INTERGLACIAL-GLACIAL VEGETATION DYNAMICS – A NATURAL LONG-TERM ECOLOGICAL LABORATORY H. John B....
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Transcript of INTERGLACIAL-GLACIAL VEGETATION DYNAMICS – A NATURAL LONG-TERM ECOLOGICAL LABORATORY H. John B....
INTERGLACIAL-GLACIAL VEGETATION DYNAMICS – A
NATURAL LONG-TERM ECOLOGICAL LABORATORY
H. John B. Birks1,2 & Katherine J. Willis1,3
1University of Bergen, 2University College London, 3University of Oxford
International Geological Congress, Oslo, 13 August 2008
Introduction
Apologies
Glacials and interglacials
Why study interglacials?
Interglacial vegetation dynamics
General patterns
Bioclimatic affinity groups
Whole-assemblage approach
Vegetation dynamics within interglacials
Differences between interglacials
Plant extinctions in interglacial-glacial cycles
Lessons from interglacial-glacial long-term experiments
Acknowledgements
INTRODUCTION
Apologies
• Kathy Willis
• Change of title and abstract
• Contains little new information but hopefully presents some new ways of thinking about interglacial and glacial vegetation dynamics as a natural long-term ecological laboratory
• Limited geographical focus – primarily NW Europe, with brief excursions to the Balkans
Glacials and Interglacials
The Quaternary period is the past 2.4 million years of Earth’s history. A time of very marked climatic and environmental changes with multiple glacial-interglacial cycles driven by variations in orbital insolation on Milankovitch time-scales of about 400, 100, 41, and 19-21 thousand year (kyr) intervals
Glacial conditions account for up to 80% of the Quaternary
Remaining 20% consist of shorter interglacial periods during which conditions were similar to, or warmer than, present day
Oxygen isotope fluctuations. Observations made from several deep sea cores (Modified from Shackleton et al. 1993 and Shackleton & Opdyke 1976)
Climate and glacier fluctuations observed in deposits on the continent in Europe. Red: warm phases, blue: cold phases.
Andersen 2000
Major climate forcing for the last 450 kyr calculated at 60N. Global ice volume (f) plotted as sea-level, so low values reflect high ice volumes.
Jackson & Overpeck 2000
WHY STUDY INTERGLACIALS?
1. Primarily studied for stratigraphical purposes. Provide main basis for local and regional terrestrial Quaternary stratigraphies. Endless discussion and disagreements between Quaternary stratigraphies about correlations and interpretations, especially at a local geographical scale (e.g. East Anglia).
2. Shackleton & Opdyke (1973, 1976) V28-238, V28-239, etc. deep-sea cores. Multiple glacial-interglacial cycles in a complete sequence to Pliocene. ‘The Rosetta Stone of the Ice Ages’
Nick Shackleton, Phil Gibbard, and others in Cambridge, about 1974. Nick jokingly asked “Why bother with these local interglacial stratigraphies when we now have a complete global stratigraphy?”
Nick suggested why not study terrestrial interglacials as ‘natural long-term ecological experiments?’
Interglacials are, after all, a series of unique natural long-term experiments in vegetation dynamics. This aspect of interglacials has been curiously ignored in long-term ecological studies and in ecological-based Quaternary vegetational history.
Using the palaeoecological record as a natural long-term ecological laboratory has been recently emphasised by the National Research Council’s (USA) report on The Geological Record of Ecological Dynamics – Understanding the Biotic Effects of Future Environmental Change
Flessa & Jackson 2005
Three major research priorities emerge from this report:
1. Use the geological (= palaeoecological) record as a natural laboratory to explore biotic responses under a range of past conditions, thereby understanding the basic principles of biological organisation and behaviour. THE GEOLOGICAL RECORD AS AN ECOLOGICAL LABORATORY. ‘Coaxing history to conduct experiments’ Deevey (1969).
2. Use the geological record to improve our ability to predict the responses of biological systems to future environmental change. ECOLOGICAL RESPONSES TO ENVIRONMENTAL CHANGE.
3. Use the more recent geological record (e.g. mid and late Holocene and ‘Anthropocene’) to evaluate effects of anthropogenic and non-anthropogenic factors on variability and behaviour of biotic systems. ECOLOGICAL LEGACIES OF SOCIETAL ACTIVITIES.
