Population Dynamics of Four Co-Occurring Tropical Bamboo Species Induced by Gregarious Flowering in a Tropical Seasonal Forest, Thailand

Population dynamics of four co-occurring bamboo species (Gigantchloa albociliata (Ga), Gigantchloa hasskariana (Gh), Bambusa tulda (Bt), Cephalostacyum pergracile (Cp)) were monitored for 13 years to investigate the culm and clump dynamics, flowering and inter-specific interaction in a 4 ha permanent plot in a mixed deciduous forest in Mae Klong Watershed Research Station, Thailand. In nine sub-quadrats (20 m & times; 20 m), all the culms > 1 m height in each clump were tagged and their demographic dynamics were monitored annually. Gh flowered in 1989 before the establishment of the plot. Ga and Cp flowered and died in 1998 and 2001, respectively, while Bt did not flower. Distributional pattern of Ga, Gh and Cp strongly associated with topographical niche differentiation. Ga was the most dominant occupying the middle and upper slope and partially overlapping with Bt and Cp. In contrast, Cp and Gh was occupying ridge and vally, respectively. After death of Ga and Cp, suppressed clumps of Bt started to grow, producing large culms and forming the mature clumps. The spatial distribution and relative dominance of four bamboo species were found to be not stable. They are regulated not only by the self-replacement through seedling establshment after the gregarious flowering and simultaneous death of the parent population, but also by release and expansion of the suppressed saplings of competing bamboo species. The presence of clumps of other bamboo underneath mature individuals partly inhibits the regeneration of the dead species and reduces the adaptive significance of simultaneous death after flowering.