Invasive grasses are a threat to some tropical savannas, but despite being fire-prone ecosystems, little is known about the relationships between fire season, climatic conditions and invasive species on these systems. We evaluated the response of the perennial invasive grasses Melinis minutiflora and Urochloa brizantha to three fire seasons in an open tropical savanna in South America: Early-Dry (May), Mid-Dry (July) and Late-Dry (October) in relation to unburned Controls. Moreover, we investigated how these responses were influenced by precipitation and extreme air temperatures. We hypothesized that biomass of both species would be reduced by fires during their reproductive period and that climatic conditions would affect them equally. We conducted prescribed burns on 15 × 15 m plots (4 plots x 4 treatment x 2 invasive species = 32 plots) in 2014. We sampled the biomass before the burn experiments and for the next two years (five 0.25 m² samples/plot). Our experiments revealed that the fire season did not influence the abundance of either species. However, the two species responded differently to fire occurrence: M. minutiflora decreased whereas U. brizantha was not affected by fires. Early-Dry and Late-Dry fire treatments enhanced the replacement of M. minutiflora by U. brizantha. We found that the influence of precipitation depended on the species: it reduced M. minutiflora but increased U. brizantha abundance. Lower monthly minimum temperatures decreased the abundance of both species. It directly reduced live M. minutiflora and increased dead U. brizantha biomass. Monthly maximum temperatures affected the invasive grasses by reducing live M. minutiflora. Since tropical savannas are predicted to face climatic instability and that climate influences the differential response of invasive species, the management of invaders should consider both the identity of the target species and the possible interactions with other invasive species. Moreover, it is essential to keep an adaptive management approach to face the uncertainties that climate change may pose to biodiversity conservation.

入侵性草种对某些热带稀树草原构成威胁，但尽管它们是易火的生态系统，但对于这些系统上的火灾季节，气候条件和入侵物种之间的关系知之甚少。我们评估了多年生入侵草Melinis minutiflora和Urochloa brizantha的响应南美开放热带稀树草原的三个火灾季节：相对于未燃烧的对照，早干（5月），中干（7月）和晚干（10月）。此外，我们调查了这些响应如何受到降水和极端气温的影响。我们假设两种物种的生物量在繁殖期都会因火灾而减少，而气候条件会同样影响它们。2014年，我们对15×15 m地块（4块地块x 4处理x 2入侵物种= 32块地块）进行了规定的燃烧。我们在燃烧实验之前和接下来的两年中对生物量进行了采样（五个0.25 m ²样本/地块） 。我们的实验表明，火灾季节不会影响任何一个物种的丰度。但是，这两种物种对火灾的反应不同：M. minutiflora减少，而U. brizantha不受火灾影响。早期干和晚期干火处理提高了更换M.糖蜜由U. brizantha。我们发现降水的影响取决于物种：减少了M. minutiflora但增加了U. brizantha的丰度。较低的每月最低温度降低了这两个物种的丰度。它直接减少了活产的M. minutiflora，增加了死去的U. brizantha生物量。每月最高温度通过减少活的M. minutiflora影响入侵草。由于预计热带稀树草原将面临气候不稳定，气候会影响入侵物种的差异响应，因此入侵者的管理应既考虑目标物种的身份，也应考虑与其他入侵物种的可能相互作用。此外，保持适应性管理方法以应对气候变化可能对生物多样性保护造成的不确定性至关重要。