In many settings, trees growing on floodplains provide an important source of indirect evidence that may be used to infer the occurrence, extent, and magnitude of floods prior to direct observations. That evidence may take several forms, including external scars caused by abrasion or impact from floating debris, anatomical changes within the annual growth increment following prolonged stem or root inundation, or tilting or uprooting due to the hydraulic pressure of floodwaters. Likely the most useful characteristic of paleoflood studies based on floodplain trees is their relatively high temporal resolution and dating accuracy compared to most other methods. Dendrochronological methods can routinely date past floods to the year of their occurrence and, in rare cases, can estimate the timing of floods that occur during the growing season to within two weeks. This high degree of chronological control, which is surpassed only by that provided by direct observation or instrumentation, can be used to determine whether floods in separate watersheds were synchronous or offset by several years and test hypotheses that suppose linkages between extreme floods and specific forcing mechanisms. Furthermore, the wide geographic distribution of tree species with dateable rings combined with the broad suite of methods available to examine interconnections between floods and tree growth allow this style of paleoflood hydrology to be applied to many settings that are not suitable for techniques that depend on geological evidence. Future paleoflood research involving tree rings will need to strike a balance between improving our understanding of the biological and fluvial processes that link tree growth to past events, and providing answers to questions about flood dynamics and hazards that are needed to safeguard people and property from future floods.

1. Maison des Sciences de l’Homme – Alpes | Université de Grenoble | June 27-30, 2016
TREES
AS FLOOD SENSORS

2. Source: Greg Brooks, Geological Survey of Canada

4. THE RIGHT TREES
IN THE RIGHT LOCATIONS
CAN PROVIDE
RELIABLE AND PRECISE INSIGHTS
INTO THE OCCURRENCE AND MAGNITUDE
OF PAST FLOODS.

5. TO TREES, RIVERS ARE HAZARDS
Source: Joe Zeleznik, North Dakota State University

6. IN WHAT MANNER DO RIPARIAN TREES
PRESERVE EVIDENCE
OF PALEOFLOODS?

7. 3TILTING OR UPROOTING BY HYDRAULIC PRESSURE

8. 2ANATOMICAL SIGNATURES WITHIN TREE RINGS

9. 1SCARRING DUE TO IMPACT OR ABRASION

11. FUNDAMENTALS OF
DENDROCHRONOLOGY

12. 12
EARLYWOOD
LATEWOOD
ONE GROWTH RING
CONIFER

13. HOW MANY
(COMPLETE) TREE RINGS
ARE VISIBLE
IN THIS MICROPHOTOGRAPH?

15. HOW MANY
(COMPLETE) TREE RINGS
ARE VISIBLE
IN THIS MICROPHOTOGRAPH?

16. Source: Daniel Griffin, University of Minnesota

17. 1871 1872 1873 1874
Source: Daniel Griffin, University of Minnesota

18. NORTHWESTERN NEW MEXICO
Source: Daniel Griffin, University of Minnesota

19. CRATER LAKE NATIONAL PARK

20. Source: Sarah Appleton, University of Minnesota

21. 1809 1811 181218081807
Source: Sarah Appleton, University of Minnesota

22. TREE-RING DATING IS NOT CONDUCTED BY SIMPLY COUNTING LAYERS (RINGS),
BUT BY MATCHING PATTERNS ACROSS DOZENS OR HUNDREDS OF TREES.

23. TREE-RING DATING IS NOT CONDUCTED BY SIMPLY COUNTING LAYERS (RINGS),
BUT BY MATCHING PATTERNS ACROSS DOZENS OR HUNDREDS OF TREES.

25. IN WHAT MANNER DO RIPARIAN TREES
PRESERVE EVIDENCE
OF PALEOFLOODS?

26. 1SCARRING DUE TO IMPACT OR ABRASION

27. ROBERT SIGAFOOS (1920-1995)
UNITED STATES GEOLOGICAL SURVEY

29. A SHARP BLOW TO A TREE TRUNK,
WHETHER MADE BY A LAWN MOWER,
BY A BASEBALL BAT IN THE HANDS OF A SMALL BOY,
OR BY DEBRIS CARRIED BY HIGH WATER,
WILL CRUSH, AND THUS KILL,
THE LIVING TISSUES BENEATH THE BARK
AND THE WOOD.
“ ”
Sigafoos, 1964
Botanical evidence of floods and flood-plain deposition

