Landscape metrics to analyze the forest fragmentation of Chitteri Hills in Eastern Ghats, Tamil Nadu

Chitteri Hills of Eastern Ghats is primarily covered by evergreen forests and deciduous forests. Forest Management, change in landuse and rapid economic development has caused a minor change in the landscape of Chitteri. In the current study the forest fragmentation was assessed using the Fragstat 4.0 software for different classes using specifi c metrics. Fragstats 4.0 spatial pattern analysis was applied for different landuse classes that was derived from landuse and landcover maps prepared using the Landsat 8 digital data. The results from the above analysis have shown that there was more fragmentation in the Chitteri Hills. Class Area (CA), Percentage of Landscape (PLAND), Largest Patch Index (LPI), Number of Patches (NP), Patch Density (PD), Area Weighted Mean Shape Index (AWMSI) at the class level was quantifi ed in the present study. These spatial metrics were found to be very simple and helpful in quantifi cation of the complex spatial processes and can be used as an effective means for monitoring the Chitteri Landscape. Research Article Landscape metrics to analyze the forest fragmentation of Chitteri Hills in Eastern Ghats, Tamil Nadu Narmada K1*, Dipjyoti Gogoi2, Dhanusree2 and Bhaskaran G3 1Post-Doctoral Fellow (ICSSR), Resource Management (CWRM), University of Madras, Guindy, 600025, Chennai, India 2Research Scholars, Resource Management (CWRM), University of Madras, Guindy, 600025, Chennai, India 3Professor and Head i/c Centre for Water, Resource Management (CWRM), University of Madras, Guindy, 600025, Chennai, Indi Received: 23 February, 2021 Accepted: 19 March, 2021 Published: 22 March, 2021 *Corresponding author: Narmada K, Post-Doctoral Fellow (ICSSR), Resource Management (CWRM), University of Madras, Guindy, 600025, Chennai, India, E-mail: https://www.peertechzpublications.com


Introduction
Loss of biodiversity has resulted in habitat loss and fragmentation. Human interference on the environment have altered natural ecosystem due to increase in human settlements and fragmented agricultural land [1,2]. Many natural reserves are enclosed by altered environment and later get functional as a separate natural ecosystem. Fragmentation is a changing phenomenon which leads to change in the habitat in the landscape over a period of time. The term "Fragmentation" has been defi ned as simultaneous reduction of forest area, increase in forest edge and subdivision of large forest areas into smaller non-contagious fragments [3]. The consequences of fragmentation include habitat loss for some plant and animal species, habitat creation for others, decreased connectivity of the remaining vegetation, decreased patch size, increased distance between patches, and an increase in edge at the expense of interior habitat [4]. The degree of fragmentation has been described as a function of the varying size, shape, spatial distribution, and density of patches [5]. Scientists have been using metrics for assessing fragmentation and its impact [4,6]. The ecological consequences of forest fragmentation may depend on the spatial confi guration of the fragments within the landscape and how the confi guration changes both temporally and spatially. Three spatial attributes of fragmentation may be particularly important: core area, shape, and isolation of forest fragments [7]. While fi eld ecologists routinely measure the abundance of species or the structure of biological communities at point locations within fragmented landscapes and then relate these measures to metrics of habitat fragmentation, such studies typically focus on biological responses to one or a few attributes of the fragments Citation: Narmada  or landscape such as area, edge-effect, shape, isolation, landscape forest cover, or matrix quality [7]. The term "spatial metrics" can be defi ned as measurements derived from the digital analysis of thematic-categorical maps exhibiting spatial heterogeneity at a specifi c scale and resolution [8]. Fragstat landscape metrics are algorithmic program that quantify specifi c spatial characteristics of patches, classes of patches, or entire landscape mosaics. Fragstat metrics has been developed to quantify landscape structure and spatial heterogeneity based on landscape composition and confi guration. As the present study is specifi cally aimed to understand and compare the magnitude of forest fragmentation in Chitteri landscape due to the infl uence of forest management and changes in land use, Fragstat has been used in this Figure 1.

