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The Western Ghats refers to the unbroken chain of hills (of which Palakkad gap is an exception) running in the North-South direction for about 1600 km parallel to the Arabian Sea from river Tapti (22˚26‟N) to Kanyakumari (about 8˚0‟ N) and extends zonally from 72˚55‟E to 78˚11‟ E covering an area of about 1, 64,280 km2. It is one of the 35 global biodiversity hotspots and the habitat to a large number of endemic plant and animal species. These species face threat of vulnerability and extinction due to habitat loss with changes in weather and climate. Climate in the Western Ghats varies with altitudinal gradation and distance from the equator. Annual rainfall in the region with proximity to the sea averages to 3000-4000 mm.
The tropical rain forests and other humid forests are known for their exceptional richness for various species of giant climbers, the lianas, than the temperate or drier tropical forests. Liana are conspicuous structural component of tropical forests and make about one fourth of the woody plant diversity of peninsular Malaysia, rated as high as South American forests in liana richness (Appanah et al., 1993; Bhat, 2014). The dark canopies in such forests permit only scanty light into the forest interior, as diffused light and sun-flecks. In the competition for light the trees grow taller until they reach the canopy or sub-canopy levels and many those requiring full exposure to sunlight emerge above the general canopy as towering giants. The plants that keep away from this race for light are adapted to the dimness of the forest floor, which is not as rich in herbs, but may be covered with seedlings and saplings of the trees as well as of the lianas. Evolution has its own ways in such situation, as one has to look up towards the crowns of trees to see bulk of the rain forest herbs clinging on to branches and trunks as epiphytes, along with wreath of mosses and ferns. It is no exaggeration to say that in the rain forest one has to look up than on to the floor for the herb layer diversity. Although woody and having own well developed root systems the lianas need physical support to hold on and climb up to reach heights to expose their foliage to the sunlight. In the younger stages lianas are more shade tolerant, have more tender stems which coil over support, which may be the trunks and branches of trees. With the passage of time their main stems and branches turn stronger and woodier, yet the lianas cannot stand on their own. Growth is slow for these ‘climbing trees’ while in the deep shade. The growth happens prolifically in tree fall gaps. Coiling on any support nearby, from tree saplings to larger trees, the lianas in gaps grow in tangles, their long slender shoots linking trees like cables, turning thicker and woody and assuming diverse forms like ropes and cables, or suspended in the air in huge loops or in serpentine coils. Many trees are affected in the stranglehold of lianas, their trunks misshapen, growth stunted, the weaker collapsing in a mass unable to bear the weight of these climbing trees. The liana cutting became an established silvicultural practice especially to free the trees in forest plantations.
Lianas have certain crucial ecological role in forest ecosystems. Tree fall in the tropical forest, forming a canopy gap, allowing sunlight onto the floor, is an occasion of immense activity on the exposed ground, where the falling light stimulates a flush of fresh growth in the vegetation. Tree saplings that have been almost dormant for years get activated, gaining height rapidly. The juvenile lianas with greater vigour, overtop these saplings creating virtually a sub-canopy in the tree fall gap. This canopy rises in the air pushed up collectively by the force of numerous juvenile trees, especially short duration pioneers, activated by sunlight. Once again a damp and dark interior is created underneath the canopy of lianas and pioneer trees (light-loving, fast growing, short lived trees like Macaranga, Trema, Ervatamia etc.). As the ‘canopy lifting’ happens, the characteristic species of the rain forest or evergreen forest find suitable microclimatic conditions driving the succession process towards the climax vegetation. The lianas help to stabilise the microclimate of the forest floor by forming a mass of leafy vegetation to close canopy gaps (Schnitzer and Bongers, 2002; Parthasarthy et al., 2004). Heavy load of lianas on trees, however, can cause mechanical damage of the hosts and also reduce their growth rates (Pérez-Salicrup, 2001). Addo-Fordjour et al., (2013) found liana species richness and abundance were significantly lower in the high disturbance forest, whereas the liana biomass was higher in low disturbance forests.
Lianas are woody stem rooted in the ground and need physical support for their growth due to weak stem. Liana competes with tree for resources such as soil nutrients, sunlight and water. Liana are prominent component of tropical forest which plays a vital role in ecosystem processes (foliage, fruit production and carbon sequestration) and species diversity. Species diversity of lianas encompasses of 25% and woody stem density accounts 10-45% mainly in tropical forests around the world. Western Ghats has higher species richness compared to Eastern Ghats and Coromandel Coast in Indian Peninsular. (Schnitzer et al., 2015, 2002, Parthasarathy et al., 2004, Muthumperumal and Parathasarathy 2010). Liana plays vital role in forest by maintaining diversity, regeneration, forest functioning includes nutrient cycling, forest transpiration, water use and carbon sequestration. Some of the liana species constitute group of non-timber forest product. Some species of Liana species has medicinal value. For instance, E. rheedii bark is used to cure scabies in Tanzania (Brink and Achigan-Dako, 2012). Liana also has wide range of benefits to arthropods, birds, arboreal mammals, primates by providing food resource (leaves, fruit, flowers, nectar, sap), exposure to a reduced suite of predators and also serve as fallback food i.e., abundant foods of relatively low quality that are used during periods of low overall food availability (Schnitzer et al., 2015). Seeds of Entada rheedei are cooked and eaten by especially forest dwelling communities. Entada is a promising candidate herb for the development of a phytomedicine against liver ailments (Gupta et al., 2011).
Liana grown successfully in a premier research campus is a breakthrough as opportunities have been opened up for various types of research – such as biomechanical characteristics of its specific parts, tropic responses, host preference, climbing mechanism, nitrogen fixation, type of photosynthesis (C3 or C4), root pressure, reproductive biology, mechanism in invasive growth and morphological response upon contact with support trees.
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