The aim of this thesis was to provide insight into past human activities in Amazonia, and the long-term forest recovery that followed, using phytolith analysis. The first part of this thesis focused on improving phytolith analysis as a proxy for vegetation changes in Amazonia. The morphological variation of 24 Amazonian palm phytoliths were assessed (Chapter 2) to improve the taxonomic resolution of palm phytolith identification, and results indicate the potential to differentiate Euterpe, Bactris, Oenocarpus, Attalea, Iriartea deltoidea, and Socratea exorrhiza. Chapter 3 demonstrated that phytolith assemblages (from terrestrial soil cores) varied across a gradient of (modern) human disturbance in Surinamese rainforests. In Chapters 4-6, we developed beta regression and GLM models to predict forest cover and biomass changes within 200 m and 1 km of Amazonian lakes, respectively, using grass phytoliths. Applying these innovations in Chapters 5-6 demonstrated that past human activities were on localized scales in Suriname and temporally heterogenous in Ecuador. Palm enrichment of Attalea, Oenocarpus and Astrocaryum occurred within 0 km, 1 km, and 8 km of an archaeological site in Suriname (Chapter 5). In Ecuador, forest cover and biomass ranged between 48-84% and 77-247 Mg/ha, respectively, and the largest decreases (between 1000-1255 CE) were paired with fires (Chapter 6). Overall, the type, intensity, timing, and frequency of disturbances are important factors influencing long-term forest recovery and ecological legacies in Amazonia.
In this article I summarize and describe the scientific research that was performed near Botopasi in Suriname, which was published in Ecology as ‘Pre-contact and post-colonial ecological legacies shape Surinamese rainforests’ (https://doi.org/10.1002/ecy.4272).
Figure 1: Our research team in the field
Background
In October 2021, between COVID-19 restrictions, I joined archaeologist dr. Cheryl White and her team to excavate the remnants of a ‘lost village’ of Saamaka Maroons in the Surinamese rainforest. Maroons are the descendants of enslaved Africans, who, in the late 1600s, fled plantations to live in freedom in the Surinamese rainforests. Dr. White has been investigating the first villages and the movements of Suriname’s Maroon communities for decades and is an expert in this topic.
Our wonderful research team consisted of Farisha Kartosemito B.Sc., Sushmeeta Ganesh B.Sc., Jõvan Samson B.Sc., Agir Axwijk B.Sc., Santosh Singh M.A., Thanya Fonkel MPA, Harrold Sijlbing, Dombi Lö, Gerno Eduards & Farik Eduards. We were welcomed in the village Botopasi, and after a day of hard work in the field, we enjoyed delicious Surinamese food and played troefcall!
As an ecologist, I was interested in the ecological effects of past human activities on the forest ecosystem. In these rainforests, Maroon and Indigenous communities often burn and remove trees near their homes to grow a variety of crops like cassava, tayer, maize and banana. After some years, the cultivation site is abandoned and forests can grow back. But do those forests recover back to their original state?
What did the forest look like before people arrived and settled in the landscape of Boven Suriname?
To study how Maroon communities have shaped Surinamese forests over time, I made a reconstruction of the landscape of the past (going back thousands of years). The landscape was near an archaeological sites called ‘Beng Tau’, where Maroons lived in the 17th century. We used plant fossils and charcoal remains to reconstruct the forest from the past, to research if people were using fire and growing crops, and how the forests recovered from that.
Results and implications
Figure 2: Phytoliths from the banana plant
The charcoal remains and plant fossils, particularly from maize and banana, confirmed Saamaka Maroons settled in the area since ca. 1700 and practiced slash-and-burn agriculture was near the archaeological site called ‘Beng Tapu’ (Figure 2). The site may have been a cooking area, because remnants of pottery with maize, rice and banana were found. Within 1 km of Beng Tapu, we found large fragments of charcoal, and plant fossils from maize and banana. Smaller charcoal fragments and banana were found within 5 km of the archaeological site. Nowadays, agriculture is practiced within 8 km of the archaeological site and Suriname river. The area used for agriculture likely expanded over time.
How did the forest recover from these activities?
