平成２９年度

環境科学院

修士論文内容の要旨

The facilitative effects of tussocks on plant establishment are weakened bydeveloping turfs(谷地坊主の植物定着促進効果は低茎草本群集の発達により低下する)

Hokkaido University, Graduate School of Environmental Science
Division of Environmental Science Development, Course in Human and Ecological Systems
Zhao Xinxue
Tussocks formed by sedges and turfs made by Rhynchospora alba established on a post-mined
peatland in Sarobetsu mire, northern Japan. The tussocks often have facilitative effects on thecohabitants. Although the turfs often developed with tussocks, the effects of turfs on cohabitants
have been unclear. To clarify the mutual effects of tussocks and turfs, field observations andexperiments were undertaken in four microsites: tussock edge with no turf (TEG), tussock edge
with turf (TRA), bareground on flat (FBG) and turf on flat (FRA). In addition, the removal
experiments of turfs on tussock edge (TRV) and flat (FRV) were conducted to detect the effects oftussocks and turfs on plant establishment. On each microsite, light intensity and temperature weremonitored in 2016 and 2017. The seeds of four common species were collected in the late autumn
of 2016 and then the seed-sowing experiments started in the early spring of 2017, to detect themutual effects on the seed germination, seedling survival and growth, and resource allocation.
Litter thickness was measured on each microsite in 2017.
The results were summarized as follows: Light intensity and temperature were lower on thetussock edge with thick litter than on flat. Vegetation cover increased by the turf, while species
richness increased on the tussock edge whether the turfs established or not. The seed germination
was highest on TEG for all the four examined species and showed no significant differences
between FBG and FRV. R. alba and Lobelia sessilifolia showed the lowest seed germination whenR. alba turf developed, in particular, on TRA where the litter was thick. The seed germination wasrestricted on TRA because of litter accumulation, although the tussocks facilitated the seedlingestablishment without the turfs. The seedling survivals of three other species were not affected by
the tussocks and turfs except the lowest survival of R. alba on the turfs. R. alba seedlings had thehighest biomass on unshaded microsites, while L. sessilifolia seedlings had the highest biomass onTEG. Both of the two species had the lowest biomass on TRA. These results indicated that theturfs restricted the seedling growth as well as the seed germination. The seedlings of R. alba and L.
sessilifolia were shorter on the flat than on the tussock edge, suggesting that the heights weredetermined by light intensity. R. alba seedlings produced the shortest shoots and roots when thetussocks and turfs established, but did not change above-ground and below-ground biomass
allocation between the microsites. The height of L. sessilifolia seedlings increased with litter, andthe seedlings increased the resource allocation of height to above-ground biomass with increasing
shade. The two most common species, R. alba and L. sessilifolia, coexisted by using the different
allocation patterns, although their preferable microsites for seed germination were overlapped.
In conclusion, the tussocks had positive effects and the turfs had negative effects on the species
richness, seed germination and seedling growth. The effects of turfs were higher than the effects oftussocks on the seed germination and seedling growth of cohabitants. Therefore, understanding thedistribution of turfs and tussocks was a key to conserve the diverse plant communities.