Seed and seedling demography of invasive and native trees of subtropical Pacific islands

Abstract

Abstract. Bischofia javanica is an invasive tree of the Bonin Islands in the western Pacific, Japan. This species has aggressive growth, competitively replacing native trees in the natural forest of the islands. The aim of this study was to examine seed and seedling factors which might confer an advantage to the establishment of Bischofia over native trees. During a 5‐yr period we compared the demographic parameters of early life history of Bischofia and Elaeocarpus photiniae‐folius, a native canopy dominant, in actively invaded forests. Predation of Elaeocarpus seeds by in troduced rodents was much higher before (27.9–32.9%) and after (41.3–100%) dispersal of seeds than that of B. javanica. Most Elaeocarpus seeds lost viability ca. 6 mo after burial in forest soil while some seeds of Bischofia remained viable for more than 2 yr. Seedling survival in the first 2 yr was much higher in Bischofia (16%) than in Elaeocarpus (1.3%). The high persistence of Bischofia in the shade, coupled to its rapid acclimation to high light levels, is an unusual combination because in forest tree species there is generally a trade‐off between seedling survival in the shade and response to canopy opening. Compared with a native canopy dominant, greater seed longevity, lower seed predation by introduced rodents, longer fruiting periods and the ability to form seedling banks under closed canopy appear to have contributed to the invasive success of Bischofia on the Bonin Islands.

Biology and Impacts of Pacific Island Invasive Species. 11.Rattus rattus,the Black Rat (Rodentia: Muridae)

“…In Hong Kong, Hau (1997) concluded that forest restoration by direct seeding would not be feasible due to rat (R. rattus and Niviventer fulvescens) predation of 12 plant species. Yamashita et al (2003) suggested that R. rattus may be facilitating the invasion of the nonnative tree Bischofia javanica in the Ogasawara Islands because R. rattus depredates the seeds of the dominant native tree Elaeocarpus photiniae-folius both before dispersal (27% -33% of the seed crop) and after dispersal (41% -100%). Several other studies of fruit and seed removal have occurred on Pacific islands that include R. rattus as part of the rodent community, but the particular rodent species responsible for such removals were not identified (e.g., Moles and Drake 1999, Uowolo and Denslow 2008, Meyer and Butaud 2009, Erwin and Young 2010, GrantHoffman et al 2010, Chimera and Drake 2011.…”

Impacts of introduced species on the biota of an oceanic archipelago: the relative importance of competitive and trophic interactions

“…Goats have also caused local extinctions and population declines in endangered plants, such as Lobelia boninensis and Crepidiastrum grandicollum, in the archipelago (Ono 1998). Furthermore, the introduced rat reportedly eats and/or damages the seeds, fruits, and twigs of many native plant species (Toyoda 2003;Watanabe et al 2003;Yamashita et al 2003;Abe 2007;Hashimoto 2010;Yabe et al 2010;Abe and Umeno 2011). Although reports on the negative impacts of introduced phytophagous insects on native plants are rare (Sugiura 2010a), the introduced weevil, Rhabdoscelus obscurus, reportedly damages the basal parts of leaves in the endemic palm Clinostigma savoryana (Karube et al 2008(Karube et al , 2009).…”

“…The tall tree species B. javanica, which was introduced and planted in the Ogasawara Islands before 1905 as a forestry tree, has invaded native forests via bird-dispersed seeds (Shimizu 2003). Bischofia javanica has advantageous features in terms of competition for resources with other plants, which include rapid seedling and sapling growth, vigorous sprouting ability, shade-tolerant juveniles, and high fecundity (Yamashita et al 2000(Yamashita et al , 2003Shimizu 2003). Hence, B. javanica has gradually replaced native forests (Tanaka et al 2010).…”

“…The introduced rat R. rattus feeds on the seeds of many native trees such as Elaeocarpus photiniaefolius (Yamashita et al 2003), resulting in less food (native tree seeds) for the endangered wood pigeon, Columba janthina nitens (Takano 2002;Toyoda 2003). However, few studies have elucidated the negative impacts of resource competition on C. janthina nitens.…”

“…However, seed predation and/or herbivory as well as interspecific competition may have impacted native plant species (Shimizu 2003;Toyoda 2003;Hashimoto 2010); for example, seed predation on the native tree E. photiniaefolius by introduced rats was much higher than that on the introduced tree B. javanica, and seedling survival (higher shade tolerance) in the first 2 years was significantly higher in B. javanica than in E. photiniaefolius (Yamashita et al 2003). Additionally, goats eat the seedlings of many native trees (Shimizu 1993(Shimizu , 2003Toyoda 2003).…”