Problems and Management of Acacia-Dominated Urban Forests on Man-Made Slopes in a Subtropical, High-Density City

Cody H Y Lee,Amos P K Tai,Derrick Y F Lai,Kathy T K Ng,Sandy C S Tong,Alan S L Leung,Felix Leung,Simon S M Leung,Donald K C Tao,Alvin M C Tang,Charis Wu

doi:10.3390/f12030323

Cody H Y Lee, Amos P K Tai + Show 9 more

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https://doi.org/10.3390/f12030323

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Abstract

Acacia spp. are exotic tree species that have been widely planted on man-made slopes in Hong Kong since the 1960s. However, as they become mature and senescent, they may become a concern and cause various problems, including soil constraints for plant growth, decreasing provision of intended ecosystem services, declining syndromes, arrested succession, and high risk of failure. In this perspective paper, we present and discuss these problems using practical examples of Acacia-dominated urban forests on man-made roadside slopes in Hong Kong, based on a cross-disciplinary survey and a literature review. To conclude, we suggest that selective cutting, specific silvicultural operations of Acacia plantations, and the management of plantation edge and soils can be exercised, along with the planting of native species, to potentially alleviate these problems associated with mature Acacia plantations, by promoting the establishment of native forests, enhancing biodiversity, expediting succession, and providing better ecosystem services.

Highlights

Acacia species (Fabaceae), including A. confusa, A. mangium and A. auriculiformis, have been extensively planted in Hong Kong, China since the 1960s
It has been shown that the litter of Acacia longifolia had relatively slow decomposition rate, in spite of a high nitrogen content and low carbon to nitrogen ratio, which would contribute to the accumulation of nitrogen-rich litter on the soil surface [24]
We evaluated the ecosystem services provided by the Acacia plantations as well as some neighboring species in terms of mitigating climate change and air pollution, which are significant concerns in Hong Kong

Summary

Introduction

Acacia species (Fabaceae), including A. confusa, A. mangium and A. auriculiformis, have been extensively planted in Hong Kong, China since the 1960s They were used as pioneer tree species for large-scale reforestation of hillside, man-made slopes and other natural terrains [1]. As a species native to Taiwan and the Philippines, Acacia confusa (Taiwan Acacia) has been widely applied and planted in places outside its native range since it grows very well on dry, infertile or rough lands. This pioneer species can quickly establish vegetation cover, prevent soil erosion, stabilize slopes, and prevent landslides [5,6,7,8]. This means that they are tolerant to nutrient-deficient environments, rendering it one of the best candidates for landscape treatment on engineered slopes in the past

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