30. Source: Mark’s Postcards from Beloit

31. IMPACT OR ABRASION SCARS
Source: Juan Antonio Ballesteros-Cánovas , University of Bern

32. Source: Brian Luckman, University of Western Ontario

33. Source: NDSU Ag Comm

34. MISTASSINI RIVER, QUÉBEC
Source: Jeff Dumais

35. Source: Annie Lagadec
MISTASSINI RIVER, QUÉBEC

36. A SCAR-HEIGHT CHRONOLOGY WAS COMBINED WITH HYDRO-CLIMATIC DATA
TO IDENTIFY CONDITIONS FAVORABLE TO TRIGGERING ICE JAMS.
Source: Lagadec et al., Hydrological Processes, 2015

37. HIGH-GRADIENT RIVERS
Source: Uday Kunwar Thapa, University of Minnesota

38. 2ANATOMICAL SIGNATURES WITHIN TREE RINGS

39. QUERCUS

40. √
24
OAK TREE RINGS
(NORMAL ANATOMY)
18

42. OAK TREE RINGS
(ANATOMY DISRUPTED BY FLOODING)

43. 11
THE RED RIVER OF THE NORTH

44. 1997
15Source: Greg Brooks, Geological Survey of Canada

45. 42
SUBFOSSIL OAKS IN THE RED RIVER
Source: Erik Nielsen, Manitoba Geological Survey

46. QUERCUS MACROCARPA (MICHX.)
GROWING ALONG THE RED RIVER, MANITOBA, CANADA,
CONTAIN AN ANATOMICAL SIGNATURE
RELATED TO
HIGH-MAGNITUDE
19TH-CENTURY FLOODS.
“ ”
St. George and Nielsen, 2000
Geology

47. FLOOD RINGS EXTENDED THE EVENT RECORD
FOR THE RED RIVER OF THE NORTH BACK TO THE MID-1600S.
Source: St. George and Nielsen, The Holocene, 2003

48. PHENOLOGY

50. FLOODING CAUSES OAKS TO FORM NARROW EARLYWOOD VESSELS,
BUT ONLY IF IT OCCURS AFTER BUDSWELL OR INTERNODE EXPANSION.
Source: Copini et al, , Frontiers in Plant Science, in press

51. Source: Wikipedia contributor Shannon1
MISSISSIPPI RIVER

52. BOTTOMLAND HARDWOODS, MISSISSIPPI
Source: Ma hew Therrell, University of Alabama

53. 3TILTING OR UPROOTING BY HYDRAULIC PRESSURE

54. Source: Juan Antonio Ballesteros-Cánovas , University of Bern

55. PALEODISCHARGE
ESTIMATES
STRUCTURAL
ENGINEERING

56. Source: Ballesteros et al., Journal of Hydrology, 2015
TILTED TREES GROWING IN FLOODPLAINS EXHIBIT REACTIONS CAUSED BY FLOOD,
AND THEIR STRUCTURAL BEHAVIOR MAY BE LINKED TO FLOW CONDITIONS.

57. TAGUS RIVER, SPAIN
Source: Flickr user dailymatador

58. MECHANICAL MODELS ARE ABLE TO REPRODUCE THE OBSERVED TREE DEFORMATION,
BUT ALSO CONSISTENTLY UNDERESTIMATE PEAK DISCHARGE.
Source: Ballesteros et al., Journal of Hydrology, 2015

59. 10

60. THE GLOBAL TREE-RING NETWORK INCLUDES DATA FROM THOUSANDS OF LOCATIONS,
BUT MOST (ALL?) OF THESE TREES ARE NOT AFFECTED BY FLOODING!
Source: St. George, Past Global Changes Magazine, 2014

61. THE RIGHT TREES
IN THE RIGHT LOCATIONS
CAN PROVIDE
RELIABLE AND PRECISE INSIGHTS
INTO THE OCCURRENCE AND MAGNITUDE
OF PAST FLOODS.

62. Source: Ballesteros-Cánovas et al., Progress in Physical Geography, 2015
PALEOFLOOD STUDIES BASED ON TREE RINGS ARE STILL FEW, AND HAVE BEEN
CONDUCTED ALMOST EXCLUSIVELY IN EUROPE, CANADA, AND THE UNITED STATES.

63. THE HISTORY OF PAST FLOODS,
NOT THE HISTORICAL IDEALIZATION
OF THEIR FUTURE POSSIBILITIES,
IS THE UNDERSTANDABLE BASIS
UPON WHICH PEOPLE
MAY BE GUIDED TO EFFECTIVE ACTION.
“ ”
Baker et al., 2002
The Scientific and Societal Value of Paleoflood Research

64. THE RED RIVER OF THE NORTH

65. 1826

66. THE FORTS NOW STAND LIKE
A CASTLE OF ROMANCE
IN THE MIDST OF
AN OCEAN OF
DEEP CONTENDING CURRENTS,
THE WATER EXTENDING
FOR AT LEAST A MILE BEHIND THEM…
“ ”
Francis Heron of the Hudson’s Bay Company
May 1826

67. 1826