Questions: How do biological invasion patterns of Larix kaempferi seedlings change with different microhabitats along an elevational gradient on a volcano? How are seedling attributes such as establishment, competitive ability and morphological plasticity, advantageous to the invasion of stressful disturbed areas?
Location: Mount Koma, Hokkaido, Japan.
Methods: Seed sowing experiments and natural seedling censuses were conducted with L. kaempferi and the dominant native tree Betula ermanii. Seed germination, seedling survival and allocation were investigated on three microhabitats (bare ground, Salix reinii patch and Larix understorey) in three elevational zones for three years.
Results: Seed germination was higher in Larix understorey than in bare ground and Salix patches, but did not differ between elevations. Survival rates were not different between elevations and microhabitats. Larix had a higher survival rate than Betula. Larix showed the highest natural seedling density in Salix patches, independent of elevational differences, while Betula density was nearly zero. Larix seedlings changed allocations between microhabitats, while the ratio of leaf to total biomass was constant. In bare ground Larix was more stunted and branched and increased its allocation to the roots. This form is adaptive to windy, nutrient-poor environments. Larix seedlings were taller and more slender in Salix patches, indicating that the priority was light acquisition in shaded habitats. Little change in Betula allocation was detected.
Conclusion: Invasive species establish themselves more efficiently than native species in every microhabitat investigated, especially at higher elevations, by having higher survival and growth rates derived from superior seedling performance. Plant communities on and above the tree line are modified by the biological invasion.
Abbreviations: BA = Bare ground; H = high elevational zones; L = Low elevational zone; LU = Larix understorey; M = Middle elevational zone; PFD = Photon flux density; RPFD = Relative photon flux density; SP = Salix reinii patch.
Nomenclature: Ohwi (1975).