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，也是世界上面积最大的热带稀树草原。该生物群系被认为是世界生物多样性热点b[2]，在巴西b[3]的水文中起着重要作用。然而，尽管塞拉多具有重要的生态意义，但自20世纪70年代以来，超过50%的塞拉多已经转变为农业用地。稀树草原是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、环境和人为因素塑造了火灾制度，对生物多样性和生物地球化学循环产生潜在影响，并产生重要的社会经济后果[5,6]。特别是，人类主要通过制造火源、破坏生态系统或采取灭火政策来改造火灾制度。此外，土地利用扩张还可能通过改变与森林砍伐和植被替代相关的当地气候和水文条件间接影响火灾。最近在南部非洲进行的研究表明，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，而人类活动水平的不同可能解释了在不同地区观察到的不同趋势的燃烧面积大小[6,9]。遥感技术被广泛用于研究火情，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。在巴西大草原，利用卫星数据的研究通过使用全球燃烧面积产品[5,11]或创建自己的数据集[12,13]来描述火灾动态的不同方面。然而，这些调查只关注火灾模式与气候驱动因素之间的关系，而没有考虑土地利用的影响。此外，这些研究要么覆盖较短的时间，可能会妨碍对年际变化趋势的确定，要么覆盖较长的时间，但仅限于塞拉多的特定地区。在接下来的几十年里，这些大草原地区的农业扩张预计将继续应对全球对肉类和农作物的需求。同时，随着气候变化的进展，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，了解火灾制度、人为活动和气候相互作用如何影响这些稀树大草原，为土地管理实践、土地法规和保护政策提供信息至关重要。我的目标是研究塞拉多的火灾制度及其与人为和气候驱动因素的关系，以了解和预测它们可能在不断增加的土地利用压力和气候变化下演变。我打算研究这些过程的整个热带稀树草原跨越大部分时期的大规模农业扩张到现在。

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.