THE EFFECT OF FRAGMENTATION IN VEGETATIVE AND ECOLOGICAL DYNAMISM OF MYRISTICA SWAMP – A FRAGILE FRESHWATER ECOSYSTEM OF WESTERN GHATS

T.S. Vilas, C.S. Gokul and * M. Rajendraprasad. Plant Systematics and Evolutionary Science Division, Jawaharlal Nehru Tropical Botanic Garden and Research Institute, Karimancode P.O., Palode, Thiruvananthapuram695 562, Kerala, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

A vast area of Western Ghats, coming under different forest types, are degraded and are threatened with ecological deprivation and biodiversity loss. Deforestation for urbanization, fragmentation due to developmental activities, over exploitation to meet the increased demand are the main anthropogenic threats. The freshwater swamps of Western Ghats dominated by the Myristicaceae members too face this loss of character. These ecosystems have unique biodiversity, bio wealth ecological functioning and supporting edaphic factors. Historically the natural landscape of Kerala is well represented by freshwater swamps and marshy lands which create a positive water regime and provide protection for unique flora and fauna. The high population density and high demand on space and livelihood of the state lead to the depletion or alteration of this natural landscape. In advanced stages, this leads to the fragmentation and isolation of the unique ecosystem. These changes in the ecological and edaphological characteristics will deprive these unique flora and fauna of the marshy condition to which it is adapted. The existing fragments of the freshwater swamp create a series of remnant patches, relic vegetation, surrounded by a matrix of different vegetation and by altered land use. Since Myristica swamps have been edaphically created with free flowing water stream, fragmentation initially results in the modification of velocity of water flow and changes in the silting or free flow of running water. The present investigation discusses the current distribution of swamps and its conservation status, ecological function and vegetational succession, by highlighting the effects of fragmentation and isolation of vegetation.
559 is structurally and functionally dominant over other members, hence, the name Myristica swamps. This water logged edaphic environment and associated vegetations are distributed in the valleys or foot hills of Western Ghats and subjected to seasonal flooding and silting. The evergreen members are amphibian in nature specially adapted for surviving in marshy water logged condition as well as in terrestrial condition. These swamps were reported from different states along the Western Ghats (Saldanha, 1984;Gadgil&Chandran, 1989;Chandran&Gadgil 1989;Chandran&Mest, 2001;Vasudeva et al., 2001) Karnataka, Goa (Santhakumaran et al., 1995(Santhakumaran et al., , 1999 and Kerala (Krishnamoorthy, 1960;Pascal, 1984). The ever green vegetation of swamps includes many endemic tree species and are well documented (Bourdillion, 1908;Sasidharan&Sivarajan, 1996;Ramesh and Pascal, 1997;Chandran& Mesta, 2011). The swamps are also inhabited by some of the red listed plants included in red data book of Indian plant (Nayar&Sastry, 1987, 1990. Hence, the Myristica swamps, with pristine vegetation are virtually live museums of ancient life of great biological interest. During the historical events of development and urbanization, these forest lands have been exploited and obviously perished. Land use changes like conversion to paddy field or plantation of areca, coffee, rubber or submergence under irrigation projects or extermination due to fire, all have had adverse impacts on these swamps (Krishnamoorthy, 1960). The existing swamps are also heading towards extinction. An example of such anthropogenic activity is evident in the Sasthanada swamp, Sankili section, Kulathupuzha Forest Range, Trivandrum Forest Division having 12 patches, extending to an area of 0.223 sq km (22.29 Ha). The fragmentation involves dividing up of continuous ecosystem into smaller areas called patches, and each patch has a relatively homogenous floristic, ecologic, and edaphic conditions. When fragments are created, plant dynamics is modified owing to changes in the forest spatial organization, such as the size, shape, and type of isolation barrier of forest patches. The functional dynamism of patches are affected with edge effects, migration and establishment of new species, decrese in the recruitment rate of specific species and increased recruitment rate of flexible species and disturbances in faunal interactions and disproportionally favoured and hence dominating species like Lagerstromeaspeciosa and while others like Myristica fatua var. magnifica are facing local extinction. This vegetational, structural and functional changes are generating changes in the availability of water, nutrients, light, wind and other basic environmental factors by creating different degrees of ecological succession in the same area viz. Core vegetation, the unchanged original vegetation; Edge vegetation, representing transformed one. In between the core and the edge there is transitional vegetation, which are in different stage of succession. In short, the fragmentation due to this change in land use causes, the vegetation which once was supported by wetland (core vegetation) changing to the terrestrial area vegetation (edge vegetation). Thus the isolation and fragmentation of Myristica swamps lead to the breakup of these natural ecosystems into smaller patches of vegetation posing threat to their conservation status. Changes in the physical edaphology and micro climate will alter the reproductive phenology of the members of the original vegetation, especially biota like Myristica fatua var. magnifica. It is also noticed that this unique ecosystems are also seen as Sacred Grove, the patches of vegetation protected in the religious ground to avoid the perceived wrath of its resident God. The community status of flagship species viz. Myristica fatua var. magnifica fluctuates in advance with vegetational succession indicating past massive fragmentation of swamp during the urbanization of the state and thus these habitats can be described as "swampy relics" especially due to fragmentation and isolation followed by the vegetational succession, ecological and edaphological changes. The present study puts emphasis on the trends of vegetational succession due to fragmentation and effect of invasion of other species in the swamp.

