Vegetation and hydrology changes in Eastern Amazonia inferred from a pollen record

Toledo, Mauro Bevilacqua de; Bush, Mark B.

doi:10.1590/s0001-37652008000100014

Cited by 17 publications

(4 citation statements)

References 40 publications

(13 reference statements)

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“…While ∆δ 18 O values are stable near zero for much of the early-to-middle Holocene, independent proxy evidence from western Amazonia indicates precipitation was decreasing during this time [24,23,68,131,77,76,132]. Thus, the ∆δ 18 O record may not fully reflect the trends in precipitation through the Holocene due to ∆δ 18 O being insensitive to precipitation at the hydrostat.…”

Section: Oxygen Isotope Gradient Reconstructionmentioning

confidence: 99%

The resilience of Amazon tree cover to past and present drying

Kukla

Ahlström

Maezumi

et al. 2021

Global and Planetary Change

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The Amazon forest is increasingly vulnerable to dieback and encroachment of grasslands and agricultural fields. Threats to these forested ecosystems include drying, deforestation, and fire, but feedbacks among these make it difficult to determine their relative importance. Here, we reconstruct the central and western Amazon tree cover response to aridity and fire in the mid-Holocene-a time of less intensive human land use and markedly drier conditions than today-to assess the resilience of tree cover to drying and the strength of vegetation-climate feedbacks. We use pollen, charcoal, and speleothem oxygen isotope proxy data to show that Amazon tree cover in the mid-Holocene was resilient to drying in excess of the driest bias-corrected future precipitation projections. Experiments with a dynamic global vegetation model (LPJ-GUESS) suggest tree cover resilience may be owed to weak feedbacks that act to amplify tree cover loss with drying. We also compare these results to observational data and find that, under limited human interference, modern tree cover is likely similarly resilient to mid-Holocene levels of aridification. Our results suggest human-driven fire and deforestation likely

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Section: Oxygen Isotope Gradient Reconstructionmentioning

confidence: 99%

The resilience of Amazon tree cover to past and present drying

Kukla

Ahlström

Maezumi

et al. 2021

Global and Planetary Change

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“…This index takes into account the abundance of each species and is used to characterize the diversity of assemblages. To estimate the degree of species turnover, Detrended Correspondence Analysis (DCA) (Hill 1975) was performed using PAST (Hammer et al 2008), based on the explanation of Toledo & Bush (2008). The matrix used included taxa with percentage values, and sample scores from axis 1 were plotted against sample depths (cm).…”

Section: Collected Corementioning

confidence: 99%

Palynological evidence of vegetation change during the last 10,000 years in the mid-valley of the Rio Doce, Brazil

2019

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In order to reconstruct the vegetation history of the last 10.000 years, palynological analyses were carried out using 17 sedimentary samples of a core drilled in Parque Estadual do Rio Doce (PERD-MG). Twenty-one species of fern spores, 52 species of pollen grains and six species of fungi were identified. Phase 1 (10.375-9.350 cal. years BP) is characterized by a low concentration and diversity of pollen grains and is thus interpreted as a fluvial system with the presence of coarse-grained sediments. Phase 2 (9.062-8.195 cal. Years BP) is interpreted as a transition from a fluvial to lacustrine environment. Phase 3 (7.905-4.785 cal years BP) is characterized by increased trend of palynomorph concentration, highlighted by a high abundance and diversity of fern spores, which are indicative of a more a humid condition. The uppermost phase, Phase 4 (4.785-50 cal. Years AP), possessed a lower abundance of herbaceous flora, which is replaced by other vegetation groups (e.g. marsh, cerrado, Atlantic Forest). The uppermost sample represents the contemporary environment (~50 years), which is characterized as seasonally-flooded.

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“…Palaeoenvironmental variation indicated by changes in vegetation are generally reported from pollen assemblages [40,41]. Some studies have demonstrated that the concentration of long chain n-alkanes (C 27 , C 29 and C 31 ) coincides well with pollen information in the same sequence [42,43,15].…”

Section: Environmental Significance Of N-alkane Variationmentioning

confidence: 99%

Effect of the Little Ice Age on Climate and Vegetation Recorded by n-Alkanes and Glycerol Dialkyl Glycerol Tetraether Proxies

Machado¹,

Froehnerb²

2015

J Earth Sci Clim Change

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Keywords: Climatic changes; Little ice age; n-Alkane distributions; GDGT proxies IntroductionThe period which was subjected to much colder winters followed by warmer periods is known as the little ice age (LIA). It documented as being between about 1300 and 1870 (Mann, 2002). However, climate change could vary geographically [1]. The period is divided into two phases; the first was around 1300 until the late 1400s and the second warmer period was in in the 1500s [2]. The period between 1600 and 1850 marks its height and was characterized by changes in the hydrological cycle and perturbation of the ecosystem [2-4].Even although there much evidence for the LIA, the causes and mechanism are still under debate. The only certainty is that it was a global event. Most studies have focused on the northern hemisphere [3][4][5], and there are few studies demonstrating the occurrence of the event in the southern hemisphere. For instance, in South America [6,7], advance in glaciers in the Andes was demonstrated [8], as well as aridity in the lowlands of Argentina [9] and Venezuela [8], and there is evidence from mountain glaciers suggesting increasing glaciation in Patagonia [10]. In Brazil, some studies have demonstrated change in vegetation composition during the LIA and sea level regression in northeastern and southeastern Brazil [11][12][13].At present, paleoclimate can be reconstructed due the widespread occurrence of biomarkers multi-proxy data derived from them. The spatial and temporal character of such putative climate epochs revived the discussion and understanding of and mechanism for the LIA, as well as of the implications for climate change in the future.Typically, n-alkanes are derived from different sources (algae, photosynthetic bacteria and higher plants [14]. Different distribution patterns of n-alkanes in sediments provides information about different climatic environments and hence is widely used to understand the evolution of vegetation and reconstruct environmental changes [14,15]. The magnitude of the anthropogenic impact on the climate and the environment was recently measured from biomarker distributions [4,14]. Yet, some biomarkers can be more specific in their information than n-alkanes. For example, increasing attention has been driven to glycerol dialkyl glycerol tetraether (GDGT) compounds, polar basic constituents of the cell membrane and comprising a polar head group bonded to a non-polar hydrocarbon [16]. The structures of GDGTs are temperature dependent. When temperature increases, cyclopentane moieties are formed within the isoprenoid chain [17]. With more cyclopentane rings, the membrane is kept in a liquid crystalline state and, as a consequence, proton permeation is reduced.According to Weijers et al. [18] there are some environmental controls on the distributions of GDGTs, so two indices were proposed for quantifying the degree of methylation (MBT) and cyclization (CBT), both being effective in palaeoenvironmental studies to reconstruct mean annual air temperature (MAAT). Since branche...

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Vegetation and hydrology changes in Eastern Amazonia inferred from a pollen record

Cited by 17 publications

References 40 publications

The resilience of Amazon tree cover to past and present drying

The resilience of Amazon tree cover to past and present drying

Palynological evidence of vegetation change during the last 10,000 years in the mid-valley of the Rio Doce, Brazil

Effect of the Little Ice Age on Climate and Vegetation Recorded by n-Alkanes and Glycerol Dialkyl Glycerol Tetraether Proxies

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