Poaceae | Ecology of the past

Introducing: Jelle Kraak

June 5, 2024
WDG

Hello Ecology of the Past readers, my name is Jelle Kraak and I’m currently doing a research project for my MSc Biological Sciences (University of Amsterdam) supervised by William Gosling (University of Amsterdam), Jemma Finch (University of KwaZulu-Natal), and Trevor Hill (University of KwaZulu-Natal). The project is entitled: “Assessing the effect of human induced fire regime changes on vegetation in the Drakensberg mountains”. During the project I will visit South Africa to work at the University of KwaZulu-Natal and visit field site thanks to partial funding from the Amsterdam University Funds.

Research project outline

As many of you know, humans have been interacting with the environment for millennia in various ways. One of the ways in which humans interact with the environment is through the ignition of fires. By doing so, humans may change fire regimes (fire frequency, severity and/or intensity), which in turn can cause changes in vegetation composition and structure. By using a combination of phytolith (local vegetation) and charcoal (fire) data from two sediment cores obtained from wetland environments in the Drakensberg mountains, we aim to assess the effect of fire regime changes on vegetation over the last 6000 years.

The phytoliths (biogenic silica microfossils) allow for the reconstruction of the past vegetation. Charcoal fragments characterize all aspects of past fire regimes: (i) frequency (time series analysis of charcoal data), (ii) severity (abundance of charcoal in samples reflecting biomass consumed), and (iii) intensity (spectral properties of individual charcoal fragments reflecting combustion temperature).

The most interesting part of this project (in my humble opinion) is that this study is the first to use micro-Fourier Transformed Infrared Spectroscopy (µFTIR) to reconstruct fire temperatures from field samples ánd combine these accurately reconstructed temperatures with local vegetation data! It is important to accurately estimate fire temperatures, as the temperature of a fire dictates the type of plant materials which are consumed in a fire (the higher the temperature, the greater the proportion of woody material burning up). Similar studies have been conducted previously, however, these studies compared fire severity i.e. total burnt biomass with vegetation data. Although this works decently, total burnt biomass is not an accurate representation of fire intensity or temperature, as at very high temperatures biomass turns to ash, which cannot be detected in sediment cores. Through parameterizing both the vegetation changes and the fire regime we will provide a comprehensive picture of how changing human fire use practices modified the vegetation. We anticipate that: (i) a decrease in fire intensity resulted in woody encroachment of the surrounding vegetation, which was concomitant with the arrival of agropastoralists c. 600 years ago, and (ii) a shift in the proportion of C3 and C4 grass species in reaction to temperature changes in the Drakensberg mountains.

Wei PhD thesis 2023

April 17, 2024
WDG

Wei, C. (2023) Morphometrics of modern and fossil Poaceae pollen from South America. PhD Thesis, University of Amsterdam, Amsterdam. ISBN:

Abstract

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.

Handle: http://hdl.handle.net/11245.1/1f4f5550-1069-423a-ace3-2192ac4160c6

PhD Thesis: Morphometrics of modern and fossil Poaceae pollen from South America

December 19, 2023
WDG

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:

Wei, C. (2023) Morphometrics of modern and fossil Poaceae pollen from South America. PhD Thesis, University of Amsterdam.

New insights from a Poaceae pollen morphological study in the Amazon

November 8, 2022
WDG

Open access:

Wei, C., Jardine, P.E., Gosling, W.D. & Hoorn, C. (2023) Is Poaceae pollen size a useful proxy in palaeoecological studies? New insights from a Poaceae pollen morphological study in the Amazon. Review of Palaeobotany and Palynology 308, 104790. DOI: 10.1016/j.revpalbo.2022.104790

In search for the historical roots of grasses

August 11, 2020
WDG

In search for the historical roots of grasses: A review of Neogene grass history in the Amazon drainage basin

Corresponding article: Kirschner, J. A., & Hoorn, C. (2019). The onset of grasses in the Amazon drainage basin, evidence from the fossil record. Frontiers of Biogeography. DOI: 10.21425/F5FBG44827

The onset of grasses in the Amazon drainage basin, evidence from the fossil record

March 23, 2020
WDG

Kirschner, J.* & Hoorn, C. (2019) The onset of grasses in the Amazon drainage basin, evidence from the fossil record Frontiers of Biogeography DOI:10.21425/F5FBG44827

*Judith conducted this work as part of her MSc Earth Sciences: Geo-ecological Dynamics degree at the Institute for Biodiversity & Ecosystem Dynamics, University of Amsterdam.

The modern pollen-vegetation relationships of a tropical forest-savannah mosaic landscape, Ghana, West Africa

August 22, 2017
WDG

Julier, A.C.M., Jardine, P.E., Adu-Bredu, S., Coe, A.L., Duah-Gyamfi, A., Fraser, W.T., Lomax, B.H., Malhi, Y., Moore, S., Owusu-Afriyie, K. & Gosling, W.D. (2017) The modern pollen-vegetation relationships of a tropical forest-savannah mosaic landscape, Ghana, West Africa. Palynology online. DOI: 10.1080/01916122.2017.1356392

Published open access:

Julier, A.C.M., Jardine, P.E., Coe, A.L., Gosling, W.D., Lomax, B.H. & Fraser, W.T. (2016) Chemotaxonomy as a tool for interpreting the cryptic diversity of Poaceae pollen. Review of Palaeobotany and Palynology 235, 140-147. DOI: 10.1016/j.revpalbo.2016.08.004

Gosling PhD thesis 2004

April 10, 2014
WDG

Gosling, W.D. (2004) Characterisation of Amazonian forest and savannah ecosystems by their modern pollen spectra. PhD Thesis, Department of Geography, University of Leicester.

