Response of Mixed-Species Bird Flocks to Forest Succession in Subtropical Ch

Biodivers Conserv (2013) 22:1965–1989 DOI 10.1007/s10531-013-0521-5 ORIGINAL PAPER Linking vegetation structure and bird organization: response of mixed-species bird flocks to forest succession in subtropical China Qiang Zhang • Richou Han • Zhongliang Huang • Fasheng Zou Received: 18 June 2012 / Accepted: 21 June 2013 / Published online: 4 July 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract As forests undergo natural succession following artificial afforestation, their bird assemblages also change. However, interspecific avian social organization associated with forest succession has not been fully understood, particularly for mixed-species bird flocks. To disentangle how mixed-species flocks change as a function of local forest structure, we analyzed flock characteristics (particularly species richness, flocking frequency and propensity) and vegetation physiognomies along a presumed successional series (early, middle, and advanced) simultaneously in subtropical forests in southern China. As hypothesized, monthly point counts demonstrated that complexity of flocks increases with the progression of natural forest succession at a local scale. Advanced forests differed significantly from pioneering plantations with respect to vegetation structure, flock characteristics and constituents (especially for understory specialists). Importantly, forest succession affected flock patterns particularly in relation to the flocking propensity of regular species, and the frequency of nuclear species (Huet’s fulvetta Alcippe hueti), which in turn determined flocking occurrence at different successional stands. Canonical correspondence analysis indicated that understory flocking species (mainly Timaliidae babblers) were significantly associated with intact native canopy cover, com- plex DBH diversity, as well as high densities of dead trees and large trees, representing a maturity level of successional stands. Our study reveals that the effect of natural forest succession on mixed-species bird flocks is species-specific and guild-dependent. From a conservation perspective, despite a high proliferation of pine plantation in southern China, priority should be placed on protecting the advanced forest with a rich collection of understory flocking specialists. Q. Zhang Á R. Han Á F. Zou (&) Guangdong Entomological Institute/South China Institute of Endangered Animals, No. 105, XinGang West Road, Guangzhou 510260, China e-mail: [email protected] Q. Zhang e-mail: [email protected] Z. Huang South China Botanical Garden, Chinese Academy of Science, Guangzhou 510650, China 123 1966 Biodivers Conserv (2013) 22:1965–1989 Keywords Flock characteristics Á Forest succession Á Mixed-species bird flock Á Nuclear species Á Southern China Introduction Most native subtropical forests in southern China have experienced severe exploitation and conversion to monocultures during the last century, leading to degradation and loss of biodiversity (Zhang et al. 2000; Liu et al. 2003). In these degraded sites, two contrasting processes of vegetation restoration are passive secondary succession and active reforestation with native trees or timber plantations (Peng 2003). As forests undergo successional changes after major disturbance events, their bird assemblages also change (Dıáz et al. 2005; Barlow et al. 2007; Ding et al. 2008; Hingston and Grove 2010; Rey-Benayasa et al. 2010). Our understanding of interspecific avian organization associated with ecological vegetation succession is limited yet. Such information would be important because subtle changes in interactions between species of a region could have cascading effects on its avifauna (Terborgh et al. 2001; Sridhar and Sankar 2008). Mixed-species bird flocks represent a common social organization in forest bird communities worldwide, that provides foraging and anti-predation benefits (Moynihan 1962; Powell 1985; Greenberg 2000). Species richness, flocking frequency and flocking propensity are representative indices used to characterize mixed-species flocks (Morse 1970; Munn and Terborgh 1979; Pomara et al. 2007). And flock characteristics mainly depended on environmental factor through species requirements (‘‘species co-dependency on environmental variables’’: Hutto 1994), and on mutualistic organization between species (‘‘interspecific interactions’’: Hino 1998). For example, in the Old World tropics, flocking species with specialized ecological traits (e.g. primary forest and understory microhabitat specialization) are more vulnerable to habitat disturbance, either through changes in frequency or in flocking propensity of the species (Lee et al. 2005; Sridhar and Sankar 2008; Peron and Crochet 2009); while, in the Neotropics, forest degradation increases the detectability of predators, and