PLANT SPECIES DIVERSITY AND SOIL PROPERTY CHANGES IN DIFFERENT-YEAR OLD TEAK PLOTS OF MAEHAD PLANTATION, NONGMUANGKHAI DISTRICT, PHRAE PROVINCE

Abstract

The Royal Forest Department had objectives for forest plantation that post-ten years maintenance plantation must avoid thinning and let them develop to natural forest. It led to this research which aimed to study 1) changing of plant species diversity in different-year old teak plots 2) changing of soil property in those teak plots and 3) the similarities between plant species in each of those teak plots and the plant species in mixed deciduous forest with teak (MDF). The research was conducted at Maehad plantation, Nongmuangkhai district, Phrae province. The 13, 18, 23 and 43 year-old teak plots were selected in this study and the nearby MDF was also used for comparison. Quadrat method was used, the plant species were investigated, and the important value index (IVI) of plant species and plant species diversity index (H) were calculated. Physical and chemical soil properties were analyzed. Index of similarity of plant species in each teak plot was compared to the plant species in the MDF The research was carried out between July and December, 2001. The results showed that tree species diversity/rai in all teak plots were less than that in the MDF. The tree species diversity tended to decrease with increasing ages of teak plots. The tree species with highest IVI values in all teak plots were Tectona grandis, which these IVI values were not less than 80%. The tree species with highest IVI value in the MDF was Pterocarpus macrocarpus (IVI value = 53.08%) and the second was Tectona grandis (IVI value = 47.54%). The index of plant species diversity (H) in all teak plots were between 2.11-2.13 and were not much different from the H value in the MDF (H = 2.35). Soil texture of top soil in all teak plots and in the MDF were sandy clay loam. The soil pH values were between 5.6-5.9. The organic matter and nitrogen contents of the top soil were higher than those in the MDF and they had tendency to increase with increasing ages of the teak plots. The similarity index of plant species in each of teak plots was less than that in the MDF, and the plant similarity index tended to decrease with increasing ages of teak plots.