1. Global change is expected to increase savanna woody encroachment as well as fire spreading into forest. Forest–savanna ecotones are the frontier of these processes and can thus either mitigate or enhance the effects of global change. However, the ecology of the forest–savanna ecotone is poorly understood. In this study, we determined whether a distinct ecotonal tree community existed between forest and savanna. We then evaluated whether the ecotonal tree community was more likely to facilitate fire spreading into the forest, woody encroachment of the savanna or the stabilisation of both forest and savanna parts of the landscape.
2. We sampled 28 vegetation transects across forest–savanna ecotones in a central African forest–savanna mosaic. We collected data on the size and species of all established (basal diameter >3 cm) trees in each transect. Split moving window dissimilarity analysis detected the location of borders delineating savanna, ecotone and forest tree communities. We assessed whether the ecotonal tree community was likely to facilitate fire spreading into the forest by burning experimental fires and evaluating shade and grass biomass along the transects. To decide whether the ecotone was likely to facilitate woody encroachment of the savanna, we evaluated if ecotonal tree species were forest pioneers.
3. A compositionally distinct and spatially extensive ecotonal tree community existed between forest and savanna. The ecotonal tree community did not promote fire spreading into forest and instead acted as a fire buffer, shading out flammable grass biomass from the understorey and protecting the forest from 95% of savanna fires. The ecotone helped stabilise the forest–savanna mosaic by allowing the fire‐dependant savanna to burn without exposing the fire‐sensitive forest to lethal temperatures.
4. The ecotonal tree community was comprised of many forest pioneer species that will promote woody encroachment in the savanna, especially if fire frequency is decreased.
5. Synthesis. A distinct fire‐buffering ecotonal tree community in this forest–savanna mosaic landscape illustrated that savanna fires are unlikely to compromise forest integrity. Conversely, suppression of fire in this landscape will likely lead to loss of savanna as the ecotone becomes the frontier of woody encroachment. Regular burning is essential for the preservation of this forest–savanna mosaic.

中文翻译：

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非洲中部森林-热带稀树草原过渡带存在一个独特的生态树木群落

1. 预计全球变化将增加热带稀树草原的侵占以及向森林蔓延的大火。森林大草原过渡带是这些过程的前沿，因此可以缓解或增强全球变化的影响。然而，人们对森林大草原过渡带的生态学知之甚少。在这项研究中，我们确定了森林和热带稀树草原之间是否存在独特的生态树木群落。然后，我们评估了生态树群落是否更可能促进火势蔓延到森林，大草原的木质侵蚀或景观的森林和大草原部分的稳定化。
2. 我们在非洲中部森林大草原马赛克中的森林大草原过渡带采样了28个植被样带。我们收集了每个横断面中所有已建立的（基径> 3 cm）树木的大小和种类的数据。分割移动窗口差异分析检测到了划定热带稀树草原，过渡带和林木群落边界的位置。我们评估了生态树木群落是否可能通过燃烧实验性大火并评估横断面的阴影和草类生物量来促进火势蔓延至森林。为了确定过渡带是否可能促进大草原的木质侵蚀，我们评估了过渡带树种是否是森林开拓者。
3. 在森林和热带稀树草原之间存在着组成独特且空间分布广泛的生态树木群落。生态树木社区并没有促进火势蔓延到森林中，而是充当了火的缓冲带，遮盖了地下层的易燃草类生物质，并保护了95％的热带稀树大火。过渡带通过使依赖火的稀树草原燃烧而不会使对火敏感的森林暴露于致命温度下，从而帮助稳定了森林大草原的镶嵌。
4. 生态树木群落由许多森林先驱物种组成，这些物种将促进热带草原上的木本性侵占，特别是在降低火频的情况下。
5. 综合。在这个森林大草原马赛克景观中，一个独特的防火生态树社区表明，大草原的大火不太可能损害森林的完整性。相反，随着过渡带成为木质侵占的前沿，在这一景观中抑制火势可能会导致稀树草原的损失。定期燃烧对于保护这种森林大草原马赛克至关重要。