Litter of an alien tree, Casuarina equisetifolia, inhibits seed germination and initial growth of a native tree on the Ogasawara Islands (subtropical oceanic islands)

Abstract

We investigated the effects of the accumulation of litter of an alien tree, Casuarina equisetifolia, on the initial establishment of Schima mertensiana, a tree native to the Ogasawara (Bonin) Islands, in the northwestern Pacific Ocean, in field and greenhouse experiments. The field experiment compared emergence of seedlings in forests dominated by C. equisetifolia with those in native forests, with and without litter removal. The greenhouse experiment compared seedling germination and biomass among 12 treatments that included two soil types (collected from the C. equisetifolia and native forests), two litter types (C. equisetifolia and native litter), and three amounts of litter (5, 15, or 45 g/pot). Significantly fewer S. mertensiana seedlings emerged at sites dominated by C. equisetifolia than at sites of native species in the field experiment. Litter removal tended to increase seedling emergence. Fewer and smaller S. mertensiana seedlings germinated with greater litter cover regardless of soil type or litter type in the greenhouse experiment. Our results demonstrate that C. equisetifolia litter suppresses germination and initial growth of S. mertensiana, and that the main cause of the suppression is the greater amount of litter accumulated under C. equisetifolia forest floor rather than factors such as the nature of the soil or litter between native and alien species.

Improving the assessment method of seed vigor in Cunninghamia lanceolata and Pinus massoniana based on oxygen sensing technology

“…Seed vigor is usually very low even though laboratory germination percentage was very high (Wilson et al 1998). Seedling emergence rates in the field experiment were much lower than those in the greenhouse experiment conducted in Schima mertensiana, a tree native to the Ogasawara (Bonin) Islands, in the northwestern Pacific Ocean (Hata et al 2010). Our research showed that GP did not significantly correlate with field emergence performances of Chinese fir in both years.…”

Seedlings of a native shrub can establish under forests dominated by an alien tree, Casuarina equisetifolia, on subtropical oceanic islands

“…Our results demonstrate that R. wrightiana seedlings can establish under C. equisetifolia forests, unlike S. mertensiana seedlings in secondary forest in the Ogasawara Islands (Hata et al 2010) or in other regions (Parrotta 1995). The opposite result suggests that the effect of C. equisetifolia on initial establishment of native woody species can be species specific, and that some species can establish even under C. equisetifolia forests with dense litter.…”

“…Koidz. (Theaceae), one of the most dominant woody species in secondary forests on the islands (Hata et al 2010). However, the effects of C. equisetifolia litter on other woody species in the Ogasawara Islands are not known.…”

Leaf litter of the invasive Casuarina equisetifolia decomposes at the same rate as that of native woody species on oceanic islands but releases more nitrogen

“…(Theaceae), one of the most dominant woody species in secondary forests on the Ogasawara Islands (Hata et al, 2009). The accumulated litter of C. equisetifolia in the C. equisetifolia forests inhibits seed germination and seedling growth of native woody species (Hata et al, 2010c), which could result in a lack of native saplings in the forests (Hata et al, 2009).…”