Corridors promote fire via connectivity and edge effects

Landscape corridors, strips of habitat that connect otherwise isolated
habitat patches, are commonly employed during management of fragmented
landscapes. To date, most reported effects of corridors have been
positive; however, there are long-standing concerns that corridors may
have unintended consequences. Here, we address concerns over whether
corridors promote propagation of disturbances such as fire. We
collected data during prescribed fires in the world's largest and best
replicated corridor experiment (Savannah River Site, South Carolina,
USA), six ca. 50-ha landscapes of open (shrubby/herbaceous) habitat
within a pine plantation matrix, to test several mechanisms for how
corridors might influence fire. Corridors altered patterns of fire
temperature through a direct connectivity effect and an indirect edge
effect. The connectivity effect was independent of fuel levels and was
consistent with a hypothesized wind-driven "bellows effect."
Edges, a consequence of corridor implementation, elevated leaf litter
(fuel) input from matrix pine trees, which in turn increased fire
temperatures. We found no evidence for corridors or edges impacting
patterns of fire spread: plots across all landscape positions burned
with similar probability. Impacts of edges and connectivity on fire
temperature led to changes in vegetation: hotter-burning plots
supported higher bunch grass cover during the field season after
burning, suggesting implications for woody/herbaceous species
coexistence. To our knowledge, this represents the first experimental
evidence that corridors can modify landscape-scale patterns of fire
intensity. Corridor impacts on fire should be carefully considered
during landscape management, both in the context of how corridors
connect or break distributions of fuels and the desired role of fire
as a disturbance, which may range from a management tool to an agent
to be suppressed. In our focal ecosystem, longleaf pine woodland,
corridors might provide a previously unrecognized benefit during
prescribed burning activities, by promoting fire intensity, which may
assist in promoting plant biodiversity.

景观连通廊道（landscape corridor），即用以连接原本孤立生境斑块（habitat patch）的生境条带，在破碎化景观（fragmented landscape）的管理工作中被广泛应用。迄今为止，学界已报道的廊道效应多为正向，但长期以来仍存在担忧：廊道可能引发非预期的后果。本研究针对廊道是否会促进火灾等干扰事件的扩散这一疑问展开探讨。我们依托全球规模最大、重复实验设计最完善的廊道研究平台——美国南卡罗来纳州萨瓦纳河站点（Savannah River Site）开展野外实验，在由人工松林景观基质环绕的6块约50公顷的开阔（灌丛/草本）生境景观中，通过控制性火烧（prescribed fire）收集数据，以验证廊道影响火灾过程的多种潜在机制。廊道通过两种效应改变了火灾温度的空间分布模式：直接连通效应与间接边缘效应。连通效应不受可燃物载量（fuel levels）的影响，且与学界提出的风力驱动"风箱效应"（bellows effect）假说相符。廊道建设所形成的边缘生境，会提升来自周边松林基质的凋落物（fuel）输入量，进而推高火灾温度。本研究未发现廊道或边缘生境对火灾蔓延模式产生影响的证据：所有景观位置的样地均以相近的概率发生燃烧。边缘效应与连通效应对火灾温度的影响进一步改变了植被群落结构：火烧后首个野外监测季内，火势更强的样地中丛生草本（bunch grass）的盖度更高，这一结果暗示廊道效应对木本/草本物种的共存过程具有潜在调控作用。据我们所知，本研究首次通过实验证实，廊道能够改变景观尺度下的火灾强度分布模式。在景观管理工作中，需审慎考量廊道对火灾过程的影响——既要关注廊道如何连接或割裂可燃物的空间分布，也要明确火灾作为干扰因子的预期功能定位：其既可能作为管理工具被加以利用，也可能成为需要被抑制的干扰源。在本研究聚焦的长叶松（longleaf pine）林地生态系统中，廊道可通过提升火灾强度，在控制性火烧作业中发挥此前未被认知的积极作用，进而助力植物生物多样性的维持与提升。