Herbaceous vegetation responses to experimental fire in savannas and forests depend on biome and climate

Fire-vegetation feedbacks potentially maintain global savanna and forest distributions. Accordingly, vegetation in savanna and forest ecosystems should have differential responses to fire, but fire response data for herbaceous vegetation has yet to be synthesized across biomes. Here, we examined herbaceous vegetation responses to experimental fire at 30 sites spanning four continents. Across a variety of metrics, herbaceous vegetation increased in abundance where fire was applied, with larger responses to fire in wetter and in cooler and/or less seasonal systems. Compared to forests, savannas were associated with a 4.8 (±0.4) times larger difference in burned versus unburned herbaceous vegetation abundance. In particular, grass cover decreased with fire exclusion in savannas, largely via decreases in C4 grass cover, whereas changes in fire frequency had a relatively weak effect on grass cover in forests. These differential responses underscore the importance of fire for maintaining the ..., ,火-植被反馈（Fire-vegetation feedbacks）可能维持全球稀树草原与森林的分布格局。据此，稀树草原与森林生态系统中的植被对火的响应理应存在差异，但目前尚未有针对草本植被的火响应数据开展跨生物群系的整合研究。本研究依托覆盖四大洲的30个实验样地，探究了草本植被对受控火烧的响应特征。通过多类观测指标评估发现，实施火烧的样地内草本植被丰度显著提升，且在水分条件更优、气候更温和且/或季节波动较弱的生态系统中，草本植被对火烧的响应幅度更大。相较于森林生态系统，稀树草原生态系统中火烧与未火烧样地的草本植被丰度差值可达前者的4.8（±0.4）倍。具体而言，稀树草原生态系统中实施禁火措施后，草本盖度会出现下降，这一现象主要源于C4草本植物（C4 grass）盖度的降低；而在森林生态系统中，火烧频率的变化对草本盖度的影响相对微弱。上述差异化响应凸显了火在维持……过程中的重要意义。