Only 1 and 2 relevant here.
Despite Nick Shackleton and Neil Opdyke’s ‘Rosetta Stone of the Ice Ages’, problems remain in correlating terrestrial interglacial records with Marine Isotope Stages (MIS) of V28-239 and ODP 677.
Coxon & Waldren 1997
INTERGLACIAL VEGETATION DYNAMICS
General Patterns
NW Europe – many inter-glacial pollen stratigraphies, e.g. East Anglia
Ipswichian(=Eemian) MIS 5cHoxnian(=?Holsteinian) MIS 11c or 7c
West 1980
Cromerian MIS? Pastonian MIS?
Bramertonian MIS?
Ludhamian, Thurnian, Baventian MIS?West 1980
All show four main phases
1. Pre-temperate phase – boreal trees (e.g. Betula, Pinus)
2. Early-temperate phase – deciduous trees (e.g. Ulmus, Quercus, Fraxinus, Corylus)
3. Late-temperate phase – mixed deciduous and coniferous trees (e.g. Carpinus, Abies, Picea)
4. Post-temperate phase – boreal trees (e.g. Betula, Pinus, Picea) and heathland development
Bioclimatic Affinity Groups
Can group pollen types into plant functional types or bioclimatic affinity groups (BAG) on basis of plant morphology, deciduous or evergreen, and modern climate affinities.
Three BAGs represent 70% of pollen assemblages at Velay, French Massif Central with 4 interglacials in one continuous record. Longest record in NW Europe.1. Conifers2. Broad-leaved deciduous trees (mainly Quercus)3. Mesophilous temperate trees (mainly Fagus or Carpinus)
Rest are mainly herbs.
Dark green = ConifersLight green = Broad-leaved deciduous treesBlue = HerbsOrange = Mesophilous temperate trees
MIS 1 MIS 5e MIS 7c MIS 9c MIS 11c
Chedaddi et al. 2005
Chedaddi et al. 2005
Dark green = ConifersLight green = Broad-leaved deciduous treesOrange = Mesophilous temperate trees
Correlation coefficients between interglacials
Chedaddi et al. 2005
1. MIS 9c, 7c, and 5e closely correlated.
2. MIS 1 and 11c less well correlated even though they have similar precessional variations. MIS 11c is closest climatic analogue to Holocene.
3. General similar vegetation dynamics in all five interglacials even though their durations were very different and their solar insolation values were different.
Whole Assemblage Approach
Ioannina, Pindus Mountains, Greece
Tzedakis & Bennett 1995
180 m sequence, Holocene + 4 interglacials
MIS 5e
MIS 11c
MIS 9c
MIS 7c
5e 7c 9c 11c5e
7c - -9c - - - -11c - - - - - +
- climate different (solar insolation)- pollen different+ pollen similar
Tzedakis & Bennett 1995
Different interglacials have different solar insolation values and different pollen stratigraphies, except for two interglacials with similar pollen stratigraphies.
Interglacial pollen stratigraphies, unsurprisingly, generally become more similar as one goes further north
5e
?
7c or 11c
5e
7c or 11c
Donner 1995
Some general patterns exist when considered ecologically
Denm
ark La
pla
nd
Vegetation Dynamics Within Interglacials
diatoms
CaCO3LOI
Inso
lub
le
silic
ate
s +
q
uart
z
Pedi
astrum
alga
e
Erosion
High lake productivity
Other nutrientsLeaching
LIGHT DEMANDING herbs, Betula, Pinus
RICH MULL SOILS deciduous forest trees
MOR HUMUS/PEAT Picea, Sphagnum, Ericales
Lake sediment evidence
Protocratic
Mesocratic
Telocratic
(Eemian, Denmark)
Cumulative pollen curves and chemical composition for the interglacial deposit at Hollerup, DenmarkAndersen 1966
MIS 5e
Eemian IG (Inter-glacial)
5e
Holstein IG
7c or 11c
Harreskov IG
?
Average percentages of the pollen of light-plants. Black columns indicate percentages and white = percentages x10
PROTOCRATIC PHASE
LIGHT PLANTS
Andersen 1969
Eemian IG (Inter-glacial)
5e
Holstein IG
7c or 11c
Harreskov IG
?
