Distributional pattern, gap formation and turnover time in dry evergreen forest at Sakaerat [Thailand]

Study on the distributional pattern, gap formation and turnover time in the dry evergreen forest at Sakaerat, Amphoe Pak Thong Chai, Changwat Nakorn Ratchasima were investigated during March, 1982 to March, 1984 by using the permanent sample plot of 100x100 sq. meter which was laid out since 1982. Patterns of spatial distribution employing Morisita's index or index of dispersion (I delta) and m*-m. regression were employed for total individuals and the nine important species. Study on gap formation, turnover time of canopy tree and the forest growth cycle were also investigated. The results revealed that total individuals (for trees larger than 4.5 cm. in DBH) showed random distribution. Seven important species showed contagious distribution while the rest showed random distribution. The statistical method was used for age determination from data of annual diameter increament in marked and numbered sample trees of different diameters during one year period, the study based on nine important species. First order difference equation was developed to determine age (n) of tree species when DBH of each species (Dn) was known. The number of gaps in 1 ha plot was 18 gaps. Gap area was 1,860 sq. meter (18.60 % of total land area). The average size of gap was 115 sq. meter and the maximum size was 420 sq. meter. Gaps were made by 1-3 gap making trees. The concentration of gap formation in particular years was not observed. In average 0.48 canopy trees per hectare was died, and gaps of 41.33-82.66 sq. meter per hectare were made annually. The turnover time of canopy tree which was calculated from four different methods was 100-230 years. Three phases were distinguished and it took about 0-45, 45-100 and 100-200 years for gap, building and mature phase, which were described by Watt (1974) and Whitmore (1978, 1982).