Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.
Centre for Invasion Biology, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.
Glob Chang Biol. 2018 Jun;24(6):2597-2606. doi: 10.1111/gcb.14118. Epub 2018 Apr 10.
Woody encroachment can lead to a complete switch from open habitats to dense thickets, and has the potential to greatly alter the biodiversity and ecological functioning of grassy ecosystems across the globe. Plant litter decomposition is a critical ecosystem process fundamental to nutrient cycling and global carbon dynamics, yet little is known about how woody encroachment might alter this process. We compared grass decay rates of heavily encroached areas with adjacent nonencroached open areas in a semi-arid South African savanna using litterbags that allowed or excluded invertebrates. We also assessed the effect of woody encroachment on the activity of termites- dominant decomposer organisms in savanna systems. We found a significant reduction in decomposition rates within encroached areas, with litter taking twice as long to decay compared with open savanna areas. Moreover, invertebrates were more influential on grass decomposition in open areas and termite activity was substantially lower in encroached areas, particularly during the dry season when activity levels were reduced to almost zero. Our results suggest that woody encroachment created an unfavourable environment for invertebrates, and termites in particular, leading to decreased decomposition rates in these areas. We provide the first quantification of woody encroachment altering the functioning of African savanna ecosystems through the slowing of aboveground plant decomposition. Woody encroachment is intensifying across the globe, and our results suggest that substantial changes to the carbon balance and biodiversity of grassy biomes could occur.
木本植物入侵可能导致开阔生境完全转变为茂密灌丛，并有潜力极大地改变全球草地生态系统的生物多样性和生态功能。植物凋落物分解是一个关键的生态过程，对养分循环和全球碳动态至关重要，但人们对木本植物入侵如何改变这一过程知之甚少。我们使用允许或排除无脊椎动物的凋落物袋，比较了半干旱南非萨瓦纳严重入侵地区和相邻未入侵开阔地区的草类腐烂速度。我们还评估了木本植物入侵对白蚁——草原系统中主要分解者生物的活动的影响。我们发现，入侵区的分解速度显著降低，与开阔草原区相比，凋落物需要两倍的时间才能腐烂。此外，无脊椎动物在开阔地区对草类分解的影响更大，而在入侵地区白蚁的活动明显较低，特别是在活动水平降低到几乎为零的旱季。我们的研究结果表明，木本植物入侵为无脊椎动物，特别是白蚁，创造了一个不利的环境，导致这些地区的分解速度降低。我们首次量化了木本植物入侵通过减缓地上植物分解来改变非洲萨瓦纳生态系统的功能。木本植物入侵在全球范围内加剧，我们的研究结果表明，草地生物群落的碳平衡和生物多样性可能会发生重大变化。