Study area
Chitteri Hills in Eastern Ghats is located in Pappireddipatti taluk, Dharmapuri District, Tamil Nadu. It is situated towards North East of Salem district within the geographical limit of 78°51'10" -78°32'40" E, longitude and 11°55'14" -12 °4'48" N latitude and covers an area of about 654 km 2 . The hills form a compact block consisting of several hill ranges and contain tangled ridges and ravines running in the North East and South West directions, enclosing many narrow valleys, rivers viz., Kallar, Varattar, Kambalai and Anaimaduvu (Harur Forest offi ce Report, 2007). In the western region, Thottilmadu rivulet join with Varattar rivulet and reach Varattar dam or Vallimadurai dam located in the foot hills of Chitteri near Vallimadurai village. Kalmaduvu rivulet fl ows towards southern region and reach Puluthikuttai dam of Salem district. The Kottar rivulet fl ows towards Eastern region and joins with Kottapatti rivulet and reach Sattanur dam of Tiruvannamalai district.

Data acquisition
Satellite images are used as a source for the study. Images of three different years were acquired for the study from USGS Earth Explorer. The study has been carried for a period of 20 years. Hence the images were acquired for 2000, 2008 and 2019. The images downloaded were as follows Table 1.

Image pre-processing
The satellite data from the sensors will have geometric errors and radiometric errors. The primary importance in image enhancement is Histogram. It refl ects the characteristic of image which can then be studied and modifi ed by changing the histogram. Histogram Equalisation is a non-linear stretch that redistributes the pixel values so that there is approximately the same number of pixels with each value within a range. The results approximate a fl at histogram. Hence Histogram Equalisation is done in order to modify the intensity distribution of the histogram [9].

Image classifi cation
Image Classifi cation is the process of labelling a pixel or a group of pixels based on its grey value. The images acquired are classifi ed into various classes depending on their spectral signatures. The study area that was delineated from the 3-satellite image for 3 different years was classifi ed using unsupervised classifi cation method using ERDAS Imagine Ver. 2014. A modifi ed version of Anderson scheme of land use [10], was utilized in this study. Unsupervised classifi cation was carried to classify the image. In this classifi cation method the spectral classes are defi ned according to some statistically determined data. The image was classifi ed into four major categories in the current study. 1. Evergreen forests 2. Deciduous Forests 3. Degraded forests 4. Scrub land and 5. Others (settlements, water body, barren land and Agriculture). As the focus was mainly on the forest fragmentation, effort was taken more to classify the forest region and not in classifying the other categories. Image classifi cation was done for 3 different years. The classifi cation was done to understand the change of the different land use pattern over the years.

Accuracy assessment
The accuracy assessment of spatial data has been defi ned by the United States Geological Survey USGS, 1990 as: "Accuracy assessment or validation is an important step in the processing of remote sensing data. It determines the information value of the resulting data to a user." The accuracy of any map may be tested by comparing the positions of points whose locations or with corresponding positions ground data that was captured at 100 ground points. The result of the assessment is derived as follows. The classifi cation accuracy was found to be satisfactory. The Kappa statistics of around 0.9 was derived from all the classifi ed images as shown in the Table 2.

Temporal change detection of Chitteri Hills
Change detection is the method or way to analyse the differences in the condition of a feature in different time periods [10]. The change detection analysis comprises of a

Selection and calculation of spatial metrics
The landscape metrics is often called as spatial metrics is used for other environments like urban areas. The term "spatial metrics" can be defi ned as measurements derived from the digital analysis of thematic-categorical maps exhibiting spatial heterogeneity at a specifi c scale and resolution [11]. Landscape

Class Area (CA)
CA is a simple metrics used to describe the pattern of urban growth in spatial metrics computation which also known as total area implying the total area covered by a land cover class in hectares [12]. This indicates how much of the landscape is comprised of a particular patch type. In addition to its direct It indicates the sum of the areas (m 2 ) of all the patches of the corresponding patch type, divided by 10000(to convert to hectares), i.e., total class area

Percentage of Landscape (PLAND)
PLAND quantifi es the proportional ratio of each patch type in the landscape. It equals the sum of the area (m 2 ) of all patches of the corresponding patch type, divided by the total landscape area (m 2 ), and multiplied by 100 (to convert to percentage) [8].