WDG Bolivia (2002)

Abstract:

Controversy surrounds the Quaternary palaeoenvironmental history of Amazonia. It is unclear whether moist evergreen forest, savannah or seasonally dry forest dominated the Amazon basin at the last glacial maximum (c. 21,000 years B.P.). In part the uncertainty surrounding the palaeoenvironmental history of Amazonia stems from a poor understanding of the ecological significance of the fossil pollen records from the region. In order to improve interpretations of the fossil pollen record it is essential to better understand the nature of the pollen rain produced by modern ecosystems.

In this thesis, three Neotropical ecosystems equivalent to those alluded to above were characterised by their modern pollen rain. This was achieved by examining samples collected in artificial pollen traps located within permanent (50 x 200 m) vegetation plots in the Noel Kempff Mercado National Park area, Bolivia. In each plot 10 traps were sampled for one field season (September 1998 to September 1999, or September 2000 to September 2001) and 5 traps were sampled from two additional field seasons (between 1998 and 2001). Pollen counts of at least 100 grains were made for each trap. In total 318 pollen taxa were distinguished, of which 116 were identified. The characteristic pollen from each of the three ecosystems were determined through a series of steps: spatial and temporal variations were explored using Spearman’s Rank correlations, the distinctive taxa of each ecosystem were identified using Principal Components Analyses (PCA), and the representativity of the pollen for each ecosystem was examined by comparing pollen and vegetation abundances. These analyses revealed a small number of taxa that can be used to characterize these ecosystems. Further PCA showed that it is possible to differentiate between the ecosystems by assessing the relative proportions of Didymopanax, Alchornea, Anadenanthera, Melastomataceae/Combretaceae, Moraceae/Urticaceae, Myrtaceae, Palmae, Pteropsidia (trilete), Poaceae and Solanum. These findings mean that it is now possible to detect these ecosystems in the fossil pollen record and consequently further information regarding the nature of the vegetation change in the Amazon basin can be gained.

Supervisors: Dr. Francis Mayle (University of Leicester, now at University of Reading) and Dr. Nicholas Tate (University of Leicester)

Examined by: Prof. Henry Lamb (University of Aberystwyth) and Prof. Andrew Millington (University of Leicester, now at Texas A & M), April 2004.

To borrow a copy from University of Leicester Library search for my name or thesis title here (item ID 7507349613), or download directly: Volume 1, Volume 2, and CD.

Miller PhD thesis 2014

March 26, 2014
lottiemiller

Miller, C.S. (2014) 520,000 years of environmental change in West Africa. PhD Thesis, Department of Environment, Earth & Ecosystems, The Open University.

CSM (2014)

Abstract:

Global temperatures are predicted to rise by 2–2.5°C by 2065, profoundly affecting the Earth’s environment. The response of ecosystems to past climate fluctuations can inform on how systems will respond in the future. This thesis focuses on Quaternary environmental changes in West Africa, a region important because of its high ecological value and role in the global carbon cycle.

In 2004, the International Continental Drilling Program recovered c. 291m of sediments spanning the last c. 1 Myr from Lake Bosumtwi (Ghana). Pollen, charcoal and nitrogen isotopes (d¹⁵N) were analysed from the most recent c. 150m (c. 520 kyr). The latitudinal position and long duration of this core makes it unique for understanding West African monsoon dynamics and vegetation change.

To aid characterisation of the Bosumtwi pollen succession, an atlas of present-day pollen was constructed for 364 pollen and spore taxa.

The pollen record from Bosumtwi reveals dynamic vegetation change over the last c. 520 kyr, characterized by eleven biome shifts between savannah and forest. Savannah vegetation is dominated by Poaceae (>55%) associated with Cyperaceae, Chenopodiaceae-Amaranthaceae and Caryophyllaceae. Forest vegetation is palynologically diverse, but broadly characterised by Moraceae, Celtis, Uapaca, Macaranga and Trema. Low d¹⁵N values correspond to forest expansion and these are driven by high lake levels. The timescale indicates that the six periods of forest expansion correspond to global interglacial periods. The record indicates that the wettest climate occurred during the Holocene, and the driest during Marine Isotope Stage 7.

The vegetation and d¹⁵N records show a strong response to glacial-interglacial variability between c. 520–320 kyr and 130–0 kyr. Between c. 320–130 kyr there is a weaker response to glacial-interglacial cycles probably related to high eccentricity during the peak of the 400-kyr component of eccentricity, with high eccentricity resulting in greater seasonality and ultimately drier conditions.

Supervisors: Dr. William Gosling, Dr. Angela Coe (both The Open University) and Dr. Tim Shanahan (University of Texas at Austin)

Examined by: Prof. Henry Lamb (University of Aberystwyth) and Dr. Pallavi Anand (The Open University).

To borrow a copy from The Open University Library click here.