Snow damage to the canopy facilitates alien weed invasion in a subtropical montane primary forest in southwestern China Xiaoyang Song a,b , James Aaron Hogan c , Calum Brown d , Min Cao a,⇑ , Jie Yang a,⇑ a Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, 666303 Yunnan, China b University of Chinese Academy of Sciences, 100049 Beijing, China c International Center for Tropical Botany, Department of Biological Sciences, Florida International University, Miami, FL 33199, USA d School of Geosciences, University of Edinburgh, Edinburgh EH8 9XP, United Kingdom article info Article history: Received 26 October 2016 Received in revised form 13 February 2017 Accepted 14 February 2017 Keywords: Invasive species Light availability Canopy openness Ageratina adenophora Subtropical forest Seedling germination Ailaoshan Forest Dynamics Plot abstract Climate-mediated disturbance often promotes the invasion of non-native species, which impact local ecosystems by altering community structure and composition. In subtropical forests, the formation of canopy gaps, which allow for rapid regeneration in the understorey, strongly affects successional dynam- ics. However, the role of canopy gaps in promoting invasive species into forest interiors has not been extensively studied. We examined the relationship between canopy disturbance and the germination of Ageratina adenophora (Asteraceae), a non-native branched herb species, using seedling population data from a 20-Ha forest dynamics plot in southwest China. The species was first recorded in 2015, after extensive snow-damage to the forest canopy. Our hypothesis was that canopy gaps increase light avail- ability on the forest floor, thereby facilitating the germination and subsequent invasion by the non-native branched herb into the forest interior. Field measurements of the Leaf Area Index before and after the snow damage was combined with measurements of canopy gaps and associated light conditions. Biotic factors (tree seedling species richness, herb species richness and herb coverage), abiotic factors (elevation, slope, convexity and soil moisture), and the density and spatial distribution of A. adenophora were also measured ten months after the snow damage. Seedling germination experiments were con- ducted in the lab to test the relationship between light availability and the germination of the invasive branched herb, showing the branched herb to be light demanding. Using spatial statistical methods, we found significant relationships between densities of recruiting A. adenophora and canopy gaps, with high densities of the invasive branched herb recruiting into gap areas. We conclude that light availability shapes the distribution of A. Adenophora in the understorey in this subtropical evergreen montane forest. Our results illustrate that disturbances leading to canopy damage can promote the establishment and proliferation of invasive understorey species in forest interiors, providing a rapid route to colonization. Ó 2017 Elsevier B.V. All rights reserved. 1. Introduction Climate change and biological invasions are two important dri- vers affecting native community composition and ecosystems around the world (Vilà et al., 2011; Valladares et al., 2015). Previ- ous studies have shown that extreme climate events may increase the probability of species invasion success (Diez et al., 2012). In many forests, canopy gaps created by climate-mediated distur- bances promote regeneration, sometimes favoring alien weeds that can more-readily respond to illumination changes in the under- storey (Qi et al., 2014; West et al., 2014; Long et al., 2015). Large-scale forest canopy disturbances due to hurricanes (Zimmerman et al., 1995; Comita et al., 2009; Shiels and Gonzalez, 2014), droughts (Gitlin et al., 2006) and snow damage (Lafon, 2004; Wu et al., 2011) are projected to become more fre- quent and severe under climate change (IPCC, 2013). Thus, analy- ses of invasions of non-native understorey species and their relationships to disturbance events are important for understand- ing invasion processes and possible impediments to forest natural successional trajectories. Colonization opportunities are improved after disturbance due to increased resource availability, possibly promoting the invasion of non-native plant species (D’Antonio et al., 1999; Sher and Hyatt, 1999; Davis et al., 2000; Hierro et al., 2006; Catford et al., 2012). For example, in Hawaii, extreme drought led to widespread mor- tality among dominant native woody plants, facilitating the inva- sion of non-native grasses (Lohse et al., 1995). In a Bangladesh http://dx.doi.org/10.1016/j.foreco.2017.02.031 0378-1127/Ó 2017 Elsevier B.V. All rights reserved. ⇑ Corresponding authors. E-mail addresses: caom@xtbg.ac.cn (M. Cao), yangjie@xtbg.org.cn (J. Yang). Forest Ecology and Management 391 (2017) 275–281 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco