In grasslands worldwide, modified fire cycles are accelerating herbaceous species extinctions. Fire may avert population declines by increasing survival, reproduction, or both. Survival and growth after fires may be promoted by removal of competitors or biomass and increasing resource availability. Fire-stimulated reproduction may also contribute to population growth through bolstered recruitment. We quantified these influences of fire on population dynamics in Echinacea angustifolia, a perennial forb in North American tallgrass prairie. We first used four datasets, 7–21 years long, to estimate fire’s influences on survival, flowering, and recruitment. We then used matrix projection models to estimate growth rates across several burn frequencies in five populations, each with one to four burns over 15 years. Finally, we estimated the contribution of fire-induced changes in each vital rate to changes in population growth. Population growth rates generally increased with burning. The demographic process underpinning these increases depended on juvenile survival. In populations with high juvenile survival, fire-induced increases in seedling recruitment and juvenile survival enhanced population growth. However, in populations with low juvenile survival, small changes in adult survival drove growth rate changes. Regardless of burn frequencies, our models suggest populations are declining and that recruitment and juvenile survival critically influence population response to fire. However, crucially, increased seedling recruitment only increases population growth rates when enough new recruits reach reproductive maturity. The importance of recruitment and juvenile survival is especially relevant for small populations in fragmented habitats subject to mate-limiting Allee effects and inbreeding depression, which reduce recruitment and survival, respectively.

在世界各地的草原上，改良的火循环正在加速草本物种的灭绝。火可以通过提高生存率、繁殖率或两者兼而有之来避免人口下降。消除竞争者或生物质并增加资源可用性可以促进火灾后的生存和增长。火刺激的繁殖也可能通过加强招募来促进人口增长。我们量化了火对狭叶紫锥菊种群动态的这些影响，北美高草草原的多年生草本植物。我们首先使用了 7-21 年的四个数据集来估计火灾对生存、开花和补充的影响。然后，我们使用矩阵预测模型来估计五个人群中几个烧伤频率的增长率，每个人在 15 年内都有一到四次烧伤。最后，我们估计了火灾引起的每个生命率变化对人口增长变化的贡献。人口增长率通常随着燃烧而增加。支持这些增长的人口统计过程取决于青少年的生存。在幼鱼存活率高的种群中，火引起的幼苗补充和幼鱼存活增加促进了种群增长。然而，在幼鱼存活率低的人群中，成鱼存活率的微小变化推动了增长率的变化。无论燃烧频率如何，我们的模型表明种群数量正在下降，招募和幼体存活率严重影响种群对火灾的反应。然而，至关重要的是，当足够多的新招募达到生殖成熟时，增加幼苗招募只会增加人口增长率。招募和幼鱼生存的重要性与支离破碎栖息地中的小种群尤其相关，这些栖息地受到限制交配的 Allee 效应和近亲繁殖抑制，这分别降低了招募和存活。