Closed-Canopy Tropical Forests of Hainan, (China) Are Resilient against Invasive Herbs and Shrubs

Xiaobo Yang,Long Li,Caiqun Liang,Donghai Li,Wenxing Long,Xiaobo Lv,Alison K S Wee,Wenqi Luo

doi:10.3390/f12111596

Abstract

The successful establishment of many plants in tropical forests often depends on species-specific adaptations related to light availability and forest successional stage. Species that are present in early successional stages generally do not occur in later successional stages. In this study, we documented the diversity, distribution, and abundance of terrestrial invasive plants across the (sub)tropical island of Hainan, China, and tested the germination of specific invasive plants in forested environments. In 97 transects positioned randomly across the island, we found nine invasive herb and shrub species were present in all human-modified habitats but not in intact forest interiors. In separate forest-specific transects, we documented a sharp drop in the abundance of invasive plants >5 m into the forest. High numbers of invasive plant seeds germinated from the soil seed bank sampled at the forest edge, but very few seeds germinated from soil sampled any distance into the forest. Finally, in experiments with four focal invasive plant species, overall germination rates were low; and much lower in shaded sites compared to full gap sites. In conclusion, our findings demonstrated that invasive herbs and shrubs do not yet form a serious threat to native species in the closed-canopy forests of Hainan.

Highlights

Biological invasions can have serious environmental and economic impacts (Dennis2004), for example through reduced forest productivity [1] and disrupted ecosystem services [2]
We investigated the presence of terrestrial invasive herbs and shrubs (TIHS) in habitats of various successional stages in order to determine the ecological barriers that prevent the establishment of TIHS
Several TIHS were found in all non-rain forest habitats (e.g., Co, Cs and Lc) and others were found in fewer habitats (e.g., Ap, Pf, and Ph)

Summary

Introduction

Biological invasions can have serious environmental and economic impacts (Dennis2004), for example through reduced forest productivity [1] and disrupted ecosystem services [2]. Biological invasions can have serious environmental and economic impacts Biological invasions may have positive impacts, including economic benefits from the introduction of new food sources for humans [3], improved soil microbial biomass and soil mineralization [4], and positive bottom-up effects on higher trophic levels [5]. Invasive species can have detrimental effects on the native flora, either directly via competition, or indirectly by altering soil chemistry [6], nutrient cycling [7], or community assembly [8]. The mechanisms of plant invasion largely involve two major hypotheses: one based on the invasive ability of the exotic species [9,10,11,12], and another based on the invasibility of the habitat [13,14].

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Methods

Discussion

Conclusion