Niche modeling to predict suitable habitat for threatened and endangered potential ornamentals of lateritic hillocks of Kerala

Abstract

Hillocks of Kerala are rich abodes of wide variety of flowering plants including grasses, herbaceous perennials, shrubs and trees. Many of these plants which were utilized in traditional medicine are either endangered or critically vulnerable due to human interventions. The habitat destruction is extremely fast and the loss of nearly 50% area has been observed during last decade. So, protection of this ecosystem and identifying suitable habitats where it could be introduced are very important. Mapping the geographical locations and predicting the potential distribution of a species is useful in identifying critical regions that may need conservation action. The study titled “Niche modeling to predict suitable habitat for threatened and endangered potential ornamentals of lateritic hillocks of Kerala” was conducted at the Department of Floriculture and Landscaping, College of Agriculture, Vellanikkara, Thrissur and at the Marine Biodiversity and Fishery Environment Management Division, Central Marine Fisheries Research Institute, Kochi, Kerala during the period from 2023-24, with an objective to identify the influencing bio-climatic variables and to predict the habitat distribution of threatened and endangered potential ornamentals of lateritic hillocks of Kerala using MaxEnt model. Frequency, Density, Importance Value Index (IVI), Shannon Diversity Index, Simpson Diversity Index and Pielous Evenness Index have been estimated for phytosociological assessment. The species which showed highest frequency were Spermacoce alata (Kumbla, Puranttukara and Puthige), Pogostemon quadrifolius (Pazhayangadi), Exacum bicolor (Periyaram, Vazhayur and Kannamvettikavu), Naregamia alata (Kudalmarkala, Neerchal, Dharmatadaka and Vazhayur), Eriocaulon sexangulare (Seethangoli), Curculigo orchiodes (Cheemeni and Kudalmarkala), Habenaria marginata (Thalakottukara and Chowwannur), Lepidogathes keralensis (Kumbla) and Habenaria diphylla (Thalakottukara, Puthige, Cheemeni). Frequency of species differed in different locations, which could be due to the high degree of dispersion of species, habitat preference for growth and evolutionary processes occurring naturally in these plants. Locations such as Thalakottukara (Thrissur), Seethangoli (Kasargod), Neerchal (Kasargod), Kannamvettikavu (Malappuram) had maximum density of herbaceous species of ornamentals because these locations had undistributed hillocks with minimum human activity and did not have forest cover. Importance value index (IVI) is used to determine the overall importance of each species in the community structure. Naregamia alata and Pogostemon quadrifolius had maximum IVI in majority of rocky hard lateritic hillocks in Malappuram and Kannur districts of Kerala. This could be due to their ability to withstand drought and extreme conditions. The highest Shannon Diversity Index and Simpson Diversity Index recorded for the location Kumbla (Kasargod) indicated that high species richness could be found in this region and the highest Pielous Evenness Index was recorded for Thalakottukara (Thrissur), indicating that all the species present in that habitat were more even. An attempt was made to study the current and future distribution of E. bicolor, H. diphylla, N. alata, P. quadrifolius, J. malabaricum and S. caryophyllatum using MaxEnt modeling. The extent of highly suitable habitat predicted by MaxEnt model for these mentioned species under current scenario was 1302 km2, 1525 km2, 1344 km2, 1738 km2, 3632 km2 and 835 km2 respectively. These species were primarily found in Thrissur, Kasargod, Kannur, Malappuram, Kozhikode and Palakkad districts of Kerala. The bioclimatic variables that contributed to the habitat modeling of different species were annual precipitation (Bio12), precipitation of the driest quarter (Bio17), mean diurnal range (Bio2), precipitation seasonality (Bio15), solar radiation (January, March, July and September) and water vapour pressure (January). Topographic variables that contributed to the model were elevation (Digital Elevation Model), Topographic Position Index (TPI), Terrain Ruggedness Index (TRI), slope and aspect. Along with bioclimatic and topographic variables, agroecological zones, soil types and Normalized Difference Vegetation Index (NDVI) had also contributed to the habitat model. Future predictions showed that under SSP370 and SSP585, the extent of high habitat suitability decreased by the period 2080-2100, and the districts such as Kannur, Malappuram, Thrissur and Kozhikode will become less suitable for the growth of E. bicolor, N. alata, H. diphylla, P. quadrifolius, J. malabaricum and S. caryophyllatum. The findings suggest that if climate continues to warm, species potential distribution areas could shrink by 2080-2100. This highlights the need for effective conservation strategies to protect plants with valuable medicinal and aesthetic properties from overexploitation and the impacts of climate change.