Abstract
The role of N2 fixation in structuring plant communities and influencing ecosystem function will be potentially large. In previous study, we investigated nodule biomass and activity, and calculated the amount of N2 fixation in a naturally established 18-year-old alder (Alnus hirsute (Turcz.) var. sibirica) stand following disturbance by road construction in Takayama, central Japan. In this study, to estimate the facilitation effects by alder on the spatial distribution of the regenerated tree species, we examined the distribution pattern of the regenerated tree species in this naturally established 18-year-old alder stand. The distribution pattern of alder and the regenerated woody species was analyzed in terms of spatial point processes and the regenerated species tended to distribute near the alder site. In particular, bird-dispersed tree species (endozoochory species) with relatively high shade tolerance showed a significant attraction to alder. These results suggest that alder will be used as roost trees and play the role of mother trees for these regenerated species at the degraded site. It was also suggested that the endozoochory species, which occupy 13 of 26 regenerated species in this stand, might regenerate faster than other species at this alder stand.
Highlights
Given the virtually ubiquitous limitation of plant growth by N supply (Vitousek & Howarth, 1991), the role of N2 fixation in structuring plant communities and influencing ecosystem function is potentially large (Chapin et al, 1994; Thomas & Bowman, 1998)
Except for Salix bakko, almost all individuals of each tree species were less than 4 m in height, while the height of the shrub species was less than 3 m, but the portion of taller individuals exceeded that of tree species
Species with relatively high shade tolerance showed a significant attraction to alder
Summary
Given the virtually ubiquitous limitation of plant growth by N supply (Vitousek & Howarth, 1991), the role of N2 fixation in structuring plant communities and influencing ecosystem function is potentially large (Chapin et al, 1994; Thomas & Bowman, 1998). Interspecific facilitation by plants may be more important in structuring plant communities and the ecosystem function than previously thought (Hunter & Aarssen, 1988; Callaway & Walker, 1997). The abundance of some species was positively associated with the presence of Trifolium, though other species were less abundant. These results suggest that N2 fixing species may exert both facilitative and inhibitive effects on the abundance and growth of plant species growing near them and, in the process, substantially influence the spatial heterogeneity in community structure and primary production
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