2.1.Study area:-
Kerala, the most south-westerly state of India, is located between latitudes 8° 17' 30" N. and 12° 47' 40" N. and longitudes 74° 27' 47" E. and 77° 37' 12" E. The state is isolated from the Deccan Plateau by the Western-Ghats, one of the biodiversity hotspots of India. The Myristica swamp of Sasthanada region, Sankili section of Kulathupuzha Forest Range (8 0 45"82"N.and 77 0 10"55"E.) is situated at an elevation of 155 MSL. The vegetation of this Myristica swamps is in the three stages of succession such as core (Figure legend

Vegetation sampling:-
A detailed exploration was made in entire study area. The vegetational type, floristic composition and anthropogenic pressure were identified. The whole area is divided into three regions the core, transition and edge area. The line transects were laid across all types. The phytosociological features and floristic status were assessed by laying quadrate of size 15 x 10 in random. All the members were identified and enumerated. Height and girth at breast height (GBH) of all trees and shrubs (≥ 10 cm GBH) were measured using clinometer and metallic measuring tape respectively. Vegetation with less than 10 cm GBH were counted and enumerated as seedlings or herb species. The identification of the species was done by referring authentic books. The following parameters were calculated using this vegetation data.

Phytosociological analysis:-
Relative frequency (rF), Relative density (rd), Relative dominance (rD) were calculated and summed up to get the Important Value Index (Barbour et al., 1947), the calculation is done by using the following formulae.

Density:-
The density of trees were found out by using point centred quadrate method (Barbour et al., 1971) Random points were located, the area around each point was divided into four 90 0 quadrates and the nearest of each quadrate was marked. Average distance for all the trees were taken together and computed for density as per the formula given, Density (Trees/ hectare) = 10000 2(Average distance in meter) 2

Whiteford index:-
It is the ratio of abundance and frequency. In general, an index value of 0.025 to 0.05 indicates that the species is random, while the value higher than 0.05 indicates increase in aggregation and value lower than 0.025 indicates a tendency towards regularity (Whiteford, 1948). It was calculated using the formula. Whiteford index = Abundance Frequency Frequency = Total no. of quadrates in which species occurred x Total no. of quadrates studie Abundance = Total no. individuals of species Total no. of quadrates occurrence 2.6. Similarity index:-The value of similarity index indicates the affinity between each community. It is derived by the formula of Sorenson (1948).

Similarity index = 2 x No. of common species
Total no. species

Floristic diversity indices:-
The species diversity within a species, community or within a habitat is calculated to assess the biodiversity. The diversity comprises of two components via, species richness and evenness or equitability. A number of indices have been reported which measure both components of species diversity, i.e. Species richness and evenness into a single index. They are discussed below.

Simpson's index (D):-
The index measures the probability that two individuals selected at random from a sample will belong to the same species and range from 0-1 (Simpson, 1949).

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This index of diversity is based on information theory. The information content is measure of the amount of uncertainty. The index is zero and maximum when all the species are represented by the same number of individuals. It generally falls between 1.5 to 3.5 and rarely exceeds 4.5 (Shannon-Wiener, 1963).
ni = Number of individuals N = total number of species

Species richness:-
The index of species richness (R) was calculated using the formula given by Menhinick (1964). = / R= Richness index S= total number of species in the community N= total number of individuals summed over all species.

Regenerative status:-
The natural germination percentage, seedling establishment and casualty rate were calculated by counting methods. Randomly selected 10x10 meter quadrates were placed, and number converted into percentage.

