[M-IS06] Extreme Weather and Water Related Disasters in Asia

[MIS06-08] El Niño-induced extreme drought impacted seedling dynamics in northern Thailand

★Invited Papers

*Prapawadee Nutiprapun^1,2, Sutheera Hermhuk³, Dokrak Marod⁴, Mamoru Kanzaki⁵, Satoshi Nanami⁶, Akira Itoh⁶ (1.Graduate School of Agricultural and Life Science, the University of Tokyo, Tokyo, Japan, 2.Graduate School of Science, Osaka City University, Osaka, Japan , 3.Faculty of Agricultural Production, Maejo University, Chiang Mai, Thailand , 4.Faculty of Forestry, Kasetsart University, Bangkok, Thailand, 5.Graduate School of Agriculture, Kyoto University, Kyoto, Japan , 6.Graduate School of Science, Osaka Metropolitan University, Osaka, Japan )

Keywords:Tropical forest

El Niño is a climate phenomenon that often leads to intensified droughts in many tropical regions. Understanding the impact of these droughts on seedling dynamics in seasonally dry tropical forests (SDTF) is crucial, as seedling plays an essential role in potential forest regeneration. This study investigated the impact of the severe 2015/16 El Niño on seedling dynamics in two forest types in an SDTF: a deciduous dipterocarp forest (DDF) dominated by deciduous species and a lower montane forest (LMF) dominated by evergreen species. We studied the seven-year seedling dynamics by monitoring seedlings monthly and recording the environmental factors, including air temperature, light intensity, soil moisture, and rainfall. After that, we analyzed the differences in seedling recruitment and seedling mortality during the El Niño and the non-El Niño periods. Our study revealed that the severe El Niño occurred from 2015 to 2016 affected rainfall amount and dry period. The amount of rainfall was reduced from the average year, and the dry period was three months longer than in other normal years. These strong drought conditions impacted seedling dynamics by causing massive seedling mortality in both two forest types. The seedling mortality in the LMF was higher than in the DDF because of the higher proportion of evergreen species. Interestingly, the massive recruitment occurred in the DDF prior to the massive mortality event. However, this massive recruitment compensated for the massive mortality in the DDF. Therefore, after the end of the El Niño event, the number of seedlings in the DDF was higher than before the El Niño event. Our findings highlight the differential impacts of El Niño-induced drought on seedling dynamics across forest types and leaf types and suggest that future changes in drought regimes may alter the species composition and spatial distribution of Asian seasonally dry tropical forests through differences in the response of seedlings to drought.