Phytosociological and edaphic attributes of forest ecosystems of Shendurney wildlife sanctuary, Kollam, Kerala

Abstract

The present study was carried out with the primary objective of studying the tree species diversity, structure, and composition, physicochemical attributes and land use and land cover change of forest ecosystems of Shendurney Wildlife Sanctuary, Kollam, Kerala viz., west coast tropical evergreen, west coast tropical semi-evergreen, southern secondary moist deciduous, myristica swamp, and tropical hilltop forest. The stratified random sampling approach was adopted for vegetation assessment with a sampling plot of 20 m × 20 m. The regeneration pattern of the tree species was studied from the plots of 5 m × 5 m for the tree saplings and 1 m × 1 m for the tree seedlings from each of the 20 m × 20m plots. The soil sample was collected horizon-wise up to 1 m from each of the forest ecosystems. The land use and land cover was studied using the supervised classification with Maximum Likelihood Algorithm and change detection comparison approach using the Landsat Enhanced Thematic Mapper (ETM±) and Landsat 8 OLITIRS using the data capture on July 01, 2001, and January 14, 2018. A total of 119 species with a density of 1053.50 ha-1 and 50.04 m2 ha-1 basal area were recorded from the west coast tropical evergreen, 101 species with the density of 914.55 ha-1 with the basal area of 41.64 m2 ha-1 basal area from west coast semievergreen, 58 species with a density of 876.97 ha-1 with the basal area of 26.88 m2 ha-1 from the moist deciduous, 33 species with a density of 1144.44 ha-1 and the basal area of 33.93 m2 ha-1 from the myristica swamp, and 44 species with a density of 619 ha-1 and basal area of 16.93 m2 ha-1 from the tropical hilltop forest, respectively. The girth class distribution of the forest ecosystems varies significantly, with the west coast tropical evergreen forest showed the reversed J-shaped distribution. And a completely L-shaped pattern for the west coast semi-evergreen and southern secondary moist deciduous forest, whereas inverted iJ-shape in the tropical hilltop forest. The percent species endemism of 85.44% was recorded in the myristica swamp forest, 79.15% for the tropical hilltop forest, 55.58% for the west coast tropical evergreen forest, 40.71% for west coast tropical semi-evergreen forest, and the lowest (29.26%) for the moist deciduous forest. The dominant families in the west coast tropical evergreen forest are Dipterocarpaceae (FIV=24.92), Clusiaceae (FIV=21.40), and Myrtaceae (FIV=20.78). The families Euphorbiaceae (FIV=31.68), Dipterocarpaceae (FIV=24.18), and Rubiaceae (FIV=18.99) were dominant for the west coast semi-evergreen forest. In the Moist deciduous forest, the dominant families are Euphorbiaceae (FIV=52.99), Combretaceae (FIV=41.23), and Malvaceae (31.73). For the myristica swamp forest, the families Myristicaceae (FIV=149.01), Dipterocarpaceae (FIV=41.08), and Anacardiaceae (FIV=25.86) are dominant. The families Lauraceae (FIV=69.92) and Clusiaceae (FIV=35.71) are dominant in the tropical hilltop forest. The Shannon-Weiner and Simpson indices were found at 4.10 and 0.97 for west coast tropical evergreen, 4.09 and 0.97 for west coast semi-evergreen, 3.22 and 0.92 for the Southern secondary moist deciduous, 3.88 and 0.95. The lowest value (2.70 and 088) was reported for the myristica swamp forest. The diversity indices of west coast evergreen and west coast semi-evergreen showed no significant variation. The Margalef value was reported higher for the evergreen forest. Moreover, this study found that most tree species showed a contagious distribution pattern for a tree, saplings, and seedling levels, with very few showing the uniform distribution pattern of distribution. The tree species regeneration was adequate for most forest ecosystems, with the highest density (3,582 ha-1 saplings and 27,777 ha-1 seedlings) recorded in the west coast tropical evergreen forest. However, most dominant species showed relatively good regeneration, especially in the west coast tropical evergreen and west coast tropical semi-evergreen forests. The diversity indices of the regenerating seedlings and saplings do not vary significantly across all the forest ecosystems. Across the forest ecosystems, the soil is slightly acidic with a moderate amount of soil organic carbon. The soil percent organic carbon, Cation Exchange Capacity, and electrical conductivity are relatively higher in the first horizon and showed decreasing trend across all the forest ecosystems. The bulk density showed low in the first horizon and increased with depth ecosystems. The higher bulk density was recorded for the Myristica swamp forest. The land use and land cover analysis indicated a rigorous land cover change in the forest ecosystems. It showed a significant increase in the proportion of degraded forest from 21.31% in 2001 to 22.97% in 2018. Substantial loss in the moist deciduous forest from 27.11 % in 2001 to 17.23 % in 2018 and semi-evergreen forest from 26.91 % in 2001 to 18.98 % in 2018 was reported. Anthropogenic activities such as pressure on land for agriculture, expansion of human settlements, forest fire, and plantation establishment were found to be the major factors that led to the drastic changes in the land cover of forest ecosystems of Shendurney Wildlife sanctuary.