Flora of herbaceous and arboreous plants in Komaba Campus of the University of Tokyo, Japan

Abstract Background Recent studies revealed that green spaces in urban areas are critical for conservation of native biodiversity and that assessment of the present flora of green spaces in urban areas is critical for protection of the native biodiversity. The Komaba Campus of the University of Tokyo embraces a relevant green area, located in a highly urbanised area in Tokyo Metropolis (35.66 N 139.68 E, Japan). The total area of this Campus is 25.4 ha, from which, 4.5 ha are covered by vegetation. Although intense urbanisation can be observed around the Campus, new insect species had been reported for the Campus area, suggesting that the biodiversity on the Campus still demands some attention. Differently from fauna surveys, no flora survey has been done for more than 30 years on the Campus. In this study, we have extensively surveyed the plants diversity on the Komaba Campus of the University of Tokyo, aiming for an update of the plants list on this green urban area in Tokyo. New information The survey covered all herbaceous and arboreous plants growing wild on the Campus. Garden plants were excluded in this survey because these plants were supposed to be cultivated. The final dataset contained, in total, 324 taxa, from which 234 were herbaceous plants and 90 were arboreous plants. The top three taxa are as follows: Poaceae (38 taxa), Asteraceae (34 taxa) and Rosaceae (14 taxa), respectively. This is the first update to the Flora of the Komaba Campus of the University of Tokyo in 30 years and represent an important contribution to conservation of native species in the Tokyo metropolis.


Introduction
Assuming a direct correlation between urbanisation and development, urban development can lead to biotic homogenisation for native plant species (Kühn and Klotz 2006). One hypothesis says that, although biotic homogenisation occurs only in very urbanised landscapes, this homogenisation originates from non-native invasion without local native extirpation (Blouin et al. 2019). Particularly, the occurrence of non-native plant species tends to increase along an urban-rural gradient, with a biased distribution towards the centre of urban areas (Whitney 1985, Kowarik 1995, McKinney 2002. In this scenario, native plant species survive in urban areas without being driven away by non-native plant species, co-existing there. Alternatively, an opposing hypothesis suggests that invasions of non-native species causes native species to be exterminated overtime (Fritts andRodda 1998, Wilcove et al. 1998). Thus, assessments of the present flora and fauna of green spaces in urban areas are critical for protecting native biodiversity.
People living in cities create green spaces (e.g. parks, pavement, gardens and lawns, road and railroad verges, vacant lots and roofs) as artificial habitats (Williams et al. 2009) and a recent study revealed that green spaces in urban areas are critical for conservation of native biodiversity and threatened species (Ives et al. 2015). The Komaba Campus of the University of Tokyo (25.4 ha) is located in a highly urbanised area in Tokyo Metropolis (Japan) and the Campus has a low area coverage of green spaces (4.5 ha). Although urbanisation has proceeded around the Campus, some new insect species had been recorded in this Campus in recent years (Yasunaga et al. 2013, Ishikawa et al. 2015, leading us to suppose a relatively high biodiversity is maintained on the Campus. Some surveys of fauna (Cerambycidae and Pentatomoidea) were performed on the Komaba Campus of the University of Tokyo in recent years (Ishikawa et al. 2015, Kishimoto-Yamada et al. 2017), but the only flora survey available for the area was performed 36 years ago (Meguro Ward office 1985). Thus, an updated study, including correct identification and classification of the plants found on Campus, is made necessary. It is expected that this flora information will provide the basic data for understanding the importance of green spaces in an urban area in Tokyo, Japan.

Sampling methods
Study extent: All specimens were collected in the Komaba I Campus of University of Tokyo, Komaba, Meguro City, Tokyo, Japan. The total area of the Campus is 25.4 ha, from which 20.9 ha consist of buildings and several athletic fields (http://www.c.u-tokyo.ac.jp/ info/about/facts/lands/index.html, accessed on June 2021). The remaining 4.5 ha are covered by vegetation, being used as our investigation site. Annual temperature in Tokyo varies between 5.2°C and 26.4°C (January to August annual average from 1981 to 2010), with mean annual precipitation of 1,598.2 mm (Japan Meteorogical Agency, https:// www.data.jma.go.jp/obd/stats/etrn/view/nml_sfc_ym.php?prec_no=44&block_no=47662, accessed in June 2021).
Sampling description: Plants with reproductive structures were collected between April 2017 and May 2019 at different times of the year. Collection was interrupted between December and February, when few plants with reproductive structures are observed. Sampling was exhaustive and performed once a month during daytime, virtually covering all vegetation areas on the Campus. Two individuals were collected for each taxon, one of those being preserved and registered at the Komaba Museum, University of Tokyo, Meguro City, Japan (KMUT). The whole plant body was collected (including roots), with the exception of large individuals (e.g. Cirsium vulgare (Savi) Ten. and Alcea rosea L.), from which only shoots were collected. For fern specimens, rhizomes and fertile leaves were collected to allow identification. Collected samples were immediately mounted as vouchers and preserved at room temperature using humidity-absorbing sheets. Vouchers' deposit numbers were issued by KMUT.

Geographic coverage
Description: The survey was performed at the Komaba I Campus of University of Tokyo, Komaba, Meguro City, Tokyo, Japan. The Campus is in a residential area, adjacent to the huge business district of Shibuya and relatively close by other green spaces in Tokyo, such as the Yoyogi Park, Shinjuku Gyoen, the Imperial Palace and Ueno Park (Fig. 1). Survey area (highlighted in red) and the adjacent green spaces of Tokyo, such as the Yoyogi Park, Shinjuku Gyoen, the Imperial Palace and Ueno Park.