In stressful and disturbed ecosystems, seedling establishment may be facilitated by early colonizing plants. We examined the mechanism of such facilitation by tussock-forming species (Carex middendorffii and Eriophorum vaginatum), focusing on the independent and interactive effects of tussock litter and tussock mound substrate. Shading by litter on tussock mounds provides a stable but dryer substrate that may negatively affect early colonizers, owing to the co-occurrence of light deficiency and limited water availability, but positively affect late colonizers by subsequent amelioration of water availability. We used seed sowing and seedling transplant experiments with un-manipulated tussocks and manipulated shading × tussock mounds to examine seedling emergence, survival, and the biomass of early (Moliniopsis japonica) and late (Lobelia sessilifolia) colonizers in a post-mined peatland in northern Japan. Carex and Eriophorum tussocks facilitated seedling emergence and the growth of M. japonica and L. sessilifolia. Manipulation experiments indicated that the major positive effect was in providing stable substrates for seeds and seedlings. While the survival and growth of both colonizers were unaffected by shading alone and were negatively affected by tussock mounds alone, shading on tussock mounds decreased both the survival and growth in M. japonica but increased it in L. sessilifolia. Overall, tussock mounds with litter shading accelerated seedling establishment, especially that of late colonizers, in post-mined peatland. Our results indicate that the importance of facilitation mechanisms, for early successional plant composition that result from independent and interactive processes that co-occur as environmental conditions change.
Carex middendorffiiEarly and late colonizers Eriophorum vaginatumInteractive factors Litter Species specificity
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We are grateful to Munemitsu Akasaka and Takashi Y. Ida for their comments on the manuscript, and we also thank Tatsuya I. Saito for his support in the field. Thanks are due to the Ministry of the Environment of Japan for permission to conduct this research. This study was partly supported by the Japan Society for the Promotion of Science and the Global Center of Excellence Program at Hokkaido University. We also thank Katja Schiffers and two anonymous reviewers for their constructive comments.
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