Pollen Analysis. -interpretation

Transcription

1 Pollen Analysis -interpretation

2 Pollen Analysis - Interpretation 1. Calculations and presentation of fossil pollen data a) % data b) concentration and accumulation rate data c) X-axis, Y-axis 2. Interpretation of pollen stratigraphical data a) construction and zonation of pollen diagrams b) Surface pollen data c) Modern analogue approach 3. Use of the computer programs 4. Complex numerical analysis of pollen analytical data

3 Pollen Analysis - Interpretation PERCENTAGES: % of each taxon effects % of all others - divisor is a predetermined pollen sum - example: Total taxa or Forest taxa only Pollen type Count % total sum % forest sum Casuarina Eucalyptus Poaceae Eleocharis undiff Sum

4 Pollen Analysis - Interpretation CONCENTRATION ~ grains/volume (cm -3 ) or / mass (g) - Volume of each pollen sample = 2 cm 3 - Spike added to each pollen sample = 1, lycopod grains - Concentration = grains counted X spike added spike counted sample volume Pollen type Count grains/cm 3 Poaceae Casuarina = 78 X Eucalyptus Eleocharis undiff Spike counted 43 Total Sum

5 Pollen Analysis - Interpretation ACCUMULATION RATE (INFLUX) ~ (grains/cm 2 /yr) - Dates: surface = yr B.P., 2 cm = 1 yr BP - Sedimentation rate = depth/age (cm/yr) = 2/1 or.5 cm/yr Influx = Concentration X Sedimentation Rate (grains/cm 2 /yr) (grains/cm- 3 ) (cm/yr) Pollen type Conc. Accum. rate Poaceae = 97 x.5 Casuarina Eucalyptus Eleocharis undiff Total Sum

6 Pollen Analysis - Interpretation Age cal yr BP Trees & Shrubs Herbs Ferns Pilgerodendron (%) Pilgerodendron 2-1 (pollen grains/cm /yr ) Y-axis: - Depth (from surface, in unit) -Time ( 14 C ages, cal yr BP) - Other (environmental sequence) X-axis: Grouping into summary % Accum. rate

7 Pollen Analysis - Interpretation Zones - Biostratigraphic zone "A biostratigraphic zone is defined solely by the fossils it contains, without reference to lithology, inferred environment, or concepts of time. - Assemblage zone A pollen assemblage zone is defined by the relative similarity of contiguous samples that can be interpreted to represent an inferred environment.

8 Pollen Analysis - Interpretation Zones - zone boundaries: times of rapid vegetation change - zones: periods of ± stable vegetation Schlerophyll Forest Taxa Rain Forest Taxa Casuarina Eucalyptus comp. Gramineae Cunoniaceae Trema Urticaceae/Moraceae Elaeocarpus Podocarpus Agathis Macaranga Mallotus Monolete fern spores Zones Cal yrs BP E-5 E-4 Cool/Dry Sub-Montane Rain Forest E-3 E-2 Warm Sub-Montane Rain Forest E-1 Cold/Dry Schlerophyll Woodland %

9 Pollen Analysis Surface Samples 75 W 74 W 73 W Isla Guafo MELINKA 44 S 44 S Northern A + Melimoyu + F + I 45 S Chonos Archipelago + Mentolat Cay Maca PUERTO AGUIRRE 45 S Southern T + PUERTO AYSEN Hudson 46 S 46 S Taitao Peninsula Cabo Raper 47 S 76 W SURVEYED LAKES 75 W 74 W 73 W 47 S

10 Pollen Analysis Surface Samples Surface Samples: calibration with modern pollen-vegetation relationship R-VALUES : ratio pollen percentage / vegetation percentage RELATIVIZED R-VALUES: divide larger ratios by smallest ratio Species Veg.% Pollen% R-VALUES RELATIVIZED R-VALUES Area 1 A B C Site-to-site variations in pollen composition precludes actual use of R-Value

11 Pollen Analysis Surface Samples REGRESSION ANALYSIS: X - Y plot of pollen percentages vs vegetation abundances Transfer Function: Y = ax + b - regression coefficient "a" is similar to R-Value - y-intercept "b" indicates over- and under-representation Constraint: the relationship of vegetation to pollen is not linear for percentage

12 Pollen Analysis Surface Samples 45 S 75 W 74 W 73 W Isla Guafo 44 S Chonos Archipelago Southern Northern + F + I T + MELINKA A + + Melimoyu Mentolat Cay Maca PUERTO AGUIRRE 44 S 45 S PUERTO AYSEN Hudson Forest of the Chonos-Taitao region - Northern Lowlands Nothofagus nitida Pilgerodendron uviferum Tepualia stipularis 46 S Taitao Peninsula 46 S - Southern & Highlands Nothofagus betuloides Podocarpus nubigena Drimys winteri Cabo Raper 47 S 76 W SURVEYED LAKES 75 W 74 W 73 W 47 S

13 Pollen Analysis Surface Samples

14 Pollen Analysis Multivariate Analysis a) Similarity - Dissimilarity Measures: calculation of dissimilarity based on several (or all) of the pollen types. e.g., between surface samples and fossil samples. b) Transfer Functions: calculation of relationship between pollen percentages and annual temperature, precipitation. c) Multivariate Statistical Analysis: calculation of patterns based on all modern pollen samples and fossil samples. i. Principal Components Analysis ii. Detrended Correspondence Analysis d) Other numerical analyses i. Rarefaction Analysis ii. Rate of Change Analysis e) Software: TILIA, Psimpoll, C2, CANOCO