Average percentages of the pollen of mull-plants and Alnus. Black columns indicate percentages and white = % x10
MESOCRATIC PHASE
MULL PLANTS
Andersen 1969
Eemian IG (Inter-glacial)
5e
Holstein IG
7c or 11c
Harreskov IG
?
ACID HUMUS PLANTS
Average percentages of the pollen of acid-humus plants. Black columns indicate percentages and white = percentages x10
OLIGOCRATIC AND TELOCRATIC PHASE
Andersen 1969
Zone averages for light-demanding, brown-earth mull, and acid humus pants in four interglacials. Zones joined in order from bottom to top. Consistent patterns but different relative abundances between interglacials. Andersen 1994
+ Homo sapiens phase in Holocene
Summary of Iversen’s (1958) glacial-postglacial (interglacial) cycle
What causes the change from the mesocratic with maximum forest cover and biomass and fertile soils to the oligocratic or telocratic phases with decreasing forest cover and biomass and less fertile soils?
Need long (> 6000 year) ecological successions where one can study vegetation, soil, and ecosystem properties along chronosequences of sites of different but known ages.
Wardle et al. 2004 Science 305: 509-513
Birks & Birks 2004 Science 305: 484-485
Maxim
al
ph
ase
Retr
og
ress
ive
ph
ase
Cooloola, Australia
>600,000 yr
Arjeplog, Sweden 6000 yr
Glacier Bay, Alaska
14,000 yr
Dunes Islands Moraines
Wardle et al. 2004
Maxim
al
ph
ase
Retr
og
ress
ive
ph
ase
Hawaii 4.1 x 106 yr
Franz Josef, New Zealand >22,000 yr
Waitutu, New Zealand
600,000 yr
Lava flows Moraines Terraces
Wardle et al. 2004
Tree basal area – unimodal or decreasing response with age
Wardle et al. 2004
Measured C:N, C:P, and N:P ratios for humus and litter
Significant increases in N:P and C:P ratios with age and forest retrogression Wardle et al. 2004
In the transition from the maximal forest biomass phase to the retrogressive phase, P becomes more limiting relative to N and P concentrations decline in the litter.
N is biologically renewable but P is not, as P is leached and bound in weathered soils. Over time, P becomes depleted and less available, relative to N.
Reduced rates of litter decomposition and release of P from litter and decreased activity of microbial decomposers.
Proportion of fungi relative to bacteria increases. Fungal-based food webs retain nutrients better than bacterial-based food webs.
Nutrient cycling thus becomes more closed and essential nutrients, especially P, become less available.
Long-term decline in biomass is accompanied by increasing P limitation relative to N, reduced rates of P release from decomposing litter, and reductions in litter decomposition, microbial biomass, and ratio of bacterial to fungal biomass.
Tree biomass thus declines as P becomes increasingly limiting at onset of oligocratic phase.
Birks & Birks 2004
Difference Between Interglacials
Differences in relative abundance
Picea Corylus
+Abies 3/8*Tsuga 3/8
Fagus 2/8*Pterocarya 4/8+Picea 6/8*Not native in Europe+Not native in UK
West 1980Taxon occurrences
These and other differences between interglacials may reflect biotic responses to
• differences in climate in different interglacials (insolation, precipitation, CO2, etc)
• differences in genetic variability of taxa between interglacials (e.g. Fagus, Corylus)
• differences in biotic interactions in different interglacials (plant competitions, plant-animal interactions, etc)
• differences in location of refugia between glacials
• different probabilities of extinction after different interglacials or in glacials
• different probabilities of external disturbance factors (fire, pathogens, etc)
• interactions between some of all of these factors
Embarrassingly ignorant of nearly all these potential drivers, especially when we consider interglacials
Different interglacials had different climates in terms of solar insolation values. Interglacial pollen stratigraphies are surprisingly broadly similar at the coarse plant functional or ecological group level but are, not surprisingly, different at the assemblage or individual taxon level.
In general each interglacial begins with high summer and low winter insolation, then both summer and winter insolation reach present-day values, and finally summer temperature decreases and winter temperature increases.
