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首页> 外文期刊>Journal of South American earth sciences >Late Holocene vegetation and fire dynamics from a savanna-forest ecotone in Roraima state, northern Brazilian Amazon
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Late Holocene vegetation and fire dynamics from a savanna-forest ecotone in Roraima state, northern Brazilian Amazon

机译：巴西北部罗赖马州热带稀树草原过渡带的晚全新世植被和火势

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摘要

Two sediment cores from Mauritia flexuosa palm swamps have been studied by pollen and charcoal analysis. The cores Fazenda Cigana (FC) and Terra Indigena Aningal (TIA) were taken from a savanna-forest ecotone area in the Roraima State, northern Brazilian Amazon. Based on 5 radiocarbon dates, these records allow the reconstruction of the vegetation fire and climate dynamics during the past 1550 years. At the FC site was recorded a higher proportion of forest cover, suggesting local wetter climatic conditions favorable for forest expansion, especially by gallery forests, between 1550 and 1400 cal yr BP. Stands of M. flexuosa started to establish on the site indicating sufficient soil moisture. From 1400 to 1050 cal yr BP, forest cover retreated while savanna, and the Mauritia palm swamp expanded considerably. The FC site was marked by savanna and Mauritia cover with a slight increase of forest between ca. 1050 and 900 cal yr BP. From 900 to 300 cal yr BP the savanna and palm swamp taxa became dominant and the forest area decreased. At the TIA site the savanna cover was dominant between 1200 and 1000 cal yr BP. From 1000 to 700 forest expanded while savanna and Mauritia palm swamp reduced. Between 700 and 300 cal yr BP savanna and Mauritia palm swamp increased and forest area decreased. The high amount of charred particles found in the sediments, indicate fires with a marked increase between 1400 to 1000 cal yr BP (FC site) and 700 to 300 cal yr BP (TIA site), and probably caused the retreat of forest cover during these two time intervals. The relatively lower fire activity after 300 cal yr BP until present-day favored the increase of forested area at both TIA and FC sites. The arrival of the European settler and the subsequent introduction of cattle, is suggested as the main reason for the decrease of fire in the study region. The results point the fire caused by indigenous people as the principal controlling factor for forest and savanna dynamics during the past 1550 years.
机译：通过花粉和木炭分析研究了柔毛毛棕榈树沼泽的两个沉积物核心。 Fazenda Cigana（FC）和Terra Indigena Aningal（TIA）的核心取自巴西亚马逊北部Roraima州的热带稀树草原交错带地区。这些记录基于5个放射性碳年代，可以重建过去1550年的植被火灾和气候动态。在FC现场记录到较高的森林覆盖率，这表明在BP（1550至1400 cal BP）之间，有利于森林扩张的局部潮湿气候条件，特别是长廊林。弯曲松毛虫的林分开始在该位置上生长，表明土壤水分充足。从1400到1050 cal BP年之间，大草原上的森林覆盖面积减少了，毛里蒂亚棕榈沼泽大大扩展了。 FC站点的特征是热带稀树草原和毛里蒂亚的覆盖，大约在两周之间森林略有增加。 1050和900 cal yr BP。从900到300 cal BP年，稀树草原和棕榈沼泽分类单元成为主要种群，森林面积减少。在TIA站点，在1200和1000 cal yr BP之间，热带稀树草原占主导地位。森林从1000扩大到700，而热带稀树草原和毛里蒂亚棕榈沼泽减少了。在700和300 cal年之间​​，BP大草原和毛里特里亚棕榈沼泽增加，森林面积减少。沉积物中发现大量烧焦的颗粒，表明大火在1400至1000 cal yr BP（FC站点）和700至300 cal yr BP（TIA站点）之间显着增加，并可能在此期间造成森林覆盖率的下降两个时间间隔。在300 cal BP之后直到今天相对较低的火灾活动有利于TIA和FC站点的森林面积增加。建议将欧洲定居者的到来以及随后引入的牛作为研究区域火势减少的主要原因。结果表明，在过去的1550年中，土著人民引发的大火是森林和热带稀树草原动态的主要控制因素。

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