Fuelwood sustainability revisited: integrating size structure and resprouting into a spatially realistic fuelshed model

Much concern has been expressed about the sustainability of fuelwood harvesting in Africa. Most models predict that demand will outstrip supply within a few decades, resulting in severe deforestation. However, despite substantial impacts of harvesting on woody vegetation structure, the ‘fuelwood crisis’ predicted since the 1970s has not materialized. We propose that this is at least partially because regeneration through coppicing has been poorly accounted for in most models.
We developed a local fuelwood model that is demographically and spatially explicit, and that incorporates coppice dynamics. The model simulates the dynamics of multiple stem size classes (seedling, sapling, pole and adult), the harvesting decisions of villagers based on fuelwood availability and village demand across the landscape. Importantly, we specify size-dependent coppice production of cut stems, and the probability of progression of coppice shoots into larger size classes, after accounting for self-thinning of shoots.
In general, our model projections for a rural South African savanna system suggest that current levels of harvesting (barring changes in human population size) are relatively sustainable. Declines in total woody biomass were predicted to be modest (˜20%), and the loss of intact stems of sapling size was predicted to be more than offset by increases in coppiced stems.
Synthesis and applications. The results from our local fuelwood model clearly demonstrate that the impact of deforestation and wood removal on tree populations and wood resources is strongly influenced by the resprouting ability of trees. This highlights the importance of considering coppice dynamics when assessing the sustainability of wood harvesting. Our model is not system specific, and can be transferred to other systems, with the relevant parameters and geographic information system layers specified. Because of the transferability of this model, it can help address key international concerns about deforestation and sustainable fuelwood management.

学界对非洲薪柴采伐的可持续性问题始终抱有高度关切。多数模型均预测，未来数十年内薪柴需求将超出供给，进而引发严重的森林砍伐。然而，尽管采伐活动已对木本植被结构造成显著影响，但自20世纪70年代起被持续预测的“薪柴危机”却始终未能成为现实。我们认为，这一现象至少部分源于多数模型未充分考量萌蘖更新（coppicing）过程。
我们研发了一款兼具人口统计学与空间显式特征的本地化薪柴模型，该模型纳入了萌蘖动态过程。该模型可模拟多个茎径级（幼苗、幼树、小径木与成树）的种群动态，同时刻画村民基于区域内薪柴可得性与村落需求做出的采伐决策。尤为关键的是，我们在模型中明确了采伐茎秆的径级依赖性萌蘖产量，以及在考量枝条自然稀疏后，萌蘖枝条晋升至更大径级的概率。
总体而言，针对南非乡村稀树草原系统的模型预测结果显示，若人类人口规模保持不变，当前的采伐水平具备相对可持续性。研究预测总木本生物量的降幅较为温和（约20%），而幼树完整茎秆的损失可通过萌蘖茎秆的增量得到超额补偿。
综合与应用。本本地化薪柴模型的研究结果清晰表明，森林砍伐与林木移除对树木种群及木材资源的影响，在很大程度上受树木萌蘖能力的调控。这凸显了在评估林木采伐可持续性时，考量萌蘖动态的重要性。本模型并非针对特定系统开发，在配置相关参数与地理信息系统（Geographic Information System, GIS）图层后，可推广应用至其他场景。鉴于该模型具备良好的可迁移性，其可为应对全球范围内关于森林砍伐与可持续薪柴管理的核心关切提供有力支撑。