Secondary forests represent significant proportions of global forest cover, with over 65% of forests in Asia classified as regenerating. While succession has been studied extensively in temperate systems, trajectories of sub-tropical forest succession remain poorly characterized in highly disturbed, urban-adjacent forests. Investigating the additive beta diversity subcomponents of Turnover and Nestedness may reveal community assembly mechanisms driving secondary succession. The present study investigated plant community assembly along a successional gradient from 7 to 70 years following the onset of succession in secondary sub-tropical forests in Hong Kong. Plant survey data for 28 plots were analysed, generating additive Simpsons and Nestedness beta diversity metrics as subcomponents of Sorenson Beta Diversity. Dissimilarity matrices were generated and modelled as a function of transformed environmental matrices of forest plant community age (years following onset of secondary succession), elevation (metres), inter-community distance (metres), soil moisture saturation (%) and soil organic carbon (g kg-1). Generalized dissimilarity models were generated for plant species Turnover and Nestedness. Nonmetric Multidimensional Scaling of plant communities was conducted with Bray-Curtis dissimilarity matrices. Our findings indicate that elevation was the primary driver of plant species Turnover, while age and inter-community distance played less prominent roles. Models of Nestedness found that plot age and soil moisture saturation were the sole drivers of Nestedness patterns in plant communities. While models of Turnover were robust, the low explanatory power of Nestedness models suggest additional unobserved factors driving patterns of plant community Nestedness during secondary succession. Turnover patterns suggest a deterministic model of community assembly, with strong patterns of species replacement between Lowland and Montaine forest types, as well as between successional age classes.

Forest litter decomposition is an essential component of global carbon and nutrient turnover. Soil invertebrates play important roles in litter decomposition, but the regional pattern of their effects is poorly understood. We examined 476 case studies across 93 sites and performed a meta-analysis to estimate regional effects of invertebrates on forest litter decomposition. We then assessed how invertebrate diversity, climate and soil pH drive regional variations in invertebrate-mediated decomposition. We found that (1) invertebrate contributions to litter decomposition are 1.5 times higher in tropical forests than forests outside the tropics, with an overall contribution of 31% to global forest litter decomposition; and (2) invertebrate diversity, particularly of termites, together with warm, humid and acidic environments in the tropics are positively associated with forest litter decomposition by soil invertebrates. Our results demonstrate the significant difference in invertebrate effects on mediating forest litter decomposition between the tropics and elsewhere. We demonstrate, also, the significance of termites in driving litter mass loss in the tropics. These results are particularly pertinent in the tropics where climate change and human disturbance threaten soil invertebrate biodiversity and the ecosystem services it provides.

1. The Millennium Ecosystem Assessment assessed ecosystem change, human well-being and scientific evidence for sustainable use of biological systems. Despite intergovernmental acknowledgement of the problem, global ecological decline has continued, including declines in insect biodiversity, which has received much media attention in recent years. 2. Several roadmaps to averting biological declines have failed, due to various economic and political factors, and so biodiversity loss continues, driven by several interacting human pressures. Humans are innately linked with nature but tend to take it for granted. The benefits we gain from the insect world are broad, yet aversion or phobias of invertebrates are common, and stand firmly in the path of their successful conservation. 3. Providing an integrated synthesis for policy teams, conservation NGOs, academic researchers and those interested in public engagement, this article considers: (1) the lack of progress to preserve and protect insects. (2) Examples relating to insect decline and contributions insects make to people worldwide, and consequently what we stand to lose. (3) How to engage the public, governmental organisations and researchers through “insect contributions to people” to better address insect declines. 4. International political will has consistently acknowledged the existence of biodiversity decline, but apart from a few narrow cases of charismatic megafauna, little meaningful change has been achieved. Public values are reflected in political willpower, the progress being made across the world changing views on insects in the public should initiate a much-needed political sea-change, but only if we as entomologists enormously expand our engagement efforts.

1. The Tea Bag Index (Keuskamp et al. 2013) has been developed to allow worldwide comparable data on litter decomposition and has become an important part of several citizen science projects. This commentary shows that it is unsuitable for assessing total decomposition in most environments as it does not account for the role of macrofauna in the decomposition process. 2. Tea bags were placed following the standardised protocol in old growth forest in Borneo (Sabah, East Malaysia). 3. The results shows that more than half of the bags were attacked by termites and they tended to remove the majority of the tea, rendering the Tea Bag Index incalculable. 4. The Tea Bag Index can measure the microbial component of decay, but will significantly underestimate total decay rates in most environments. This method will not give an accurate estimate of decomposition in most biomes.