(Hong Kong – 23 May 2025) A newly published study by Kadoorie Farm and Botanic Garden (KFBG) reveals that native tree species respond differently to various environmental conditions and management interventions during the early stage of forest restoration, and that these responses change as the trees grow. The study was conducted at KFBG’s site in Hong Kong.

In 2013, almost 4,000 tree seedlings belonging to 12 different native species were planted in seven 20 m × 20 m restoration plots. These included Hog Plum (Choerospondias axillaris) and Bamboo-leaved Oak (Quercus neglecta). The seedlings were tended to with different management interventions to learn which factors work best, including the installation of different types of tree guards, the application of two types of fertiliser and the use of cardboard weeding mats. The researchers modelled topographic features of the site where each seedling was planted, including altitude, slope and aspect, and then measured the height and basal diameter of each seedling in 2014, 2015 and 2017. The relationships among these factors and their impacts on survival and growth rate were then analysed. Through this approach, it was possible to disentangle which individual factors, and which combination of factors, have the greatest influence on performance over the first four years of active restoration.

The results show that installing a tree guard around each seedling not only helps protect them from browsing by wild animals with a marked improvement in survival (which was still >86% four years after planting), but that the tree guards actually promote seedling growth over the first two years of establishment. Indeed, once the saplings grow out of the top of their tree guard (that is, about 90 cm tall), the growth rate of most species decreases. However, a few species, such as Formosa Privet (Ligustrum liukiuense), had a relatively constant growth rate and were not so sensitive to restoration methods, such as the use of tree guards. When all species are considered together, the various topographic features and restoration methods explain only a limited proportion of seedling survival and growth overall, but when each species is considered individually, these same factors have better explanatory power in terms of performance, and this explanatory power changes with species and at different growth stages.

Dr Stephan Gale, Head of the Flora Conservation Department at KFBG, who leads KFBG’s forest restoration programme, says: “Growing native tree species is a prerequisite for restoring healthy forests that are high in biodiversity and able to confer a host of ecological functions. However, the ecology and growth requirements of most native Hong Kong tree species are poorly understood. Deducing how forest structure forms, and how this promotes ecological function, is a complex but critical challenge in forest restoration. Moreover, as forest restoration takes time, manpower and resources, it is important to maintain focus and funding throughout. The systematic collection of data, in-depth analysis, interpretation of results, and contributing new knowledge to the scientific community all require a dedicated, professional research team.”

The lead and corresponding author of the study, Dr Jinlong Zhang, a Senior Ecologist in the Flora Conservation Department, says: “Forest restoration is not just about planting trees – it has to be done scientifically and through learning-by-doing, because ultimately human society requires biodiverse, functioning forests that offer ecosystem services, and this needs to be informed by ecological rules. The results of this study suggest that species diversity is critical in forest restoration. We need to understand the role of each species in forest restoration, especially in the process of community assembly. This study was mainly conducted at the individual tree level, but we will further explore at the macro scale, such as how climate, functional traits and evolutionary history affect species and communities undergoing restoration, allowing us to piece together how to optimise restoration outcomes.”

KFBG’s Flora Conservation Department launched its forest restoration project on its site on the northern slopes of Tai Mo Shan in 2013. Each year, more than 3,000 trees belonging to scores of native species are planted. All these seedlings are raised in KFBG’s nurseries. Since 2022, the project has been financially supported through funding from CLP Holdings Limited, with the aim of revitalising degraded tropical landscapes, recovering biodiversity and building a scientific understanding of the ecological rules that govern forest restoration. In recognition of its pioneering work in this field, KFBG became a regional hub of The Global Biodiversity Standard (TGBS) in 2024. This recently launched certification scheme sets forth a framework to ensure that native biodiversity and ecological function are placed front and foremost in ecological restoration, and that they remain key objectives throughout the restoration process via adaptive management. Several KFBG staff have become certified TGBS assessors and the organisation is now underway applying the methodology to become competent in assessing third-party restoration projects in Hong Kong and South China.

Further reading:
Zhang, J., Cardoso, F. C. G., Zhu, H., Cheuk, M. L., Fischer, G. A., & Gale, S. W. (2025). Temporal shifts in the importance of environmental factors and management interventions among species in the early stages of forest restoration. Journal of Forestry Research, 36(1), 56. https://doi.org/10.1007/s11676-025-01857-4