Eco-physiological studies in a tropical evergreen forest ecosystem (of Nelliampathy area, in Kerala)
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Date
1991
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Department of Forestry, College of Forestry, Vellanikkara
Abstract
Eco – physiological studies in a tropical evergreen forest ecosystem of Nelliampathy area in Kerala
The physiological ecology of tropical vegetation in general and that of evergreen forest in particular is poorly understood. As regards to South indian forest ecosystems studies on these lines are virtually absent. The present investigation attempts to generate some basic information on ecological aspects of evergreen forests and also to identify the changes caused by human interference. The study was carried out in three locations adjacent to the Nelliampathy tract representing undisturbed and selection felled evergreen forests and cardamom plantation.
In each of these three ecosystems, 50 x 50m plots were established in most typical sites of one hectare and the vegetation, structure, phytosociology and floristics were analysed. Estimation of leaf area index, leaf litter and nutrient input through litter, soil nutrients and natural regeneration was carried out. Monthly measurements of micrometeorological parameters namely, air temperature, relative humidity, rainfall soil temperature and soil moisture were taken. Light environment was studied both in vertical and horizontal profiles.
The evergreen forest ecosystem presented diverse physiognomic features exemplified by size of trunks, crown, branching pattern, coppicing power, buttressine, colour and blaze of bark, cauliflory and ramiflory. The disturbance to the ecosystem by way of selection felling and /or raising of cardamom in the understory has caused drastic changes in the structure. There is marked difference in the distribution of trees among the three storeys and also in various girth classes.
The dominant species association, as indicated by the Importance Value Index is Palaquium ellipticum – Cullenia exarillata in the undisturbed and cardamom plots, while it is Mesua ferrea – Palaguium ellipticum in the selection felled plot. Of the 20 species of trees (> 30 cm girth at breast height), 17 were present in the undisturbed, 15 in the selection felled and 11 in the cardamom plot. The index of species diversity was 0.85 and 0.86 for undisturbed and selection felled areas respectively, with the cardamom plot possessing an index of 0.76. The most important plant families occurring in the area are Sapotaceae, Bombacaceae, Clusiaceae and Euphorbiaceae.
The undisturbed evergreen plot has the maximum leaf area index and the cardamom plot the minimum, while the selection felled area occupies the median position as a result of the varying degrees of canopy removal. The vertical distribution of light reveals that while 60 percent radiant energy is received at 30 m height, 30 percent at 20 m and 15 percent at 10 m, only 10 percent is available at the ground level. There is a striking difference in the horizontal distribution of light categorised into varying intensities among the three plots which is affected by the disturbances in the canopy.
The monthly soil temperature did not vary between the undisturbed and selection felled plots, while it was higher in the cardamom plot. A reverse trend was observed in the case of soil moisture with the undisturbed plot having maximum soil moisture. The ecosystems under consideration are phenologically active due to the dry spell and flowering of most species occurs in January – March. While fruiting is towards the monsoon period, maximum leaf fall takes place during the summer. There is significant variation in the total annual litterfall among the three ecosystems with the undisturbed plot occupying the top position and the cardamom plot the bottom. The same trend is followed with regards to the input of N,P,K Ca and Mg though leaflitter into the ecosystem. The highest value for soil nutrients (0-20 cm) was estimated in the undisturbed plot and least in the cardamom plot.
Natural regeneration was normal in the undisturbed evergreen forest, almost absent in the selection felled plot due to the invasion of Strobilanthes sps., while only unestablished seedlings were available in the cardamom plot due to successive weeding operations.
The study reveals that slight and heavy modifications in the evergreen forest ecosystem brings about significant changes in structure, floristics, microclimatic environment and features relating to the functioning of the system, namely, nutrient input and regeneration.
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Citation
170258