Effects of Chromolaena odorata on mammalian biodiversity in Hluhluwe-iMfolozi Park, South Africa

This study investigated the effects of the Triffid weed Chromolaena odorata on small and large mammals in Hluhluwe-iMfolozi Park. C. odorata is a widespread invasive alien plant that poses threat to the highly maintained natural vegetation in HiP and most other protected areas in KwaZulu-Natal. Following the opinion that the effects of invasive alien plants on all levels of biodiversity need to be recognised for their effective control, we compared small and large mammal species richness and diversity between areas with differing C. odorata invasion durations, areas with differing clearing times and an area with no history of invasion as a control area. Small mammal trapping was done using Sherman live traps and mark-recapture techniques. Track counts were used to estimate large mammal species abundance, richness and diversity. The control area had higher small mammal species richness and diversity than the invaded areas, which suggests that invaded areas were not suitable habitats for small mammals. It was also found that small and large mammal species richness and diversity decreased with the increase in invasion duration, which shows that the more time C. odorata is left to establish the more disturbance it causes to the habitat. We found the uninvaded treatment to have the highest diversity of large mammal species than all the invaded treatments, which suggests that large mammalian species show some degree of avoidance to the invaded areas. We also found that there were significant differences between the treatments with regard to large mammal species diversity indices. Some of the large mammalian species appeared to neither avoid nor prefer invaded areas. It is hypothesized that they use invaded areas to hide away from predators as most of them fall prey to many carnivores. Also, C. odorata invaded areas could provide suitable shelter from climatic extremes. The treatments cleared of C. odorata showed an increase in both small and large mammalian species richness and diversity, suggesting that clearing of this plant helps in rehabilitation of the ecosystem. However, large mammal species composition in the cleared treatments remained different to pre-invasion state, which suggests that the habitat may remain changed for a long time after clearing. Managers of conservation areas should therefore prioritise alien plant removal in order to maintain healthy ecosystems.

本研究针对赫卢赫卢韦-印姆弗鲁兹公园（Hluhluwe-iMfolozi Park，简称HiP）内俗称魔鬼草（Triffid weed）的紫茎泽兰（Chromolaena odorata）对小型及大型哺乳动物的影响展开调查。紫茎泽兰是一种分布广泛的外来入侵植物，对该公园及夸祖鲁-纳塔尔省（KwaZulu-Natal）多数其他保护区内高度管护的自然植被构成威胁。鉴于学界普遍认为，需明确外来入侵植物对生物多样性各层级的影响方能实现有效防控，本研究对比了不同入侵时长、不同清除时长的紫茎泽兰入侵区域，以及无入侵历史的对照区域内的小型、大型哺乳动物物种丰富度与多样性。小型哺乳动物活捕采用谢尔曼活捕笼（Sherman live traps）结合标记重捕技术开展；大型哺乳动物调查则通过足迹计数法估算其物种丰度、丰富度与多样性。对照区域的小型哺乳动物物种丰富度与多样性均高于入侵区域，表明入侵区域并不适宜小型哺乳动物栖息。研究同时发现，小型、大型哺乳动物的物种丰富度与多样性随入侵时长增加而下降，这意味着紫茎泽兰定植时间越长，对栖息地的干扰越强。本研究发现，未入侵区域的大型哺乳动物物种多样性高于所有入侵处理区域，提示大型哺乳动物对入侵区域存在一定程度的回避行为。此外，不同处理组间的大型哺乳动物物种多样性指数存在显著差异。部分大型哺乳动物物种既未表现出对入侵区域的回避，也未表现出偏好，推测它们或利用入侵区域躲避天敌——这类物种多为多种食肉动物的猎物。同时，紫茎泽兰入侵区域或可提供遮蔽，帮助动物抵御极端气候。经紫茎泽兰清除的处理区域，其小型、大型哺乳动物的物种丰富度与多样性均有所提升，表明清除该入侵植物有助于生态系统的修复。但需注意的是，清除处理区域的大型哺乳动物物种组成仍与入侵前状态存在差异，提示栖息地在清除入侵植物后可能长期处于改变状态。因此，保护区管理者应优先开展外来植物清除工作，以维持健康的生态系统。