In low-gradient, low energy rivers, forms of tree-ring evidence such as impact scars or stem deformation do not provide useful evidence of past floods. In this talk, I explain the strengths and limitations of wood anatomy as tools in in paleoflood hydrology.

1. Development of a Framework for Technical Review of Paleoflood Information | Rockville, Maryland | May 29-30, 2019
PALEOFLOOD EVIDENCE IN TREE-RING WOOD ANATOMY
FLOOD RINGS

3. CRATER LAKE, OREGON

4. 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

5. ?
HOW DOES ONE
DETERMINE
SPECIFIC FLOODS
FROM
TREE RINGS?

6. SCARRING DUE TO
IMPACT OR ABRASION

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

8. Source: NDSU Ag Comm

9. TILTING OR UPROOTING
BY HYDRAULIC PRESSURE

10. PALEODISCHARGE
ESTIMATES
STRUCTURAL
ENGINEERING

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

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

13. Source: Greg Brooks, Geological Survey of Canada
LOW-GRADIENT RIVERS

14. WOOD ANATOMY

16. DECIDUOUS TREES GROWING ON
THE POTOMAC RIVER FLOOD PLAIN NEAR WASHINGTON, D.C.
ARE OCCASIONALLY FLOODED DURING THE GROWING SEASON.
IF CROWNS ARE DAMAGED,
THE SUBSEQUENT RADIAL GROWTH OF STEMS
PRODUCES WOOD THAT IS OFTEN
ANATOMICALLY DIFFERENT
FROM THAT OF UNDAMAGED TREES.
“ ”
Tom Yanosky
USGS Professional Paper 1296, 1983

17. ANNUAL GROWTH RINGS IN RIPARIAN TREES
THAT CONTAIN UNUSUAL WOOD ANATOMICAL FEATURES
CAUSED BY INUNDATION OR DEFOLIATION
DUE TO FLOODING.

19. 1997
Source: Dr. Greg Brooks, Geological Survey of Canada

20. GRAND FORKS, NORTH DAKOTA

21. Source: Dr. Greg Brooks, Geological Survey of Canada
WINNIPEG, CANADA

22. QUERCUS

23. √
24
OAK TREE RINGS
(NORMAL ANATOMY)
18

24. Source: Mike Rastiello

26. OAK TREE RINGS
(ANATOMY DISRUPTED BY FLOODING)

27. 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

28. 1826

29. STEM
POSITION

30. WOOD ANATOMICAL SIGNATURES CAUSED BY FLOODING
ARE MOST PROMINENT NEAR THE ROOT AND DISAPPEAR UP THE STEM.
Source: St. George et al., Tree-Ring Research, 2002

32. PHENOLOGY/
TIMING

33. Source: Paul Copini, Wagenegin University
EXPERIMENTAL FLOODING

34. 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, 2016

35. CENSORING/
SCREENING

36. THE GROWTH LOCATION OF TREES ACTS TO CENSOR SMALLER FLOODS
FROM ANY POTENTIAL RECORD DERIVED FROM WOOD ANATOMY.

37. ALL FLOOD RINGS
ARE CAUSED BY
MAJOR FLOODS
NOT ALL
MAJOR FLOODS
CAUSE OAKS
TO FORM FLOOD RINGS

38. ALTHOUGH THE TREE-RING PALEOFLOOD RECORD HAS
EXCELLENT TEMPORAL RESOLUTION AND
GOOD OVERALL SUCCESS
AS A TOOL IN IDENTIFYING PAST EXTREME FLOODS,
IT IS EFFECTIVELY
A MINIMUM ESTIMATE
OF BOTH FLOOD FREQUENCY AND MAGNITUDE.
“ ”
St. George and Nielsen,
The Holocene, 2003

39. FLOOD RINGS

40. OAK FORESTS IN NORTH AMERICA
Source: Report on Forests of North America (Exclusive of Mexico), 1884

41. @sco stgeorge