Ecosystem-scale impacts of non-timber forest product harvesting: effects on soil nutrients

1. The harvesting of non-timber forest products (NTFPs) is a global phenomenon, the sustainability of which has been studied for many species at the individual and population level. However, the broader scale impacts of NTFP harvesting have been acknowledged but rarely examined. 2. We assessed plant size and the soil attributes undercanopy and in the open, in replicate, paired harvested and non-harvested sites for three NTFPs differing in the extent of biomass removed, i.e. timber for firewood from a tree (Acacia karroo), fruits from a cactus (Opunita ficus-indica) and flowering culms from a grass (Cymbopogon marginatus). Soil variables tested included pH, resistivity, P, total N, nitrate nitrogen, ammonium nitrogen, K, Na, Ca and Mg. 3. The extent of loss of soil nutrients decreased across the three NTFPs relative to the proportion of biomass removed. Thus, significant differences in more soil variables were evident for the firewood species, least for the fruit species and intermediate for the grass species. Lower soil pH, P, C and K were evident in soils collected underneath A. karroo, whilst losses in cations of Na, Ca and Mg were reported in soils underneath C. marginatus, and only NO3N losses were recorded underneath O. ficus-indica. 4. Synthesis and applications. Our study reveals that whilst non-timber forest product (NTFP) harvesting may affect soil nutrients, this is not uniform between species and is likely to be a function of the extent of biomass removed and harvesting frequency. This indicates the need for caution in generalisations about the ecosystem-level impacts of NTFP harvesting as well as a concerted effort to better understand impacts at a greater range of scales than has been the case to date.09-Feb-2017

1. 非木材林产品（non-timber forest products, NTFPs）的采收是一种全球性现象，其可持续性已针对多个物种在个体与种群层面开展了大量研究。然而，非木材林产品采收的更大尺度影响虽已被学界认知，却极少得到系统性考察。2. 本研究针对三种生物量移除量存在差异的非木材林产品，在重复设置的成对采收样地与未采收样地中，分别测定了冠层下及开阔区域的植株大小与土壤属性。这三种产品分别为：取自乔木的薪柴用材（阿拉伯胶树Acacia karroo）、仙人掌的果实（Opunita ficus-indica）、以及禾本科植物的开花秆（亚香茅Cymbopogon marginatus）。本次测试的土壤变量涵盖pH值、电阻率、有效磷（P）、全氮（total N）、硝态氮（nitrate nitrogen）、铵态氮（ammonium nitrogen）、钾（K）、钠（Na）、钙（Ca）与镁（Mg）。3. 土壤养分的流失程度随三种非木材林产品的生物量移除占比呈递减趋势。具体而言，薪柴树种对应的土壤变量差异最为显著，果实树种的差异最小，禾本科植物则处于中间水平。阿拉伯胶树（A. karroo）冠层下的土壤表现出更低的pH值、有效磷、碳（C）与钾（K）含量；亚香茅（C. marginatus）冠层下的土壤出现了钠、钙、镁阳离子的流失；而仅梨果仙人掌（O. ficus-indica）冠层下的土壤记录到硝态氮（NO₃N）的流失。4. 综合与应用。本研究揭示：尽管非木材林产品（NTFP）采收可能会对土壤养分产生影响，但该影响因物种而异，且大概率取决于生物量移除程度与采收频率。这表明，在对非木材林产品采收的生态系统级影响进行概括性论断时需保持审慎，同时也需要协同开展更多研究，以在比以往更广的尺度范围内更好地理解其影响。2017年2月9日