Main lesson from interglacials is the seemingly wide climatic tolerances of major tree taxa that dominate interglacials.
Virtually nothing is known about tree refugia prior to the Eemian (MIS 5e).
As regards the Weichselian, knowledge of tree refugia in Last Glacial Maximum (LGM) is greatly changing, thanks to an increasing emphasis on plant macrofossil remains.
Interglacial
LGM
S N
Traditional refugium model – narrow belt in southern mountains
van der Hammen et al. 1971
1. Trees in the LGM southern and Mediterranean refugia
Location of Ioannina basin in Pindus Mountains, NW Greece
Tzedakis et al. 2002
LGM
Pinus
Quercus
Fagus
Ulmus
Corylus
Alnus
Pistacia
Tilia
Betula
Abies
Bennett et al. 1991
Pollen and plant macrofossil evidence for traditional southern European LGM refugial model
2. What about trees in central, eastern, and northern Europe during the LGM?
Detection difficult
1. Low pollen values – do these result from long-distance pollen transport or from small, scattered but nearby populations?
Classic problem in pollen analysis since Hesselman’s question to Lennart von Post in 1916. No satisfactory answer.
2. Few continuous sites of LGM age
3. Pollen productivity related to temperature and some trees cease producing pollen under cold conditions
4. Pollen productivity may also be reduced by low atmospheric CO2 concentrations
5. Other sources of fossil evidence critically important – macrofossils, macroscopic charcoal, and conifer stomata
Scanning electron microscope images of wood charcoal
Willis & van Andel 2004
SloCro
Aus
Svk
Hun
CzR PolUkr
Rom
SerB&H
CzR–Czech Republic; Aus–Austria; Slo–Slovenia; Cro–Croatia; Pol–Poland; Svk–Slovakia; Hun–Hungary; Ukr– Ukraine; Rom–Romania; Ser–Serbia; B&H–Bosnia & Herzegovina
Occurrences of macroscopic charcoal in central Europe
Willis & van Andel 2004
Tree taxa that have reliable macrofossil evidence for LGM presence in central, eastern, or northern European refugia
Abies alba Pinus cembra
Alnus glutinosa Pinus mugo
Betula pendula Pinus sylvestris
Betula pubescens Populus tremula
Corylus Quercus
Carpinus betulus Rhamnus cathartica
Fagus sylvatica Salix aucuparia
Fraxinus excelsior Sorbus
Juniperus communis Taxus baccata
Picea abies Ulmus
Bhagwat & Willis 2008
Results from QUEST LGM plant macrofossil data-base for Eurasia, particularly former USSR for 25000-17000 cal yr BP
(LGM ice and shorelines follow Peltier 2004)
Some trees (Picea, Larix) very close to ice-sheet margin as in eastern North America
Alnus - 25-17kyr cal BPLarix - 25-17kyr cal BP
Pinus – 25-17kyr cal BP Picea – 25-17kyr cal BP
Binney et al. submitted
MediterraneanLGM refugia
Northerly LGM refugia
Ice sheet
Willis et al. 2008 (in press)
3. Current LGM refugium model based on all currently available fossil plant evidence
PLANT EXTINCTIONS IN INTERGLACIAL-GLACIAL CYCLES
Well known that the European flora, especially trees and shrubs, has become increasingly impoverished from Miocene to Holocene.
Temp
Arcto-Tertiary flora
8 taxa
91 taxa
van der Hammen et al. 1971
In current discussions about consequences of future global warming on population and species survival, critical to discover if past extinctions took place in glacial or in interglacial stages.
Lack basic data from glacial stage prior to the Eemian.
Losses in NW Europe
Weichselian 2 taxa ?Bruckenthalia (=Erica) spiculifolia, Picea omorika
Eemian 5 taxa Dulichium arundinaceum, Brasenia schreberi, Chamaecyparis thyoides, Cotoneaster acuticarpa, Aldrovanda vesiculosa
Holsteinian 7 taxa Azolla filiculoides, Pterocarya, Nymphoides cordata, N. peltata, Rhododendron ponticum, Osmunda cinnamomea, Osmunda claytoniana
Cromerian 6 taxa Eucommia, Celtis, Parthenocissus, Liriodendron, Tsuga, Aesculus
Many of these appear to be less frost-tolerant than currently widespread European plants. Extinction may have occurred in glacial rather than interglacial stages
Tenaghi Philippon 1.4 myr
1. More diverse flora before MIS 22-24
2. Remaining taxa extinct in MIS 16 or soon after (e.g Cedrus, Carya, Eucommia)
3. No extinctions in MIS 12 (maximum extent of ice sheets based on benthic 18O isotopes)
Tzedakis et al. 2006
Late Pliocene pollen record from Pula Maar, Hungary, 320,000 year record
Kathy Willis et al.
