An experimental study on the establishment and competition of Salix koreensis and Phragmites australis

Abstract

The process of vegetation change from perennial herb to woody plant have been observed in many wetlands. For understanding the vegetational succession, it is important to know ecological characteristics at early life stage of plants and interspecific competition according to environmental condition. The goal of this study was to predict the process of initial establishment for a year from seed recruitment according to different environment condition for Salix koreensis, a woody plant and Phragmites australis, a perennial herb, which are common wetland species in Korea. This study quantifies the effects of water level, light intensity and seed storage time on germination, survival and growth of early seedlings and competition of two species. The initial establishments from seed to 1-year-old seedlings of two species coincided each other temporally and spatially. The effects of water level (0 ㎝ and +2 ㎝) and relative light intensity (100%, 30% and 0%) on seed germination rate of two species were tested. Germination rate of S. koreensis varied at different relative light intensity, and that of P. australis was not influenced by light intensity and water level. Germination rate of both species were relatively high in all treatment (S. koreensis: 76.5%-97.4%, P. australis: 60.9%-71.5%), so flooding and shading were not limiting factor at germination of two species. Seed viability of S. koreensis was lost within a few days (16 days), and all seedlings originated from old seeds (10 days) died. Seedlings growth rate of both species showed peak from mid June to mid August, and P. australis growed quickly and largely than S. koreensis (final height ratio of S. koreensis to P. australis without both flooding and shading = 0.70). We examined the effect of water level (-4㎝, +1㎝, +2㎝ and +4㎝) and relatively light intensity (100% and 30%) on survival and growth of young seedlings (1 ㎝ in height). Water level (-10㎝, +4㎝ and +12㎝) and relatively light intensity (100% and 30%) on survival and growth of old seedlings (about 40 days in age) was also tested. When seedlings are very young (1 ㎝ in height), any S. koreensis seedlings could not survive under flooding of twice level as its height, but 30% of P. australis seedlings overcame the same flooding. In the case of about 40-day-old seedlings, flooding level of 12 ㎝ reduced the survival and growth of S. koreensis seedlings, but did not influence on P. australis seedlings. On the contrary to flooding, shading had relatively stronger influence on P. australis than S. koreensis. Shading of 70% affected survival and growth of both species irrespective of its age, but relatively more harmful to P. australis than S. koreensis. Especially, under shading of 70%, all young P. australis seedlings (1 ㎝ in height) could not overcome water level twice their heights, and old P. australis seedlings could not flower. Without both of flooding and shading, P. australis had relatively dominant than S. koreensis in competitive situation of two species. When flooding was given, P. australis had more relatively competitive ability, and when shading was given, S. koreensis did. S. koreensis seedlings were taller than P. australis under -10 ㎝-water level and 30%-light intensity, whereas P. australis was dominant under the others treatment. This study shows that the competition of two species in initial establishment process is changed according to environmental conditions. Unless appropriate moisture condition for germination is formed in a few days (about eight days), S. koreensis could not establish from seed. Flooding has an adverse affect on establishment of both species, but is more harmful to S. koreensis than P. australis, especially right after germination. On the contrary, in shaded understory, growth of P. australis seedlings is worse than S. koreensis.