Data from: Burning for enhanced non-timber forest product yield may jeopardize the resource base through interactive effects

Non-timber forest product (NTFP) harvest is frequently accompanied by resource management practices that interact with the harvesting itself, other disturbances and abiotic conditions. These interactions, in turn, lead to diverse environmental effects. Few studies focus on these practices in the context of harvesting NTFPs, product properties and environmental impacts, including biological invasions. In Pine woodlands in Eastern Bhutan, Cymbopogon flexuosus East Indian Lemon Grass is harvested and distilled to obtain essential oil, an economically important NTFP. Prescribed fires are applied in late winter (before annual harvest in summer) to induce regeneration of new tillers with increased essential oil content. This practice is based on local ecological knowledge and renders the utilization of C. flexuosus economically viable. On two sites with contrasting stand structure, we evaluated the effects of different prescribed burning regimes (no burning vs. burning with two levels of frequency and intensity) on the sustainability of annually harvested C. flexuosus, regarding cover, biomass yield, essential oil yield and quality. At the same time, we evaluated the effects of prescribed burning on the spread of the invasive shrub Chromolaena odorata. Cymbopogon flexuosus biomass declined over time, likely as a result of harvesting. In more closed stands, it was moreover marginally negatively influenced by fire. We confirmed local ecological knowledge regarding significantly higher essential oil yield on burned plots, without differences between fire regimes. In open stands, fire led to rapid expansion of C. odorata, specifically with frequently applied, higher intensity fires. Additionally, the spread of C. odorata showed adverse effects on C. flexuosus cover. Synthesis and applications. Our results highlight the importance of studying the wider impacts of non-timber forest product (NTFP) harvest. We confirmed local ecological knowledge that fire increases lemon grass essential oil yield, making prescribed burning an attractive land management tool for farmers. Nevertheless, the practice of annual harvesting may lead to resource decline that may be exacerbated by fire in closed stands. Caution needs to be practiced on open sites where invasive C. odorata may spread rapidly after fires. Management needs to focus on preventing concentration of annual harvesting and associated prescribed burning in the same areas. Amending national forestry rules to legalize fire as a land management tool can support local economies and potentially prevent wildfires that regularly devastate human infrastructure across eastern Bhutan.

非木材林产品（Non-timber Forest Product, NTFP）的采收活动往往伴随一系列资源管理措施，这些措施与采收行为、其他干扰因子及非生物环境条件相互交织作用。此类交互作用继而会引发多样的环境效应。目前鲜有研究围绕非木材林产品采收、产品特性及环境影响（涵盖生物入侵）展开相关管理措施的探讨。在不丹东部的松林群落中，人们采收香茅（Cymbopogon flexuosus，东印度柠檬草）并通过蒸馏获取精油——这是一类具备重要经济价值的非木材林产品。当地于每年夏季采收前的晚冬时节实施计划火烧（prescribed fire），以诱导新分蘖萌发并提升精油含量。该措施依托本土生态知识，让香茅的开发利用具备了经济可行性。我们在两个林分结构差异显著的样地中，评估了不同计划火烧制度（无火烧、两种不同频率与强度的火烧方案）对年度采收香茅可持续性的影响，评估指标包括盖度、生物量产量、精油产量与品质。与此同时，我们还探讨了计划火烧对入侵灌木飞机草（Chromolaena odorata）扩散过程的影响。研究发现，香茅生物量随时间推移逐渐下降，这大概率与采收活动有关；在林分更为郁闭的样地中，火烧还会对香茅产生轻微的负面影响。我们验证了本土生态知识：火烧样地的精油产量显著更高，且不同火烧制度间无显著差异。在林分开阔的样地中，火烧（尤其是高频高强度的火烧方案）会促使飞机草快速扩散。此外，飞机草的扩散还会对香茅盖度产生不利影响。综合与应用。本研究结果凸显了探究非木材林产品采收综合影响的重要性。我们证实了“火烧可提升柠檬草精油产量”的本土生态知识，这表明计划火烧是一项颇具吸引力的农户土地管理工具。不过，年度采收可能会导致资源衰减，在郁闭林分中该效应还会因火烧而进一步加剧。在林分开阔的样地需格外谨慎，因为火烧后入侵植物飞机草可能会快速扩散。相关管理措施应聚焦于避免在同一区域集中开展年度采收及配套的计划火烧。修订国家林业法规，将火烧合法化作为土地管理工具，可助力地方经济发展，并有望遏制不丹东部地区频繁摧毁人类基础设施的野火灾害。