Within 1 km of the archaeological site, forests were burnt and used multiple times. Here, forests have a lower biomass than further away from Beng Tapu, meaning fewer or smaller trees have grown back. Also, Attalea and Oenocarpus palm trees increased. Still today, the Saamaka Maroon community uses the maripa palm to make oil. Therefore, the number of maripa palms may have increased due to human activities like cooking and oil production! Attalea and Oenocarpus palms are also adapted to open conditions and fire, showing the influence people had on the environment and how the forest responded to fires.
Further (2-7 km) away from the archaeological site, where disturbances were fewer, the forests recovered much better but Astrocaryum palms grew back in higher numbers in the understory of the forests. What makes these palms so resilient? We are still uncertain. The forests furthest away (>8km) from Beng Tapu showed little signs of disturbances.
Figure 3: View from the Suriname River
A long human history, and an Indigenous archaeological site?
The Saamaka Maroons were not the first people to have inhabited the forests near Botopasi. Charcoal fragments show that people were in region (the ca. 20 km radius we studied) already 2000 years ago, and fire events occurred ca. 2000, 1700,1500, 1300, 1200 and 800 years ago. We don’t know which Indigenous Cultures may have inhabited this region, because of limited archaeological and historical research here. Large charcoal fragments were found ca. 7 km away from Beng Tapu, across the Suriname River. Could this be an Indigenous archaeological site?
Conclusion
Our results show the timing, intensity and frequency of past disturbances are very important for good forest recovery and some disturbances from the past can still impact the modern vegetation.
Unravelling the past not only tells us about the ancestors of Maroons and the lives of Indigenous communities before the 1500s. The past also helps us to understand how forests respond to human impacts. To better guide conservation strategies, we need to do more archaeological and ecological research in Surinamese rainforests.
Next to the Suriname River, past human activities shaped the forest andincreased local palm abundances. The broader forested region showed a healthy recovery. These results indicate that the Saamaka Maroon community preserved most of the forests they inhabited since the 1700s. We can learn from traditional knowledge about which management practices are sustainable to keep forests healthy.
If you want to know more about the “hows” of this research…dive with me into the methodology!
Amazonian rainforests are incredibly biodiverse and provide global ecosystem services, but are threatened by fires, which completely alter ecosystem function and structure. Fires, especially in western Amazonia, almost always have an anthropogenic origin. However, much is unknown about the long-term recovery and multi-generational successional processes following fire events. Due to the long lifespan of tropical trees, past fires may have left ecological legacies in modern forest composition in Amazonia. The goal of this thesis is to investigate how past fire events impact successional trajectories of past vegetation change and whether these fire events and related human impacts have left ecological legacies in modern Amazonian forests. I specifically focus on western Amazon and changes in palm abundances and composition through time, as palms were an economically important plant family to past peoples. I compared lake charcoal records across the Amazon Basin and found fire was least prevalent in western Amazonia. On a local scale, very limited evidence of past disturbances was present in forest plots in northwestern Amazonia. Palm abundances have been increasing since the mid-Holocene, but this increase is not related to past fire events. Past fire likely have left low to none ecological legacies in these forest plots. Modern trait composition across western Amazonia is associated with past fire events, but more research is necessary to disentangle relationships between past fire, soils, and modern vegetation. Overall, western Amazonia likely contains the least intense ecological legacies in comparison with the rest of Amazonia.
Poaceae (the grass family) is one of the most diverse angiosperm families on Earth, comprising close to 12,000 species. The history of grass-dominated biomes extends back over 20 million years, yet the spatial and temporal development of these biomes and the underlying drivers remains unresolved. This thesis addresses these questions in South America, focusing on modern grass pollen and ancient samples dating from the early Miocene to the present. The thesis reveals several key points: (i) Grass pollen size varies significantly both among genera and species and within species. Pollen size shows no correlation with (a)biotic factors, indicating its limited utility as a generally applicable proxy for reconstructing past vegetation and climate; (ii) Grass pollen exhibits high diverse on surface ornamentation. The morphotypes identified by descriptive terminology are well-supported by a combination of SEM images of pollen surface patterns and computational image analysis. The findings reveal that pollen sculpture is unrelated to (a)biotic variables but is diverse across the phylogeny; (iii) Tropical grass pollen morphology suggests a gradual rather than punctuated evolution, based on the trend toward a less dense ornamentation of the exine since c. 23 Ma. The changes in the exine of grass pollen since the early Miocene might be driven by evolutionary processes (evolutionary drift and/or directional selection), and potentially immigration at the continental scale. In summary, the thesis reveals the trajectory of grass pollen morphological changes over time and examining the drivers that have contributed to their evolution and geographical expansion at the continental scale.