15 Pollen Analysis Modern Analogue Principal Components Analysis Lepidothamnus fonkii Northern Chonos Southern Chonos Mainland Taitao Species Axis 2 (eigenvalue = 33%) Temperature Astelia Podocarpus Amomyrtus Nothofagus dombeyi Pilgerodendron uviferum Misodendron Weinmannia Nutrients/Precipitation? Axis 1 (eigenvalue = 36%) Tepualia stipularis

16 Pollen Analysis Modern Analogue Principal Components Analysis 2 Modern mud-water interface samples Geographical location Northern Chonos Southern Chonos & Taitao Pen. - Modern analogues defined by surface samples from region 1 - Non-analogue samples found in fossil samples Constraint to reconstructing past environments is our poor understanding of non- analogue assemblages Laguna Facil Pollen Zones Fac-5 Fac-4 - Alternative is to focus on single taxa. Fac-3 Fac-2 Fac

17 INTERPRETATION OF POLLEN DIAGRAMS: a. understand the horizontal and vertical axes b. subdivide pollen diagram into zones c. identify modern analogs for each zone d. interpret vegetation history e. interpret climate history

18 Case Study. Tropical Rain Forest of Northern Australia The rainforest vegetation includes mixtures with sclerophyll tree species that occur as emergent and co-dominant species in the canopy. Fringing the rainforests are areas of tall, open forest and tall, medium and low woodland. The palaeoecological record is from Lake Euramoo, a small crater lake at 73 masl near the boundary of sub-montane rainforest and schlerophyll woodland.

19 Tropical Rain Forest of Northern Australia Lake Euramoo Depth m 16 Age (cal yr BP) RAINFOREST ANGIOSPERMS RAINFOREST GYMNOSPERMS SCHLEROPHYLL WOODLAND HERBS INTRODUCED Charcoal density Rate of Change Palaeodiversity Zones Eu ka: Cold/Dry Schlerophyll Woodland Low turnover Eu-4 Eu-3 Urtic././Mor. Eucalyptus Cunoniaceae Trema Podocarpus Mallotus E. intermedia Callitris Casuarina Eu-2 Eu-1 Elaeocarpus PCA Agathis Asteraceae Melalueca Poaceae

20 Tropical Rain Forest of Northern Australia Lake Euramoo Depth m Age (cal yr BP) RAINFOREST ANGIOSPERMS RAINFOREST GYMNOSPERMS SCHLEROPHYLL WOODLAND HERBS INTRODUCED Charcoal density Rate of Change Palaeodiversity Zones Eu-5 Eu-4 Eu-3 Eu-2 Eu ka: Mosiac Schlerophyll Woodland- Sub-Montane Rain Forest Punctuated high turnover episodes Urtic././Mor. Elaeocarpus PCA Eucalyptus Cunoniaceae Trema Podocarpus Mallotus Agathis Asteraceae E. intermedia Callitris Melalueca Casuarina Poaceae

21 Tropical Rain Forest of Northern Australia Lake Euramoo Depth m 16 Age (cal yr BP) RAINFOREST ANGIOSPERMS RAINFOREST GYMNOSPERMS SCHLEROPHYLL WOODLAND HERBS INTRODUCED Charcoal density Rate of Change Palaeodiversity Zones Eu ka: Warm Sub-Montane Rain Forest Very low turnover Eu-4 Eu-3 Urtic././Mor. Eucalyptus Cunoniaceae Trema Podocarpus Mallotus E. intermedia Callitris Casuarina Eu-2 Eu-1 Elaeocarpus PCA Agathis Asteraceae Melalueca Poaceae

22 Tropical Rain Forest of Northern Australia Lake Euramoo Depth m Age (cal yr BP) RAINFOREST ANGIOSPERMS RAINFOREST GYMNOSPERMS SCHLEROPHYLL WOODLAND HERBS INTRODUCED Charcoal density Rate of Change Palaeodiversity Zones Eu-5 Eu-4 Eu-3 Eu-2 Eu ka: Cool/Dry Sub-Montane Rain Forest with increasing turnover Loss of long-lived trees (eg Agathis) Urtic././Mor. Elaeocarpus PCA Eucalyptus Cunoniaceae Trema Podocarpus Mallotus Agathis Asteraceae E. intermedia Callitris Melalueca Casuarina Poaceae

23 Tropical Rain Forest of Northern Australia Lake Euramoo Depth m 16 Age (cal yr BP) RAINFOREST ANGIOSPERMS RAINFOREST GYMNOSPERMS SCHLEROPHYLL WOODLAND HERBS INTRODUCED Charcoal density Rate of Change Palaeodiversity Zones Eu-5 Last 12 years: Cold/Dry Sub-Montane Rain Forest with High Turnover Invasion of exotic plants Eu-4 Eu-3 Urtic././Mor. Eucalyptus Cunoniaceae Trema Podocarpus Mallotus E. intermedia Callitris Casuarina Eu-2 Eu-1 Elaeocarpus PCA Agathis Asteraceae Melalueca Poaceae

24 Implications of long-term increases in biomass burning for rain forest ecosystems and terrestrial carbon cycle Increase disturbance frequency higher turnover rates loss of large long-lived trees and reduced above ground C storage capacity internal fragmentation alters species composition and increases C partitioning greater opportunity for invasion by fast growing plants (eg. gap-dependent species, weeds and lianas) and rapid recovery of C storage after loss Phillips et al. (22) Nature 418,

25 Conclusions Tropical biomass burning appears to be at least partly controlled by El Niño-related climate variability (~orbital precession). Changes in the frequency of disturbance events and forest fragmentation as a result of biomass burning are two of the most significant processes related to the carbon cycle. Biomass burning as a result of human activity has become an increasingly significant factor during the Holocene and is likely to have had an impact on climate change.