[HDS10-04] Effects of abandoned paddy field use for the conservation of threatened hydrophyte after the 2011 Tohoku-oki tsunami.
Keywords:Threatened plant, Seed bank, Soil disturbance, Abandoned paddy field, Tsunami
Threatened plant species, Ottelia alismoides, Monochoria korsakowii, Najas graminea, Najas minor, and Chara braunii were found in swampy paddy field after the 2011 Tohoku-oki tsunami Japan. These hydrophyte are classified as near-threatened or vulnerable species in the Red Data book of Ministry of environment, Japan. Hygrophyte communities were vanishing rapidly as reconstruction of road and agriculture proceeds. Therefore, surface soil of hygrophytes community was transplanted to abandoned paddy field 5km away from the original hygrophyte community.
In the present study, we transplanted soil seed to examine whether abandoned paddy field is effective for the hygrophytes species conservation. We investigated 1) whether hygrophytes including threatened species emerge and grow in the abandoned paddy field and 2) management methods of abandoned paddy field to conserve hygrophytes species.
The sturdy site was located at Hadenya district in Miyagi prefecture Japan (lat.38°38¢37.9’’ N. and long.141°28¢10.5’’ E). vegetation survey conducted on July and September during 2014-2016 in accordance with the methodology of Braun-Blanquet (1964). The surface soil of paddy field was puddled by human power on April 2014 and 2015, and was strongly puddled by agricultural tractor on April 2016. water temperature was recorded using a thermo-logger (Tidbit, Onset, USA) at the center of each quadrate frame in transplantation sites and donor seed bank. water temperature was measured from May to September during 2014-2016 in transplantation site. The water depth was measured with ruler in the center of each quadrate frame.
Monochoria korsakowii were recoveried in transplantation site from 2014 to 2016. In particular, Monochoria korsakowii formed large community in 2016, and the volume of plant increased singnificantly hihger than that in 2014 and 2015. Ottelia alismoides and Chara braunii were found in 2014 and 2016. The intensity disturbance with a agricultural tractor suppressed the flourishing of the herbaceous plants of Phragmites australis and Typhaceae spp. in 2016. Consequently, Ottelia alismoides and Chara braunii regenerated again in taransplantation site. Najas graminea and Najas minor were not found during vegetation survey. Salvinia natans and Alisma plantago-aquatica were newly appeared in transplantion site. Our findings suggest that transplantation of surface soil including seed bank to abandoned paddy field is effective for the conservation of hygrophyte, Monochoria korsakowii, Ottelia alismoides and Chara braunii. The intensity disturbance for suppression of herbaceous perennial plant is needed to maitain the habitat of threatened plant species.
For the future, keeping the intensity disturbance with tractor is desirable on April. In addition, weeding of Echinochloa spp by human work is needed to conserve threatened plant species. Furthermore, we must develop the field at water depth 25 cm for the habitat of Najas graminea and Najas minor and re-transplantation. Long-term field monitoring is needed to elucidate frequency, intensity and period of suitable disturbance and water depth to maintain threatened hygrophytes.