In landscape ecology, biodiversity is considered as an integral part of the broader concept of landscape heterogeneity for management and conservation. Therefore to characterize a landscape, diversity plays an important role. The spatial data on forest/vegetation and land use are generated using satellite remote sensing data through digital classification. Database can create in GIS domain for further analysis. The spatial, non-spatial data and other ancillary data sources are combined to generate habitat maps. Landscape analysis for determining the parameters like fragmentation, porosity, proximity and other patch characteristics have been used to derive Disturbance Index using proximity from settlements and roads. Cover map to spatially present the disturbance regimes. A spatial model incorporating ground based biodiversity attributes of the landscape elements, land use change patterns, disturbance regimes of the landscape and terrain complexity have been used to delineate the spatial pattern of biological richness. Disturbance is widely believed to be one of the main factors influencing variations in species diversity. In this context satellite remote sensing plays a vital role in delineation of different species assemblages. However the delineation depends on spatial, spectral and temporal resolution of the satellite sensor on one hand and the spatial extent and degree of homogeneity of the species assemblages on the other hand. The satellite remote sensing data in conjunction with spatial information on topography, soils, climate and ground floristic data are also used to delineate detailed vegetation formations.

The satellite remote sensing, over the last few decades, has advanced in providing coarse to very high resolutions. This is helpful in generating products depicting coarser to very high information on distribution of species at different levels of ecological hierarchy. The products include global vegetation type maps providing information on predominant climatic and physiognomic vegetation types, region specific vegetation type maps depicting local gregarious formations and unique habitats, communities, disturbance types and land use. On the other hand, very high resolution data have facilitated in developing species level distribution maps along with structural information on dominance, canopy diameters and age class distribution. These data products have effectively facilitated in implementation of several global and country level biodiversity programs. Global and regional level vegetation and land cover maps were prepared taking advantage of the rapid revisit time and large swath width capabilities of NOAA - AVHRR satellite sensor. Under Global Land Cover (GLC, 2000), global land cover maps were developed using multitemporal SPOT 4 vegetation data and other ancillary resolution as a collaborative effort of 30 research teams around the world. Another recent attempt on global LULC vegetation is use of MODIS data as one of the critical global datasets. The global vegetation type maps, analyses of land-cover changes and burnt areas in conjunction with trends in human disturbance, are effectively used to generate coarse-scale biodiversity maps and identification of biodiversity hotspots. High-resolution data of IRS, Landsat or SPOT satellites has been extensively used to generate information on forest type distribution, critical habitats and rapid change in land-use and land cover especially in tropics. Tropical evergreen forest along with other phenological types and local habitats (grassland, orchards, mangroves, Myristica swamps and Ochlandra) were mapped for North-East India, Western Himalayas and Western Ghats of India, on 1:250,000 scale by using IRS LISS data.

Forest type maps were analysed in conjunction with climate and topography in Geographic Information System to categorize habitats a priori and then determined the relationship between remotely sensed habitat categories and species distribution patterns. The degree of correspondence between habitat and species distributions depends on the degree of habitat map generalization, and this should also be optimized to get maximum information on species diversity. Habitats appear capable of providing information on the distribution of large numbers of species in a wide variety of areas. However, this is restricted to the spatial scale of tens of square kilometres. In smaller, local areas with limited species diversity, direct mapping can provide detailed information on the distribution of certain high canopy tree species or associations. Very-high-resolution satellite images of IKONOS, QUICKBIRD, CARTOSAT-1,Terra Aster or aerial multispectral scanner and laser scanner data can be applied to the assessment of heights of single trees, tree-wise timber volume calculations, and the detection of even single trees dominant species The synergy of these different data sources can guarantee foresters a high level of information extraction for these applications.

Light detection and ranging (LiDAR) accurately measure topography, vegetation height, and cover, as well as more complex attributes of canopy structure and function. LIDAR have the capability to provide data on three dimensional space. This will help for characterising forest structures through vegetation heights, vertical distribution of canopy materials, crown volume, sub canopy topography, biomass, vertical foliage diversity & multiple layers, height to live crown, large tree density, leaf area index, physiographic or life form diversity etc., through direct and indirect retrievals. Hyperspectral Remote Sensing has the capacity to monitor biodiversity in species level. These systems with more than 60+ spectral bands in the range 0.3-1 μm range can best used for vegetation assessment. This can effectively use for the mapping of endemic, economically important and invasive species.

Figure 1: The electromagnetic spectrum: ‘optical’ and ‘microwave’ wavelength regions

Figure 2: Remote sensing for biodiversity characterization at landscape level

Figure 3: Potential roles of remote sensing in mapping, modelling and monitoring of biodiversity

Figure 4: Geospatial model for biodiversity characterisation using Spatial Landscape Model (SPLAM) (Roy et al.2005)

Table 1: Major Indian Sensors and its platforms for studying biodiversity

Table 2: Various data sets/techniques used for the mapping of biodiversity

References:

Roy P S, Kushwaha S P S, Murthy M S R, Roy A, Kushwaha D, Reddy C S, Behera M D, Mathur V B, Padalia H, Saran S, Singh S, Jha C S and Porwal M C (2012)Biodiversity Characterisation at landscape level: National Assessment Indian Institute of remote Sensing, Dehradun, India pp.140, ISBN 81-901418-8-0

Roy P S, Padalia H, Chauhan N, Porwal M C, Gupta S, Biswas S and Jagdale R (2005) Validation of Geospatial model for Biodiversity Characterisation at Landscape level - a study in Andaman and Nicobar Islands, India. Ecological Modeling 185 (2-4) 349-369.