Long-term vegetation dynamics. Richard Bradshaw University of Liverpool and Lund

Transcription

1 Long-term vegetation dynamics Richard Bradshaw University of Liverpool and Lund

2 Long-term vegetation dynamics What has changed during the Holocene? Climate change or migration biology? Role of people Future forecasts

3 er/webviewer.html

4 Cryptic refugia reduce estimated migration rates Anderson LL, Hu FS, Nelson DM, et al Ice-age endurance: DNA evidence of a white spruce refugium in Alaska. P Natl Acad Sci USA 103:

5 Vegetation models usually generate potential vegetation maps (Prentice & Guiot)

6 Forest map of Europe

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9 Hypotheses Holocene spread has tracked climatic change Spreading rate reflects dispersal properties People, soils, disturbance...

10 Picea abies Fagus sylvatica

11 Good relationship between simple climatic parameters and modern tree distributions USGS 1999

12 Data Model The dynamic vegetation model LPJ-GUESS captures much of the past dynamics of north European vegetation

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14 Convincing datamodel comparison for past spruce dynamics in Sweden. Bradshaw et al. 2000

15 Pollen data record forest dynamics at local and regional scales

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17 Rate of vegetation change has increased during the last 1000 years

18 Deciduous forest has reduced in area as agricultural land has increased in southern Sweden

19 Mixed deciduous forest has become monocultures of beech and spruce forest today in southern Sweden

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21 History of forest cover in southern Sweden

22 Forest cover is increasing in Europe % Forest cover 7 Sweden 30 Denmark Ireland Iceland Time (yrs)

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25 Foley et al. Science 200

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28 e.g. Barley

29 Distribution of (a) dolmens and (b) passage graves in Denmark (Jensen 2001)

30 Within a three hundred year period ( years ago) as many as dolmens and 000 passage graves were built in Denmark alone as part of an enormous construction boom throughout Western Europe.

31 Pollen percentages (continuous curves), plant macrofossil and charcoal concentrations per 30 ml sediment (bars) from Tjørnuvik, Faroe Islands illustrating the impact of first human settlement. The horizontal line indicates the first cereal pollen. (Hannon et al. 2009)

32 Loss of trees from the Neolithic onwards 6000 years ago. Modern situation dates from AD (Molloy & O Connell 2004)

33 Reconstructed proportion of open, non-forest vegetation at different times in Denmark and northern Germany, northcentral Europe (Nielsen et al. 2010).

34 Types of data used for study of millennial ecosystem dynamics and their drivers. Unfilled circles indicate irregular or fragmentary datasets (Bradshaw & Sykes in press). Direct and indirect proxy observations. Natural science, archaeology, written archives etc.

35 Evidence for land-cover change during the last 2000 years based on classical literature and archaeology (after Reale & Dirmeyer 2000).

36 Changing percentage of woodland area in four counties within Pennsylvania, USA since European settlement (Whitney & DeCant 2003). Opening up the mid-west drove major changes in landuse in the USA.

37 Danish forest cover in AD 1820 and 1997 (Bradshaw & Sykes in press)

38 Dallund Sø Period AD Modern Time Mediaeval 00 0 Iron Age Bronze Age 2000 BC Neolithic Mesolithic % mg cm -2 yr -1 % µg L -1 Analysed by Peter Rasmussen & Emily Bradshaw, GEUS

39 The west European landscape was created in the Late Bronze Age

40 Tree distributions are constantly changing

41 % Fagus % Picea pollen pollen Fagus Picea * Lovenholm * Draved * Suserup * * Ryfors Fulltofta * * Asa ** * * * * Ekenäs* * Mattarp Bocksten Skärsgölarna Flahult Storasjö Holkåsen Osaby Nissatorp * Siggaboda Eriksberg * Fiby * Bohult N Years BC/AD

42 Age 0 Fagus Picea Charcoal Trees

43 Diversity 1 Baseline conditions 2 Cultural influence 3 Abandonment/ Agriculture/ Managed forest Fire/Storm disturbance grazing mowing fire Traditional cultural disturbance Modern cultural disturbance Time (thousands of years)

44 Emanuelsson

45 Bradshaw & Sykes in press

46 SWECLIM

47 Regional climate change effects on potential natural vegetation of Sweden LPJ-GUESS cohort mode* Picea abies Pinus sylvestris Fagus sylvatica Tilia cordata Quercus robur Betula spp. Herbaceous spp. Biomass Change by RCM scenario RCAO-HadCM3-A2 *Koca et al Climatic Change

48 Conclusions Continuous change. Spread of boreal species. Climate change is primary driver during the early-mid Holocene. Human impact dominates the late Holocene. Combined human impact and rapid climate change gives an uncertain future.

49 References Lindbladh, M., Bradshaw, R.H.W. & Holmqvist, B. (2000) Pattern and process in south Swedish forests during the last 3000 years sensed at stand and regional scales. Journal of Ecology 88, Seppä, H., Alenius, T., Bradshaw, R.H.W., Giesecke, T., Heikkila, M. & Munkkonen, P. (2009) The invasion of Norway spruce (Picea abies) and the rise of the boreal ecosystem in Fennoscandia. Journal of Ecology 97,