Results:-
The  (Table 1). As we look into the similarity of these three zones closely using the similarity index, the vegetative structure clearly represents an inverse relation. The core and the edge show very less similarity (29.5%) compared to the core and transition zone (45.9%). whereas the transition zone shows more affinity towards edge vegetation (72%).This represents the invasion of other species from edge to the transition and this trend will later result in the extinction of the swamp and the replacement of the terrestrial forest vegetation. The floristic composition and diversity of Myristica swamps also vary with vegetational succession, due to the isolation and fragmentation. The floristic composition of swamp includes 82 species belonging to 72 genera of 44 families. The distribution pattern of swampy vegetation shows, 32% of species random in occurrence, 65% in aggregate distribution and the remaining 03% with regular distribution pattern. This indicates the conservation value of the system; hence any alteration in ecosystem will lead to the massive extinction of species (Fig.1).
In The density of tree species also shows changes with advancement of the ecosystem. In the core area of the swamp the tree density is 642 individuals per hectare, it decreases to 421(68.5% of core area) in transition zone and further to 314 (48.9% of core area) in edge zone. The fragmentation and isolation of the specific ecological niche of the unique species of swamp ecosystems are declining or eroding gradually and lead to evolution and development of new vegetation and forest types (Fig.2).
The study about the reproductive capacity and aggressive capacity of Myristica fatua shows that the species has high degree of reproductive capacity with gregarious flowering and good fruit setting. The average seeding is 56 seeds in one sq. meter area and 92% of these seeds are viable. The primary dispersal rate is 58-66 %, mainly by Ocecerosgriseus (Hornbill), Phaethontidaepsittaciformes (Parrot) and Ratafaindica (Malabar Squirrel). The premature shedding due to the feeding of avian fauna like Phaethontidaepsittaciformes (Parrot),Ocecerosgriseus (Hornbill) and mammalian fauna like Ratafaindica (Malabar Squirrel), Rhesus macaqus(common Monkey) were 565 also noticed. 48% of secondary dispersal was also noticed. The main dispersing agents are the common crustacean Barytelphusaguerini(tropical freshwater Crabs) and Rattusrattus(Rat). The germination percentage in natural condition is varies from 76.10 % to 23.37 % (core to edge) with an average value of 57.00 % (Fig.3). The subsequent growth and establishment of seedlings up to two years were analysed and the same trend was observed as for Myristica fatua and it also varies in accordance with different degree of succession and fluctuation. In the core area, the casualty rate is 91.70 %, in the transition zone, 92.90 % and 97.05 % in edge area. (Fig.4) The Myristica swamps are the edaphic variant of tropical freshwater swamps and are evergreen in nature. These succumb to many threats due to the destructive and interactive face created by the natural and artificial factors. In turn it formulates various ecological and edaphological units. The population of unique species Myristica fatua var. magnifica in its different age class shows aggressive trends of declining population size through the advancement of transition of vegetation. In core area, the rate of population of Myristica fatua is 57%. While in transition vegetation the rate of population of Myristica fatua is 41%, in edge vegetation, surviving with other forest intruders, the Myristica fatuapopulation is drastically declines to 18% of the total population. The analysis shows that invading of other evergreen species to the swampy area will cause the switch over of the swampy vegetation to evergreen vegetation (Fig. 5&6). The core area shows high degree of germination percentage and initial survival rate. The

Conclusion:-
Myristica Swamps are unique fresh water phyto-geographic ecosystems of Western Ghats, once distributed in low laying areas of Kerala State in a continuous manner. The floristic composition, ecology and edaphology are specific with high occurrence and distribution of Myristicaceae members, especially of flag ship species, Myristica fatua var. magnifica. The members are structurally modified due to inundated during greater part of the year. Presently, due to natural and manmade changes these are under threat and in path of extinction. The existing treasure home of biowealh, fresh water swamps, requires more attention to conserve, especially to check the local extinction of a few vital species and its associate. The typical swamps are characterised by low floristic diversity and high stem density. The vegetation is amphibian features, adapted to survive in marshy conditions. The germination and recruitment of new members of the important species are related to general ecology and physical edaphology including some faunal associations. These forest relics are facing various levels of disturbance, among which fragmentation is in prime position, which would be causative factor regarding the loss of swamp ecosystems. The fragmentation and isolation alter floristic structure, composition, micro climate, and water regime. These initial floristic, ecological and edaphological changes ends with formation of new ecosystem with common floristic composition, terrestrial ever green forest.