Changes in forest structure and composition after fire in tropical montane cloud forests near the Andean treeline

Background: In tropical montane cloud forests (TMCFs) fires can be a frequent source of disturbance near the treeline. Aims: To identify how forest structure and tree species composition change in response to fire and to identify fire-tolerant species, and determine which traits or characteristics are associated with fire tolerance. Methods: Shifts in forest structure and diversity were assessed on 15 paired plots in burnt and unburnt (control) forests, along a fire chronosequence. Species were classified as fire-sensitive, fire survivors or fire thrivers, using a fire tolerance index. Regression and tree analyses were used to determine which traits contributed to the fire tolerance of species. Results: There were more small- and medium-sized trees in the burnt plots independent of time since the last fire. There were shifts in family importance value and in species diversity among the plots. Of the 73 species analysed there were 39 fire-sensitive species, 19 fire survivors and 14 fire thrivers. Sprouting ability and biomass showed a positive relationship with the fire tolerance of species. Conclusions: There were immediate as well as long-term (up to 15 years) effects of fire on forest structure and species composition, suggesting that TMCFs take more than 15 years to regenerate from a fire. Long-term studies are needed to fully understand regeneration patterns of TMCFs after fires.背景：在热带山地云雾林（Tropical Montane Cloud Forests，TMCFs）中，林线附近的火灾往往是一种频发的干扰源。 研究目标：明确森林结构与乔木物种组成如何响应火灾发生变化，识别耐火物种，并确定哪些性状或特征与物种耐火性相关。 研究方法：沿火灾年代序列，在火烧与未火烧（对照）林分中设置15组配对样地，以此评估森林结构与物种多样性的变化。采用火灾耐性指数将物种划分为火敏感物种、火存活物种与火繁盛物种三类。通过回归分析与分类树分析，明确哪些性状对物种的耐火性具有贡献。 研究结果：无论末次火烧距今时长如何，火烧样地内的中小型乔木数量均显著多于对照样地。各样地的科重要值与物种多样性均发生显著变化。在所分析的73个物种中，39个为火敏感物种，19个为火存活物种，14个为火繁盛物种。物种的萌蘖能力与生物量与其耐火性呈显著正相关关系。 研究结论：火灾对森林结构与物种组成兼具短期与长期（最长可达15年）影响，这表明TMCFs在火烧后需要超过15年的时间才能完成植被恢复。未来需开展长期研究，以全面阐明TMCFs火烧后的植被恢复模式。