Pula Maar, Hungary
• sediments composed of finely laminated oil-shales, each couplet represents a single year of accumulation
• sequence contains c. 320,000 years in annual layers between c. 3.0-2.67 Myr
• analysed for pollen, isotopes, and geochemistry at interval of every 2500 years
Fossil pollen %
Palaeo-richness
Palaeo-energy (Laskar’s 2004 insolation calculations)
Palaeo-water balance (δ18O)
Willis et al. 2007
Dark grey = warm temperateWhite = herbsLight grey = cool temperateBlack = boreal
Insolation (scaled)
Taxon
om
ic
rich
ness
(sc
ale
d)
r2= 0.22
Non-linear relationship
Highest richness corresponds to intermediate insolation
Energy-based model – Laskar energy calculations vs pollen richness
Willis et al. 2007
Combined water-energy model (energy2 + water)
Combined water-energy model provides much better predictor of richness than water or energy alone
Willis et al. 2007
High amplitude fluctuations appear to lead to low taxonomic richness
Local extinctions of Sequoia, Nyssa, Parrotia, Fagus, etc. occur in periods of high amplitude fluctuations – reductions of regional species pool
Willis et al. 2007
Global extinction of Picea critchfieldii, abundant in LGM of south-eastern US, occurred during last deglaciation (16,000-10,000 yr BP), a time of rapid climate change (Jackson & Weng 1999).
Glacial stages are highly dynamic climatically with cold, dry conditions in response to Heinrich events and Dansgaard-Oeschger interstadial-stadial variability. High amplitude fluctuations during glacial stages may be responsible for extinctions.
All other late-Quaternary extinctions are thought to be the result of human activity (e.g. Easter Island palm).
Regional late-Quaternary extinctions are surprisingly rare (e.g. Koenigia islandica from central Europe in LGM, Larix sibirica from central Sweden in mid-Holocene, Picea omorika from north-west Europe).
LESSONS FROM INTERGLACIAL-GLACIAL LONG-TERM EXPERIMENTS
1. Considerable climatic fluctuations and environmental changes in the Quaternary with many glacial-interglacial cycles
2.Biotic responses to major climatic changes
• distribution changes• high rates of population turnover• changes in abundance and/or richness• extinctions• speciations• stasis
3. The interglacial–glacial ‘laboratory’ results show that biotic responses to rapid climate change were mainly redistribution of species, genera, families, and vegetation types, high turnover, abundance changes often resulting in local or regional extinctions but very rarely any global extinctions. No evidence for speciation. Vegetation types often have no convincing modern palynological analogue.
4. Biotic responses have been varied, dynamic, complex, and individualistic.
5. Interactions between climate change and biodiversity may be non-linear and possibly unpredictable. Important to identify thresholds and irreversible changes at time-scales realistic to the organism’s life-history (100-250 yr rather than 4 yrs of PhD projects, 5-10 yrs of funded projects, or 10-50 yrs of ‘long-term’ ecological plots).
6. A combined use of these ‘laboratory’ results and molecular phylogenies could help understand rates and thresholds of climate-biodiversity interactions and provide some independent tests of current models and predictions of biodiversity response to future climate change.
ACKNOWLEDGEMENTS
The late Nick Shackleton for convincing me in 1974 that interglacials are ecologically very interesting!
Kathy Willis for many stimulating discussions and ideas, access to the QUEST plant macrofossil data, and being a co-author.
Heikki Seppä and Karin Helmens for organising this symposium
Hilary Birks, Keith Bennett, Bill Watts, and Herb Wright for many helpful
discussions about interglacial vegetation dynamics
Cathy Jenks for invaluable help