Studies on angiosperm flora and bio – monitoring of walayar hill ranges of southern western ghats, Kerala, India

Abstract

The present investigation focuses on the angiosperm diversity and bio-monitoring of Walayar Forest range which lies on the north-western side of the Palghat Gap. The hill tracts flanks an area of 125.65 sq.km. As the forest range is having human - animal conflicts, the floristic explorations were meager and a comprehensive study of angiosperm diversity in this range is lacking. In this context, an attempt was hereby made to account the diversity of angiosperms, their habitat diversity, biomonitoring and resource mapping in Walayar hill ranges including the discrete hillocks scattered in the range.The extensive exploration resulted in the documentation of 1077 taxa which includes 1056 species, 11 subspecies and 10 varieties under 610 genera in 133 families. Fabaceae is the largest family followed by Poaceae and Cyperaceae. Cyperus is the most speciose genus followed by Ipomoea and Ficus. Herbaceous taxa predominates the vegetation followed by tree members. Among the forest types, deciduous forests form the prominent vegetation, with characteristic drier elements specific to this range in the district, followed by semi - evergreen forests and Grasslands.The vegetation profile under this range showed reserve forests, vested forests, EFL sites and discrete low altitude hillocks. The range has two reservoirs and two major rivers along with small rivulets. The study area shows a range of altitudinal gradients from below 60m asl to 1700m asl and maximum species diversity was observed in medium altitudes. Raunkiaer lifeform spectrum analysis revealed 39.36% of the taxa as therophytes followed by Phanerophytes (30.45%) and lianas (13.74%).The floristic diversity of hillocks documented 411 taxa belonging to 296 genera among 86 families. Nine different microhabitats were found to occur with special plant associations and a shift in vegetation with gradual disappearance of microhabitats with increasing temperature regimes during post monsoon period could be observed in the range. Adaptive traits like pubescence, succulence, semi - parasitism, carnivory, subterranean organs etc. were found among the plants in Walayar hills to thrive harsh edaphic and climatic conditions operating in the Palghat Gap zone. About 14% of the collected taxa were found to be endemic to various geographical regions of the country and could document 27 threatened taxa under various IUCN categories. Phenological studies revealed peak flowering between the months of September to December and from January to March. About 46.70% of the vegetation is confined to Indo - Pacific zone. Apart from the Indo - Pacific zone, the taxa showed more affinity to South American, African and Holarctic zones and least affinity towards Australian zone.Three new plant novelties Amorphophallus sp. nov., Ouret sp. nov. and Impatiens sp. nov. along with recollection of Oldenlandia hygrophila Bremek. from its type location could be documented from Walayar hills. In addition to this, several taxa showed morphological variations in tune with the adverse environmental stresses of extremities in temperature, acute water shortage, higher wind velocity through the Gap etc. Further, taxonomic notes on the status of new taxa described viz., Polycarpaea palakkadensis V. S. A. Kumar, Sindhu Arya & V. Suresh and Allmania multiflora V. S. A. Kumar, V. Suresh, Sindhu Arya & Iamonico from Palghat Gap is also included. Out of the taxa collected, 87 were found to be an addition to Flora of Palghat (Vajravelu, 1990) and 98 taxa were found to have extended distribution to Palakkad district. Analysis of vegetation across Palghat Gap using PAST software revealed a demarcating difference in the vegetation on the northern and southern sides of the Gap.Out of the 610 genera recorded, 401 were found to have single species and of the 133 families, 63 families contain a single genus. The taxonomic singularity of vegetation at Walayar hills at genus level is 0.83 and at family level is 0.61. In addition to this, a total of 33 monotypic genera could be recorded from Walayar hills. The ethnobotanical survey revealed that a total of 124 taxa were found to be collected and used by three tribal groups Irulars, Paniyars and Mudugars of the forest range.The geographical peculiarities of the study area revealed the incidence of more anemophilous and anemochorous taxa. A total of 389 medicinal plants, 139 wild edibles and 115 taxa as wild relatives of cultivated plants could also be documented. Since the study area is one of the most disturbed hill tracts in Palakkad district, about 93 alien invasive taxa along with 87 degraded forest elements were found to occur in the range.GIS mapping of Walayar hills for understanding the forest cover change over decades using Land Use Land Cover analysis could classify 11 land cover classes. Deciduous forests formed the major forest type followed by semi - evergreen and grasslands. There is a slight difference in the deciduous, semi - evergreen and grassland elements over decades. Analysis of vegetation in different altitudinal gradients revealed the occurrence of more deciduous elements below 1000m asl. The evergreen elements are found to be more above 400m asl and grassland elements in higher altitudes above 1300 m asl. Slope wise analysis revealed that the majority of the study area falls under gentle and medium slope areas. NDVI analysis of the health of vegetation over decades and mapping of landslide affected areas in the range could also be done.Several threat factors adversely affect the health of the vegetation in Walayar hills. These include natural causes such as landslides, flood, forest fire and alien invasive taxa, and anthropogenic factors like mines and quarries, construction of highways, tourism, unscientific agricultural practices, pollution, waste disposal, grazing, man - animal conflicts etc. As the range lies in the vicinity of Palghat Gap, which plays a major role in regulating climate of the state, the conservation of existing vegetation and protection initiatives along with greening the Gap is essential to sustain the life support systems in this hill range.