The Number of Patches (NP)
It is the measure of discontinuous urban areas or individual units in the landscape (Gezahegn Awake Abebe, 2013). Due to the rapid core development, the number of patches is expected to increase due to the emergence of new fragmented patches around the cores. Number of patches indicates the diversity or richness of the landscape. In other word it gives a simple measure of the extent of subdivision or fragmentation of the patch type [8].

= (3)
Where = number of patches in the landscape of patch type NP≥, without limit NP=1 when the landscape contains only one patch of the corresponding patch type;

Patch Density (PD)
It is one more measure of landscape fragmentation of the patches of a land cover class which specifi es the density of the fragmented urban units within a quantifi ed area. Values of this indicator are affected by the size of the pixel and also the

AWMSI (Area -Weighted Mean Shape Index (AWMSI)
The The AWMSI, in other words, is the average shape index of the corresponding patch type, weighted by size so that larger patches weigh more than smaller ones [8].

Results and discussion
The images were classifi ed and the area occupied by each       (Table 6). From the analysis it was found out that 2696.35

Analysis of habitat fragmentation of Chitteri Hills using Fragstat spatial metrics
The below table was  As an overall change, there was a net increase of 1675.38 hectares of non-forested areas in the last 20 years. The observed trends of decreasing forest and increasing non forest areas in the Hills could be explained by the following four reasons. First, among the general and main causes of deforestation are human population pressure and an increasing demand of land for living and agriculture and timber products from forests [13,14]. In Chitteri Hills, human population increased to nearly 5.6% in the period of 2001 to 2011. However, there is no important change in population in the last 11 years. It is important to note that there is a gradual decrease in the rural population which can be explained by the fact that demographic movement of rural areas which concentrated in the neighbouring towns of Dharmapuri and Salem. Many villages were abandoned and more people left the rural areas to become resident in the urban centres for their livelihood. Abandoned areas were covered with young plants and trees. These areas are categorised as degraded forests as these don't have any crown culture. This is the reason of increasing degraded forest area. This situation is the reason of increasing degraded forest area. In Chitteri, besides inequity in land ownership, low productivity in agriculture and the domestic net income per person was far below the threshold to keep the rural communities in their homeland, allowing the urban population to increase. The quantitative evidences of forest cover patterns showed that human activities have affected the forest cover type changes. Second, plantation by the forest department has contributed to the increase in plantation area. Third, Insects that primarily attack individual species have an effect similar to selective cutting on a multi-species stand within a forest. Insect infestation may or may not cause signifi cant change in species composition (i.e., associated plant and animal species) and forest-stand structure. A lot depends on the diversity, site conditions and overall health of the original stand [15]. The major reason for the loss of biodiversity is the change in forest cover [16,17] which in turn is due to forest fragmentation, habitat loss and urbanisation. The fragmentation of the forest is shown by the increase in the number of patches and increase in the number of smaller patches [15]. This in turn affects the species richness, habitat isolation and many more. There is decrease in the evergreen cover and deciduous forest in the last 20 years and from the result it shows there is increase in the number of smaller patches. Patchiness is an important indicator of natural habitat fragmentation [3]. The evergreen forest in the study area has fragmented and is indicated by the Citation: Narmada

Conclusion
From the analysis it is found that there is increase in number of fragments, leading to isolation of patches and there was further decrease in mean patch size. The increase in the number of patches could be attributed to conversion of the forest to other categories, road construction. Urban population has also increased in the last 20 years. The forest landscape was found to be altered due to this increasing fragmentation. The overall change in the structure of the natural habitat has led to the degradation of the forest. The forest landscape has deteriorated or fragmented due to increase in the number of patches, mean patch size and patch density. Forest degradation in this area is mainly due to mismanagement, heavy grazing of pasture land adjacent to forest areas. People using the forest resources illegally for their livelihood is also one of the reasons. The major impact of this change is that the people concentrating more on the improvement of the products that are useful for them, thereby disturbing the natural habitats and further leading to soil erosion and carbon emission into the atmosphere. To conclude, monitoring the spatial metrics for these forest ecosystems help us to analyse the change in composition and confi guration of the ecosystem. This can be used as a major tool in forest management for biodiversity conservation and sustainable forest management.