Seed Production and Seedling Establishment of Parah Trees in Khao Nan National Park, Thailand

Abstract

Parah (Elateriospermum tapos Blume) is a native species of southern Thailand, and is a dominant tree in Khao Nan National Park. There have been few studies of Parah seeds or of seedling establishment. Biotic and abiotic environmental factors interact with seeds and may affect the future of tree populations. This is the first study to determine the factors affecting seeds and seedlings of Parah trees in Khao Nan National Park, Thailand, during 2014 - 2016. We tested 3 factors: (1) parental tree diameter at breast height (DBH), (2) altitude, and (3) distance from the main road. We studied seeds collected from trees, seeds harvested by humans, seed predation, seeds left on the forest floor, and rotten seeds. We measured seed weight, seed size, seedling height, and seedling root collar diameter (RCD). Our results showed that the number of seeds and seedlings per tree, seed weight, seed size, seed harvesting, seed predation, seeds left on the forest floor, rotten seeds, and seedling height varied between the years of study. There was no difference in seeds harvested by humans from 2014 - 2016. The number of seeds per tree and seeds harvested by humans were positively associated with parental tree DBH in 2015 and 2016. The number of seeds left on the forest floor was positively associated with parental tree DBH, and distance from the main road, but was negatively associated with altitude, in 2015, and there was no association in 2016. The number of seeds predated by frugivores was positively associated with altitude in 2016. The number of seedlings per tree was positively associated with distance from the main road. Seedling height was positively associated with distance from the main road, and negatively associated with tree DBH in 2015 and altitude in both years. We found significant results which led to the conclusion that seed production and seeds harvested by humans were positively associated with parental tree size.