1. Principles of Dendrochronology

2. Uniformitarianism Principle
James Hutton, British geologist (published 1785–1788)
“The present is the key to the past.”
Corollary to this principle: “The past is the key to the future.”
Illustrates the “trajectory of science,” past, present, and future:
Study processes as they occur at present
Improved understanding comes from the past
Extrapolate/predict the future = applied!

3. Uniformitarianism Principle
Examples:
A. Reconstructions of past climate = Dendroclimatology
Future?
Past
Present
Assumes that climatic processes operating today were operating similarly in the past.

4. Uniformitarianism Principle
Examples:
B. Reconstructions of past fire = Dendropyrochronology
Assumes that wildfires operate today as an ecosystem process just as they did in the past.
Future?
Past
Present

5. Uniformitarianism Principle
In recent years, this principle has come under scrutiny because research is showing issues in three main areas:
1. The “Divergence” Issue: trees in the higher latitudes are no longer tracking temperature as they faithfully did prior to Basically, since then, temperature has been steadily rising but tree growth has been declining! What gives?
2. Temporal Instability in Climate Response: dendrochronologists are finding that the response to climate in many tree species at many sites has actually been variable over time, this placing doubt in our reconstructions of climate.
3. No-Analog Conditions in the 20th and 21st centuries: well, guess what? The “present” we live in is unique (why?), so is it fair to say now that the present is the key to the past? Our forests have changed and therefore so have the processes (like wildfire) that operate in them.

6. 2. Principle of Limiting Factors
Basic principle in biology
Adaptation to dendrochronology:
“Tree growth can proceed only as fast as allowed by the primary environmental and physiological mechanisms that restrict growth.”
Sometimes, more than one mechanism operates to restrict growth.
But whichever mechanisms limit growth, they must vary year to year for tree-ring dating to work.
In other words, we MUST have variable tree growth!
And we specifically key in on those narrower rings that indicate limiting conditions.

7. Wide ring, thick latewood
Narrow ring, thin latewood

8. 2. Principle of Limiting Factors

9. The “low precip – high temp” model:

10. The “high precip – low temp” model:

11. 2. Principle of Limiting Factors

12. 2. Principle of Limiting Factors

13. Latitudinally and longitudinally:
3. Ecological Amplitude
Species have well defined ranges based on environmental controls. (BTW, this is related to what former paradigm in geography?)
A tree species will be more responsive and sensitive to changes in environmental conditions in the outer limits of its range.
Latitudinally and longitudinally:
Stressful locations, increased sensitivity N S E W
Optimal growth conditions, reduced sensitivity

14. 3. Ecological Amplitude
Range map of ponderosa pine.
Note: different spatial scales will help us isolate several locations where ponderosa pines may be especially responsive.

15. 3. Ecological Amplitude
Range map of sugar maple.
NOTE: Recent research in the eastern U.S. is showing that this principle is less important. Environmental conditions at range margins appear to be not as stressful as conditions that exist in the western U.S.

16. 3. Ecological Amplitude
A tree species will be more responsive and sensitive to changes in environmental conditions in the outer limits of its range.
Also, elevationally!
Good
Not so good

19. 4. Principle of Site Selection
Within any given area chosen for study, specific site characteristics should be sought that will enhance a tree’s responsiveness to environmental factors.
Notice how this is related to the principle of limiting factors. We should select sites where factors are more limiting.
Notice also that recognizing the growth forms of trees will provide clues where such sensitive sites exist.

20. 4. Principle of Site Selection
Notice vastly different growth forms of these trees
Valley bottom: not good
Slope: better
Thick soil: not good
Thin soil with rocky substrate: better
Notice vastly different ring patterns

21. What to look for in trees that indicate longevity:
Dead spike top or broken top
Heavy, drooping lower limbs
Short stature, inverted carrots
Erratic growth forms
Stripbark
Sparse foliage in crown
Exposed roots
Isolated individuals
El Malpais National Monument, NM

22. Five feet tall, broken top, inside ring = AD 1406
El Malpais National Monument, NM
Five feet tall, broken top, inside ring = AD 1406

23. Alta Peak, Sierra Nevada, CA

24. San Mateo Mountains, NM

25. Magdalena Mountains, NM

26. El Malpais National Monument, NM

27. 5. Aggregate Tree Growth
Tree growth can be “decomposed” into five basic parts:
R = ring width, t = the current year, and δ = presence (1) or absence (0) indicator
A = age-related trend
C = climate
D1 = exogenous (external) disturbance processes (examples?)
D2 = endogenous (internal) disturbance processes (examples?)
E = random error

28. 5. Aggregate Tree Growth
Tree growth can be “decomposed” into five basic parts:
Only ONE can be the desired signal. All OTHERS constitute noise. We wish to maximize the signal to noise (S/N) ratio (concept borrowed from engineering).
For example, if climate is our desired signal, we must (1) mathematically minimize the effects of other parts, and (2) sample to ensure other noise minimizes any affects on tree growth in our study area.

29. 5. Aggregate Tree Growth
Ideal age trend
Ideal age trend
Disturbance!

30. 5. Aggregate Tree Growth Ice storm Release from logging
Death of nearby tree
Release after wildfire

31. 6. Principle of Replication
The environmental signal being investigated can be maximized (and the amount of noise minimized) by sampling more than one stem radius per tree and more than one tree per site.
Obtaining more than one increment core per tree reduces the amount of "intra-tree variability" = the amount of undesirable environmental signal peculiar to only that tree.
Obtaining numerous trees from one site (and perhaps several sites in a region) ensures that the amount of "noise" is minimized.

32. 6. Principle of Replication
Follows the basic statistical rule: INCREASE YOUR SAMPLE DEPTH !!! MORE IS BETTER !!!

33. 7. Principle of Crossdating
Matching patterns in ring widths or other ring characteristics (such as ring density patterns) among several tree-ring series allows the identification of the exact year in which each tree ring was formed.
Both a principle and a technique. Without either, dendrochronology is unscientific ring-counting.
The Principle of Crossdating concerns why trees have the same ring patterns.
The Technique of Crossdating concerns how we can use this property to (1) ensure we have precisely assigned the correct calendar year to each tree ring, and (2) at the same time, account for those problem rings, such as false or locally absent rings.
We’ll cover the Technique of Crossdating later.

34. Why does crossdating work?
Because trees within a region will be responding similarly to the overall climate regime in which they grow.
Different rates of growth may occur due to local micro-environmental effects, but this does not matter!

35. Look at these cores (taken from six different trees) from Mt
Look at these cores (taken from six different trees) from Mt. Graham in southeastern Arizona, and pick out the wide and narrow rings they have in common.

36. Again, these three cores (taken from three trees growing in El Malpais National Monument in New Mexico) have ring patterns in common. For example…
1793 = wide ring with thick latewood
1816 Year Without a Summer wide ring
1847 = very narrow ring
1806 = narrow ring (absent on bottom)
1840 = wide ring

37. Notice that crossdating uses both wide rings and narrow rings, although the narrow rings are (for some reason) easier to visually key in on. These narrow rings will be used later when we learn the technique of crossdating.