fossil record | Ecology of the past

Number crunching in palynology

May 10, 2012
HayleyKeen

Simulated pollen counts

HOW DO WE UNDERSTANT PAST VEGETATION CHANGE?
Our understating of vegetation in the past, and how it has changed through time, comes mainly from the examination of macrofossils (e.g. wood and leaves) and microfossils (e.g. pollen and spores) found in the sedimentary record. The potential for microscopic fossils to provide an insight into past vegetation change on a landscape scale was pioneered by von Post (Von Post, 1916, reprinted 1967) and has been subsequently used to understand changes in regional floras (Godwin, 1956), and address conservation issues (Willis et al., 2007). Analysis of fossil pollen and spores (palynology) is now widely used on late Quaternary timescales to answer ecological questions linking vegetation and wider environmental/climatic change; these include:

Has there been a change in major vegetation type (biome)? For example a change between woodlands and grassland vegetation.
How have the ecosystem dynamics altered? For example the presence or absence of fire.
How has the diversity within the ecosystem changed? For example increase or decrease in sample richness.

Palynological analysis relies on obtaining a sub-sample of the pollen contained within the sediment at a specific depth (time) which allows the vegetation at that time to be reconstructed. This sub-sample is known as a pollen count. To build up a picture of vegetation change through time it is necessary to generate a sequence of pollen counts. The size of the sub-sample (pollen count) required from any particular depth (time period) is dependent on the nature of the vegetation association being investigated and the ecological question being addressed . For example, the amount of pollen analysed to determine if the vegetation was predominantly wooded or grassland is different to that required to provide information on the biological diversity within the vegetation assemblage.

Discussed below are some of the conventions related to choosing an appropriate pollen count size within palynology, with particular reference to the challenges of dealing with diverse tropical floras.

Thinking about proxies

January 31, 2012
Fray

COMMENT ON DISCUSSION OF PROXIES IN HUNTLEY (2012)
All areas of research have strengths and limitations which are readily acknowledged by the scientists involved. The reconstruction of past climates (palaeoclimates) from biological indicators contained within the fossil record (proxies) presents some specific challenges; for example key limitations might be gaps in a sedimentary sequence or post-depositional degradation of samples. Understanding and interpreting data sets in the face of these challenges require the researcher to develop a wide range of skills. Huntley (2012) focuses upon the uncertainties within palaeoclimate reconstruction which he considers to be “frequently overlooked” (p. 2) by scientists making climate reconstructions from proxy records. Specifically Huntley urges researchers to consider carefully:

What a given proxy is actually capable of reconstructing, i.e. what climate variables controls its distribution?
What other variables might be influencing the proxy, i.e. could there be multiple influences, might these vary through time?
What is the spatial relevance of the proxy, i.e. macro versus micro scale?
Can multiple proxies be compared, either within or between sites?

In other words: which and how many climatic variables can be reconstructed form any one aspect of the fossil record?

Below I review and comment on some key arguments made by Huntley (2012) related to the use of proxies in reconstructing palaeoclimates.

REFERENCE
Huntley, B. (2012) Reconstructing palaeoclimates from biological proxies: Some often overlooked sources of uncertainty. Quaternary Science Reviews 31: 1-16.

Continue Reading

Environmental change in the humid tropics and monsoonal regions

January 27, 2012
WDG

JUST PUBLISHED
Bush, M.B. & Gosling, W.D. (2012) Environmental change in the humid tropics and monsoonal regions. The SAGE handbook of environmental change: Volume 2. Human Impacts and Response (ed. by J.A. Matthews, P.J. Bartlein, K.R. Briffa, A.G. Dawson, A. De Vernal, T. Denham, S.C. Fritz and F. Oldfield), pp. 113-140. SAGE, London. ISBN: 978-0-857-02360-5

Biodiversity & Ecosystem Services

January 10, 2012
WDG

PAGES (Past Global Changes)
Focus 4: (Past) Human-Climate-Ecosystem Interaction (PHAROS)
Biodiversity Theme Workshop at the Department of Zoology, University of Oxford (9-11 Jan)

Using fossil records to map potential threats, opportunities and likely future developments for biodiversity and ecosystem services
Organised by: Dr. Elizabeth Jeffers, Dr. Shonil Bhagwat and Prof. Kathy Willis

This small (about 30 attendees) workshop brought together academic researchers mainly working in the field of past environmental change to discuss the use, and potential use, of data sets in understanding the key environmental challenges facing society. The bulk of the discussion took place with reference to ‘ecosystem services’. Three types of ecosystem service were mentioned early on for which it was thought that the fossil record can provide a unique long term perspective (beyond historical records): 1) provisioning services (e.g. food, timber, biofuels), 2) regulating services (e.g. carbon), and 3) cultural services (e.g. national parks, tourism).

Below I will summarize some of the issues discussed. Please note that this does not cover the full range of discussion or all of the many high quality contributions. For further information click here to visit the workshop web page.