Integrative Zoology 2011; 6: 97-109

doi: 10.1111/j.1749-4877.2011.00235.x

REVIEW

Seed dispersal in Hong Kong, China: past, present and possible futures Richard T. CORLETT Department of Biological Sciences, National University of Singapore, Singapore

Abstract In the present article, published and unpublished information regarding seed dispersal in the degraded landscape of Hong Kong, China, is reviewed. Information was available for 1681 native plant species, of which 1165 were assigned to probable seed dispersal modes. Endozoochory accounted for one-third (34.4%) of all species evaluated, half (54.4%) of those from forests, and more than two-thirds (69.2%) of all trees and tall shrubs. Wind dispersal (25.9%) and dispersal by an unknown agent (30.7%) accounted for most of the rest, with the unknown species mostly small-seeded herbs. Although the frugivore fauna of the Hong Kong region has been truncated since the late Pleistocene, there are few clear examples of failed mutualisms. The most striking is the absence of scatter-hoarding rodents from Hong Kong, despite the presence of forest trees that appear to require them for effective dispersal. There are also some large Lauraceae fruits that appear to be targeted at larger-gaped birds than currently present. Most endozoochorous species are dispersed by 3 small passerine birds (Pycnonotus jocosus, P. sinensis, and Zosterops japonicus), with larger birds, fruit bats (Cynopterus sphinx, Rousettus leschenaulti), rhesus macaques (Macaca mulatta), civets (Paguma larvata, Viverricula indica), and muntjacs (Muntiacus muntjac) accounting for the remainder. The low plant diversity in frugivore droppings, seed traps, and secondary vegetation suggests plant succession may be dispersal limited, although this has not been investigated experimentally. Planting underdispersed species is the simplest solution but, in the longer term, the (re)introduction of a scatter-hoarding rodent should be considered as well as that of other locally and regionally extinct frugivores. Key words: China, extinctions, frugivory, reintroduction, seed dispersal.

INTRODUCTION There have been many studies of seed dispersal in tropical Asia (Corlett 1998) but, with a few exceptions, each has focused on 1 or a few species of animal or plant. Studies that attempt to assess the seed dispersal relationships for entire communities are rare and based mostly on in-

Correspondence: Richard T. Corlett, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543. Email: [email protected]

© 2011 ISZS, Blackwell Publishing and IOZ/CAS

ferences from fruit and seed characteristics (e.g. Chen et al. 2004; Du et al. 2009). Studies in degraded landscapes are even less common because most ecological work in the region has been concentrated in relatively well-protected areas. Yet, most landscapes in tropical Asia are now more or less degraded, with reduced plant and animal diversity and greatly reduced biomass compared with their pristine state (Corlett 2009a). Seed dispersal is a necessary, and possibly rate-limiting, step in the recovery of both biomass and diversity in such landscapes (Martínez-Garza & Howe 2003; Corlett 2007a) and the importance of seed dispersal for plant species will be increased as anthropogenic climate change necessitates compensatory move-

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ments over large distances (Corlett 2009b). On the negative side, seed dispersal facilitates the spread of invasive plant species (Buckley et al. 2006). The present study reviews published and unpublished information on seed dispersal in the highly degraded, but exceptionally wellstudied, landscape of Hong Kong, China.

STUDY AREA AND DATA SOURCES Hong Kong The Hong Kong Special Administrative Region (SAR) of the People’s Republic of China (hereafter Hong Kong) is a biogeographically arbitrary 1100 km2 section of coastal southern China and adjacent islands. It has a subtropical monsoon climate, with hot, wet summers and cool, dry winters (Dudgeon & Corlett 2004). The mean monthly temperature at sea level ranges from 15.8 °C in January to 28.8 °C in July and the mean annual rainfall ranges from 1300 mm at the driest sites to >3000 mm on the highest peaks. The geology is largely igneous and the topography is very rugged, with the highest point 957 m above sea level. Natural open habitats in the Hong Kong region must have been rare, with coastal cliffs, beaches, and perhaps seasonally flooded riverine grasslands in the Zhujiang (Pearl River) delta west of Hong Kong the only ones extensive enough to support a non-forest flora and fauna (Corlett 2009c). Although early human settlements in the region must have had some impacts on the biota (see below), the major period of deforestation seems to have followed increased Chinese immigration in the 11th and 12th centuries. The process accelerated with population increases in the 16th and 17th centuries, and was essentially completed by the end of the 18th century. The total forest cover probably reached a low point in the 19th century and again in 1945, when