Yoshinori Tokuoka

Influence of aphid–host plant pairs on the survivorship and development of the multicolored Asian ladybird beetle: implications for the management of vegetation in rural landscapes

Although the value of noncrop vegetation for biological control has been extensively studied in agricultural landscapes, there are few reports on how it functions mechanistically. When focusing on the pest control function provided by noncrop vegetation, tritrophic interactions among a predatory natural enemy, its prey, and the prey’s host plant need to be examined. In Japan, the multicolored Asian ladybird beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), an aphidophage, serves as a natural pest control agent in agricultural production, although the species’ introduction into Europe and North America for pest control has had a negative impact on native ecosystems. In the present study, 33 aphid–plant pairs from an agricultural landscape in the eastern Kanto region of Japan were examined experimentally for initial larval survivorship and development of H. axyridis. Significant differences were found among plant–aphid pairs with regard to these parameters. In addition, the larval survivorship of H. axyridis was not consistently determined by host plant or aphid species alone but was context-dependently influenced by the aphid–plant combination. Some alien host plants showed positive effects on the ladybird beetle. Others, however, served as hosts for unsuitable prey species, such as the competitive alien plants Solidago canadensis L. and Robinia pseudoacacia L., which are the host plants of Uroleucon nigrotuberculatum (Olive) and Aphis craccivora Koch, respectively. These findings suggest that various noncrop plants could be managed to promote ladybird beetle populations in rural landscapes.

Interactions among dwarf bamboo, litter and consumption by small vertebrates place multiple constraints on the establishment of native tree seedlings in a Japanese agricultural landscape

Faunal assemblage alterations due to anthropogenic impacts have changed herbivore–vegetation relationships in various ecosystems, but the influences of small vertebrates on revegetation processes remain unclear. In a peri-urban agricultural landscape in eastern Japan that lacks large ungulates but supports small generalist herbivores, fewer native seedlings have become established in thickets dominated by native dwarf bamboo, Pleioblastus chino (Franch. et Sav.) Makino. The mechanisms limiting tree seedling establishment are unknown. Our aim here was to evaluate the influence of interactions among the dwarf bamboo, its litter cover and small vertebrate herbivores on the microsite conditions governing the establishment of native tree seedlings from different successional stages in an old field in temperate Japan. First, seedling emergence and survival of seeded Pinus densiflora Siebold et Zucc., Celtis sinensis Pers., Aphananthe aspera (Thunb.) Planch., Quercus serrata Murray, Quercus myrsinifolia Blume and Castanopsis sieboldii (Makino) Hatus. ex T. Yamaz. et Mashiba were observed in a factorial design that accounted for the presence or absence of dwarf bamboo and its litter cover, as well as the exclusion or access of small vertebrate fauna, in 2009 and 2010. To identify small vertebrate herbivores that reduced the emergence or survival of tree seedlings in the first experiment, reseeding experiments using P. densiflora, C. sinensis, A. aspera and Q. myrsinifolia were conducted by video trapping in 2011 and video and still-camera trapping in 2012. The abiotic conditions under the dwarf bamboo were lethal to early- to mid-successional P. densiflora, C. sinensis, A. aspera and Q. serrata but led to better survival—although spindly growth—of late-successional Q. myrsinifolia and C. sieboldii. The main consumers and the plants they found palatable differed between the bamboo thickets and the intervening gaps. Predation by mice appeared to have severely limited the emergence of all species, particularly in the bamboo thickets but occasionally in the gaps, whereas litter cover slightly mitigated this limitation. However, bamboo litter cover reduced the emergence of P. densiflora in the gaps. Chinese bamboo partridge (Bambusicola thoracicus Temminck), an introduced game bird, selectively and severely fed on the cotyledons—and probably seeds—of A. aspera and moderately preyed upon those of P. densiflora in the gaps. Apparent consumption of seedlings in the gaps by the Japanese hare (Lepus brachyurus Temminck) suppressed the growth of all species but apparently did not severely affect emergence and survival. Thus, the net balance of positive and negative interactions at the bamboo thicket scale (i.e. the presence of dominant dwarf bamboo cover or intervening gaps and the herbivore behaviours in these two environments) and at the microsite level (i.e. litter cover) shapes the early establishment patterns of native tree seedlings, and this balance differs among tree seedling species.

Diverse Patterns of Vegetation Change after Upland Field Abandonment in Japan

Vegetation changes in abandoned farmland that deviates from locally targeted states pose conservation and restoration problems in various parts of the world. Here, we review the patterns of vegetation change after upland field abandonment in Japan. Inconsistent invasiveness and weediness of exotic species such as Phyllostachys edulis and Leucaena leucocephala in rural habitats indicated that even if an exotic species is present in a focal area, its impacts on revegetation pathways vary depending on the local species pool, species recruitment order, and interspecific competition. Improved soil nutrients for crop production before abandonment decreased the presence of native grasses and forbs during early successional stages. Buried seeds and resprouting plants maintained under slash-and-burn cultivation led to the dominance of native tree species. After the recent abandonment of conventional farming in warm-temperate regions of Japan, competitive clonal native species such as a dwarf bamboo (Pleioblastus chino) and kudzu ( Pueraria lobata) became dominant and limited the seedling establishment of various native tree species. The drastic decrease of grassland areas in the past century suggests that many fewer seeds of Miscanthus sinensis , which serves as a facilitator of various plants in grassland systems, are dispersing into abandoned fields than in the past. Studies of wildlife in abandoned farmland in Japan indicated that herbivore damage by rodents, Japanese hare, and sika deer are potent factors affecting forest recovery. These results suggest that vegetation change after upland field abandonment occurs in diverse ways, reflecting historical differences in environmental factors such as local flora and fauna, agricultural technologies and practices, and landscape mosaics. This implies that revegetation pathways after upland field abandonment tend toward novel states and that deterministic predictions of upland field succession will be easily violated in many cases.