therefore reduce flocking propensity, which are mediated by mutual habitat dependencies or species-specific interactions within flocks (Latta and Wunderle 1996; Thiollay 1999). Furthermore, flocks become less cohesive after the dis- appearance or low occurrence of nuclear species in fragments of Atlantic forests (Maldonado-Coelho and Marini 2000, 2004). Thus, by altering vegetation structure and composition, the extent of secondary forest succession may influence the aggregation of flocks at different serial stages. Forest succession is a fundamental ecological process which can ameliorate stand conditions and microclimate factors, and change vegetation physiognomy and floristics (Shugart 1984; Guariguata and Ostertag 2001). Vegetation complexity has long been known as a significant factor influencing bird communities, including species composition, diversity, and local abundance (MacArthur and MacArthur 1961). In instances where bird species are associated with specific vegetation structure, it may be related to provision of specific resources such as invertebrates, seeds, fruits and nest sites or preferred micro- habitats for foraging (Wiens 1989; Helle and Mo¨nkko¨nen 1990). However, despite the fact that mixed-species flocks are a clearly defined subset of the local avifaunas, the ecological consequences of woodland structure on the occurrence and characteristics of flocks across successional stands is not well understood. Indeed, responses of flocks to advancing forest 123 Biodivers Conserv (2013) 22:1965–1989 1967 serial stages over time vary widely, possibly because mechanisms are scale-dependent and species-specific (Croxall 1976; Maldonado-Coelho and Marini 2000; Kotagama and Goodale 2004). Therefore, the identification of preferred elements of vegetation physiognomy and their relationships to flock characteristics will advance our understanding and may inform avian conservation and forest management practices. The subtropical monsoon evergreen forests are important for their high biodiversity and critical role in watershed protection in southern China (Zhou et al. 2006, 2007). Unfor- tunately, these regional climax forests were severely damaged by large-scale deforestation and land use change during the 1960s. They now exhibit marked variability along successional gradients (temporal scale). In order to restore forest ecosystems, a large-scale reforestation and reclamation program (mainly Masson pine plantation) was launched in the late 1980s in Guangdong Province. During natural succession of forests in subtropical China, concern that bird assemblages change as species that inhabit newly disturbed plantations are progressively replaced by those favoring regional climax forests has been noted (Zhou 1986; Zhang et al. 2011; Zou et al. 2013). Due to the extensive proliferation of pine plantations and regeneration of mixed forests over time, it may be advantageous to study bird social organization response, such as mixed-species flocks to forest succession. In addition, characteristics of mixed-species flocks might be an effective ecological indi- cator of forest disturbance and restoration (Maldonado-Coelho and Marini 2004; Lee et al. 2005). In this study, we evaluate flock characteristics and vegetation structure in three habitat types, including Masson pine forest (PF), pine-broadleaved mixed forest (MF), and subtropical monsoon evergreen broadleaved forest (MEBF). These systems are well main- tained at Dinghushan Nature Reserve, and provide a controlled model for the study of changes in mixed-species flocks along a natural successional gradient (early, middle, and advanced stages). The specific objectives of this study were: (1) to determine differences in species richness, flocking frequency and propensity to form mixed-species flocks, among different successional stage forest stands; (2) to assess the role of nuclear species in maintaining the cohesion of flocks among different sites; and (3) to define specific structural components of forests that create bird habitats and promote flock organization. Methods Study area The study was conducted in the Dinghushan Nature Reserve (DNR) in the mid-west of Guangdong, China (112°3003900–112°3304100E, 23°0902100–23°1103000N). DNR located west of the Pearl River Delta, is one of the most densely populated and industrialized areas in China. The reserve is hilly with an altitude varying locally between 100 and 700 m, with an area of 1155 ha. The region is characterized by typical subtropical monsoon climate, with an annual mean temperature of 21.4 °C and mean relative humidity of 80 %. The mean annual precipitation of 1,927 mm is distributed seasonally, with the rainy season from April to October and the dry season from November to March (Mo et al. 2006; Yan et al. 2009). Because

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