Developing new applications for plant wax n-alkane biomarkers can deepen our understanding of ecosystem history. In this thesis I study modern and sedimentary n-alkane signals, sourced along the tropical Andes, to better understand how they can be used as a proxy for past environmental change. The overarching question addressed in this thesis is: what do n-alkane patterns extracted from sedimentary records reflect? Specifically, I address:• Do environmental or taxonomic factors dominate the n-alkane signal?• Does the n-alkane signal alter as the plant material degrades?• How much of the n-alkane variability can be explained by our analytical protocols?I find that the taxonomic and environmental signals of n-alkane patterns are entangled, especially in leaf n-alkanes. Soil n-alkane patterns reflect environmental conditions at the site, but the results cannot rule out a taxonomic signal in soil n-alkane patterns. I also find that, as the source material degrades (leaves), the n-alkane patterns are altered. Although the n-alkane signal is recognizable as having plant origin, there is a reduction in n-alkane pattern variability and the metric for degradation becomes an increasingly important descriptor of the n-alkane pattern shifts observed in soils and sediments. I find evidence that the metric for degradation can be used as proxy for past environmental change, but the application of this n-alkane signal proxy is not straightforward. Finally, I find there is little understanding of how much extraction and measurement protocols contribute to the n-alkane pattern variability and what implications this has on interpretations of the n-alkane signal.
The high tropical Andes harbours vital ecosystems that sustain biodiversity, carbon storage, and environmental service provision for millions of people. They are identified as one of the most vulnerable terrestrial ecosystems to global environmental changes, particularly to climate change and land use conversion. Despite their vulnerability and the importance of global biodiversity conservation and Andean societies, they are among the least studied ecosystems in the world. In this thesis, I studied the patterns of summit plant community’s across the tropical section of the Andes. Further, I studied what environmental factors influence plant community composition, species diversity, and thermal niche traits in high tropical alpine ecosystems. Based on the thermal niche traits, I assessed the potential vulnerability of species and communities to climate warming, considering the effect of the climate variability hypothesis on the species niche breadths. Further, I synthesised the current state of knowledge and assessed the current and projected landscape changes in the high Andes due to the combined effect of glacier retreat and climate warming. I reviewed documented glacier changes and landscape evolution over past decades to millennia and assessed projected future glacier shrinkage until 2100 for two case studies in the Andes of Ecuador and Peru. I also evaluated the capacity of high Andean ecosystems to recover from land use changes using the aptitude to store and take up carbon together with plant diversity. Lastly, I carried out an applied research analysis aimed at informing conservation policy formulation in continental Ecuador through defining critical areas for biodiversity conservation.
On November 17, 2023, Caixia Wei (魏彩霞) accomplished a pivotal milestone by successfully defending her thesis titled “Morphometrics of Modern and Fossil Poaceae Pollen from South America” at the distinguished Agnietenkapel (University of Amsterdam). During the defense ceremony, Caixia showcased her professional knowledge and expertise in the field of paleoecology in a relaxed and cheerful manner. The committee members, promoters (Carina Hoorn, William Gosling, Phillip Jardine), and attendees (~50 people) responded with frequent smiles, laughter, and numerous rounds of applause! After the defense, a delightful reception and dinner were held, where Caixia was showered with an abundance of hugs, kisses, heartfelt wishes, and thoughtful gifts. These wonderful memories will support Caixia on her journey ahead…
For a glimpse into the event, you can watch Caixia’s insightful 10-minute project presentation here:
Additionally, most of Caixia’s thesis is available for download at this link:
Ludgate, N. (2014) Organic matter preserved in cave sediments: A new environmental proxy. PhD thesis, Department of Environment, Earth & Ecosystems, The Open University.
