The evolution of the Brazilian savannahs' fire regimes under large-scale land use expansion and climate change

巴西塞拉多是南美洲第二大生物群落区，也是世界上最广泛的热带萨凡纳[1]。该生物群落被认为是世界生物多样性热点[2]，在巴西的水文学中发挥着重要作用[3]。然而，尽管它的生态重要性，自1970年以来，塞拉多的50%已被转化为农业用地[3]。稀树草原是一种适应火灾的生态系统，其功能和连续性依赖于这种自然干扰[1，4]。一系列气候，环境和生物成因因素形成了对生物多样性和地球化学循环具有潜在影响的火灾制度，以及重要的社会经济后果[5，6]。特别是，人类主要通过点火、破坏生态系统或采取灭火政策来改变火灾状况[7]。此外，土地利用扩张也可能通过与森林砍伐和植被替代相关的当地气候和水文条件的改变间接影响火灾[8]。最近在南部非洲的研究表明，不同的火灾活动驱动因素可能在不同的时间和空间尺度上占主导地位，不同的人类存在水平可能解释了在不同地区观察到的烧毁面积大小的相反趋势[6，9].遥感技术被广泛用于研究火灾状况，因为它们可以提供比实地研究或政府机构通常提供的更大的时间和空间覆盖范围[10]。在巴西热带草原，使用卫星数据的研究已经描述了火灾动态的不同方面，例如全球烧毁面积产品[5]，或者说，自己的作品。然而，这些调查仅关注火灾模式和气候驱动因素之间的关系，而没有研究土地利用的影响。此外，这些研究要么覆盖的时间较短，可能会阻碍对年际变化趋势的识别[9]，要么覆盖的时间较长，但仅限于塞拉多的特定地区。在未来几十年，预计这些稀树草原的农业扩张将继续响应全球对肉类和农作物的需求[3]。同时，随着气候变化的发展，干旱和热浪等极端事件可能会变得更加频繁。考虑到塞拉多的重要性，了解火机制、植被活动和气候如何相互作用并影响这些稀树草原，以告知土地管理做法、土地法规和保护政策是至关重要的。我的目标是研究塞拉多的火机制及其与人为和气候驱动因素的关系，以了解和预测它们在不断增加的土地利用压力和气候变化下可能如何演变。我打算研究这些热带稀树大草原的整个过程，这些过程跨越了大规模农业扩张到现在的大部分时期。

The BrazilianCerrado is the second largest biome in South America and the most extensive tropical savannah of the world[1]. Thisbiome is considered a world biodiversity hotspot [2]and plays an important role in the hydrology of Brazil[3]. However, despite its ecological importance,since the 1970sover 50% of the Cerrado has been transformed to agricultural lands[3]. Savannahs are fire-adapted ecosystems that dependon this natural disturbanceagentfor their functioning and continuity[1, 4].A range of climatic, environmental and anthropogenicfactorsshape fire regimes with potentialimpacts onbiodiversityandbiogeochemical cycles, andimportant socioeconomic consequences[5, 6]. In particular, humansmodify fire regimes primarily through the creation of ignitions, the fragmentation of ecosystems or the adoption of fire-suppression policies[7]. Furthermore, land-use expansion may also indirectly affect firesthrough the modification of local climatic and hydrological conditions associated to deforestation and vegetation substitution[8].Recent studiesin SouthernAfricasuggest that differentdrivers of fireactivitymay predominate at different temporal and spatial scalesand thatdiffering levels ofhuman presencemay explain the opposing trendsin burned area sizeobserved in different regions[6, 9].Remote sensing techniques are widely used to study fire regimesas they can offer larger temporal and spatial coverage than is often available from field studies or government agencies[10].In the Brazilian savannahs, studies usingsatellite datahave characterised different aspects of thefire dynamicsusingglobal burned area products[5, 11]or creatingtheir own datasets[12, 13]. However, these investigationsonly focus onrelations between firepatterns andclimatic drivers and do not considerland-use effects. In addition, either these studiescover short time periods, potentially hampering the identification of trends against inter-annual variability[9],or they cover longer periods but are restricted to specific areas of the Cerrado.In the next decades, agricultural expansionin these savannahsis expected to continuein responsetoglobal demand for meat and crops[3]. Simultaneously, as climate change progresses, extreme events like droughts and heatwaves may become more frequent. Considering the importance of the Cerrado,it is crucial to understand how fire regimes, anthropogenicactivities and the climate interactand affect these savannahs to inform land management practices, land regulationsand conservation policies.I aim to study Cerrado's fire regimes and their relation with anthropogenic and climatic drivers to understandand predicthow they may evolve under increasing land use pressure and climate change. I intend to study these processes for the entirety of these tropical savannahs spanning most of the period of large-scale agricultural expansion to present.