Comparisons of recruitment, survival, and growth in invasive and native saplings on a volcano

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We monitored the recruitment, survival, and growth of tree saplings on invasive (Larix kaempferi) versus native species (Betula and Populus) using 16 20 m × 20 m plots established along elevation gradient on the volcano Mount Koma, Japan, for 7 years because the sapling behaviors should determine forest structures. The crowding of overstory consists mostly of Larix decreased with increasing elevation. Larix recruits were conspicuous, particularly at middle elevation where overstory crowding was intermediate, while Betula recruits were least. Larix overstory crowding inhibited the recruitment of all the taxa, although intermediate crowding promoted the recruitment of Larix. The restriction of sapling emergence was conspicuous at lower elevation where the overstory crowding was highest, probably because of shading, and/or competition with overstory trees. Sapling recruitment for all taxa was restricted at higher elevation, due to high stresses derived from direct solar radiation and strong wind without overstory. The survival of saplings was 96% for Larix and Betula, while it was ca. 50% for Populus. Larix overstory decreased the survival and growth of all the taxa, except Larix survival and Betula growth. The results implied that Larix could establish by high survival once the recruits succeeded everywhere and native sapling regeneration was restricted by Larix overstory. Strong recruitment, survival, and growth of Larix, together with resistance to overstory crowding, enables it to dominate and persist in such disturbed areas regardless of the canopy closure.

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