Abstract
Exploring new terrestrial archives to investigate past climate and the resultant impact on ecosystems is key to assessing changing climate within large continents, where major records are limited. This study presents the first comprehensive geochemical investigation of clastic cave sediments, a previously under-explored field, demonstrating the effective use of caves as an environmental archive, and recovering useable records of moisture and vegetation regime within the complicated monsoonal system of South East Asia.
Clastic cave sediments were recovered from a 2.4 m deep archaeological trench covering ~24 ka to ~12 ka within Hang Trõng, Vietnam. Clay mineral, bulk carbon, pollen, terrestrial snail shells and plant-derived lipid biomarkers were analysed to provide a multi-proxy approach. No diagenetic alteration was found below 20 cm despite clay mineral and bulk carbon δ13C analysis demonstrating microbial action and weathering of surface sediments. As previously observed in cave sediments, poor preservation lead to limited pollen recovery, however δ13C values from CSIA and shell carbonate indicates C3 vegetation persisted around the cave during the last glacial maximum.
The time-series δ18O record from recovered shells shows clear fluctuations corresponding to global climatic events including the LGM and Heinrich 1. It is hypothesised that these reflect moisture availability, with heavier isotopic values indicating drier periods. Most higher plant lipid biomarkers provide evidence for a stable forest composition, however a shift in n-alkane lipid from C31 to C27 can also be linked with the Heinrich 1 event. The warm Greenland interstadial 1 event is also expressed within the record by low δ18O shell values attributed to more available moisture and higher bulk δ13C values, which indicate greater micro-organism action.
Hang Trõng’s multi-proxy record adds to a growing body of evidence demonstrating the importance of global teleconections when assessing the impact of climate change on monsoons and local vegetation. The data collected here proves clastic cave sediments can hold valuable climatic proxies; something which is of especial importance as palaeoenvironmental archives rely on limited capture and preservation for long term environmental records.
The montane cloud forests of South America are some of the most biodiverse habitats in the world, whilst also being especially vulnerable to climate change and human disturbance.
Today much of this landscape has been transformed into a mosaic of secondary forest and agricultural fields. This thesis uses palaeoecological proxies (pollen, non-pollen palynomorphs, charcoal, organic content) to interpret ecosystem dynamics during the late Quaternary, unravelling the vegetation history of the landscape and the relationship between people and the montane cloud forest of the eastern Andean flank of Ecuador. Two new sedimentary records are examined from the montane forest adjacent to the Río Cosanga (Vinillos) and in the Quijos Valley (Huila). These sites characterise the natural dynamics of a pre-human arrival montane forest and reveal how vegetation responded during historical changes in local human populations.
Non-pollen palynomorphs (NPPs) are employed in a novel approach to analyse a forest cover gradient across these sites. The analysis identifies a distinctive NPP assemblage connected to low forest cover and increased regional burning. Investigation into the late Pleistocene Vinillos sediments show volcanic activity to be the primary landscape-scale driver of ecosystem dynamics prior to human arrival, influencing montane forest populations but having little effect on vegetation composition.
Lake sediments at Huila from the last 700 years indicate the presence of pre-Hispanic peoples, managing and cultivating an open landscape. The subsequent colonization of the region by Europeans in the late 1500’s decimated the indigenous population, leading to the abandonment of the region in conjunction with an expansion in forest cover ca. 1588 CE. After approximately 130 years of vegetation recovery, montane cloud forest reached a stage of structural maturity comparable to that seen in the pre-human arrival forest. The following 100 years (1718-1822 CE) of low human population and minimal human impact in the region is proposed as a shifted ecological baseline for future restoration and conservation goals. This ‘cultural ecological baseline’ features a landscape that retains many of the ecosystem service provided by a pristine montane forest, while retaining the cultural history of its indigenous people within the vegetation. Continue Reading
Ecology of the past 